- Email: [email protected]
Comparison of the efficacy of a subcutaneous array electrode with a subcutaneous patch electrode, a prospective randomized study
International Journal of Cardiology 78 (2001) 247–256 www.elsevier.com / locate / ijcard
Comparison of the efficacy of a subcutaneous array electrode with a subcutaneous patch electrode, a prospective randomized study *, Volker Dornberger, ¨ ¨ Volker Kuhlkamp Christian Mewis, Ludger Seipel ¨ ¨ ¨ , Otfried Muller Str. 10, D-72076 Tubingen , Germany Medical Department III, University Hospital Tubingen Received 25 July 2000; received in revised form 8 December 2000; accepted 10 January 2001
Abstract The patch electrode and the array electrode are the two types of subcutaneous leads available as an adjunct to a transvenous lead system in patients with high defibrillation thresholds. A prospective randomized study was conducted in 30 consecutive patients comparing the efficacy and the long-term performance of a patch electrode with an array electrode. After determination of the defibrillation threshold for the transvenous lead alone, a subcutaneous patch or an array electrode was implanted in random order. Adding a patch electrode decreased the defibrillation threshold in seven out of 15 patients (47%) from 13.266.6 to 10.565.1 J (P,0.05). In 13 out of 15 patients (87%), the implantation of an array electrode caused a significant lowering of the defibrillation threshold from 15.466.6 to 8.265.0 J (P,0.0001). The array electrode was significantly more effective in lowering the defibrillation threshold than the patch electrode (P,0.01). Complications during follow-up associated with the subcutaneous patch electrode were observed in four patients whereas no complications were associated with the array electrode (P,0.01). The additional implantation of an array electrode is more effective and associated with fewer complications compared to a patch electrode. 2001 Elsevier Science Ireland Ltd. All rights reserved. Keywords: Implantable cardioverter defibrillator; Subcutaneous patch electrode; Subcutaneous array electrode; Defibrillation threshold; Randomized comparison
1. Introduction With the use of transvenous lead systems in combination with an implantable cardioverter defibrillator (ICD) capable of biphasic shocks, the success rate of nonthoracotomy lead systems has increased to almost 100% and surgical mortality is also dramatically reduced [1–4]. At present one of the major problems of ICD therapy is the longevity and size of the devices. Devices with a maximum output lower than the present 29–34 J could be
significantly smaller in size. With a ‘low energy’ ICD, the additional implantation of a subcutaneous electrode might be necessary in selected cases. The purpose of the present study was to evaluate, in a prospective randomized fashion, the value of adding a subcutaneous patch electrode as compared to a subcutaneous array electrode to a transvenous lead system in a consecutive population of patients undergoing ICD implantation.
2. Methods *Corresponding author. Tel.: 149-7071-298-4090; fax: 149-7071294121. E-mail address: [email protected] (V. ¨ Kuhlkamp).
2.1. Patient population Thirty-two consecutive patients were eligible for
0167-5273 / 01 / $ – see front matter 2001 Elsevier Science Ireland Ltd. All rights reserved. PII: S0167-5273( 01 )00381-3
¨ et al. / International Journal of Cardiology 78 (2001) 247 – 256 V. Kuhlkamp
248
the study protocol. Two patients were excluded during the study due to a defibrillation threshold below 6 J, which does not require the implantation of an additional subcutaneous electrode. Hence, 30 patients were included (Table 1). The index arrhythmia was sustained ventricular tachycardia in 17 (57%) patients and ventricular fibrillation associated with cardiac arrest in 13 (43%) patients. Prior to implantation, all patients received coronary angiography and a left ventricular angiogram to determine left ventricular function. All patients underwent an electrophysiologic study and had inducible ventricular tachycardia (n519, 63%) or ventricular fibrillation (n511, 37%).
2.2. Study protocol The aim of the present study was to compare in a randomized fashion the value of adding a subcutaneous patch or a subcutaneous array electrode to a transvenous lead system to lower the defibrillation threshold in combination with a defibrillator capable of biphasic shocks. The study protocol was approved by the local ethics committee. Informed written
consent was obtained prior to implantation of the device and the electrode system. Defibrillation threshold testing was initially performed with the lead alone. Thereafter, a subcutaneous lead was added and the effect of the additional electrode on the defibrillation threshold was determined (Fig. 1). The defibrillation threshold obtained in the operating room was reconfirmed at a second test prior to discharge from the hospital, and again 3 months after implantation of the defibrillator.
2.3. Implantable cardioverter defibrillator and lead systems The Medtronic PCD 7219D was implanted subpectorally in 16 patients. In these 16 patients, the Medtronic TransveneE-RV-6936 lead system was placed in the right ventricle and a unipolar shocking lead was placed in the left subclavian vein (Medtronic TransveneE-SVC-6933). The Medtronic TransveneE-RV-6936 is a tripolar active fixation integrated sensing, pacing and shocking lead, whereas the MedtronicTransveneE SVC-6933 lead is a floating unipolar shocking lead. The CPI PRX IIIE models 1720 and 1725 were
Table 1 Patient characteristics, implanted devices and lead system a
Gender Age (years) Heart disease Clinical functional status (NYHA)
Clinical arrhythmia Left ventricular ejection fraction Implanted device Implanted transvenous lead Implanted subcutaneous lead Site of device implantation Antiarrhythmic medication at implant
a
Group 1 (patch, n515)
Group 2 (array, n515)
P-value
1/ / 14? 56613 (23–74) 11 CAD 4 DCM 1 NYHA I 12 NYHA II 2 NYHA III 8 VT 7 VF 30612% (15–50%) 8 Medtronic PCD 7119DE 7 CPI PRX III 1725E, 1720E 8 Medtronic TransveneE 6936 with 6939 7 EndotakE 0094, 0095, 00125 8 Medtronic 6933 7 CPI patch 0063 14 pectoral 1 abdominal 2 amiodarone 1 d / l sotalol 12 none
2/ / 13? 6068 (43 to 73) 12 CAD 3 DCM 2 NYHA I 12 NYHA II 1 NYHA III 9 VT 6 VF 34610% (20–52%) 8 Medtronic PCD 7119DE 7 CPI PRX III 1725E, 1720E 8 Medtronic TransveneE 6936 with 6939 7 EndotakE 0094, 0095, 00125 15 CPI SQ array 0049
1.0 0.29 1.0
12 pectoral 3 abdominal 3 amiodarone 1 d / l sotalol 1 metoprolol 10 none
0.6
CAD, coronary artery disease; DCM, dilated cardiomyopathy; VT, ventricular tachycardia; VF, ventricular fibrillation.
0.67
1.0 0.33 1.0 1.0 n.d.
0.78
¨ et al. / International Journal of Cardiology 78 (2001) 247 – 256 V. Kuhlkamp
249
Fig. 1. Flow chart of the study protocol used: 30 consecutive patients were randomized after the defibrillation threshold for the lead-only configuration was obtained. In 15 patients an additional patch electrode was implanted, and 15 patients received a subcutaneous array electrode. If the subcutaneous electrode did not decrease the defibrillation threshold it was removed. Only those patients who had a decrease of the intra operative defibrillation threshold received the subcutaneous electrode. The intra operative defibrillation threshold was reconfirmed at the hospital discharge test and at 3 months of follow up. ICD, implantable cardioverter defibrillator; DFT, defibrillation threshold; SQ patch: subcutaneous patch electrode; SQ array, subcutaneous array electrode.
used in 14 patients. Ten patients received a pectoral implant while an abdominal approach was chosen for four patients. The Endotak CE lead models 0094, 0095 and 0125 were implanted in 14 patients. The leads differ only in length (0094 and 0095, length 100 cm; 0125, length 70 cm) and connectors. The Endotak CE lead is a tripolar integrated pacing, sensing and shocking lead. The distal coil was placed in the right ventricle and the proximal coil was placed at the transition of the superior vena cava to the right atrium. In combination with the TransveneE lead system, eight patients received the TransveneE-SQ patch electrode (TransveneE-SQ Unipolar, model 6999).
The patch electrode has a surface area of 6.60 cm 2 and the electrode coil is constructed of a platinum alloy. In seven patients, a CPI model 0063 patch electrode (EndotakE SQ) was implanted in combination with the EndotakE lead system. The surface area of the patch is 28.0 cm 2 and its electrode coil is made of titanium. Technical details of the subcutaneous lead systems are summarized in Table 2. The CPI model 0048 and 0049 subcutaneous array electrodes were used in 15 patients in this study. This array electrode was used in combination with the Medtronic TransveneE and the CPI EndotakE lead system. Model 0048 and model 0049 differ only in regard to the connector. The electrode coil consists of
Table 2 Technical data for implanted subcutaneous lead systems
Medtronic TransveneE SQ 6933 CPI EndotakE SQ model 0063 CPI EndotakE SQ array model 0048 / 0049
Surface area (cm 2 )
Electrode material
DC resistance (V)
6.6 28.0 51.0
Platinum alloy Titanium Platinum / platinum–iridium alloy
1.2 2 2
250
¨ et al. / International Journal of Cardiology 78 (2001) 247 – 256 V. Kuhlkamp
a platinum–iridium alloy with a surface area of 51.0 cm 2 (Table 2).
All implants were performed under general anesthesia. The transvenous lead system was introduced by direct puncture of the subclavian vein in 21 patients whereas the cephalic vein was used in nine patients. The cardioverter was implanted in a submuscular pectoral pocket in 26 patients and in the subrectus tissue of the left upper abdomen in four patients. The subcutaneous lead systems were placed deep subcutaneously on the left thorax between the anterior and the posterior axillary line at the level of the cardiac apex. For implantation of the array, a lead introducer with a stylet and a tunneling set were used. From a separate incision in the anterior axillary line, the fingers of the array electrode were placed subcutaneously with the tip of the electrode as posteriorly as possible. The middle finger of the electrode was positioned at the level of the cardiac apex, the first and third finger of the electrode were placed about 3–4 cm superior or inferior, respectively. A straight position of the finger electrodes was attempted, however, wrinkling of the finger electrode was allowed as long as the finger electrodes did not roll up. Fluoroscopy was used to control the position of the patch and the array electrodes.
tion threshold for the lead alone. Polarity of shocks was not changed during defibrillation threshold testing. If the subcutaneous electrode did not decrease the defibrillation threshold, it was removed. At the hospital predischarge test, ventricular fibrillation was induced via the implanted device. Again ventricular fibrillation had to last 10 s and the shock was triggered manually. The device was programmed to the energy of the defibrillation threshold that was determined during intra operative testing to reconfirm the defibrillation threshold. If this shock terminated ventricular fibrillation, the defibrillation threshold was considered to be unchanged. Whether the defibrillation threshold actually decreased was not tested. If this shock failed, ventricular fibrillation was terminated with a 34-J shock. The energy of the first shock was increased in steps of 2 J below 12 J and in steps of 3 J above 12 J until induced ventricular fibrillation was terminated by the first shock. In this case, an increase in the defibrillation threshold was assumed. For analysis of changes in impedance (V), only shocks with the same amount of stored energy were used. At 3 months follow-up, a third test to reconfirm the defibrillation threshold was performed. The initial energy was programmed to the intra operative defibrillation threshold value irrespective of the result obtained for the defibrillation threshold at the hospital discharge test.
2.5. Defibrillation threshold testing protocol
2.6. Statistics
At implant, ventricular fibrillation was induced using a ‘T-wave shock’ via an external cardioverter defibrillator (Medtronic model 5358) or by applying a 50-Hz alternating current with an external fibrillation box. In all patients, ventricular fibrillation lasted 10 s before the ICD shock was applied. A very strict step down protocol, starting with a 24 J biphasic shock, was employed (24, 20, 18, 15, 12, 10, 8, 6, 3 J). The defibrillation threshold was defined as the lowest shock strength (stored energy) which terminated VF. After determination of the defibrillation threshold with the transvenous lead only, either a subcutaneous patch electrode or a subcutaneous array electrode was implanted in a randomized fashion. Defibrillation threshold testing was then continued starting with the energy determined as the defibrilla-
The data are presented as mean61 S.D. Statistical analysis was done using the Student’s t-test. The two-way ANOVA test was used to determine how the defibrillation threshold or the impedance were affected by the two different types of leads used. Frequency distributions were calculated using the Fisher’s exact test. A probability value of less than 0.05 was considered to indicate statistical significance.
2.4. Implantation procedure
3. Results
3.1. Patient population Patients in the two study groups did not differ in
¨ et al. / International Journal of Cardiology 78 (2001) 247 – 256 V. Kuhlkamp
respect to age, sex, underlying cardiac disease, left ventricular function or clinical functional status (Table 1). The implantation procedure required 109638 min for patients with a subcutaneous patch electrode and 121637 min for patients with a subcutaneous array electrode (P5n.s.). Implantation-associated mortality was zero. No patient developed severe bleeding, infection of the lead system or other complications requiring additional therapy. Post-operatively, a substantial hematoma was seen in two patients with the patch electrode. After a follow-up of 5 and 21 months, respectively, one patch electrode had to be removed because the patient experienced severe pain in the area surrounding the implanted patch, while the second patient suffered recurrent seroma in the area of the patch. No such complications associated with the array electrode were seen during follow-up. Complications arose in four out of seven patients with the patch electrode. No complications were observed in the 13 patients receiving an array electrode (P,0.01).
251
Fig. 2. Change of the defibrillation threshold (J) for each individual patient (patient number 1 to 15) after additional implantation of the subcutaneous patch electrode. Data are presented in the order of inclusion into the study. j, defibrillation threshold with the Endotak lead (CPI) only; d, defibrillation threshold with the Transvene lead (Medtronic) only; m, defibrillation threshold with the Endotak lead and the subcutaneous patch electrode (Endotak SQ 0063); ♦, defibrillation threshold with the Transvene lead and the subcutaneous patch electrode (Medtronic TransveneE SQ 6933).
or an array electrode cannot be explained by different baseline values of the two study groups. In addition, baseline defibrillation thresholds and the impedances obtained with the Endotak lead were not significantly different from values obtained with the Transvene lead (Table 3). By adding the patch electrode, the defibrillation threshold was significantly decreased from 13.266.6 to 10.565.1 J (mean decrease 2.7 J, 95% confidence limit 0.2–5.1 J, P,0.05, Fig. 2 and Table 3). The addition of the patch electrode did not reduce the defibrillation threshold in six patients (40%, Fig. 2)
3.2. Defibrillation threshold and impedance of the high voltage circuit The initial defibrillation threshold with the leadonly configuration was 13.266.6 J in the patients receiving the patch electrode and 15.466.6 J in those receiving the array electrode (P5n.s., Table 3). The impedance of the lead-only system was 57611 V in the patch group and 5269 V in the array group (P5n.s.). The differences obtained by adding a patch Table 3 Two-way ANOVA table a DFT lead alone (J)
DFT lead1SQ patch or array (J)
CPI / Guidant (n57) Medtronic (n58) Total (n515) P-value
13.666.5 12.967.1 13.266.6
11.064.1 b 10.466.0 b 10.565.1 b
CPI / Guidant (n57) Medtronic (n58) Total (n515) P-value
14.168.0 16.565.5 15.466.6
P-value 0.26 ,0.05
Impedance lead alone (V) 5969 56613 57611
4366 b 4367 b 4366 b 0.75
55611 5068 5269
3664 c 3565 c 3664 c 0.28
0.77 8.065.9 c 8.464.5 c 8.265.0 c 0.54
,0.005 ,0.01
Impedance lead1SQ patch or array (V)
P-value ,0.001 ,0.001
,0.001 ,0.001
a DFT, defibrillation threshold. The effect of the patch or array electrode on the defibrillation threshold and the impedance was not significantly affected by the type of transvenous lead system. b SQ patch. c SQ array.
252
¨ et al. / International Journal of Cardiology 78 (2001) 247 – 256 V. Kuhlkamp
and the electrode was removed in these patients. An increase in the defibrillation threshold by 3 J was noted in one patient. In another patient, ventricular fibrillation was not terminated with the energy that had terminated ventricular fibrillation with the lead only. However, the ‘new’ defibrillation threshold was not tested. In both patients the patch electrode was removed. Therefore, the defibrillation threshold was not decreased by the additional subcutaneous patch electrode in eight patients. At the hospital discharge test an increase in the defibrillation threshold by 4 J in one patient and 5 J in two patients was observed. The defibrillation threshold in the group with implanted patch was 12.764.2 J. In those patients whose patch electrode was removed, three patients had an increase in the defibrillation threshold by 2, 4 and 8 J, respectively. In this group, the mean defibrillation threshold was 11.866.1 J. Since we did not perform a complete defibrillation threshold test, a direct comparison of these values to the intra operative values is not possible. At the 3-month follow up, an increase in the defibrillation threshold compared to the intra operative defibrillation threshold was present in one patient (from 6 to 8 J) whose patch electrode was removed and in another patient with an implanted patch electrode (increase from 10 to 15 J). The additional implantation of a patch electrode decreased the impedance of the system from 57611 to 4366 V (P,0.0001). The type of lead used had no significant effect on the impedance results (Table 3) and there was no correlation between the decrease of the impedance and the decrease of the defibrillation threshold (r 2 50.06, Fig. 3). As has been mentioned before, an increase in the defibrillation threshold cannot be ruled out in those patients without a decrease in the defibrillation threshold. The addition of an array electrode lowered the defibrillation threshold from 15.466.6 to 8.265.0 J (P,0.001, mean decrease 7.3 J, 95% confidence interval 4.4–10.1 J, Fig. 4 and Table 3). The decrease of the defibrillation threshold was not significantly different between the two types of leads used (Table 3). In two patients, the defibrillation threshold remained unchanged with the additional array electrode and the array electrode was removed. Similar to the patients with a patch electrode, the defibrillation threshold was 11.264.4 J at the hospital predischarge test. At the 3-month follow-up defibrillation test, two
Fig. 3. Relation of the change in impedance (delta-impedance HV electrode, V) to the change observed in the defibrillation threshold (delta DFT, J) in patients who received a patch electrode as an adjunct to the transvenous lead system. A 2 sign denotes an increase in the defibrillation threshold; in seven patients, no change of the defibrillation threshold was obtained with the subcutaneous patch electrode. One patient had an increase in the defibrillation threshold with the additional lead.
patients had an increase in the defibrillation threshold as compared to the intra operative value (intraoperative, 3 J in both patients; 3 months follow up, 8 J in one patient, 10 J in the other patient). In the two patients where the array electrode was removed, the
Fig. 4. Change of the defibrillation threshold (J) for every individual patient (patient number 1 to 15) after additional implantation of the subcutaneous array electrode (CPI EndotakE SQ array model 0048 / 0049). Data are presented in the order of inclusion in the study. j, defibrillation threshold with the Endotak lead (CPI) only; d, defibrillation threshold with the Transvene lead (Medtronic) only; m, defibrillation threshold with the Endotak lead and the subcutaneous array electrode (CPI EndotakE SQ array model 0048 / 0049); ♦, defibrillation threshold with the Transvene lead and the subcutaneous array electrode (CPI EndotakE SQ array model 0048 / 0049).
¨ et al. / International Journal of Cardiology 78 (2001) 247 – 256 V. Kuhlkamp
defibrillation threshold remained unchanged at 3 and 10 J, respectively at the hospital discharge test and the 3-month follow up test. Associated with the marked decrease of the defibrillation threshold in the array group was a decrease of the lead impedance from 5269 to 3664 V (P,0.0001). However, there was no correlation between the decrease in the defibrillation threshold achieved and the effect of the array electrode on the impedance of the shocking lead (r 2 50.01, Fig. 5). The decrease of impedance with the additional subcutaneous array electrode was not different between the Endotak and the Transvene lead (Table 3b). The effect on the defibrillation threshold of the array electrode (decrease 7.265.1 J) as an adjunct to a transvenous lead system was significantly larger than the effect of the patch electrode (decrease 2.764.4 J, P,0.05). Moreover, significantly more patients had a decrease of the defibrillation threshold with the array electrode (n513) than with the patch electrode (n57, P,0.05). Despite the larger surface area of the array electrode there was no significant difference in the decrease of impedance obtained with the array electrode (decrease 1768 V) compared to the patch electrode (decrease 1468 V). The results obtained with the patch or the array lead were independent of the type of transvenous lead
Fig. 5. Relation of the change in impedance (delta-impedance HV electrode, V) to the change observed in the defibrillation threshold (delta DFT, J) in patients who received an array electrode as an adjunct to the transvenous lead system. A 2 sign denotes an increase in the defibrillation threshold; in two patients no change in the defibrillation threshold was obtained with the subcutaneous array electrode. An increase in the defibrillation threshold was not seen with the additional lead.
253
system, the mode of induction of ventricular fibrillation or the device used.
4. Discussion The value of an additional subcutaneous electrode in achieving a sufficiently low defibrillation threshold for an implantable cardioverter defibrillator with a nonthoracotomy lead system has been shown in experimental and clinical studies [5–13]. The present study compares an array electrode and a subcutaneous patch electrode in a randomized fashion with a very strict defibrillation threshold testing protocol. Complications such as bleeding, severe pain or a seroma, were observed postoperatively or during follow-up only in association with the patch electrode (P,0.01). No complications arose from the array electrode. The problems associated with the patch electrode have been reported by others [10,11,14]. The time required for the implantation procedure was not different between the two types of electrodes used. If a single incision is used for implantation of the array electrode, the procedure could be considerably shortened [8]. Of specific importance is the fact that a marked reduction of the defibrillation threshold could be obtained irrespective of the baseline value with the lead alone. However, the effect on the defibrillation threshold was not related to the decrease in impedance (Figs. 3 and 5). The change of the defibrillation field may have been more important than the effects on impedance which has also been shown in experimental studies [9,15,16]. It has been shown recently that a two-element array and a single element array are as effective as the three-element array used in this study [17,18]. Hence, the defibrillation threshold may be influenced mainly by the change of the defibrillation field. This is consistent with experimental studies showing that defibrillation is successful if a sufficient voltage gradient is achieved in about 90% of the myocardial mass [19]. The defibrillation field obtained with the array electrode might be more advantageous than the field with the subcutaneous patch electrode. The area ‘covered’ by the array electrode is larger and increases the defibrillation field to the more posterior area. This seems to be the most likely explanation besides a
254
¨ et al. / International Journal of Cardiology 78 (2001) 247 – 256 V. Kuhlkamp
decrease of impedance for the lower defibrillation thresholds obtained with the array electrode. Similar data have been obtained with a single element subcutaneous array electrode [20]. In this regard, the positioning of the patch electrode on the thorax will also have a marked influence on the defibrillation field and hence the defibrillation threshold [21,22]. However, different positions of the patch electrode were not tested in this study. Usually defibrillators are implanted with the shell of the defibrillator acting as an active part of the defibrillation circuit. The effect of the shell of the defibrillator might be similar to the effect seen with the subcutaneous patch. The data on the use of a transvenous lead system with two defibrillation coils in addition to an active can system are inconclusive with some investigators reporting a significant advantage and others a reporting only a minor effect [2,23–25]. This may be explained in part by different positions of the vena cava superior lead [26]. However, the patch electrode is usually placed lower on the thorax in the midaxillary line. The position of the patch has an important effect on the defibrillation threshold and therefore the data obtained with the active can system cannot be transferred to a dual lead transvenous system with an additional patch electrode. Two recent studies compared the clinical efficacy of a subcutaneous array electrode with a subcutaneous patch electrode in a large patient population. The results of these investigations suggest that a subcutaneous array is superior to a patch as a subcutaneous electrode to lower the defibrillation threshold [11,27]. However in both studies only monophasic shocks were used. Chronic defibrillation thresholds or complications occurring during longterm follow-up are not reported. Adding a patch electrode or an array electrode to a transvenous electrode significantly decreases the energy requirements for successful termination of ventricular fibrillation. An unexpected finding of our study was that the addition of a patch electrode was of no value in about 50% of our patients. In six patients the defibrillation threshold remained unchanged. In one patient, the defibrillation threshold actually increased after the implantation of the patch electrode. In one of the above cited studies, the addition of the patch electrode to the transvenous lead did not decrease the defibrillation threshold [27]. This
has also been observed with the implantation of an array electrode in combination with monophasic shocks [11]. One possible explanation is, since the subcutaneous electrode was always implanted after determination of the defibrillation threshold for the lead only, the overall hemodynamic situation worsened with subsequent increase in the defibrillation threshold [28]. However, the defibrillation threshold with the lead-only configuration was reconfirmed by the final shock delivered by the implanted device programmed to the energy of the defibrillation threshold. Hence, a change in the defibrillation field can be disadvantageous, leading to an increase in the energy requirements for successful defibrillation. There are several limitations of the present study. First we used two different transvenous lead systems and defibrillators in this study. However, the two systems behaved very similarly making it less likely that different results would have been obtained if only the Endotak or the Transvene system had been used. A further limitation is inherent to the clinical method of determining a defibrillation threshold [29]. A step down protocol for measurement of the defibrillation threshold does not take into account that the probability of successful defibrillation of ventricular fibrillation only increases with increasing amounts of energy. This problem can clearly be overcome by multiple tests and determining the probability of terminating ventricular fibrillation at each energy level. However, it has been shown that the defibrillation threshold usually has a predictable relationship to the ‘dose–response curve’ [30,31]. We tried to reconfirm the defibrillation threshold obtained during intra operative testing using the same amount of stored energy at two final tests in the operating room, at the hospital discharge test and at the 3-month follow up test. Furthermore, we always started with testing of the defibrillation threshold of the lead only. This type of protocol was chosen since it is closer to actual clinical conditions where an additional electrode is usually implanted after the lead-only configuration has failed. Simple clinical predictors for biphasic defibrillation thresholds have not been found [32]. Since defibrillation thresholds are highly variable, measuring defibrillation thresholds with the additional patch and the additional array electrode in a randomized manner
¨ et al. / International Journal of Cardiology 78 (2001) 247 – 256 V. Kuhlkamp
in the same patient is probably superior to a comparison of two groups. It is concluded that the addition of a subcutaneous array electrode to a transvenous lead is more efficient than a subcutaneous patch electrode. Lead associated complications were only observed with the patch electrode. We therefore recommend implantation of a subcutaneous array electrode if an additional electrode is necessary to achieve an acceptable biphasic defibrillation threshold.
References [1] Zipes DP, Roberts D. Results of the international study of the implantable pacemaker cardioverter-defibrillator — A comparison of epicardial and endocardial lead systems. Circulation 1995;92:59–65. [2] Bardy GH, Dolack GL, Kudenchuk PJ, Poole JE, Mehra R, Johnson G. Prospective, randomized comparison in humans of a unipolar defibrillation system with that using an additional superior vena cava electrode. Circulation 1994;89:1090–3. [3] Saksena S, An H, Mehra R, DeGroot P, Krol RB, Burkhardt E, Mehta D, John T. Prospective comparison of biphasic and monophasic shocks for implantable cardioverter defibrillators using endocardial leads. Am J Cardiol 1992;70:304–10. [4] Bardy GH, Ivey TD, Allen MD, Johnson G, Mehra R, Greene HL. A prospective randomized evaluation of biphasic versus monophasic waveform pulses on defibrillation efficacy in humans. J Am Coll Cardiol 1989;14:728–33. [5] Wetherbee JN, Chapman PD, Klopfenstein HS, Bach SM, Troup PJ, McDowell CA. Nonthoracotomy internal defibrillation in dogs: Threshold reduction using a subcutaneous chest wall electrode with a transvenous catheter electrode. J Am Coll Cardiol 1987;10:406– 11. [6] Scott S, Accorti P, Callaghan F, Abels D, Bojeva B. Ventricular and atrial defibrillation using new transvenous tripolar and bipolar leads with 5 french electrodes and 8 french subcutaneous catheters. PACE 1991;14:1893–8. [7] Bardy GH, Hofer B, Johnson G, Kudenchuk PJ, Poole JE, Dolack GL, Gleva M, Mitchell R, Kelso D. Implantable transvenous cardioverter-defibrillators. Circulation 1993;87:1152–68. [8] Kall JG, Kopp D, Lonchyna V, Blakeman BP, Cadman C, O’Connor M, Kinder C, Gilkerson J, Avery R, Wilber DJ. Implantation of a subcutaneous lead array in combination with a transvenous defibrillation electrode via a single infraclavicular incision. PACE 1995;18:482–5. [9] Lang DJ, Heil JE, Hahn SJ, Lindstrom CC, Derfus DL. Implantable cardioverter defibrillator lead technology: Improved performance and lower defibrillation thresholds. PACE 1995;18(II):548–59. [10] Jordaens LJ, Vertongen P, Bellegham YV. A subcutaneous lead array for implantable cardioverter defibrillators. PACE 1993;16:1429–32. [11] Higgins SL, Alexander DC, Kuypers CJ, Brewster SA. The subcutaneous array: A new lead adjunct for the transvenous ICD to lower defibrillation thresholds. PACE 1995;18:1540–8. [12] Jordaens LJ, Trouerbach J-W, Vertongen P, Herregods L, Poelaert J, Van Nooten G. Experience of cardioverter-defibrillators inserted without thoracotomy: evaluation of transvenously inserted leads alone or with a subcutaneous axillary patch. Br Heart J 1993;69:14– 9.
255
[13] Yee R, Klein GJ, Leitch JW, Guiraudon GM, Guiraudon CM, Jones DL, Norris C. A permanent transvenous lead system for an implantable pacemaker cardioverter-defibrillator. Circulation 1992;85:196–205. [14] Saksena S, Breithardt G, Dorian P, Greene HL, Madan N, Block M. Nonpharmacological therapy for malignant ventricular arrhythmias: Implantable defibrillator trials. Prog Cardiovasc Dis 1996;38:429– 44. [15] Nogami A, Takahashi A, Nitta J, Aonuma K, Iesaka Y, Hiroe M, Marumo F, Hiraoka M. Comparative efficacy of a subcutaneous mesh and plate electrodes for nonthoracotomy canine defibrillation. PACE 1991;14:1402–10. [16] Tang A, Wolf P, Afework Y, Smith WM, Ideker RE. Three-dimensional potential gradient fields generated by intracardiac catheter and cutaneous patch electrodes. Circulation 1992;85:1857–64. [17] Seidl K, Block M, Hammel D, Hauer B, Isgro F, Brunn J, Seifert T, Breithardt G. Ist der mittlere Finger einen subcutanen Array-Elek¨ die Defibrillation verzichtbar? Z Kardiol 1995;84(Suppl. trode fur I):106, (Abstr.). ¨ ¨ [18] Kuhlkamp V, Khalighi K, Dornberger V, Ziemer G. Single-incision and single-element array electrode to lower the defibrillation threshold. Ann Thorac Surg 1997;64:1177–9. [19] Frazier DW, Wolf PD, Wharton JM, Tang ASL, Smith WM, Ideker RE. Stimulus-induced critical point: Mechanism for electrical initiation of reentry in normal canine myocardium. J Clin Invest 1989;83:1039–52. ¨ ¨ [20] Kuhlkamp V, Dornberger V, Khalighi K, Mewis C, Suchalla R, Ziemer G, Seipel L. Effect of a single element subcutaneous array electrode added to a transvenous electrode configuration on the defibrillation field and the defibrillation threshold. PACE 1998;21:2596–605. [21] Desai P, DeGroot P, Casavant D. Is patch position critical for successful nonthoracotomy (NTL) ICD implant with biphasic shocks? Circulation 1993;88(Suppl. I):215, (Abstr.). [22] Swartz JF, Fletcher RD, Solomon AJ, Donofrio J, DeGroot P. Subscapular patch reduces defibrillation threshold when used with a pectoral can and a biphasic implantable defibrillator. PACE 1994;17:850, (Abstr.). [23] Mouchawar GA, Wolsleger WK, Doan PD, Causey JD, Kroll MW. Does an SVC electrode further reduce DFT in a hot-can ICD system? PACE 1997;20:163–7. [24] Haffajee C, Martin D, Bhandari A, Bardy GH, Desouza C, ¨ Kuhlkamp V, Church T. A multicenter randomized trial comparing an active can implantable defibrillator with a passive can system. Jewel Active Can Investigators. PACE 1997;20:215–9. [25] Gold MR, Foster AH, Shorofsky SR. Effects of an active pectoralpulse generator shell on defibrillation efficacy with a transvenous lead system. Am J Cardiol 1996;78:540–3. [26] Markewitz A, Kaulbach H, Mattke S, Dorwarth U, Hoffmann E, Weinhold C, Steinbeck G, Reichart B. The left subclavian vein as an alternative site for implantation of the second defibrillation lead. PACE 1995;18:401–5. [27] The Endotak / PRX Investigator Group, Baker JH, Epstein AE, Voshagestahl L. A prospective randomized evaluation of a nonthoracotomy implantable cardioverter defibrillator lead system. PACE 1997;20:72–8. [28] Steinbeck G, Dorwarth U, Mattke S, Hoffmann E, Markewitz A, Kaulbach H, Tassani P. Hemodynamic deterioration during ICD implant: predictors of high-risk patients. Am Heart J 1994;127:1064–7. [29] McDaniel WC, Schuder JC. The cardiac ventricular defibrillation threshold — inherent limitations in its application and interpretation. Med Instrum 1987;21:170–6.
256
¨ et al. / International Journal of Cardiology 78 (2001) 247 – 256 V. Kuhlkamp
[30] Rattes MF, Jones DL, Sharma AD. Defibrillation threshold: A simple and quantitative estimate of the ability to defibrillate. PACE 1987;10:70–7. [31] Jones DL, Irish WD, Klein GJ. Defibrillation efficacy — comparison of defibrillation threshold versus dose response curve determination. Circ Res 1991;69:45–51.
[32] Raitt MH, Johnson G, Dolack GL, Poole JE, Kudenchuk PJ, Bardy GH. Clinical predictors of the defibrillation threshold with the unipolar implantable defibrillation system. J Am Coll Cardiol 1995;25:1576–83.
Comparison of the efficacy of a subcutaneous array electrode with a subcutaneous patch electrode, a prospective randomized study *, Volker Dornberger, ¨ ¨ Volker Kuhlkamp Christian Mewis, Ludger Seipel ¨ ¨ ¨ , Otfried Muller Str. 10, D-72076 Tubingen , Germany Medical Department III, University Hospital Tubingen Received 25 July 2000; received in revised form 8 December 2000; accepted 10 January 2001
Abstract The patch electrode and the array electrode are the two types of subcutaneous leads available as an adjunct to a transvenous lead system in patients with high defibrillation thresholds. A prospective randomized study was conducted in 30 consecutive patients comparing the efficacy and the long-term performance of a patch electrode with an array electrode. After determination of the defibrillation threshold for the transvenous lead alone, a subcutaneous patch or an array electrode was implanted in random order. Adding a patch electrode decreased the defibrillation threshold in seven out of 15 patients (47%) from 13.266.6 to 10.565.1 J (P,0.05). In 13 out of 15 patients (87%), the implantation of an array electrode caused a significant lowering of the defibrillation threshold from 15.466.6 to 8.265.0 J (P,0.0001). The array electrode was significantly more effective in lowering the defibrillation threshold than the patch electrode (P,0.01). Complications during follow-up associated with the subcutaneous patch electrode were observed in four patients whereas no complications were associated with the array electrode (P,0.01). The additional implantation of an array electrode is more effective and associated with fewer complications compared to a patch electrode. 2001 Elsevier Science Ireland Ltd. All rights reserved. Keywords: Implantable cardioverter defibrillator; Subcutaneous patch electrode; Subcutaneous array electrode; Defibrillation threshold; Randomized comparison
1. Introduction With the use of transvenous lead systems in combination with an implantable cardioverter defibrillator (ICD) capable of biphasic shocks, the success rate of nonthoracotomy lead systems has increased to almost 100% and surgical mortality is also dramatically reduced [1–4]. At present one of the major problems of ICD therapy is the longevity and size of the devices. Devices with a maximum output lower than the present 29–34 J could be
significantly smaller in size. With a ‘low energy’ ICD, the additional implantation of a subcutaneous electrode might be necessary in selected cases. The purpose of the present study was to evaluate, in a prospective randomized fashion, the value of adding a subcutaneous patch electrode as compared to a subcutaneous array electrode to a transvenous lead system in a consecutive population of patients undergoing ICD implantation.
2. Methods *Corresponding author. Tel.: 149-7071-298-4090; fax: 149-7071294121. E-mail address: [email protected] (V. ¨ Kuhlkamp).
2.1. Patient population Thirty-two consecutive patients were eligible for
0167-5273 / 01 / $ – see front matter 2001 Elsevier Science Ireland Ltd. All rights reserved. PII: S0167-5273( 01 )00381-3
¨ et al. / International Journal of Cardiology 78 (2001) 247 – 256 V. Kuhlkamp
248
the study protocol. Two patients were excluded during the study due to a defibrillation threshold below 6 J, which does not require the implantation of an additional subcutaneous electrode. Hence, 30 patients were included (Table 1). The index arrhythmia was sustained ventricular tachycardia in 17 (57%) patients and ventricular fibrillation associated with cardiac arrest in 13 (43%) patients. Prior to implantation, all patients received coronary angiography and a left ventricular angiogram to determine left ventricular function. All patients underwent an electrophysiologic study and had inducible ventricular tachycardia (n519, 63%) or ventricular fibrillation (n511, 37%).
2.2. Study protocol The aim of the present study was to compare in a randomized fashion the value of adding a subcutaneous patch or a subcutaneous array electrode to a transvenous lead system to lower the defibrillation threshold in combination with a defibrillator capable of biphasic shocks. The study protocol was approved by the local ethics committee. Informed written
consent was obtained prior to implantation of the device and the electrode system. Defibrillation threshold testing was initially performed with the lead alone. Thereafter, a subcutaneous lead was added and the effect of the additional electrode on the defibrillation threshold was determined (Fig. 1). The defibrillation threshold obtained in the operating room was reconfirmed at a second test prior to discharge from the hospital, and again 3 months after implantation of the defibrillator.
2.3. Implantable cardioverter defibrillator and lead systems The Medtronic PCD 7219D was implanted subpectorally in 16 patients. In these 16 patients, the Medtronic TransveneE-RV-6936 lead system was placed in the right ventricle and a unipolar shocking lead was placed in the left subclavian vein (Medtronic TransveneE-SVC-6933). The Medtronic TransveneE-RV-6936 is a tripolar active fixation integrated sensing, pacing and shocking lead, whereas the MedtronicTransveneE SVC-6933 lead is a floating unipolar shocking lead. The CPI PRX IIIE models 1720 and 1725 were
Table 1 Patient characteristics, implanted devices and lead system a
Gender Age (years) Heart disease Clinical functional status (NYHA)
Clinical arrhythmia Left ventricular ejection fraction Implanted device Implanted transvenous lead Implanted subcutaneous lead Site of device implantation Antiarrhythmic medication at implant
a
Group 1 (patch, n515)
Group 2 (array, n515)
P-value
1/ / 14? 56613 (23–74) 11 CAD 4 DCM 1 NYHA I 12 NYHA II 2 NYHA III 8 VT 7 VF 30612% (15–50%) 8 Medtronic PCD 7119DE 7 CPI PRX III 1725E, 1720E 8 Medtronic TransveneE 6936 with 6939 7 EndotakE 0094, 0095, 00125 8 Medtronic 6933 7 CPI patch 0063 14 pectoral 1 abdominal 2 amiodarone 1 d / l sotalol 12 none
2/ / 13? 6068 (43 to 73) 12 CAD 3 DCM 2 NYHA I 12 NYHA II 1 NYHA III 9 VT 6 VF 34610% (20–52%) 8 Medtronic PCD 7119DE 7 CPI PRX III 1725E, 1720E 8 Medtronic TransveneE 6936 with 6939 7 EndotakE 0094, 0095, 00125 15 CPI SQ array 0049
1.0 0.29 1.0
12 pectoral 3 abdominal 3 amiodarone 1 d / l sotalol 1 metoprolol 10 none
0.6
CAD, coronary artery disease; DCM, dilated cardiomyopathy; VT, ventricular tachycardia; VF, ventricular fibrillation.
0.67
1.0 0.33 1.0 1.0 n.d.
0.78
¨ et al. / International Journal of Cardiology 78 (2001) 247 – 256 V. Kuhlkamp
249
Fig. 1. Flow chart of the study protocol used: 30 consecutive patients were randomized after the defibrillation threshold for the lead-only configuration was obtained. In 15 patients an additional patch electrode was implanted, and 15 patients received a subcutaneous array electrode. If the subcutaneous electrode did not decrease the defibrillation threshold it was removed. Only those patients who had a decrease of the intra operative defibrillation threshold received the subcutaneous electrode. The intra operative defibrillation threshold was reconfirmed at the hospital discharge test and at 3 months of follow up. ICD, implantable cardioverter defibrillator; DFT, defibrillation threshold; SQ patch: subcutaneous patch electrode; SQ array, subcutaneous array electrode.
used in 14 patients. Ten patients received a pectoral implant while an abdominal approach was chosen for four patients. The Endotak CE lead models 0094, 0095 and 0125 were implanted in 14 patients. The leads differ only in length (0094 and 0095, length 100 cm; 0125, length 70 cm) and connectors. The Endotak CE lead is a tripolar integrated pacing, sensing and shocking lead. The distal coil was placed in the right ventricle and the proximal coil was placed at the transition of the superior vena cava to the right atrium. In combination with the TransveneE lead system, eight patients received the TransveneE-SQ patch electrode (TransveneE-SQ Unipolar, model 6999).
The patch electrode has a surface area of 6.60 cm 2 and the electrode coil is constructed of a platinum alloy. In seven patients, a CPI model 0063 patch electrode (EndotakE SQ) was implanted in combination with the EndotakE lead system. The surface area of the patch is 28.0 cm 2 and its electrode coil is made of titanium. Technical details of the subcutaneous lead systems are summarized in Table 2. The CPI model 0048 and 0049 subcutaneous array electrodes were used in 15 patients in this study. This array electrode was used in combination with the Medtronic TransveneE and the CPI EndotakE lead system. Model 0048 and model 0049 differ only in regard to the connector. The electrode coil consists of
Table 2 Technical data for implanted subcutaneous lead systems
Medtronic TransveneE SQ 6933 CPI EndotakE SQ model 0063 CPI EndotakE SQ array model 0048 / 0049
Surface area (cm 2 )
Electrode material
DC resistance (V)
6.6 28.0 51.0
Platinum alloy Titanium Platinum / platinum–iridium alloy
1.2 2 2
250
¨ et al. / International Journal of Cardiology 78 (2001) 247 – 256 V. Kuhlkamp
a platinum–iridium alloy with a surface area of 51.0 cm 2 (Table 2).
All implants were performed under general anesthesia. The transvenous lead system was introduced by direct puncture of the subclavian vein in 21 patients whereas the cephalic vein was used in nine patients. The cardioverter was implanted in a submuscular pectoral pocket in 26 patients and in the subrectus tissue of the left upper abdomen in four patients. The subcutaneous lead systems were placed deep subcutaneously on the left thorax between the anterior and the posterior axillary line at the level of the cardiac apex. For implantation of the array, a lead introducer with a stylet and a tunneling set were used. From a separate incision in the anterior axillary line, the fingers of the array electrode were placed subcutaneously with the tip of the electrode as posteriorly as possible. The middle finger of the electrode was positioned at the level of the cardiac apex, the first and third finger of the electrode were placed about 3–4 cm superior or inferior, respectively. A straight position of the finger electrodes was attempted, however, wrinkling of the finger electrode was allowed as long as the finger electrodes did not roll up. Fluoroscopy was used to control the position of the patch and the array electrodes.
tion threshold for the lead alone. Polarity of shocks was not changed during defibrillation threshold testing. If the subcutaneous electrode did not decrease the defibrillation threshold, it was removed. At the hospital predischarge test, ventricular fibrillation was induced via the implanted device. Again ventricular fibrillation had to last 10 s and the shock was triggered manually. The device was programmed to the energy of the defibrillation threshold that was determined during intra operative testing to reconfirm the defibrillation threshold. If this shock terminated ventricular fibrillation, the defibrillation threshold was considered to be unchanged. Whether the defibrillation threshold actually decreased was not tested. If this shock failed, ventricular fibrillation was terminated with a 34-J shock. The energy of the first shock was increased in steps of 2 J below 12 J and in steps of 3 J above 12 J until induced ventricular fibrillation was terminated by the first shock. In this case, an increase in the defibrillation threshold was assumed. For analysis of changes in impedance (V), only shocks with the same amount of stored energy were used. At 3 months follow-up, a third test to reconfirm the defibrillation threshold was performed. The initial energy was programmed to the intra operative defibrillation threshold value irrespective of the result obtained for the defibrillation threshold at the hospital discharge test.
2.5. Defibrillation threshold testing protocol
2.6. Statistics
At implant, ventricular fibrillation was induced using a ‘T-wave shock’ via an external cardioverter defibrillator (Medtronic model 5358) or by applying a 50-Hz alternating current with an external fibrillation box. In all patients, ventricular fibrillation lasted 10 s before the ICD shock was applied. A very strict step down protocol, starting with a 24 J biphasic shock, was employed (24, 20, 18, 15, 12, 10, 8, 6, 3 J). The defibrillation threshold was defined as the lowest shock strength (stored energy) which terminated VF. After determination of the defibrillation threshold with the transvenous lead only, either a subcutaneous patch electrode or a subcutaneous array electrode was implanted in a randomized fashion. Defibrillation threshold testing was then continued starting with the energy determined as the defibrilla-
The data are presented as mean61 S.D. Statistical analysis was done using the Student’s t-test. The two-way ANOVA test was used to determine how the defibrillation threshold or the impedance were affected by the two different types of leads used. Frequency distributions were calculated using the Fisher’s exact test. A probability value of less than 0.05 was considered to indicate statistical significance.
2.4. Implantation procedure
3. Results
3.1. Patient population Patients in the two study groups did not differ in
¨ et al. / International Journal of Cardiology 78 (2001) 247 – 256 V. Kuhlkamp
respect to age, sex, underlying cardiac disease, left ventricular function or clinical functional status (Table 1). The implantation procedure required 109638 min for patients with a subcutaneous patch electrode and 121637 min for patients with a subcutaneous array electrode (P5n.s.). Implantation-associated mortality was zero. No patient developed severe bleeding, infection of the lead system or other complications requiring additional therapy. Post-operatively, a substantial hematoma was seen in two patients with the patch electrode. After a follow-up of 5 and 21 months, respectively, one patch electrode had to be removed because the patient experienced severe pain in the area surrounding the implanted patch, while the second patient suffered recurrent seroma in the area of the patch. No such complications associated with the array electrode were seen during follow-up. Complications arose in four out of seven patients with the patch electrode. No complications were observed in the 13 patients receiving an array electrode (P,0.01).
251
Fig. 2. Change of the defibrillation threshold (J) for each individual patient (patient number 1 to 15) after additional implantation of the subcutaneous patch electrode. Data are presented in the order of inclusion into the study. j, defibrillation threshold with the Endotak lead (CPI) only; d, defibrillation threshold with the Transvene lead (Medtronic) only; m, defibrillation threshold with the Endotak lead and the subcutaneous patch electrode (Endotak SQ 0063); ♦, defibrillation threshold with the Transvene lead and the subcutaneous patch electrode (Medtronic TransveneE SQ 6933).
or an array electrode cannot be explained by different baseline values of the two study groups. In addition, baseline defibrillation thresholds and the impedances obtained with the Endotak lead were not significantly different from values obtained with the Transvene lead (Table 3). By adding the patch electrode, the defibrillation threshold was significantly decreased from 13.266.6 to 10.565.1 J (mean decrease 2.7 J, 95% confidence limit 0.2–5.1 J, P,0.05, Fig. 2 and Table 3). The addition of the patch electrode did not reduce the defibrillation threshold in six patients (40%, Fig. 2)
3.2. Defibrillation threshold and impedance of the high voltage circuit The initial defibrillation threshold with the leadonly configuration was 13.266.6 J in the patients receiving the patch electrode and 15.466.6 J in those receiving the array electrode (P5n.s., Table 3). The impedance of the lead-only system was 57611 V in the patch group and 5269 V in the array group (P5n.s.). The differences obtained by adding a patch Table 3 Two-way ANOVA table a DFT lead alone (J)
DFT lead1SQ patch or array (J)
CPI / Guidant (n57) Medtronic (n58) Total (n515) P-value
13.666.5 12.967.1 13.266.6
11.064.1 b 10.466.0 b 10.565.1 b
CPI / Guidant (n57) Medtronic (n58) Total (n515) P-value
14.168.0 16.565.5 15.466.6
P-value 0.26 ,0.05
Impedance lead alone (V) 5969 56613 57611
4366 b 4367 b 4366 b 0.75
55611 5068 5269
3664 c 3565 c 3664 c 0.28
0.77 8.065.9 c 8.464.5 c 8.265.0 c 0.54
,0.005 ,0.01
Impedance lead1SQ patch or array (V)
P-value ,0.001 ,0.001
,0.001 ,0.001
a DFT, defibrillation threshold. The effect of the patch or array electrode on the defibrillation threshold and the impedance was not significantly affected by the type of transvenous lead system. b SQ patch. c SQ array.
252
¨ et al. / International Journal of Cardiology 78 (2001) 247 – 256 V. Kuhlkamp
and the electrode was removed in these patients. An increase in the defibrillation threshold by 3 J was noted in one patient. In another patient, ventricular fibrillation was not terminated with the energy that had terminated ventricular fibrillation with the lead only. However, the ‘new’ defibrillation threshold was not tested. In both patients the patch electrode was removed. Therefore, the defibrillation threshold was not decreased by the additional subcutaneous patch electrode in eight patients. At the hospital discharge test an increase in the defibrillation threshold by 4 J in one patient and 5 J in two patients was observed. The defibrillation threshold in the group with implanted patch was 12.764.2 J. In those patients whose patch electrode was removed, three patients had an increase in the defibrillation threshold by 2, 4 and 8 J, respectively. In this group, the mean defibrillation threshold was 11.866.1 J. Since we did not perform a complete defibrillation threshold test, a direct comparison of these values to the intra operative values is not possible. At the 3-month follow up, an increase in the defibrillation threshold compared to the intra operative defibrillation threshold was present in one patient (from 6 to 8 J) whose patch electrode was removed and in another patient with an implanted patch electrode (increase from 10 to 15 J). The additional implantation of a patch electrode decreased the impedance of the system from 57611 to 4366 V (P,0.0001). The type of lead used had no significant effect on the impedance results (Table 3) and there was no correlation between the decrease of the impedance and the decrease of the defibrillation threshold (r 2 50.06, Fig. 3). As has been mentioned before, an increase in the defibrillation threshold cannot be ruled out in those patients without a decrease in the defibrillation threshold. The addition of an array electrode lowered the defibrillation threshold from 15.466.6 to 8.265.0 J (P,0.001, mean decrease 7.3 J, 95% confidence interval 4.4–10.1 J, Fig. 4 and Table 3). The decrease of the defibrillation threshold was not significantly different between the two types of leads used (Table 3). In two patients, the defibrillation threshold remained unchanged with the additional array electrode and the array electrode was removed. Similar to the patients with a patch electrode, the defibrillation threshold was 11.264.4 J at the hospital predischarge test. At the 3-month follow-up defibrillation test, two
Fig. 3. Relation of the change in impedance (delta-impedance HV electrode, V) to the change observed in the defibrillation threshold (delta DFT, J) in patients who received a patch electrode as an adjunct to the transvenous lead system. A 2 sign denotes an increase in the defibrillation threshold; in seven patients, no change of the defibrillation threshold was obtained with the subcutaneous patch electrode. One patient had an increase in the defibrillation threshold with the additional lead.
patients had an increase in the defibrillation threshold as compared to the intra operative value (intraoperative, 3 J in both patients; 3 months follow up, 8 J in one patient, 10 J in the other patient). In the two patients where the array electrode was removed, the
Fig. 4. Change of the defibrillation threshold (J) for every individual patient (patient number 1 to 15) after additional implantation of the subcutaneous array electrode (CPI EndotakE SQ array model 0048 / 0049). Data are presented in the order of inclusion in the study. j, defibrillation threshold with the Endotak lead (CPI) only; d, defibrillation threshold with the Transvene lead (Medtronic) only; m, defibrillation threshold with the Endotak lead and the subcutaneous array electrode (CPI EndotakE SQ array model 0048 / 0049); ♦, defibrillation threshold with the Transvene lead and the subcutaneous array electrode (CPI EndotakE SQ array model 0048 / 0049).
¨ et al. / International Journal of Cardiology 78 (2001) 247 – 256 V. Kuhlkamp
defibrillation threshold remained unchanged at 3 and 10 J, respectively at the hospital discharge test and the 3-month follow up test. Associated with the marked decrease of the defibrillation threshold in the array group was a decrease of the lead impedance from 5269 to 3664 V (P,0.0001). However, there was no correlation between the decrease in the defibrillation threshold achieved and the effect of the array electrode on the impedance of the shocking lead (r 2 50.01, Fig. 5). The decrease of impedance with the additional subcutaneous array electrode was not different between the Endotak and the Transvene lead (Table 3b). The effect on the defibrillation threshold of the array electrode (decrease 7.265.1 J) as an adjunct to a transvenous lead system was significantly larger than the effect of the patch electrode (decrease 2.764.4 J, P,0.05). Moreover, significantly more patients had a decrease of the defibrillation threshold with the array electrode (n513) than with the patch electrode (n57, P,0.05). Despite the larger surface area of the array electrode there was no significant difference in the decrease of impedance obtained with the array electrode (decrease 1768 V) compared to the patch electrode (decrease 1468 V). The results obtained with the patch or the array lead were independent of the type of transvenous lead
Fig. 5. Relation of the change in impedance (delta-impedance HV electrode, V) to the change observed in the defibrillation threshold (delta DFT, J) in patients who received an array electrode as an adjunct to the transvenous lead system. A 2 sign denotes an increase in the defibrillation threshold; in two patients no change in the defibrillation threshold was obtained with the subcutaneous array electrode. An increase in the defibrillation threshold was not seen with the additional lead.
253
system, the mode of induction of ventricular fibrillation or the device used.
4. Discussion The value of an additional subcutaneous electrode in achieving a sufficiently low defibrillation threshold for an implantable cardioverter defibrillator with a nonthoracotomy lead system has been shown in experimental and clinical studies [5–13]. The present study compares an array electrode and a subcutaneous patch electrode in a randomized fashion with a very strict defibrillation threshold testing protocol. Complications such as bleeding, severe pain or a seroma, were observed postoperatively or during follow-up only in association with the patch electrode (P,0.01). No complications arose from the array electrode. The problems associated with the patch electrode have been reported by others [10,11,14]. The time required for the implantation procedure was not different between the two types of electrodes used. If a single incision is used for implantation of the array electrode, the procedure could be considerably shortened [8]. Of specific importance is the fact that a marked reduction of the defibrillation threshold could be obtained irrespective of the baseline value with the lead alone. However, the effect on the defibrillation threshold was not related to the decrease in impedance (Figs. 3 and 5). The change of the defibrillation field may have been more important than the effects on impedance which has also been shown in experimental studies [9,15,16]. It has been shown recently that a two-element array and a single element array are as effective as the three-element array used in this study [17,18]. Hence, the defibrillation threshold may be influenced mainly by the change of the defibrillation field. This is consistent with experimental studies showing that defibrillation is successful if a sufficient voltage gradient is achieved in about 90% of the myocardial mass [19]. The defibrillation field obtained with the array electrode might be more advantageous than the field with the subcutaneous patch electrode. The area ‘covered’ by the array electrode is larger and increases the defibrillation field to the more posterior area. This seems to be the most likely explanation besides a
254
¨ et al. / International Journal of Cardiology 78 (2001) 247 – 256 V. Kuhlkamp
decrease of impedance for the lower defibrillation thresholds obtained with the array electrode. Similar data have been obtained with a single element subcutaneous array electrode [20]. In this regard, the positioning of the patch electrode on the thorax will also have a marked influence on the defibrillation field and hence the defibrillation threshold [21,22]. However, different positions of the patch electrode were not tested in this study. Usually defibrillators are implanted with the shell of the defibrillator acting as an active part of the defibrillation circuit. The effect of the shell of the defibrillator might be similar to the effect seen with the subcutaneous patch. The data on the use of a transvenous lead system with two defibrillation coils in addition to an active can system are inconclusive with some investigators reporting a significant advantage and others a reporting only a minor effect [2,23–25]. This may be explained in part by different positions of the vena cava superior lead [26]. However, the patch electrode is usually placed lower on the thorax in the midaxillary line. The position of the patch has an important effect on the defibrillation threshold and therefore the data obtained with the active can system cannot be transferred to a dual lead transvenous system with an additional patch electrode. Two recent studies compared the clinical efficacy of a subcutaneous array electrode with a subcutaneous patch electrode in a large patient population. The results of these investigations suggest that a subcutaneous array is superior to a patch as a subcutaneous electrode to lower the defibrillation threshold [11,27]. However in both studies only monophasic shocks were used. Chronic defibrillation thresholds or complications occurring during longterm follow-up are not reported. Adding a patch electrode or an array electrode to a transvenous electrode significantly decreases the energy requirements for successful termination of ventricular fibrillation. An unexpected finding of our study was that the addition of a patch electrode was of no value in about 50% of our patients. In six patients the defibrillation threshold remained unchanged. In one patient, the defibrillation threshold actually increased after the implantation of the patch electrode. In one of the above cited studies, the addition of the patch electrode to the transvenous lead did not decrease the defibrillation threshold [27]. This
has also been observed with the implantation of an array electrode in combination with monophasic shocks [11]. One possible explanation is, since the subcutaneous electrode was always implanted after determination of the defibrillation threshold for the lead only, the overall hemodynamic situation worsened with subsequent increase in the defibrillation threshold [28]. However, the defibrillation threshold with the lead-only configuration was reconfirmed by the final shock delivered by the implanted device programmed to the energy of the defibrillation threshold. Hence, a change in the defibrillation field can be disadvantageous, leading to an increase in the energy requirements for successful defibrillation. There are several limitations of the present study. First we used two different transvenous lead systems and defibrillators in this study. However, the two systems behaved very similarly making it less likely that different results would have been obtained if only the Endotak or the Transvene system had been used. A further limitation is inherent to the clinical method of determining a defibrillation threshold [29]. A step down protocol for measurement of the defibrillation threshold does not take into account that the probability of successful defibrillation of ventricular fibrillation only increases with increasing amounts of energy. This problem can clearly be overcome by multiple tests and determining the probability of terminating ventricular fibrillation at each energy level. However, it has been shown that the defibrillation threshold usually has a predictable relationship to the ‘dose–response curve’ [30,31]. We tried to reconfirm the defibrillation threshold obtained during intra operative testing using the same amount of stored energy at two final tests in the operating room, at the hospital discharge test and at the 3-month follow up test. Furthermore, we always started with testing of the defibrillation threshold of the lead only. This type of protocol was chosen since it is closer to actual clinical conditions where an additional electrode is usually implanted after the lead-only configuration has failed. Simple clinical predictors for biphasic defibrillation thresholds have not been found [32]. Since defibrillation thresholds are highly variable, measuring defibrillation thresholds with the additional patch and the additional array electrode in a randomized manner
¨ et al. / International Journal of Cardiology 78 (2001) 247 – 256 V. Kuhlkamp
in the same patient is probably superior to a comparison of two groups. It is concluded that the addition of a subcutaneous array electrode to a transvenous lead is more efficient than a subcutaneous patch electrode. Lead associated complications were only observed with the patch electrode. We therefore recommend implantation of a subcutaneous array electrode if an additional electrode is necessary to achieve an acceptable biphasic defibrillation threshold.
References [1] Zipes DP, Roberts D. Results of the international study of the implantable pacemaker cardioverter-defibrillator — A comparison of epicardial and endocardial lead systems. Circulation 1995;92:59–65. [2] Bardy GH, Dolack GL, Kudenchuk PJ, Poole JE, Mehra R, Johnson G. Prospective, randomized comparison in humans of a unipolar defibrillation system with that using an additional superior vena cava electrode. Circulation 1994;89:1090–3. [3] Saksena S, An H, Mehra R, DeGroot P, Krol RB, Burkhardt E, Mehta D, John T. Prospective comparison of biphasic and monophasic shocks for implantable cardioverter defibrillators using endocardial leads. Am J Cardiol 1992;70:304–10. [4] Bardy GH, Ivey TD, Allen MD, Johnson G, Mehra R, Greene HL. A prospective randomized evaluation of biphasic versus monophasic waveform pulses on defibrillation efficacy in humans. J Am Coll Cardiol 1989;14:728–33. [5] Wetherbee JN, Chapman PD, Klopfenstein HS, Bach SM, Troup PJ, McDowell CA. Nonthoracotomy internal defibrillation in dogs: Threshold reduction using a subcutaneous chest wall electrode with a transvenous catheter electrode. J Am Coll Cardiol 1987;10:406– 11. [6] Scott S, Accorti P, Callaghan F, Abels D, Bojeva B. Ventricular and atrial defibrillation using new transvenous tripolar and bipolar leads with 5 french electrodes and 8 french subcutaneous catheters. PACE 1991;14:1893–8. [7] Bardy GH, Hofer B, Johnson G, Kudenchuk PJ, Poole JE, Dolack GL, Gleva M, Mitchell R, Kelso D. Implantable transvenous cardioverter-defibrillators. Circulation 1993;87:1152–68. [8] Kall JG, Kopp D, Lonchyna V, Blakeman BP, Cadman C, O’Connor M, Kinder C, Gilkerson J, Avery R, Wilber DJ. Implantation of a subcutaneous lead array in combination with a transvenous defibrillation electrode via a single infraclavicular incision. PACE 1995;18:482–5. [9] Lang DJ, Heil JE, Hahn SJ, Lindstrom CC, Derfus DL. Implantable cardioverter defibrillator lead technology: Improved performance and lower defibrillation thresholds. PACE 1995;18(II):548–59. [10] Jordaens LJ, Vertongen P, Bellegham YV. A subcutaneous lead array for implantable cardioverter defibrillators. PACE 1993;16:1429–32. [11] Higgins SL, Alexander DC, Kuypers CJ, Brewster SA. The subcutaneous array: A new lead adjunct for the transvenous ICD to lower defibrillation thresholds. PACE 1995;18:1540–8. [12] Jordaens LJ, Trouerbach J-W, Vertongen P, Herregods L, Poelaert J, Van Nooten G. Experience of cardioverter-defibrillators inserted without thoracotomy: evaluation of transvenously inserted leads alone or with a subcutaneous axillary patch. Br Heart J 1993;69:14– 9.
255
[13] Yee R, Klein GJ, Leitch JW, Guiraudon GM, Guiraudon CM, Jones DL, Norris C. A permanent transvenous lead system for an implantable pacemaker cardioverter-defibrillator. Circulation 1992;85:196–205. [14] Saksena S, Breithardt G, Dorian P, Greene HL, Madan N, Block M. Nonpharmacological therapy for malignant ventricular arrhythmias: Implantable defibrillator trials. Prog Cardiovasc Dis 1996;38:429– 44. [15] Nogami A, Takahashi A, Nitta J, Aonuma K, Iesaka Y, Hiroe M, Marumo F, Hiraoka M. Comparative efficacy of a subcutaneous mesh and plate electrodes for nonthoracotomy canine defibrillation. PACE 1991;14:1402–10. [16] Tang A, Wolf P, Afework Y, Smith WM, Ideker RE. Three-dimensional potential gradient fields generated by intracardiac catheter and cutaneous patch electrodes. Circulation 1992;85:1857–64. [17] Seidl K, Block M, Hammel D, Hauer B, Isgro F, Brunn J, Seifert T, Breithardt G. Ist der mittlere Finger einen subcutanen Array-Elek¨ die Defibrillation verzichtbar? Z Kardiol 1995;84(Suppl. trode fur I):106, (Abstr.). ¨ ¨ [18] Kuhlkamp V, Khalighi K, Dornberger V, Ziemer G. Single-incision and single-element array electrode to lower the defibrillation threshold. Ann Thorac Surg 1997;64:1177–9. [19] Frazier DW, Wolf PD, Wharton JM, Tang ASL, Smith WM, Ideker RE. Stimulus-induced critical point: Mechanism for electrical initiation of reentry in normal canine myocardium. J Clin Invest 1989;83:1039–52. ¨ ¨ [20] Kuhlkamp V, Dornberger V, Khalighi K, Mewis C, Suchalla R, Ziemer G, Seipel L. Effect of a single element subcutaneous array electrode added to a transvenous electrode configuration on the defibrillation field and the defibrillation threshold. PACE 1998;21:2596–605. [21] Desai P, DeGroot P, Casavant D. Is patch position critical for successful nonthoracotomy (NTL) ICD implant with biphasic shocks? Circulation 1993;88(Suppl. I):215, (Abstr.). [22] Swartz JF, Fletcher RD, Solomon AJ, Donofrio J, DeGroot P. Subscapular patch reduces defibrillation threshold when used with a pectoral can and a biphasic implantable defibrillator. PACE 1994;17:850, (Abstr.). [23] Mouchawar GA, Wolsleger WK, Doan PD, Causey JD, Kroll MW. Does an SVC electrode further reduce DFT in a hot-can ICD system? PACE 1997;20:163–7. [24] Haffajee C, Martin D, Bhandari A, Bardy GH, Desouza C, ¨ Kuhlkamp V, Church T. A multicenter randomized trial comparing an active can implantable defibrillator with a passive can system. Jewel Active Can Investigators. PACE 1997;20:215–9. [25] Gold MR, Foster AH, Shorofsky SR. Effects of an active pectoralpulse generator shell on defibrillation efficacy with a transvenous lead system. Am J Cardiol 1996;78:540–3. [26] Markewitz A, Kaulbach H, Mattke S, Dorwarth U, Hoffmann E, Weinhold C, Steinbeck G, Reichart B. The left subclavian vein as an alternative site for implantation of the second defibrillation lead. PACE 1995;18:401–5. [27] The Endotak / PRX Investigator Group, Baker JH, Epstein AE, Voshagestahl L. A prospective randomized evaluation of a nonthoracotomy implantable cardioverter defibrillator lead system. PACE 1997;20:72–8. [28] Steinbeck G, Dorwarth U, Mattke S, Hoffmann E, Markewitz A, Kaulbach H, Tassani P. Hemodynamic deterioration during ICD implant: predictors of high-risk patients. Am Heart J 1994;127:1064–7. [29] McDaniel WC, Schuder JC. The cardiac ventricular defibrillation threshold — inherent limitations in its application and interpretation. Med Instrum 1987;21:170–6.
256
¨ et al. / International Journal of Cardiology 78 (2001) 247 – 256 V. Kuhlkamp
[30] Rattes MF, Jones DL, Sharma AD. Defibrillation threshold: A simple and quantitative estimate of the ability to defibrillate. PACE 1987;10:70–7. [31] Jones DL, Irish WD, Klein GJ. Defibrillation efficacy — comparison of defibrillation threshold versus dose response curve determination. Circ Res 1991;69:45–51.
[32] Raitt MH, Johnson G, Dolack GL, Poole JE, Kudenchuk PJ, Bardy GH. Clinical predictors of the defibrillation threshold with the unipolar implantable defibrillation system. J Am Coll Cardiol 1995;25:1576–83.