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Bipolar atrial application of a new temporary pacing lead after cardiac operations
J THORAC
CARDIOVASC SURG
85:625-631, 1983
Bipolar atrial application of a new temporary pacing lead after cardiac operations A new temporary pacing lead, Medtronic Model 6400, with a defined electrode surface area of 7.5 mm", has been clinically and electrophysiologically evaluated during bipolar atrial application in 20 patients after cardiac operations. A silicon disc was used for fixation of the electrodes to the right atrium in 10 patients, and an atrial plication technique was used in the other 10. Myocardial stimulation threshold and resistance were measured throughout the postoperative period. Atrial electrograms were recorded on magnetic tape for computer analysis of amplitudes, slew rates, and signal source impedance. No significant differences (p > 0.1) were found in myocardial stimulation threshold between the two fixation modes. During constant-current pacing, median threshold rose from 0.65 rnA to 2.3 rnA. Stimulation resistance, measured during constant-voltage pacing, fell from 567 to 365 n, with a subsequent rise to 425 n before electrode removal. Again no difference was found between silicon disc and plication fixation of the electrodes. Pswave amplitudes were significantly higher with plication than with silicon disc fixation (2.26 versus 0.86 mV, p < 0.01), as were slew rates (0.34 versus 0.18 Vis, p < 0.05). Signal source impedance had a magnitude of 6 kn. The electrodes were used successfully in 12 (60%) of the patients for diagnosis and lor treatment of arrhythmias. We find the new lead well suited for atrial application.
Kjell Breivik, M.D., Hogne Engedal, M.D., Fin Resch, M.D., Leidulf Segadal, M.D., and Ole-Jergen Ohm, M.D., Bergen. Norway
Use of temporary pacing leads after cardiac operations has become routine in most centers. Several reports have emphasized the hemodynamic improvements from atrial or atrioventricular sequential pacing. Atrial electrode application is also recommended for the diagnosis and treatment of tachyarrhythmias." " The multifilamental braided wire electrodes in common use have a relatively high pacing and sensing failure rate.": 8 We have clinically evaluated a new temporary pacing lead (Model 6400*), and report our experience with this lead used in the bipolar mode on the right atrium in 20 patients.
Patients and methods The study population consisted of 16 men and four women with a mean age of 57 years (range 46 to 65). From the Medical Department A and Surgical Department. Section of Thoracic and Cardiovascular Surgery. Haukeland Sykehus, University of Bergen. School of Medicine, Bergen, Norway. K. Breivik is a recipient of a scholarship from the Norwegian Council on Cardiovascular Diseases. Received for publication March 29, 1982. Accepted for publication May 10. 1982. Address for reprints: Kjell Breivik , M.D., Medical Department A, N-5016 Haukeland Sykehus, Bergen, Norway. *Medtronic B. V., Kerkrade, Holland.
Fourteen of the patients had aorta-coronary bypass operations, three had mitral valve replacement, two open mitral commissurotomy, and one patient had a combined aortic valve replacement and a single aortacoronary bypass graft. All patients gave their informed consent to take part in the study. Electrode and surgical method. The temporary pacing lead is made of a Teflon-coated stainless steel wire connected to a solid electrode with a defined stimulation and sensing area of 7.5 mm- (Fig. 1). To the electrode is fastened a polypropylene fiber, proximally coiled and distally ending in an atraumatic curved needle. At the proximal end of the lead is a straight needle for tunnelling the lead through the upper abdominal wall. The lead was used in the bipolar mode. In order to examine possible effects of the electrode fixation technique on the electrophysiological parameters, we used the atrial plication technique in 10 patients and fixed the lead with a silicon disc (Fig. 1) in the remaining 10. Plication was performed with one or two sutures, and the atrial wall was wrapped around the electrode to create direct tissue contact with the complete electrode surface. The two electrodes were placed 2 to 3 em apart. With the other technique, using the silicon disc, the two electrodes were inserted into the disc 5 mm 625
The Journal of Thoracic and Cardiovascular Surgery
626 Breivik et al .
Teflon insulated conductor wire
\
Polypropylene coil
I
I(~~
Electrode with area of 7.5 mm 2
----
F 14mm ~ Fig. 1. Medtronic Model 6400 temporary pacing lead (top). The stainless steel electrode has an area of 7.5 mm". To the electrode is connected a polypropylene coil for fixation of the electrode to the disc or in the myocardium. Bottom. Silicon disc with two electrodes for optimal fixation to the atrium.
apart (Fig. I) before being attached to the atrial wall with two sutures. The electrodes were fastened to the right atrium at the end of the operation. The leads were brought out through the upper abdominal wall and sutured to the skin. They were then connected to an external pulse generator or capped off for future use. Eighteen of the patients also had ventricular electrodes implanted to have the option of atrioventricular sequential pacing. All leads were removed on postoperative day 13, and the patients were monitored for I more day before discharge from the hospital. Myocardial stimulation threshold and resistance. Myocardial threshold was measured both at constantvoltage pacing, with a pacing system analyzer of the condenser discharge type (Medtronic 5300 PSA*), and during constant-current pacing (Medtronic 5880 A). The PSA gives the current on a digital display 90 usee into the pulse, and stimulation resistance was thus calculated at myocardial threshold at I msec pulse width. Measurements were made within I hour postoperatively and then daily or every second day until explantation of the electrodes. Electrogram amplitudes and slew rates. The patients' electrograms were recorded on magnetic tape (Tandberg Instrumentation Recorder, TIR 115t), unloaded, and loaded with resistors and capacitors for further computer analysis (Digital Equipment, PDPI It) of P-wave amplitudes and slew rates. 9 Recordings *Medtronic Inc., Minneapolis, Minn. tTandberg Radiofabrikk AIS, Oslo, Norway. :j:Digital Equipment Corporation, Maynard, Mass.
were made within I hour postoperatively and then on the sixth and thirteenth postoperative days. Signal source impedance. The recorded signals were subjected to Fast Fourier Transform. The spectral ratios between loaded and unloaded electrograms were used to calculate the signal source impedance. to Statistical methods. For statistical comparison between the two fixation techniques, Student's t test was used. Differences were considered statistically significant when p < 0.05. Results We encountered no problems or complications with the use of the leads. Removal of the leads was easy and caused little discomfort to the patients. Myocardial stimulation threshold and resistance. Myocardial threshold at I msec pulse duration rose from median 0.7 V/1.5 rnA to 2.2 V/6.4 rnA with a subsequent reduction to 2.1 VI 4.7 rnA until electrode removal (Table I, Fig. 2). Constant-current threshold (1.8 msec pulse duration) rose from 0.65 to 2.3 rnA, with a small reduction to 2.2 rnA. There were no significant differences in thresholds between the two fixation methods (p > 0.1). No stimulation failures were seen, but one patient had a somewhat unusual threshold rise to 8.3 V124.7 rnA. We have therefore chosen to use median values instead of mean values to give the most correct expression for electrode performance. Atrial fibrillation developed on the third postoperative day in one patient operated upon for mitral stenosis. She had a large left atrium with long-standing atrial fibrillation before the operation. Electroversion was
Volume 85
Temporary pacing lead
Number 4 April, 1983
627
(mA) 23 3
20
~,
1
VOLTAGE
CURRENT
18 13.1'\
(volts)
10
8 6 4 2
0.1 0.25
2.0
Fig. 2. Strength duration curves (median and quartiles) for myocardial stimulation threshold I hour postoperatively (/ h PO) (n = 20) and on thirteenth postoperative day (/3 POD) (n = 19).
Table I. Atrial stimulation threshold in the 20 patients studied
Table II. Atrial stimulation resistance during constant-voltage pacing at myocardial threshold *
Atrial stimulation threshold Median
Atrial stimulation resistance
Range
Median p Value
(fl)
One hour postop. Constant voltage* (V ImA) Constant currentt (rnA) Maximum value Constant voltage* (V ImA) Constant currenrt (rnA) Postop. day 13 Constant voltage* (V ImA) Constant currenrr (rnA)
0.7/1.5 0.65
0.25-3.3/0.6-5.4 0.2-3.3
2.2/6.4 2.3
15-8.312.4-24.7 1.1-8.0
2.1/4.7 2.2
1.15-8.3/2.4-24.7 1.05-8.0
'Measured with Medtronic 5300 PSA at I msec pulse duration. f Measured with Medtronic 5880 A at 1.8 msec pulse duration.
therefore not tried. In 14 of the remaining 19 patients (70%), maximum threshold was found before electrode removal, median on eighth postoperative day. In five of the patients there was a continuous but small increase in threshold throughout the observation period. . Myocardial stimulation resistance fell from median 567 to 365 n (p < 0.001), but there was a subsequent rise to 425 n before electrode removal (Table II) (p < 0.01). Minimum resistance was usually found on postoperative days 4 to 6. Electrogram amplitudes and slew rates. There was a significant difference in both P-wave amplitude (2.26 versus 0.86 mV on postoperative day 6, p < 0.01) and slew rate (0.34 versus 0.18 on postoperative day 6,
One hour postop. Minimum value Postop. day 13
567 365 425
304-1,000 270-552 333-605
p < 0.001 P < 0.01
'Calculated 90 f.Lsec into the pulse from measurements made on a condenser discharge-type pulse generator (Medtronic 5300 PSA) at I msec pulse duration.
p < 0.05) between the plication and silicon disc fixation techniques (Table III). The P-wave amplitude had a minimum value less than 0.7 m V intermittently in only one of the patients subjected to the plication technique compared to six patients with silicon discs. Very low slew rates « 0.2 V/sec) were found in more than half of the patients in both groups. Both amplitudes and slew rates fell from 1 hour postoperatively until the sixth postoperative day, with a small but significant increase in amplitude (p < 0.01) until the thirteenth postoperative day. The small rise in slew rate was not statistically significant (p > 0.1). Signal source impedance. Because of very low P-wave amplitudes and also irregular atrial rhythms in some patients, data analysis could be done in only 17 patients 1 hour postoperatively and in seven patients on the sixth and thirteenth postoperative days. One hour postoperatively there were no significant differences in
628
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Breivik et al.
Table HI. Computer analysis of atrial electrogram amplitudes and slew rates One hour postop, Slew rate (V/sec)
Amplitude (mV)
Fixation technique
Mean 1: SEM
Plication Silicon disc p Values*
2.56 1: 0.25 1.62 1: 0.28 <0.001
I
Postop. day 6
Range
Mean 1: SEM
1.69-4.39 0.42-3.29
0.571:0.06 0.331:0.06 <0.01
I
Amplitude (mV)
Range
Mean 1: SEM
0.27-1.04 0.14-0.86
2.26 ± 0.44 0.861:0.09 <0.01
I
Slew rate (V/sec)
Range
Mean ± SEM
0.42-4.36 0.38-1.28
0.341: 0.07 0.181:0.01 <0.05
I
Range
0.13-0.58 0.14-0.21
*Statistical differences in electrogram amplitudes and slew rates between the two fixation techniques.
Table IV. Signal source impedance calculated from resistive and capacitive loaded and unloaded electrograms in seven of the patients* One hour postop. n = l7t
Tissue resistance, RT (0) Helmholtz capacitance, C H (JLF) Faraday resistance R, (kO)
1,2261:51 2.01:0.1 20.1 1: 1.3
I
Mean 1: SEM
1,164 1: 75 2.01:0.1 19.8 ± 2.3
POSlOp. day 6
I
Range
820-1,450 1.7-2.5 11.7-30.6
p Value
<0.01
NS NS
Mean 1: SEM
1,006 1: 35 2.0 ± 0.1 20.1 1: 2.2
I
Range
900-1,190 J .7-2.2 11.8-28.5
Legend: NS. Not significant.
*RT is calculated in frequency regions 15 to 75 Hz, CH in 20 to 40 Hz, and R.. at 0 to 10 Hz. The wire resistance. which is small «8fl) is incorporated in RT . tn = 17 indicates total number of electrograms that could be investigated I hour postoperatively.
tissue resistance (R T ) , Helmholtz capacitance (C H ) , or Faraday resistance (Rs) between the two fixation modes, and these results are therefore combined (Table IV). The- data from postoperative days 6 and 13 are all from seven patients in whom the plication technique was used. R T fell by about 20% from I hour postoperatively to the sixth postoperative day (p < 0.001), with a subsequent rise until the thirteenth day (p < 0.05), but C H and R r showed no significant variations (p > 0.2). If the mean values for RT , C H , and a, found in this study are used for calculating signal source impedance, to the value will be =6 kf! in the frequency region of IS to 20 Hz. Clinical use of the electrodes. In seven patients (35%), the atrial leads were used for postoperative pacing of bradyarrhythmias (sinoatrial blocks, sinus bradycardia). In six patients (30%), including one of those mentioned earlier, the electrodes were used on II occasions for confirming the diagnosis of a supraventricular tachyarrhythmia (Fig. 3). Overdrive conversion was tried in three of the patients with type I atrial flutter (atrial rate ~ 350 beats/min), with success in two cases (Fig. 4). In the third patient, who had an enlarged atrium and longstanding arrhythmia before the operation, the attempt was unsuccessful.
Discussion Patients who fulfilled the department's criteria for placement of temporary pacing wires were selected for the study. The two groups were not randomized but are comparable with respect to etiologic diagnosis and age. The new lead has a small solid electrode tip with a defined area of 7.5 mm", By contrast, multifilamental temporary wires have much greater areas and, consequently, are subject to frequent stimulation and sensing failures. 7, 8 Some centers also have been reluctant in using these wire electrodes on the atria because of their size and somewhat rough surface, although modifications in construction and fixation technique have been proposed. 6, lI-t3 Waldo and associates" recommended placement of two electrodes on the atria, so that bipolar pacing could be achieved. The bipolar lead configuration primarily records deflections, which represent atrial activation, and rejects ventricular activation and external electromagnetic interference. During bipolar stimulation, the pacing artifact will not distort the baseline of the electrocardiogram. Two electrodes also give redundancy in changing polarity if stimulation or sensing failure should occur. The new lead is provided with a specially designed silicon disc (Fig. 1), so that one has the choice between this disc or conventional plication and suture technique
Volume 85 Number 4
Temporary pacing lead
April. 1983
Postop. day 13 Amplitude (mV)
Slew rate (V / sec)
Mean ± SEM
Range
Mean ± SEM
Range
2.79 ± 0.38 0.93 ± 0.17 <0.01
121-4.45 0.36-1.84
0.37 ± 0.07 0.19 ± 0.02 <0.02
0.15-0.65 0.13-0.26
Postop. dav 13 p Value
<0.05
NS NS
Mean ± SEM
1,0% ± 60 2.0 ± o.t 21.6 ± 2.2
Range
870-1,380 1.7-2.2 12.3-28.3
for fixation of the electrodes. With the silicon disc, firm attachment to the atrium is ensured and the risk of dislodgment is minimal. The disc will remain on the atrium when the electrodes are explanted. However, this should be a minor objection to its use, as silicon has earlier proved to be a biocompatible material. In our opinion, a disadvantage to the disc is that its size and shape may hinder its optimal placement near the superior vena cava. Furthermore, only part of the electrode surface is brought into contact with the atrial wall. The plication technique is more flexible and allows better localization and contact of the electrodes. Myocardial threshold. There was no significant difference in median threshold with the two fixation techniques. The rise in threshold was relatively moderate and was of the same magnitude as earlier found in studies in which this electrode was used on the right ventricle. 14. 15 Mashhour and associates 16 found atrial threshold to be one third with this electrode compared to a series with the Garlock multifilamental heart wires. 'Ye14 found similar results for this new lead compared with a braided wire electrode (Davis & Geck) during right ventricular application. Myocardial stimulation resistance. The relatively high resistance found on the pair of electrodes is an advantage in securing normal pacemaker function. The 20% to 30% reduction in stimulation resistance up to the fourth to sixth postoperative days, with subsequent rise, is similar to that found in studies of the right
629
ventricle. 7. 14. 15 However, stimulation resistance was about 25% lower than that found in the ventricles" (p < 0.01). This difference may be caused by the greater myocardial mass of the ventricles. Different implantation techniques, with greater tissue trauma to the ventricles, where the electrode is completely buried in the myocardium, may also be of importance. Electrogram amplitudes and slew rates. There was no significant difference in P-wave amplitudes measured I hour postoperatively and at explantation (p > 0.1). Slew rates had decreased by about 40% (Table III), which is of the same magnitude as that found during studies of the right ventricle. 14. 15 Both P-wave amplitudes and slew rates were better when the plication technique was used (Table III). The reason for these better results may be the difficulties in getting an optimal placement of the silicon disc, which often had to be placed relatively low on the right atrial wall. Furthermore, less than half of the electrode surface is in direct tissue contact. The short distance between the two electrodes (5 to 6 mm) in the disc may also be of importance. The relatively short dipolar distance increases the possibility of recording a lower bipolar electrogram, since the depolarization wave front may reach the two electrodes almost simultaneously. With the plication technique, one may place the electrodes closer to the area of the sinus node, and the distance between the electrodes can usually be increased to 2 to 4 cm. Mashhour and associates'" used the silicon disc fixation technique in 16 patients and found P-wave amplitudes similar to those that we recorded during the plication technique. They measured the P-wave amplitudes intraoperatively to find an optimal site for electrode placement; this technique may be required if one applies the silicon disc. With the newer external atrial pulse generators, the highest P-wave sensitivity is usually 0.6 to 0.7 rnA. According to the values for minimal P-wave amplitudes found in this study, sensing failure would have occurred only intermittently in one patient with the plication technique versus six of the patients with the silicon disc fixation. Regarding signal source impedance, R T was =25% lower (p < 0.01) whereas C H and R F were of the same magnitude (p > 0.1) as found during ventricular use of these electrodes.:" The signal source impedance of about 6 kil indicates that the external pulse generator preferably should have a high input impedance, i.e., 50 kil,8. 9 in order to avoid too great attenuation of the low atrial electro grams . During this study the atrial electrodes were used in 12 (60%) of the patients on one or more occasion, most
The Journal of
630
Thoracic and Cardiovascular Surgery
Breivik et al.
Atrial .picardical leads Fig. 3. Electrocardiogram from monitoring lead in patient with tachycardia (upper strip). Registration from atrial electrodes (bottom strip) clearly identifies type I atrial flutter with atrial rate =300 beats/min. (Paper speed 25 mm/sec).
II
III
* * * * * * * * * Fig. 4. Electrocardiographic recording from the same patient as in Fig. 3 during an attempt at overdrive conversion with rapid atrial pacing. Atrial capture is shown in Lead V 2 (pacemaker pulses are denoted with asterisks). After 10 seconds of stimulation (only the last 4 seconds shown) at a pacemaker rate of 400 beats/min, the external pacemaker is turned off, and regular sinus rhythm is restored.
often for pacing of bradyarrhythmias, but also for the diagnosis and treatment of tachyarrhythmias. Waldo and associates" found that atrial electrodes were used for diagnosis or treatment of arrhythmias in 85% of a random patient sample in their clinic. They state that routine placement of both atrial and ventricular wire
electrodes at the time of the operation is indicated irrespective of the nature of the cardiac procedure or preoperative rhythm. Other authorst" have found significant improvement in cardiac output during both atrial and atrioventricular sequential pacing compared with ventricular pacing. In
Volume 85
Temporary pacing lead
Number 4
April,1983
this study, two of 18 patients (11. 1%) who also received ventricular electrodes were paced during episodes of slow atrial fibrillation. Both patients were operated upon for mitral stenosis and had enlarged atria. In these patients both atrial and ventricular electrodes seem clearly indicated, because of their tendency toward atrial fibrillation in the postoperative period. None of our patients required atrioventricular sequential pacing, because their hemodynamic status was satisfactory in the postoperative phase.
Conclusions The new electrode is well suited for use on the atria after cardiac operations. The plication technique was found to be better than using a silicon disc for fixation of the electrodes with regard to P-wave sensing. In patients in whom prophylactic postoperative electrode placement is indicated, both atrial and ventricular electrodes should be implanted.
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3
4
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REFERENCES Friesen WG, Woodson RO, Ames AW, Herr RH, Starr A, Kassebaum OG: A hemodynamic comparison of atrial and ventricular pacing in postoperative cardiac surgical patients, 1 THORAC CARDIOVASC SURG 55:271-279. 1968 Hodam RP. Starr A: Temporary postoperative epicardial pacing electrodes. Their value and management after open-heart surgery, Ann Thorac Surg 8:506-510. 1969 Fields 1, Berkovits BV, Matloff 1M: Surgical experience with temporary and permanent A- V sequential demand pacing. 1 THORAC CARDIOVASC SURG 66:865-877, 1973 Curtis 11, Maloney 10, Barnhorst OA, Pluth 1R, Hartzler GO, Wallace RB: A critical look at temporary ventricular pacing following cardiac surgery. Surgery 82:888-893. 1977 Hartzler GO, Maloney 10. Curtis 11. Barnhorst OA: Hemodynamic benefits of atrioventricular sequential pacing after cardiac surgery. Am 1 Cardiol 40:232-236. 1977 Waldo AL, MacLean WAH. Cooper TB, Kouchoukos
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8
9
10
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13
14
15
16
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NT, Karp RB: Use of temporarily placed epicardial atrial wire electrodes for the diagnosis and treatment of cardiac arrhythmias following open-heart surgery. 1 THoRAc CARDIOVASC SURG 76:500-505. 1978 Ohm 0-1, Merkrid L, Skagseth E: Temporary pacemaker treatment in open heart surgery. Variation in myocardial threshold, tissue and interface impedances in man. PACE 2: 162-174, 1979 Ohm 0-1, Skagseth E: Temporary pacemaker treatment in open heart surgery: Pre- to postoperative changes in the electrogram characteristics. PACE 3:150-158,1980 Ohm 0-1: The interdependence between electrogram, total electrode impedance and pacemaker input impedance necessary to obtain adequate function of demand pacemakers. PACE 2:465-485, 1979 Merkrid L, Ohm 0-1, Hammer E: Signal source impedance of implanted pacemaker electrodes estimated from the spectral ratio between loaded and unloaded electrograms in man. Med BioI Eng Comput 18:223-232, 1980 Aris A, Flemma R1. Tector A1, Schmahl T, Lepley 0: An improved implantable temporary pacemaker electrode. 1 THORAC CARDIOVASC SURG 67:708-711, 1974 Spyrou PG: A simple technique of placing temporary atrial pacemaker electrodes. Ann Thorac Surg 31:377378, 1981 Sakurai 1. Murakita K. Bandi T. Iwa T: A new myocardial electrode for temporary pacing (abstr). PACE 3: 386, 1980 Breivik K, Engedal H, Segadal L, Ohm 0-1: New temporary pacing lead for use after cardiac operation. 1 THoRAc CARDIOVASC SURG 84:787-794, 1982 Breivik K, Engedal H, Resch F, Segadal L, Ohm 0-1: Clinical and electrophysiological properties of a new temporary pacemaker lead after open-heart surgery. PACE 5:600-606. 1982 Mashhour YAS, Bredee 11, Wijers TS, EI Gamal MIH, van Gelder LM, Lindemans FW: A new atrial lead with bipolar configuration for temporary pacing after open heart surgery. A comparison with a series of Garlock electrodes (abstr). PACE 4:A-90, 1981
CARDIOVASC SURG
85:625-631, 1983
Bipolar atrial application of a new temporary pacing lead after cardiac operations A new temporary pacing lead, Medtronic Model 6400, with a defined electrode surface area of 7.5 mm", has been clinically and electrophysiologically evaluated during bipolar atrial application in 20 patients after cardiac operations. A silicon disc was used for fixation of the electrodes to the right atrium in 10 patients, and an atrial plication technique was used in the other 10. Myocardial stimulation threshold and resistance were measured throughout the postoperative period. Atrial electrograms were recorded on magnetic tape for computer analysis of amplitudes, slew rates, and signal source impedance. No significant differences (p > 0.1) were found in myocardial stimulation threshold between the two fixation modes. During constant-current pacing, median threshold rose from 0.65 rnA to 2.3 rnA. Stimulation resistance, measured during constant-voltage pacing, fell from 567 to 365 n, with a subsequent rise to 425 n before electrode removal. Again no difference was found between silicon disc and plication fixation of the electrodes. Pswave amplitudes were significantly higher with plication than with silicon disc fixation (2.26 versus 0.86 mV, p < 0.01), as were slew rates (0.34 versus 0.18 Vis, p < 0.05). Signal source impedance had a magnitude of 6 kn. The electrodes were used successfully in 12 (60%) of the patients for diagnosis and lor treatment of arrhythmias. We find the new lead well suited for atrial application.
Kjell Breivik, M.D., Hogne Engedal, M.D., Fin Resch, M.D., Leidulf Segadal, M.D., and Ole-Jergen Ohm, M.D., Bergen. Norway
Use of temporary pacing leads after cardiac operations has become routine in most centers. Several reports have emphasized the hemodynamic improvements from atrial or atrioventricular sequential pacing. Atrial electrode application is also recommended for the diagnosis and treatment of tachyarrhythmias." " The multifilamental braided wire electrodes in common use have a relatively high pacing and sensing failure rate.": 8 We have clinically evaluated a new temporary pacing lead (Model 6400*), and report our experience with this lead used in the bipolar mode on the right atrium in 20 patients.
Patients and methods The study population consisted of 16 men and four women with a mean age of 57 years (range 46 to 65). From the Medical Department A and Surgical Department. Section of Thoracic and Cardiovascular Surgery. Haukeland Sykehus, University of Bergen. School of Medicine, Bergen, Norway. K. Breivik is a recipient of a scholarship from the Norwegian Council on Cardiovascular Diseases. Received for publication March 29, 1982. Accepted for publication May 10. 1982. Address for reprints: Kjell Breivik , M.D., Medical Department A, N-5016 Haukeland Sykehus, Bergen, Norway. *Medtronic B. V., Kerkrade, Holland.
Fourteen of the patients had aorta-coronary bypass operations, three had mitral valve replacement, two open mitral commissurotomy, and one patient had a combined aortic valve replacement and a single aortacoronary bypass graft. All patients gave their informed consent to take part in the study. Electrode and surgical method. The temporary pacing lead is made of a Teflon-coated stainless steel wire connected to a solid electrode with a defined stimulation and sensing area of 7.5 mm- (Fig. 1). To the electrode is fastened a polypropylene fiber, proximally coiled and distally ending in an atraumatic curved needle. At the proximal end of the lead is a straight needle for tunnelling the lead through the upper abdominal wall. The lead was used in the bipolar mode. In order to examine possible effects of the electrode fixation technique on the electrophysiological parameters, we used the atrial plication technique in 10 patients and fixed the lead with a silicon disc (Fig. 1) in the remaining 10. Plication was performed with one or two sutures, and the atrial wall was wrapped around the electrode to create direct tissue contact with the complete electrode surface. The two electrodes were placed 2 to 3 em apart. With the other technique, using the silicon disc, the two electrodes were inserted into the disc 5 mm 625
The Journal of Thoracic and Cardiovascular Surgery
626 Breivik et al .
Teflon insulated conductor wire
\
Polypropylene coil
I
I(~~
Electrode with area of 7.5 mm 2
----
F 14mm ~ Fig. 1. Medtronic Model 6400 temporary pacing lead (top). The stainless steel electrode has an area of 7.5 mm". To the electrode is connected a polypropylene coil for fixation of the electrode to the disc or in the myocardium. Bottom. Silicon disc with two electrodes for optimal fixation to the atrium.
apart (Fig. I) before being attached to the atrial wall with two sutures. The electrodes were fastened to the right atrium at the end of the operation. The leads were brought out through the upper abdominal wall and sutured to the skin. They were then connected to an external pulse generator or capped off for future use. Eighteen of the patients also had ventricular electrodes implanted to have the option of atrioventricular sequential pacing. All leads were removed on postoperative day 13, and the patients were monitored for I more day before discharge from the hospital. Myocardial stimulation threshold and resistance. Myocardial threshold was measured both at constantvoltage pacing, with a pacing system analyzer of the condenser discharge type (Medtronic 5300 PSA*), and during constant-current pacing (Medtronic 5880 A). The PSA gives the current on a digital display 90 usee into the pulse, and stimulation resistance was thus calculated at myocardial threshold at I msec pulse width. Measurements were made within I hour postoperatively and then daily or every second day until explantation of the electrodes. Electrogram amplitudes and slew rates. The patients' electrograms were recorded on magnetic tape (Tandberg Instrumentation Recorder, TIR 115t), unloaded, and loaded with resistors and capacitors for further computer analysis (Digital Equipment, PDPI It) of P-wave amplitudes and slew rates. 9 Recordings *Medtronic Inc., Minneapolis, Minn. tTandberg Radiofabrikk AIS, Oslo, Norway. :j:Digital Equipment Corporation, Maynard, Mass.
were made within I hour postoperatively and then on the sixth and thirteenth postoperative days. Signal source impedance. The recorded signals were subjected to Fast Fourier Transform. The spectral ratios between loaded and unloaded electrograms were used to calculate the signal source impedance. to Statistical methods. For statistical comparison between the two fixation techniques, Student's t test was used. Differences were considered statistically significant when p < 0.05. Results We encountered no problems or complications with the use of the leads. Removal of the leads was easy and caused little discomfort to the patients. Myocardial stimulation threshold and resistance. Myocardial threshold at I msec pulse duration rose from median 0.7 V/1.5 rnA to 2.2 V/6.4 rnA with a subsequent reduction to 2.1 VI 4.7 rnA until electrode removal (Table I, Fig. 2). Constant-current threshold (1.8 msec pulse duration) rose from 0.65 to 2.3 rnA, with a small reduction to 2.2 rnA. There were no significant differences in thresholds between the two fixation methods (p > 0.1). No stimulation failures were seen, but one patient had a somewhat unusual threshold rise to 8.3 V124.7 rnA. We have therefore chosen to use median values instead of mean values to give the most correct expression for electrode performance. Atrial fibrillation developed on the third postoperative day in one patient operated upon for mitral stenosis. She had a large left atrium with long-standing atrial fibrillation before the operation. Electroversion was
Volume 85
Temporary pacing lead
Number 4 April, 1983
627
(mA) 23 3
20
~,
1
VOLTAGE
CURRENT
18 13.1'\
(volts)
10
8 6 4 2
0.1 0.25
2.0
Fig. 2. Strength duration curves (median and quartiles) for myocardial stimulation threshold I hour postoperatively (/ h PO) (n = 20) and on thirteenth postoperative day (/3 POD) (n = 19).
Table I. Atrial stimulation threshold in the 20 patients studied
Table II. Atrial stimulation resistance during constant-voltage pacing at myocardial threshold *
Atrial stimulation threshold Median
Atrial stimulation resistance
Range
Median p Value
(fl)
One hour postop. Constant voltage* (V ImA) Constant currentt (rnA) Maximum value Constant voltage* (V ImA) Constant currenrt (rnA) Postop. day 13 Constant voltage* (V ImA) Constant currenrr (rnA)
0.7/1.5 0.65
0.25-3.3/0.6-5.4 0.2-3.3
2.2/6.4 2.3
15-8.312.4-24.7 1.1-8.0
2.1/4.7 2.2
1.15-8.3/2.4-24.7 1.05-8.0
'Measured with Medtronic 5300 PSA at I msec pulse duration. f Measured with Medtronic 5880 A at 1.8 msec pulse duration.
therefore not tried. In 14 of the remaining 19 patients (70%), maximum threshold was found before electrode removal, median on eighth postoperative day. In five of the patients there was a continuous but small increase in threshold throughout the observation period. . Myocardial stimulation resistance fell from median 567 to 365 n (p < 0.001), but there was a subsequent rise to 425 n before electrode removal (Table II) (p < 0.01). Minimum resistance was usually found on postoperative days 4 to 6. Electrogram amplitudes and slew rates. There was a significant difference in both P-wave amplitude (2.26 versus 0.86 mV on postoperative day 6, p < 0.01) and slew rate (0.34 versus 0.18 on postoperative day 6,
One hour postop. Minimum value Postop. day 13
567 365 425
304-1,000 270-552 333-605
p < 0.001 P < 0.01
'Calculated 90 f.Lsec into the pulse from measurements made on a condenser discharge-type pulse generator (Medtronic 5300 PSA) at I msec pulse duration.
p < 0.05) between the plication and silicon disc fixation techniques (Table III). The P-wave amplitude had a minimum value less than 0.7 m V intermittently in only one of the patients subjected to the plication technique compared to six patients with silicon discs. Very low slew rates « 0.2 V/sec) were found in more than half of the patients in both groups. Both amplitudes and slew rates fell from 1 hour postoperatively until the sixth postoperative day, with a small but significant increase in amplitude (p < 0.01) until the thirteenth postoperative day. The small rise in slew rate was not statistically significant (p > 0.1). Signal source impedance. Because of very low P-wave amplitudes and also irregular atrial rhythms in some patients, data analysis could be done in only 17 patients 1 hour postoperatively and in seven patients on the sixth and thirteenth postoperative days. One hour postoperatively there were no significant differences in
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Table HI. Computer analysis of atrial electrogram amplitudes and slew rates One hour postop, Slew rate (V/sec)
Amplitude (mV)
Fixation technique
Mean 1: SEM
Plication Silicon disc p Values*
2.56 1: 0.25 1.62 1: 0.28 <0.001
I
Postop. day 6
Range
Mean 1: SEM
1.69-4.39 0.42-3.29
0.571:0.06 0.331:0.06 <0.01
I
Amplitude (mV)
Range
Mean 1: SEM
0.27-1.04 0.14-0.86
2.26 ± 0.44 0.861:0.09 <0.01
I
Slew rate (V/sec)
Range
Mean ± SEM
0.42-4.36 0.38-1.28
0.341: 0.07 0.181:0.01 <0.05
I
Range
0.13-0.58 0.14-0.21
*Statistical differences in electrogram amplitudes and slew rates between the two fixation techniques.
Table IV. Signal source impedance calculated from resistive and capacitive loaded and unloaded electrograms in seven of the patients* One hour postop. n = l7t
Tissue resistance, RT (0) Helmholtz capacitance, C H (JLF) Faraday resistance R, (kO)
1,2261:51 2.01:0.1 20.1 1: 1.3
I
Mean 1: SEM
1,164 1: 75 2.01:0.1 19.8 ± 2.3
POSlOp. day 6
I
Range
820-1,450 1.7-2.5 11.7-30.6
p Value
<0.01
NS NS
Mean 1: SEM
1,006 1: 35 2.0 ± 0.1 20.1 1: 2.2
I
Range
900-1,190 J .7-2.2 11.8-28.5
Legend: NS. Not significant.
*RT is calculated in frequency regions 15 to 75 Hz, CH in 20 to 40 Hz, and R.. at 0 to 10 Hz. The wire resistance. which is small «8fl) is incorporated in RT . tn = 17 indicates total number of electrograms that could be investigated I hour postoperatively.
tissue resistance (R T ) , Helmholtz capacitance (C H ) , or Faraday resistance (Rs) between the two fixation modes, and these results are therefore combined (Table IV). The- data from postoperative days 6 and 13 are all from seven patients in whom the plication technique was used. R T fell by about 20% from I hour postoperatively to the sixth postoperative day (p < 0.001), with a subsequent rise until the thirteenth day (p < 0.05), but C H and R r showed no significant variations (p > 0.2). If the mean values for RT , C H , and a, found in this study are used for calculating signal source impedance, to the value will be =6 kf! in the frequency region of IS to 20 Hz. Clinical use of the electrodes. In seven patients (35%), the atrial leads were used for postoperative pacing of bradyarrhythmias (sinoatrial blocks, sinus bradycardia). In six patients (30%), including one of those mentioned earlier, the electrodes were used on II occasions for confirming the diagnosis of a supraventricular tachyarrhythmia (Fig. 3). Overdrive conversion was tried in three of the patients with type I atrial flutter (atrial rate ~ 350 beats/min), with success in two cases (Fig. 4). In the third patient, who had an enlarged atrium and longstanding arrhythmia before the operation, the attempt was unsuccessful.
Discussion Patients who fulfilled the department's criteria for placement of temporary pacing wires were selected for the study. The two groups were not randomized but are comparable with respect to etiologic diagnosis and age. The new lead has a small solid electrode tip with a defined area of 7.5 mm", By contrast, multifilamental temporary wires have much greater areas and, consequently, are subject to frequent stimulation and sensing failures. 7, 8 Some centers also have been reluctant in using these wire electrodes on the atria because of their size and somewhat rough surface, although modifications in construction and fixation technique have been proposed. 6, lI-t3 Waldo and associates" recommended placement of two electrodes on the atria, so that bipolar pacing could be achieved. The bipolar lead configuration primarily records deflections, which represent atrial activation, and rejects ventricular activation and external electromagnetic interference. During bipolar stimulation, the pacing artifact will not distort the baseline of the electrocardiogram. Two electrodes also give redundancy in changing polarity if stimulation or sensing failure should occur. The new lead is provided with a specially designed silicon disc (Fig. 1), so that one has the choice between this disc or conventional plication and suture technique
Volume 85 Number 4
Temporary pacing lead
April. 1983
Postop. day 13 Amplitude (mV)
Slew rate (V / sec)
Mean ± SEM
Range
Mean ± SEM
Range
2.79 ± 0.38 0.93 ± 0.17 <0.01
121-4.45 0.36-1.84
0.37 ± 0.07 0.19 ± 0.02 <0.02
0.15-0.65 0.13-0.26
Postop. dav 13 p Value
<0.05
NS NS
Mean ± SEM
1,0% ± 60 2.0 ± o.t 21.6 ± 2.2
Range
870-1,380 1.7-2.2 12.3-28.3
for fixation of the electrodes. With the silicon disc, firm attachment to the atrium is ensured and the risk of dislodgment is minimal. The disc will remain on the atrium when the electrodes are explanted. However, this should be a minor objection to its use, as silicon has earlier proved to be a biocompatible material. In our opinion, a disadvantage to the disc is that its size and shape may hinder its optimal placement near the superior vena cava. Furthermore, only part of the electrode surface is brought into contact with the atrial wall. The plication technique is more flexible and allows better localization and contact of the electrodes. Myocardial threshold. There was no significant difference in median threshold with the two fixation techniques. The rise in threshold was relatively moderate and was of the same magnitude as earlier found in studies in which this electrode was used on the right ventricle. 14. 15 Mashhour and associates 16 found atrial threshold to be one third with this electrode compared to a series with the Garlock multifilamental heart wires. 'Ye14 found similar results for this new lead compared with a braided wire electrode (Davis & Geck) during right ventricular application. Myocardial stimulation resistance. The relatively high resistance found on the pair of electrodes is an advantage in securing normal pacemaker function. The 20% to 30% reduction in stimulation resistance up to the fourth to sixth postoperative days, with subsequent rise, is similar to that found in studies of the right
629
ventricle. 7. 14. 15 However, stimulation resistance was about 25% lower than that found in the ventricles" (p < 0.01). This difference may be caused by the greater myocardial mass of the ventricles. Different implantation techniques, with greater tissue trauma to the ventricles, where the electrode is completely buried in the myocardium, may also be of importance. Electrogram amplitudes and slew rates. There was no significant difference in P-wave amplitudes measured I hour postoperatively and at explantation (p > 0.1). Slew rates had decreased by about 40% (Table III), which is of the same magnitude as that found during studies of the right ventricle. 14. 15 Both P-wave amplitudes and slew rates were better when the plication technique was used (Table III). The reason for these better results may be the difficulties in getting an optimal placement of the silicon disc, which often had to be placed relatively low on the right atrial wall. Furthermore, less than half of the electrode surface is in direct tissue contact. The short distance between the two electrodes (5 to 6 mm) in the disc may also be of importance. The relatively short dipolar distance increases the possibility of recording a lower bipolar electrogram, since the depolarization wave front may reach the two electrodes almost simultaneously. With the plication technique, one may place the electrodes closer to the area of the sinus node, and the distance between the electrodes can usually be increased to 2 to 4 cm. Mashhour and associates'" used the silicon disc fixation technique in 16 patients and found P-wave amplitudes similar to those that we recorded during the plication technique. They measured the P-wave amplitudes intraoperatively to find an optimal site for electrode placement; this technique may be required if one applies the silicon disc. With the newer external atrial pulse generators, the highest P-wave sensitivity is usually 0.6 to 0.7 rnA. According to the values for minimal P-wave amplitudes found in this study, sensing failure would have occurred only intermittently in one patient with the plication technique versus six of the patients with the silicon disc fixation. Regarding signal source impedance, R T was =25% lower (p < 0.01) whereas C H and R F were of the same magnitude (p > 0.1) as found during ventricular use of these electrodes.:" The signal source impedance of about 6 kil indicates that the external pulse generator preferably should have a high input impedance, i.e., 50 kil,8. 9 in order to avoid too great attenuation of the low atrial electro grams . During this study the atrial electrodes were used in 12 (60%) of the patients on one or more occasion, most
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Breivik et al.
Atrial .picardical leads Fig. 3. Electrocardiogram from monitoring lead in patient with tachycardia (upper strip). Registration from atrial electrodes (bottom strip) clearly identifies type I atrial flutter with atrial rate =300 beats/min. (Paper speed 25 mm/sec).
II
III
* * * * * * * * * Fig. 4. Electrocardiographic recording from the same patient as in Fig. 3 during an attempt at overdrive conversion with rapid atrial pacing. Atrial capture is shown in Lead V 2 (pacemaker pulses are denoted with asterisks). After 10 seconds of stimulation (only the last 4 seconds shown) at a pacemaker rate of 400 beats/min, the external pacemaker is turned off, and regular sinus rhythm is restored.
often for pacing of bradyarrhythmias, but also for the diagnosis and treatment of tachyarrhythmias. Waldo and associates" found that atrial electrodes were used for diagnosis or treatment of arrhythmias in 85% of a random patient sample in their clinic. They state that routine placement of both atrial and ventricular wire
electrodes at the time of the operation is indicated irrespective of the nature of the cardiac procedure or preoperative rhythm. Other authorst" have found significant improvement in cardiac output during both atrial and atrioventricular sequential pacing compared with ventricular pacing. In
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Temporary pacing lead
Number 4
April,1983
this study, two of 18 patients (11. 1%) who also received ventricular electrodes were paced during episodes of slow atrial fibrillation. Both patients were operated upon for mitral stenosis and had enlarged atria. In these patients both atrial and ventricular electrodes seem clearly indicated, because of their tendency toward atrial fibrillation in the postoperative period. None of our patients required atrioventricular sequential pacing, because their hemodynamic status was satisfactory in the postoperative phase.
Conclusions The new electrode is well suited for use on the atria after cardiac operations. The plication technique was found to be better than using a silicon disc for fixation of the electrodes with regard to P-wave sensing. In patients in whom prophylactic postoperative electrode placement is indicated, both atrial and ventricular electrodes should be implanted.
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REFERENCES Friesen WG, Woodson RO, Ames AW, Herr RH, Starr A, Kassebaum OG: A hemodynamic comparison of atrial and ventricular pacing in postoperative cardiac surgical patients, 1 THORAC CARDIOVASC SURG 55:271-279. 1968 Hodam RP. Starr A: Temporary postoperative epicardial pacing electrodes. Their value and management after open-heart surgery, Ann Thorac Surg 8:506-510. 1969 Fields 1, Berkovits BV, Matloff 1M: Surgical experience with temporary and permanent A- V sequential demand pacing. 1 THORAC CARDIOVASC SURG 66:865-877, 1973 Curtis 11, Maloney 10, Barnhorst OA, Pluth 1R, Hartzler GO, Wallace RB: A critical look at temporary ventricular pacing following cardiac surgery. Surgery 82:888-893. 1977 Hartzler GO, Maloney 10. Curtis 11. Barnhorst OA: Hemodynamic benefits of atrioventricular sequential pacing after cardiac surgery. Am 1 Cardiol 40:232-236. 1977 Waldo AL, MacLean WAH. Cooper TB, Kouchoukos
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NT, Karp RB: Use of temporarily placed epicardial atrial wire electrodes for the diagnosis and treatment of cardiac arrhythmias following open-heart surgery. 1 THoRAc CARDIOVASC SURG 76:500-505. 1978 Ohm 0-1, Merkrid L, Skagseth E: Temporary pacemaker treatment in open heart surgery. Variation in myocardial threshold, tissue and interface impedances in man. PACE 2: 162-174, 1979 Ohm 0-1, Skagseth E: Temporary pacemaker treatment in open heart surgery: Pre- to postoperative changes in the electrogram characteristics. PACE 3:150-158,1980 Ohm 0-1: The interdependence between electrogram, total electrode impedance and pacemaker input impedance necessary to obtain adequate function of demand pacemakers. PACE 2:465-485, 1979 Merkrid L, Ohm 0-1, Hammer E: Signal source impedance of implanted pacemaker electrodes estimated from the spectral ratio between loaded and unloaded electrograms in man. Med BioI Eng Comput 18:223-232, 1980 Aris A, Flemma R1. Tector A1, Schmahl T, Lepley 0: An improved implantable temporary pacemaker electrode. 1 THORAC CARDIOVASC SURG 67:708-711, 1974 Spyrou PG: A simple technique of placing temporary atrial pacemaker electrodes. Ann Thorac Surg 31:377378, 1981 Sakurai 1. Murakita K. Bandi T. Iwa T: A new myocardial electrode for temporary pacing (abstr). PACE 3: 386, 1980 Breivik K, Engedal H, Segadal L, Ohm 0-1: New temporary pacing lead for use after cardiac operation. 1 THoRAc CARDIOVASC SURG 84:787-794, 1982 Breivik K, Engedal H, Resch F, Segadal L, Ohm 0-1: Clinical and electrophysiological properties of a new temporary pacemaker lead after open-heart surgery. PACE 5:600-606. 1982 Mashhour YAS, Bredee 11, Wijers TS, EI Gamal MIH, van Gelder LM, Lindemans FW: A new atrial lead with bipolar configuration for temporary pacing after open heart surgery. A comparison with a series of Garlock electrodes (abstr). PACE 4:A-90, 1981