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Intracardiac electrocardiography during permanent pacemaker implantation: Predictors of cardiac perforation
Intracardiac Electrocardiography During Permanent Pacemaker Implantation: Predictors of Cardiac Perforation
KALYANASUNDARAM VENKATARAMAN, MICHAEL
BILITCH,
MD, MD,
FACC
FACC
Los Angeles, California
From the Department of Internal Medicine, Division of Cardii, Los Angeles County, University of Southern California Medical Center, Los Angeles, California. Manuscript received February 6, 1979; revised manuscript received March 27, 1979, accepted April 2, 1979. Address for reprints: Kalyanasundaram Venkatararnan, MD, Pacemaker Center, University of Southem California School of Medicine, 1420 San Pablo Street, Los Angeles, California 90033.
Intracardiac electrograms from 50 successive patients undergoing permanent pacemaker implantation have been analyzed. There were 29 male and 21 female patients aged 14 to 93 years (mean age 68.4 years). The electrograms were obtained using methods that simulated the wave form that would be detected by unipolar cardiac pacemakers. Three types of electrographk patterns were identmed: qR pattern with a q/R ratio of less than 1 (type I): OR pattern with a Q/R ratio between 1 and 4.4 (type II); and Qr pattern with a O/r ratio between 12 and 15 (type III). A type I pattern was seen in 29 patients (58 percent), type II in 18 (36 percent) and type Ill in 3 patients (6 percent). The duration of the follow-up period ranged from 3 weeks to 20 months (mean 9.7 months); three patients were lost to follow-up study. There were four deaths apparently unrelated to the pacemaker. Recognizable problems (either pacing or sensing failure) occurred in one patient (6 percent) with a type II pattern, in two patlents (66.7 percent) with a type III pattern and in no patient with a type I pattern. On the basis of these data it is suggested that at the time of pacemaker implantation, intracardiac electrograms with a type I pattern indicating good pacing thresholds and sensing shoukf be sougfM.ff type II wave forms occur with good pacing thresf#oids and sensing then the electrode could probably be left in position. The in&fence of a type III pattern is rare; when it does occur it is greatly suggestive of myocardial perforation. When this pattern is seen, the pacemaker catheter must be repositioned.
Myocardial perforation is an important complication of transvenous temporary and permanent pacemaker therapy.*-21 Although effective pacemaker function may continue in some patients,l*2 perforation is often accompanied by sensing or pacing malfunction, or both,3-s symptoms and signs of cardiac tamponade7-lo and sometimes death.4J1J2 The diagnosis of perforation should be suspected when failure of pacing occurs without electrode displacement.5J3 Chest roentgenograms and electrocardiograms are of limited use in confirming perforation. 14,15Rubenfire et a1.14described a radiographic “epicardial fat pad sign,” useful in the diagnosis of perforation. The usefulness of intracardiac electrograms obtained from the catheter tip electrode (tip electrograms) during withdrawal of the catheter was first reported by Barold and Center.5 Subsequently, other workers12J3J6 confirmed the usefulness of the technique, indicating that R, Rs, RS and rS patterns are among the QRS patterns in the tip electrograms that suggest perforation.5J2J3J6 It has also been proposed that perforation could be avoided if intracardiac electrograms were obtained routinely at the time of pacemaker insertion.12J6 Hurzeler et a1.22obtained intracardiac electrograms in 96 patients at the time of initial pacemaker implantation or pulse generator replacement. They observed large negative deflections, biphasic deflections and
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Methods The records were reviewed of 51 successive patients who received unipolar permanent pacemakers during a 2 year period (under the supervision of one of us). One patient without any intrinsic cardiac rhythm was excluded from the study because an intracardiac electrogram could not be obtained. There were 29 male and 21 female patients; their ages ranged from 14 to 93 years (mean age 68.4 years). The duration of the follow-up period ranged from 3 weeks to 20 months (mean 9.7 months). Three patients were lost to follow-up. The indications for permanent pacemakers included atrioventricular (A-V) block (30 patients, 60 percent), sick sinus syndrome (18 patients, 36 percent), and other conduction problems (2 patients, 4 percent). Technique of pacemaker implantation: Under local anesthesia, the cephalic vein was isolated and a pacing catheter with a curved stylet introduced. Under fluoroscopic guidance, the catheter was advanced into the right atrium, right ventricle and pulmonary artery. The stylet was removed halfway and the catheter withdrawn into the right ventricle. With the patient taking a deep breath, the tip of the catheter was gently wedged into the apex of the right ventricle. As far as possible, catheter placement was achieved without in-
monophasic positive deflections. According to the previously cited studies,5J2J3J6 the Rs and RS patterns they found would suggest perforation, but Hurzeler et al. did not consider that possibility. Furthermore, in 100 successive autopsies in our institution we found no evidence of perforation, although we assume the intracardiac electrograms of these patients, had they been performed, would have shown all types of QRS configuration electrograms (Bilitch M, unpublished observations). In addition, we have seen patients whose intracardiac electrograms obtained at the time of pacemaker replacement suggested perforation, although the pacemakers were functioning well. During the past few years, we have routinely obtained intracardiac electrograms at the time of permanent pacemaker implantation. In this report, we describe two instances in which intracardiac electrography was useful in diagnosing perforation. We classified the intracardiac electrograms of patients in a series of 50 consecutive pacemaker implantations to assess whether any particular QRS configuration is associated more frequently with pacemaker failure. On the basis of this experience, we propose guidelines for action when encountering different types of intracardiac electrograms at the time of permanent pacemaker implantation.
20 rnsec
I
I
5mv
I
5mv
500 msec V-Lead Ground
FIGURE 1. Intracardiac electrograms obtained in a patient with the oscilloscopic method (left) and the V lead method (right). The polarity of the electrogram obtained with the V lead method (right) has a polarity opposite to that of the tracing obtained with the oscilloscopic method (left). The tracing at right was retouched.
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serting the stylet all the way; however, in a few patients satisfactory threshold could not be obtained, and the complete reinsertion of the stylet was necessary. Stabilization of the catheter tip was checked with the patient taking deep breaths and coughing. Strength duration curves (at 0.1,0.2,0.5,1.0,1.5 and 2.0 msec pulse width) were measured with an external pacemaker (Medtronic model 5300). Both current and voltage thresholds were recorded. Impedance at 1 msec pulse width was calculated by the formula: Volts/Milliamps X 1,000 = R(ohms). Technique of recording intracardiac electrograms: After satisfactory positioning of the electrode and appropriate thresholds were obtained, the catheter was fixed to the vein with a single nonabsorbable suture. Intracardiac electrograms were recorded using a storage oscilloscope (Tektronix, type 564B) with filter settings of 0.1 to 3,000 hertz and an input impedance of 30 k 1-2. The tip of the unipolar pacing catheter was connected to the negative input of the oscilloscope. The ground plate (28 cm2) placed inside the wound was connected to the positive input of the oscilloscope. The intracardiac electrogram was recorded at sweep speeds of 50 to 1,000 mm/set. Polaroid@ photographs were used as permanent records. In addition, all data were recorded on tape (Ampex FR 1300) together with simultaneous surface electrocardiograms (leads 1, aVF and Vs). Both surface and intracardiac leads were recorded at filter frequencies of 0.1 to 2,500 hertz. This method of recording intracardiac wave forms was utilized to approximate the clinical situation. In the two patients (Cases 1 and 2) with suspected perforation, intracardiac electrograms were obtained
with the V lead method (Fig. 1, right), as described by Barold and Center.” A multichannel photographic re-
TYPE
I
TYPE
II
TYPE
III
V LEAD METHOD
ELECTROCARDIOGRAPHY-VENKATARAMAN
AND BILITCH
corder (Electronics for Medicine DR-8) was used to record the intracardiac electrogram. Wave forms obtained with the oscilloscopic technique had polarity opposite to those obtained with the V lead method (Fig. 1). The configuration of the native QRS complexes in the 12 lead electrocardiogram recorded before pacemaker implantation was analyzed. In addition, the QRS configuration of the paced beats (left or right bundle branch block pattern) was assessed in the electrocardiograms obtained routinely after implantation (within 24 hours). Results
Intracardiac electrograms: These electrocardiograms could be classified into three major patterns: a qR pattern with a q/R ratio less than 1 (type I); a QR pattern with a Q/R ratio between 1 and 4.4 (type II); and a Qr pattern with a Q/r ratio between 12 and 15 (type III) (Fig. 2). A type I pattern was seen in 29 patients (58 percent), a type II pattern in 18 (36 percent) and a type III pattern in three patients (6 percent). There were four deaths, all unrelated to the pacemaker. Two deaths occurred in patients with a type I pattern, one death in a patient with a type II pattern and one in a patient with a type III pattern. Pacing or sensing failure, or both, occurred in one patient (6 percent) with a type II pattern, in two patients with a type III pattern (66.7 percent) and in none with a type I pattern. Types of catheter electrodes used: The surface areas of the different electrodes used are shown in Table I. Twenty-seven patients (54 percent) received a Cordis ball tip electrode, 15 (30 percent), a Medtronic model 6907-58 and 6 (12 percent), a Cordis model 322-620. A Vitatron MIP 2,000 fixation electrode was used in two patients (4 percent) in whom an electrode with a smaller surface area could not be left in a stable position. The intracardiac electrograms in these two patients revealed a type I pattern in one and type II pattern in the other. These patients had no pacemaker-related problems during the follow-up period (17 and 12 months, respectively). Distribution of the highest current density electrode (Cordis ball tip) in the three types of electrographic patterns were: 55.2 percent in type I, 50 percent in type II and 66.7 percent in type III. These differences were not statistically significant (chi square analysis). However, all three patients who had pacemaker problems had an electrode with a surface area of 11 mm2 or
TABLE I Surface Areas of the Four Types of Electrodes Used
OSCILLOSCOPE METHOD
Cases (no.1
Manufacturer
27 15 6 2
Cordis Medtronic Cordis Vitatron
FIGURE 2. Schematic illustration of the three types of intracardiac electrograms obtained with the oscilloscopic method and their corresponding appearance in the V lead method.
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Model Ball tip 6907 322-620 MIP 2000
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Surface Area (mm2) 1: 17.5 30
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TABLE II
Illustrative Case Reports
Pacing Thresholds (1 msec pulse width) Pattern of Electrogram
Patients (no.)
Milliamperage
Voltage
Impedance (ohms)
Type l Type II Type Ill
29 18 3
0.8 f 0.3 0.7 f 0.3 1.2 f 1.2
0.5 f 0.2 0.5 f 0.1 0.8 f 0.6’
651 f 143 724 f 145t 950 f 260t
Values for voltage threshold differed significantly (P <0.05) between types I and Ill. f Values for calculated impedance of the wire differed between types I and Ill (P <0.05) and between types I and II (P <0.05). l
less (two patients with Cordis ball tip electrode and one with Medtronic 6907). Pacing thresholds: The 1 msec pacing threshold in patients belonging to the three types are shown in Table II. There were no significant differences in current thresholds among the three. However, the voltage threshold was significantly greater in those with a type III pattern than in those with a type I pattern (mean f standard deviation 0.8 f 0.6 versus 0.5 f 0.2; P < 0.05). The calculated impedance of the electrode catheters in the three types showed an increase from type I to type III; these differences were statistically significant. However, these values could be due to minor variations in the distribution of the four kinds of electrodes among the three types. The impedance of the electrode catheter was unusually high in one patient (Case 2) at the time of perforation; the impedance decreased dramatically after repositioning of the lead. The native QRS complexes were classified into six categories (Table III). All patients with a type III pattern had a normal QRS complex. Differences in various kinds of QRS complexes in patients with type I and type II patterns were not statistically significant (chi square analysis). The QRS configuration of the paced beats in all cases revealed a left bundle branch block pattern. In one patient with a type I pattern, a right bundle branch block pattern alternated with a left bundle branch block configuration. This patient died in the hospital; the clinical course was consistent with acute myocardial infarction.
Case 1: A 72 year old woman was hospitalized for congestive heart failure. The electrocardiogram on admission revealed a sinus rhythm of 80 beatsfmin with a 2:l A-V block; the QRS complexes were narrow. Four days after admission the patient had a permanent pacemaker implanted. A high current density electrode (Cordis 322-462 ball tip) was used. The threshold (1 msec pulse width) was 0.4 v and 0.5 milliamperes. The postoperative electrogram revealed a continuous pacing rhythm; paced QRS complexes showed a left bundle block pattern with left axis deviation. Four weeks after implantation routine pacemaker evaluation revealed appropriate sensing but no ventricular capture. Chest X-ray films indicated a proper right ventricular apical electrode position. At operation, attempts to pace the ventricle through the lead using the maximal output of the external pacemaker (Medtronic model 5300) were unsuccessful. The intracardiac electrocardiogram revealed a type III pattern (Fig. 3). Electrograms during withdrawal of the catheter electrode were obtained using the V lead method (Fig. 4). During this maneuver there was progressive S-T segment elevation. A “give way” sensation felt by the operator when the catheter electrode returned to the right ventricular cavity was also evident under fluoroscopy. The QRS pattern changed from an Rs to an rS type. This clearly documented the perforation. The same catheter electrode was repositioned; the intracardiac electrogram showed a type I pattern. Retrospective analysis of the intracardiac electrogram obtained at the time of the first procedure also revealed a type III pattern indicating that the perforation had occurred intraoperatively during the pacemaker implantation. A follow-up examination 6 months later showed appropriate pacing and sensing. Case 2: A 64 year old woman was admitted to the hospital with syncope; a diagnosis of sick sinus syndrome was made. At the time of permanent pacemaker implantation, a high current density electrode (Cordis model 322-462) was inserted. Thresholds at 1 msec pulse width were 0.5 V and 0.4 milliamperes. The calculated impedance of the electrode was high (1,250 ohms). Careful inspection did not reveal any evidence of faulty connections and repeated measurements of thresholds were identical. The Medtronic model 5300 pacemaker system analyzer would not register an R wave. The intracardiac electrocardiogram obtained with the V lead method revealed an Rs pattern (type III), which suggested perforation. The patient was asymptomatic. The intracardiac electrocardiogram obtained during withdrawal of the catheter electrode showed changes in S-T segments that were less dramatic than in Case 1. However, a “give way” sensation was felt by the
TABLE III Fdrm of Native BRS Complexes Pattern of Electroaram
Type 1 (no. = Type II (no. = Type Ill (no. = Total Inn =
Narrow QRS
0000
0000 + LASFB
8 (27.6%)
3 (10.3%)
4 (13.8%)
9 (50%)
3 (16.7%)
3 (16.7%)
LB00 11 (39%)
LASFB
0000 + LPIFB
.
3 (10.3%)
29) 2(11.1%)
1 (5.5%)
18) 3 (100%)
.
3) 20 (40%)
6 (12%)
7 (14%)
13 (26%)
1(2%)
3 (6%)
5m
LASFB = left anterior-superior fascicular block; LB00 = left bundle branch block; LPIFB = left posterior-inferior fascicular block; R000 = right bundle branch block.
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operator and the QRS changed to an rS pattern. Ventricular premature beats were seen during and after withdrawal. The catheter electrode was repositioned in the right ventricular apex with an rS pattern (V lead). The calculated impedance of the wire was reduced to 700 ohms. An intracardiac R wave sensed by the pacemaker system analyzer measured between 7.4 and 8.2 mv. The postoperative course was uneventful. Three months after discharge the patient had a massive cerebral hemorrhage and died. Case 3: An 85 year old woman was admitted to the hospital with syncope; sick sinus syndrome was diagnosed. Two days after admission she underwent permanent pacemaker implantation. A Medtronic model 6907-58 lead was used. Thresholds (1 msec pulse width) were 0.6 v and 0.9 milliam-
peres; the calculated impedance was 667 ohms. The intracardiac electrocardiogram obtained with the oscilloscopic method revealed a QR pattern with a Q/R ratio of 2.3 (type II). The paced postoperative electrocardiogram showed a left bundle branch block pattern. On the 2nd postoperative day the pacemaker system was not sensing or capturing. Chest X-ray films showed that the electrode tip was located in the apex of the right ventricle without evidence of gross perforation. An intracardiac electrogram was not obtained during withdrawal. The electrode was repositioned. The clinical course thereafter was uneventful (follow-up period 19 months). Perforation was not documented by intracardiac electrocardiogram; however, the clinical course suggests the diagnosis.
Discussion Pacemaker failure due to myocardial perforation: Our study has confirmed the previous observation that pacemaker failure occurring without a change in electrode position suggest myocardial perforation5J6 and it has again documented the value of intracardiac
2 mv
50 msec FIGURE 3. Case 1. Intracardiac electrogram obtained with the oscilloscopic method showing a Qr pattern (type Ill).
electrocardiograms in confirming the clinical suspicion of perforation. .5,12~13~16 Characteristic changes in intraoccardiac QRS configuration and S-T segments curred. The reported incidence rate of myocardial perforation by temporary pacemakers ranges from 4 to 20 percent.e2” In contrast, perforation by a permanent pacemaker has a reported incidence rate of approximately 5 to 7 percent.5,2sT24 Rubenfire et a1.,14 using the “fat-pad sign,” observed perforation in 11 of 31 cases (35.5 percent). However, only four patients (13 percent) diagnosed as having perforation had failure of the clinical
A I
--..-.h-
FIGURE 4. Case 1. Simultaneous leads I, aVF and intracardiac etectrogram (E) obtained with the V lead method during withdrawal of the catheter electrode. Panels A, B and C are not continuous. Before withdrawal an Rs pattern was seen in the electrogram (not illustrated). During withdrawal the Rs pattern changed significantly into RS and rS patterns. Note the dramatic upward shift in the S-T segment in panels B and C. The arrow in panel C indicates the moment when a “give way” sensation was felt by the operator and the pacemaker tip entered the right ventricular cavity.
--A
I,---
E.0. 3/27/78 408-44-20
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pacemaker system. Vera et a1.12documented perforation in 11 percent of a group of 96 patients. Our pacemaker failure rate of 6 percent (3 of 50 patients) secondary to perforation is somewhat similar to that of previous reports. Intracardiac electrography to detect perforation: On the basis of available information, type II and type III intracardiac electrograms would be indicative of perforation5J2J3J6 Interestingly, Barold and Center reported one case with a type I intracardiac electrogram.5 In the present series, two of three (67 percent) patients with a type III pattern had recognizable problems and 1 of 18 (6 percent) patients with a type II pattern had clinical pacemaker failure. All deaths were believed to be unrelated to the pacemaker. All paced beats had a left bundle branch block configuration, irrespective of the type of intracardiac electrogram, except in the one case mentioned. It has been suggested that the routine use of intracardiac electrograms would be helpful in recognizing intraoperative perforation, allowing the operator to reposition the lead and thus prevent subsequent problems.12J6 Using this technique in a series of 31 patients, Vera et al-l2 found no instances of perforation whereas in their previous experience with 96 patients, they found 11 (11 percent) examples of perforation. Intracardiac electrography should be performed routinely. One can expect that all three types of intracardiac wave forms may be seen; the operator should, on the basis of our data, make every effort to achieve adequate pacing thresholds and type I wave forms of adequate amplitude and skew-rate (maximal voltage deflection/time or dv/dt).25,26 Parenthetically, data from a study at three centers27 showed that adequate S-T segment elevation (minimum 2 mv) favors a successful long-term pacing system. The chance of pacemaker failure with a type II intracardiac electrogram in our study was 6 percent; this incidence rate is lower than that of lead displacement
(7.5 percent).27 We therefore believe that it is probably not necessary to reposition the catheter electrode when type II wave forms occur in association with good pacing thresholds and adequate S-T segment displacement and QRS amplitude. Two of our three patients with type III wave forms had recognizable problems. Therefore, when this pattern is seen, the pacemaker catheter must be repositioned. To obtain proper data referable to QRS wave form during acute permanent pacemaker implantation, direct measurement is essential. Neither the polarity of the major QRS deflection in the electrogram nor S-T segment elevation can be identified with so-called pacemaker system analyzers. Furthermore, to make data during implantation comparable with those presented here, it is important to have proper identification of the polarity of the input signals to the recording devices used. Figure 1 indicates that the major deflections in type I of our series will be a predominantly negative deflection when the V lead method is used. When the method used in our series is utilized, the major deflection in type I will be positive. If a standard electrocardiographic instrument is used, our data can be compared when using the right and left arm leads with the unipolar intracardiac catheter being attached to the right arm lead and ground plate to the left arm lead. Implications: Our data do not indicate unequivocally whether all patients with type II and type III wave forms had indeed had myocardial perforation. However, we believe that a type III wave form is highly indicative of perforation. One might argue that a type II wave form represents a partial perforation or penetration of the myocardium; however, the incidence of complications in patients with this pattern appears to be small. We conclude that with use of the intracardiac electrogram together with fluoroscopy one can identify potential or actual perforation at the time of initial permanent transvenous pacemaker implantation.
References 1. Fort ML, Sharp JT: Perforation of the right ventricle by pacing catheter electrode. Two cases of asymptomatic perforation with survival. Am J Cardiol 16:610-613, 1965 2. Meyer JA. Mlllar K: Perforation of the right ventricle by electrode catheters. A review and report of nine cases. Ann Surg 168: 1048-1060, 1968 3. Koeowsky BD, Barr I: Complications and malfunctions of electrical cardiac pacemakers. Prog Cardiovasc Dis 14501-514, 1972 4. Goswaml M. Gould L. Gomprecht RF, lmperlale A: Perforation of the heart by flexible transvenous pacemaker. JAMA 216: 2013-2014, 1971 5. Barold SS, Center S: Electrocardiographic diagnosis of perforation of the heart by pacing catheter electrode. Am J Cardiol 24: 274-278, 1969 6. Nathan DA, Center S, Plna RE, Medow A, Keller W: Perforation during indwelling catheter pacing. Circulation 33:128-130, 1966 7. Furman S, Schwedel JB, Robinson G, Hurwltt ES: Use of an intracardiac pacemaker in the control of heart block. Surgery 49: 98-108.1961 8. Mullen JJ, Porter JM, Thompson HK, Sliver 0: Cardiac tamponade from ventricular perforation by transvenous pacemaker. JAMA 203:142-144, 1968
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9. Morris JJ, Whalen RE, McIntosh HD, Thompson HK, Brown IW, Young G Jr: Permanent ventricular pacemakers: comparison of transthoracic and transvenous implantation. Circulation 36: 587-597, 1967 10. Schwedel JB, Furman S, Escher DJW: Use of an intracardiac pacemaker in the treatment of Stokes-Adams seizures. Prog Cardiovasc Dis 3: 170- 177. 1960 11. Wheel18 RF, Cobb LA: Pathologic findings in perforation of the myocardium by a permanent endocardial electrode. JAMA 2 10: 1278-1280, 1969 12. Vera Z, Foerster JM, Janzen D, McMlllan DP, Klein RC, Mason DT: Perforation of right ventricle by endocardial pacemaker electrodes: clinical observations with special reference to role of intracardiac electrography (abstr). Clin Res 26:276A, 1978 13. Van Durme JP, Heyndrlokx G, Shoe& J, Vermeke P, Pannier R: Diagnosis of myocardial perforation by intracardiac electrograms recorded from the indwelling catheter. J Electrocardiol6:97-102. 1973 14. Rubenfire M, Anbe DT, Drake EH, Ckmend RS: Clinical evaluation of myocardial perforation as a complication of permanent transvenous pacemakers. Chest 63:185-188, 1973 15. Slddons H, Sowton E: Cardiac Pacemakers. Springfield, IL, Charles C Thomas, 1967, p 60
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16. Mutd HO, Stuckey JG, Sbman 0: The diagnosis of right ventricular perforation by an endocamial pacemaker electrode. Pace 1:62-67. 1976 17. Danlelsen GK, Shebatai R, Bryant LR: Failure of endocardial pacemaker due to late myocardial perforation. Successful restoration of cardiac pacing by conversion to an epicardial system. J Thorac Cardiovasc Surg 54:42-48, 1967 18. Birch LM, Berger M, Thomas PA: Synchronous diaphragmatic contraction. A complication of transvenous cardiac pacing. Am J Cardiol 21:88-90. 1968 19. Stlllman MT, Richards AM: Perforation of the interventricular septum by transvenous pacemaker catheter. Diagnosis by change in pattern of depolarization on the electrocardiogram. Am J Cardiol 24:269-273, 1989 20. Gorfin, R: Perforations and other cardiac complications. Circulation 37:Suppl lll:lll-36-111-38, 1968 2 1. Jorgensen EO, Lynborg K, Wennevold A: Unusual sign of perforation of a pacemaker catheter. Am Heart J 741732-733, 1967
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22. Hurrefer P, GeCaprlo V, Furman S: Endocardial electrograms and pacer sensing: In, Advances in Pacemaker Technology (Schakiach M, Furman S, ed). Heidelburg, New York, Springer-Verlag, 1975, p 307-316 23. Bernstefn V, Rotem CE, Perelz Dk Permanent pacemakers: &year follow-up study. Ann Intern Med 74:361-369, 1971 24. Furman S, Escher DJW, Sofomon N: Experience with myocardial and transvenous implanted cardiac pacemakers. Am J Cardiol 23:66-72, 1968 25. Furman S, Hurreler P, DeCaprlo V: The ventricular electrogram and pacemaker sensing. J Thorac Cardiovasc Surg 73:258-266, 1977 26. Furman S: Cardiac pacing and pacemakers. VI. Analysis of pacemaker malfunctions. Am Heart J 94:378-386, 1977 27. Parsonnet V, Billlch M, Furman S, Flsher J, Escher D, Myers G, Cassady E: Early malfunction of transvenous pacemaker electrodes-a three-center study. Circulation, in press
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KALYANASUNDARAM VENKATARAMAN, MICHAEL
BILITCH,
MD, MD,
FACC
FACC
Los Angeles, California
From the Department of Internal Medicine, Division of Cardii, Los Angeles County, University of Southern California Medical Center, Los Angeles, California. Manuscript received February 6, 1979; revised manuscript received March 27, 1979, accepted April 2, 1979. Address for reprints: Kalyanasundaram Venkatararnan, MD, Pacemaker Center, University of Southem California School of Medicine, 1420 San Pablo Street, Los Angeles, California 90033.
Intracardiac electrograms from 50 successive patients undergoing permanent pacemaker implantation have been analyzed. There were 29 male and 21 female patients aged 14 to 93 years (mean age 68.4 years). The electrograms were obtained using methods that simulated the wave form that would be detected by unipolar cardiac pacemakers. Three types of electrographk patterns were identmed: qR pattern with a q/R ratio of less than 1 (type I): OR pattern with a Q/R ratio between 1 and 4.4 (type II); and Qr pattern with a O/r ratio between 12 and 15 (type III). A type I pattern was seen in 29 patients (58 percent), type II in 18 (36 percent) and type Ill in 3 patients (6 percent). The duration of the follow-up period ranged from 3 weeks to 20 months (mean 9.7 months); three patients were lost to follow-up study. There were four deaths apparently unrelated to the pacemaker. Recognizable problems (either pacing or sensing failure) occurred in one patient (6 percent) with a type II pattern, in two patlents (66.7 percent) with a type III pattern and in no patient with a type I pattern. On the basis of these data it is suggested that at the time of pacemaker implantation, intracardiac electrograms with a type I pattern indicating good pacing thresholds and sensing shoukf be sougfM.ff type II wave forms occur with good pacing thresf#oids and sensing then the electrode could probably be left in position. The in&fence of a type III pattern is rare; when it does occur it is greatly suggestive of myocardial perforation. When this pattern is seen, the pacemaker catheter must be repositioned.
Myocardial perforation is an important complication of transvenous temporary and permanent pacemaker therapy.*-21 Although effective pacemaker function may continue in some patients,l*2 perforation is often accompanied by sensing or pacing malfunction, or both,3-s symptoms and signs of cardiac tamponade7-lo and sometimes death.4J1J2 The diagnosis of perforation should be suspected when failure of pacing occurs without electrode displacement.5J3 Chest roentgenograms and electrocardiograms are of limited use in confirming perforation. 14,15Rubenfire et a1.14described a radiographic “epicardial fat pad sign,” useful in the diagnosis of perforation. The usefulness of intracardiac electrograms obtained from the catheter tip electrode (tip electrograms) during withdrawal of the catheter was first reported by Barold and Center.5 Subsequently, other workers12J3J6 confirmed the usefulness of the technique, indicating that R, Rs, RS and rS patterns are among the QRS patterns in the tip electrograms that suggest perforation.5J2J3J6 It has also been proposed that perforation could be avoided if intracardiac electrograms were obtained routinely at the time of pacemaker insertion.12J6 Hurzeler et a1.22obtained intracardiac electrograms in 96 patients at the time of initial pacemaker implantation or pulse generator replacement. They observed large negative deflections, biphasic deflections and
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AND BILITCH
Methods The records were reviewed of 51 successive patients who received unipolar permanent pacemakers during a 2 year period (under the supervision of one of us). One patient without any intrinsic cardiac rhythm was excluded from the study because an intracardiac electrogram could not be obtained. There were 29 male and 21 female patients; their ages ranged from 14 to 93 years (mean age 68.4 years). The duration of the follow-up period ranged from 3 weeks to 20 months (mean 9.7 months). Three patients were lost to follow-up. The indications for permanent pacemakers included atrioventricular (A-V) block (30 patients, 60 percent), sick sinus syndrome (18 patients, 36 percent), and other conduction problems (2 patients, 4 percent). Technique of pacemaker implantation: Under local anesthesia, the cephalic vein was isolated and a pacing catheter with a curved stylet introduced. Under fluoroscopic guidance, the catheter was advanced into the right atrium, right ventricle and pulmonary artery. The stylet was removed halfway and the catheter withdrawn into the right ventricle. With the patient taking a deep breath, the tip of the catheter was gently wedged into the apex of the right ventricle. As far as possible, catheter placement was achieved without in-
monophasic positive deflections. According to the previously cited studies,5J2J3J6 the Rs and RS patterns they found would suggest perforation, but Hurzeler et al. did not consider that possibility. Furthermore, in 100 successive autopsies in our institution we found no evidence of perforation, although we assume the intracardiac electrograms of these patients, had they been performed, would have shown all types of QRS configuration electrograms (Bilitch M, unpublished observations). In addition, we have seen patients whose intracardiac electrograms obtained at the time of pacemaker replacement suggested perforation, although the pacemakers were functioning well. During the past few years, we have routinely obtained intracardiac electrograms at the time of permanent pacemaker implantation. In this report, we describe two instances in which intracardiac electrography was useful in diagnosing perforation. We classified the intracardiac electrograms of patients in a series of 50 consecutive pacemaker implantations to assess whether any particular QRS configuration is associated more frequently with pacemaker failure. On the basis of this experience, we propose guidelines for action when encountering different types of intracardiac electrograms at the time of permanent pacemaker implantation.
20 rnsec
I
I
5mv
I
5mv
500 msec V-Lead Ground
FIGURE 1. Intracardiac electrograms obtained in a patient with the oscilloscopic method (left) and the V lead method (right). The polarity of the electrogram obtained with the V lead method (right) has a polarity opposite to that of the tracing obtained with the oscilloscopic method (left). The tracing at right was retouched.
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serting the stylet all the way; however, in a few patients satisfactory threshold could not be obtained, and the complete reinsertion of the stylet was necessary. Stabilization of the catheter tip was checked with the patient taking deep breaths and coughing. Strength duration curves (at 0.1,0.2,0.5,1.0,1.5 and 2.0 msec pulse width) were measured with an external pacemaker (Medtronic model 5300). Both current and voltage thresholds were recorded. Impedance at 1 msec pulse width was calculated by the formula: Volts/Milliamps X 1,000 = R(ohms). Technique of recording intracardiac electrograms: After satisfactory positioning of the electrode and appropriate thresholds were obtained, the catheter was fixed to the vein with a single nonabsorbable suture. Intracardiac electrograms were recorded using a storage oscilloscope (Tektronix, type 564B) with filter settings of 0.1 to 3,000 hertz and an input impedance of 30 k 1-2. The tip of the unipolar pacing catheter was connected to the negative input of the oscilloscope. The ground plate (28 cm2) placed inside the wound was connected to the positive input of the oscilloscope. The intracardiac electrogram was recorded at sweep speeds of 50 to 1,000 mm/set. Polaroid@ photographs were used as permanent records. In addition, all data were recorded on tape (Ampex FR 1300) together with simultaneous surface electrocardiograms (leads 1, aVF and Vs). Both surface and intracardiac leads were recorded at filter frequencies of 0.1 to 2,500 hertz. This method of recording intracardiac wave forms was utilized to approximate the clinical situation. In the two patients (Cases 1 and 2) with suspected perforation, intracardiac electrograms were obtained
with the V lead method (Fig. 1, right), as described by Barold and Center.” A multichannel photographic re-
TYPE
I
TYPE
II
TYPE
III
V LEAD METHOD
ELECTROCARDIOGRAPHY-VENKATARAMAN
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corder (Electronics for Medicine DR-8) was used to record the intracardiac electrogram. Wave forms obtained with the oscilloscopic technique had polarity opposite to those obtained with the V lead method (Fig. 1). The configuration of the native QRS complexes in the 12 lead electrocardiogram recorded before pacemaker implantation was analyzed. In addition, the QRS configuration of the paced beats (left or right bundle branch block pattern) was assessed in the electrocardiograms obtained routinely after implantation (within 24 hours). Results
Intracardiac electrograms: These electrocardiograms could be classified into three major patterns: a qR pattern with a q/R ratio less than 1 (type I); a QR pattern with a Q/R ratio between 1 and 4.4 (type II); and a Qr pattern with a Q/r ratio between 12 and 15 (type III) (Fig. 2). A type I pattern was seen in 29 patients (58 percent), a type II pattern in 18 (36 percent) and a type III pattern in three patients (6 percent). There were four deaths, all unrelated to the pacemaker. Two deaths occurred in patients with a type I pattern, one death in a patient with a type II pattern and one in a patient with a type III pattern. Pacing or sensing failure, or both, occurred in one patient (6 percent) with a type II pattern, in two patients with a type III pattern (66.7 percent) and in none with a type I pattern. Types of catheter electrodes used: The surface areas of the different electrodes used are shown in Table I. Twenty-seven patients (54 percent) received a Cordis ball tip electrode, 15 (30 percent), a Medtronic model 6907-58 and 6 (12 percent), a Cordis model 322-620. A Vitatron MIP 2,000 fixation electrode was used in two patients (4 percent) in whom an electrode with a smaller surface area could not be left in a stable position. The intracardiac electrograms in these two patients revealed a type I pattern in one and type II pattern in the other. These patients had no pacemaker-related problems during the follow-up period (17 and 12 months, respectively). Distribution of the highest current density electrode (Cordis ball tip) in the three types of electrographic patterns were: 55.2 percent in type I, 50 percent in type II and 66.7 percent in type III. These differences were not statistically significant (chi square analysis). However, all three patients who had pacemaker problems had an electrode with a surface area of 11 mm2 or
TABLE I Surface Areas of the Four Types of Electrodes Used
OSCILLOSCOPE METHOD
Cases (no.1
Manufacturer
27 15 6 2
Cordis Medtronic Cordis Vitatron
FIGURE 2. Schematic illustration of the three types of intracardiac electrograms obtained with the oscilloscopic method and their corresponding appearance in the V lead method.
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Model Ball tip 6907 322-620 MIP 2000
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Surface Area (mm2) 1: 17.5 30
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TABLE II
Illustrative Case Reports
Pacing Thresholds (1 msec pulse width) Pattern of Electrogram
Patients (no.)
Milliamperage
Voltage
Impedance (ohms)
Type l Type II Type Ill
29 18 3
0.8 f 0.3 0.7 f 0.3 1.2 f 1.2
0.5 f 0.2 0.5 f 0.1 0.8 f 0.6’
651 f 143 724 f 145t 950 f 260t
Values for voltage threshold differed significantly (P <0.05) between types I and Ill. f Values for calculated impedance of the wire differed between types I and Ill (P <0.05) and between types I and II (P <0.05). l
less (two patients with Cordis ball tip electrode and one with Medtronic 6907). Pacing thresholds: The 1 msec pacing threshold in patients belonging to the three types are shown in Table II. There were no significant differences in current thresholds among the three. However, the voltage threshold was significantly greater in those with a type III pattern than in those with a type I pattern (mean f standard deviation 0.8 f 0.6 versus 0.5 f 0.2; P < 0.05). The calculated impedance of the electrode catheters in the three types showed an increase from type I to type III; these differences were statistically significant. However, these values could be due to minor variations in the distribution of the four kinds of electrodes among the three types. The impedance of the electrode catheter was unusually high in one patient (Case 2) at the time of perforation; the impedance decreased dramatically after repositioning of the lead. The native QRS complexes were classified into six categories (Table III). All patients with a type III pattern had a normal QRS complex. Differences in various kinds of QRS complexes in patients with type I and type II patterns were not statistically significant (chi square analysis). The QRS configuration of the paced beats in all cases revealed a left bundle branch block pattern. In one patient with a type I pattern, a right bundle branch block pattern alternated with a left bundle branch block configuration. This patient died in the hospital; the clinical course was consistent with acute myocardial infarction.
Case 1: A 72 year old woman was hospitalized for congestive heart failure. The electrocardiogram on admission revealed a sinus rhythm of 80 beatsfmin with a 2:l A-V block; the QRS complexes were narrow. Four days after admission the patient had a permanent pacemaker implanted. A high current density electrode (Cordis 322-462 ball tip) was used. The threshold (1 msec pulse width) was 0.4 v and 0.5 milliamperes. The postoperative electrogram revealed a continuous pacing rhythm; paced QRS complexes showed a left bundle block pattern with left axis deviation. Four weeks after implantation routine pacemaker evaluation revealed appropriate sensing but no ventricular capture. Chest X-ray films indicated a proper right ventricular apical electrode position. At operation, attempts to pace the ventricle through the lead using the maximal output of the external pacemaker (Medtronic model 5300) were unsuccessful. The intracardiac electrocardiogram revealed a type III pattern (Fig. 3). Electrograms during withdrawal of the catheter electrode were obtained using the V lead method (Fig. 4). During this maneuver there was progressive S-T segment elevation. A “give way” sensation felt by the operator when the catheter electrode returned to the right ventricular cavity was also evident under fluoroscopy. The QRS pattern changed from an Rs to an rS type. This clearly documented the perforation. The same catheter electrode was repositioned; the intracardiac electrogram showed a type I pattern. Retrospective analysis of the intracardiac electrogram obtained at the time of the first procedure also revealed a type III pattern indicating that the perforation had occurred intraoperatively during the pacemaker implantation. A follow-up examination 6 months later showed appropriate pacing and sensing. Case 2: A 64 year old woman was admitted to the hospital with syncope; a diagnosis of sick sinus syndrome was made. At the time of permanent pacemaker implantation, a high current density electrode (Cordis model 322-462) was inserted. Thresholds at 1 msec pulse width were 0.5 V and 0.4 milliamperes. The calculated impedance of the electrode was high (1,250 ohms). Careful inspection did not reveal any evidence of faulty connections and repeated measurements of thresholds were identical. The Medtronic model 5300 pacemaker system analyzer would not register an R wave. The intracardiac electrocardiogram obtained with the V lead method revealed an Rs pattern (type III), which suggested perforation. The patient was asymptomatic. The intracardiac electrocardiogram obtained during withdrawal of the catheter electrode showed changes in S-T segments that were less dramatic than in Case 1. However, a “give way” sensation was felt by the
TABLE III Fdrm of Native BRS Complexes Pattern of Electroaram
Type 1 (no. = Type II (no. = Type Ill (no. = Total Inn =
Narrow QRS
0000
0000 + LASFB
8 (27.6%)
3 (10.3%)
4 (13.8%)
9 (50%)
3 (16.7%)
3 (16.7%)
LB00 11 (39%)
LASFB
0000 + LPIFB
.
3 (10.3%)
29) 2(11.1%)
1 (5.5%)
18) 3 (100%)
.
3) 20 (40%)
6 (12%)
7 (14%)
13 (26%)
1(2%)
3 (6%)
5m
LASFB = left anterior-superior fascicular block; LB00 = left bundle branch block; LPIFB = left posterior-inferior fascicular block; R000 = right bundle branch block.
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operator and the QRS changed to an rS pattern. Ventricular premature beats were seen during and after withdrawal. The catheter electrode was repositioned in the right ventricular apex with an rS pattern (V lead). The calculated impedance of the wire was reduced to 700 ohms. An intracardiac R wave sensed by the pacemaker system analyzer measured between 7.4 and 8.2 mv. The postoperative course was uneventful. Three months after discharge the patient had a massive cerebral hemorrhage and died. Case 3: An 85 year old woman was admitted to the hospital with syncope; sick sinus syndrome was diagnosed. Two days after admission she underwent permanent pacemaker implantation. A Medtronic model 6907-58 lead was used. Thresholds (1 msec pulse width) were 0.6 v and 0.9 milliam-
peres; the calculated impedance was 667 ohms. The intracardiac electrocardiogram obtained with the oscilloscopic method revealed a QR pattern with a Q/R ratio of 2.3 (type II). The paced postoperative electrocardiogram showed a left bundle branch block pattern. On the 2nd postoperative day the pacemaker system was not sensing or capturing. Chest X-ray films showed that the electrode tip was located in the apex of the right ventricle without evidence of gross perforation. An intracardiac electrogram was not obtained during withdrawal. The electrode was repositioned. The clinical course thereafter was uneventful (follow-up period 19 months). Perforation was not documented by intracardiac electrocardiogram; however, the clinical course suggests the diagnosis.
Discussion Pacemaker failure due to myocardial perforation: Our study has confirmed the previous observation that pacemaker failure occurring without a change in electrode position suggest myocardial perforation5J6 and it has again documented the value of intracardiac
2 mv
50 msec FIGURE 3. Case 1. Intracardiac electrogram obtained with the oscilloscopic method showing a Qr pattern (type Ill).
electrocardiograms in confirming the clinical suspicion of perforation. .5,12~13~16 Characteristic changes in intraoccardiac QRS configuration and S-T segments curred. The reported incidence rate of myocardial perforation by temporary pacemakers ranges from 4 to 20 percent.e2” In contrast, perforation by a permanent pacemaker has a reported incidence rate of approximately 5 to 7 percent.5,2sT24 Rubenfire et a1.,14 using the “fat-pad sign,” observed perforation in 11 of 31 cases (35.5 percent). However, only four patients (13 percent) diagnosed as having perforation had failure of the clinical
A I
--..-.h-
FIGURE 4. Case 1. Simultaneous leads I, aVF and intracardiac etectrogram (E) obtained with the V lead method during withdrawal of the catheter electrode. Panels A, B and C are not continuous. Before withdrawal an Rs pattern was seen in the electrogram (not illustrated). During withdrawal the Rs pattern changed significantly into RS and rS patterns. Note the dramatic upward shift in the S-T segment in panels B and C. The arrow in panel C indicates the moment when a “give way” sensation was felt by the operator and the pacemaker tip entered the right ventricular cavity.
--A
I,---
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pacemaker system. Vera et a1.12documented perforation in 11 percent of a group of 96 patients. Our pacemaker failure rate of 6 percent (3 of 50 patients) secondary to perforation is somewhat similar to that of previous reports. Intracardiac electrography to detect perforation: On the basis of available information, type II and type III intracardiac electrograms would be indicative of perforation5J2J3J6 Interestingly, Barold and Center reported one case with a type I intracardiac electrogram.5 In the present series, two of three (67 percent) patients with a type III pattern had recognizable problems and 1 of 18 (6 percent) patients with a type II pattern had clinical pacemaker failure. All deaths were believed to be unrelated to the pacemaker. All paced beats had a left bundle branch block configuration, irrespective of the type of intracardiac electrogram, except in the one case mentioned. It has been suggested that the routine use of intracardiac electrograms would be helpful in recognizing intraoperative perforation, allowing the operator to reposition the lead and thus prevent subsequent problems.12J6 Using this technique in a series of 31 patients, Vera et al-l2 found no instances of perforation whereas in their previous experience with 96 patients, they found 11 (11 percent) examples of perforation. Intracardiac electrography should be performed routinely. One can expect that all three types of intracardiac wave forms may be seen; the operator should, on the basis of our data, make every effort to achieve adequate pacing thresholds and type I wave forms of adequate amplitude and skew-rate (maximal voltage deflection/time or dv/dt).25,26 Parenthetically, data from a study at three centers27 showed that adequate S-T segment elevation (minimum 2 mv) favors a successful long-term pacing system. The chance of pacemaker failure with a type II intracardiac electrogram in our study was 6 percent; this incidence rate is lower than that of lead displacement
(7.5 percent).27 We therefore believe that it is probably not necessary to reposition the catheter electrode when type II wave forms occur in association with good pacing thresholds and adequate S-T segment displacement and QRS amplitude. Two of our three patients with type III wave forms had recognizable problems. Therefore, when this pattern is seen, the pacemaker catheter must be repositioned. To obtain proper data referable to QRS wave form during acute permanent pacemaker implantation, direct measurement is essential. Neither the polarity of the major QRS deflection in the electrogram nor S-T segment elevation can be identified with so-called pacemaker system analyzers. Furthermore, to make data during implantation comparable with those presented here, it is important to have proper identification of the polarity of the input signals to the recording devices used. Figure 1 indicates that the major deflections in type I of our series will be a predominantly negative deflection when the V lead method is used. When the method used in our series is utilized, the major deflection in type I will be positive. If a standard electrocardiographic instrument is used, our data can be compared when using the right and left arm leads with the unipolar intracardiac catheter being attached to the right arm lead and ground plate to the left arm lead. Implications: Our data do not indicate unequivocally whether all patients with type II and type III wave forms had indeed had myocardial perforation. However, we believe that a type III wave form is highly indicative of perforation. One might argue that a type II wave form represents a partial perforation or penetration of the myocardium; however, the incidence of complications in patients with this pattern appears to be small. We conclude that with use of the intracardiac electrogram together with fluoroscopy one can identify potential or actual perforation at the time of initial permanent transvenous pacemaker implantation.
References 1. Fort ML, Sharp JT: Perforation of the right ventricle by pacing catheter electrode. Two cases of asymptomatic perforation with survival. Am J Cardiol 16:610-613, 1965 2. Meyer JA. Mlllar K: Perforation of the right ventricle by electrode catheters. A review and report of nine cases. Ann Surg 168: 1048-1060, 1968 3. Koeowsky BD, Barr I: Complications and malfunctions of electrical cardiac pacemakers. Prog Cardiovasc Dis 14501-514, 1972 4. Goswaml M. Gould L. Gomprecht RF, lmperlale A: Perforation of the heart by flexible transvenous pacemaker. JAMA 216: 2013-2014, 1971 5. Barold SS, Center S: Electrocardiographic diagnosis of perforation of the heart by pacing catheter electrode. Am J Cardiol 24: 274-278, 1969 6. Nathan DA, Center S, Plna RE, Medow A, Keller W: Perforation during indwelling catheter pacing. Circulation 33:128-130, 1966 7. Furman S, Schwedel JB, Robinson G, Hurwltt ES: Use of an intracardiac pacemaker in the control of heart block. Surgery 49: 98-108.1961 8. Mullen JJ, Porter JM, Thompson HK, Sliver 0: Cardiac tamponade from ventricular perforation by transvenous pacemaker. JAMA 203:142-144, 1968
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9. Morris JJ, Whalen RE, McIntosh HD, Thompson HK, Brown IW, Young G Jr: Permanent ventricular pacemakers: comparison of transthoracic and transvenous implantation. Circulation 36: 587-597, 1967 10. Schwedel JB, Furman S, Escher DJW: Use of an intracardiac pacemaker in the treatment of Stokes-Adams seizures. Prog Cardiovasc Dis 3: 170- 177. 1960 11. Wheel18 RF, Cobb LA: Pathologic findings in perforation of the myocardium by a permanent endocardial electrode. JAMA 2 10: 1278-1280, 1969 12. Vera Z, Foerster JM, Janzen D, McMlllan DP, Klein RC, Mason DT: Perforation of right ventricle by endocardial pacemaker electrodes: clinical observations with special reference to role of intracardiac electrography (abstr). Clin Res 26:276A, 1978 13. Van Durme JP, Heyndrlokx G, Shoe& J, Vermeke P, Pannier R: Diagnosis of myocardial perforation by intracardiac electrograms recorded from the indwelling catheter. J Electrocardiol6:97-102. 1973 14. Rubenfire M, Anbe DT, Drake EH, Ckmend RS: Clinical evaluation of myocardial perforation as a complication of permanent transvenous pacemakers. Chest 63:185-188, 1973 15. Slddons H, Sowton E: Cardiac Pacemakers. Springfield, IL, Charles C Thomas, 1967, p 60
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16. Mutd HO, Stuckey JG, Sbman 0: The diagnosis of right ventricular perforation by an endocamial pacemaker electrode. Pace 1:62-67. 1976 17. Danlelsen GK, Shebatai R, Bryant LR: Failure of endocardial pacemaker due to late myocardial perforation. Successful restoration of cardiac pacing by conversion to an epicardial system. J Thorac Cardiovasc Surg 54:42-48, 1967 18. Birch LM, Berger M, Thomas PA: Synchronous diaphragmatic contraction. A complication of transvenous cardiac pacing. Am J Cardiol 21:88-90. 1968 19. Stlllman MT, Richards AM: Perforation of the interventricular septum by transvenous pacemaker catheter. Diagnosis by change in pattern of depolarization on the electrocardiogram. Am J Cardiol 24:269-273, 1989 20. Gorfin, R: Perforations and other cardiac complications. Circulation 37:Suppl lll:lll-36-111-38, 1968 2 1. Jorgensen EO, Lynborg K, Wennevold A: Unusual sign of perforation of a pacemaker catheter. Am Heart J 741732-733, 1967
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22. Hurrefer P, GeCaprlo V, Furman S: Endocardial electrograms and pacer sensing: In, Advances in Pacemaker Technology (Schakiach M, Furman S, ed). Heidelburg, New York, Springer-Verlag, 1975, p 307-316 23. Bernstefn V, Rotem CE, Perelz Dk Permanent pacemakers: &year follow-up study. Ann Intern Med 74:361-369, 1971 24. Furman S, Escher DJW, Sofomon N: Experience with myocardial and transvenous implanted cardiac pacemakers. Am J Cardiol 23:66-72, 1968 25. Furman S, Hurreler P, DeCaprlo V: The ventricular electrogram and pacemaker sensing. J Thorac Cardiovasc Surg 73:258-266, 1977 26. Furman S: Cardiac pacing and pacemakers. VI. Analysis of pacemaker malfunctions. Am Heart J 94:378-386, 1977 27. Parsonnet V, Billlch M, Furman S, Flsher J, Escher D, Myers G, Cassady E: Early malfunction of transvenous pacemaker electrodes-a three-center study. Circulation, in press
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