The Results of Demand Pacing

Transcription

1 The Results of Demand Pacing in Cardiac Arrhythmias Peter Allen, M.D., and C. Eve Rotem, M.D. I n the majority of patients with established 3" heart block the fixedrate cardiac pacemaker has successfully controlled symptoms. In patients with intermittent 2" and 3" heart,block, however, the fixed-rate pacer has occasionally produced serious arrhythmias and sudden death as a result of competition for cardiac capture between the intrinsic and the external pacemakers. Stimulated by the significant incidence of arrhythmic complications with fixed-rate pacemakers in intermittent 2" and 3" heart block, Chardack et al. [2], Zuckerman et al. [6], and Lemberg et al. [3] developed the principle of demand cardiac pacing. The following report presents our experience with temporary and permanent demand pacing in 48 patients at the Vancouver General and Shaughnessy hospitals. The follow-up period was 6 to 24 months, ending December, PATIENTS AND TECHNIQUES Twenty-six patients, admitted to the Intensive Coronary Care Unit with acute myocardial infarction, developed either sinus bradycardia below 45 beats per minute, or 2" or 3" heart block. These arrhythmias were an indication for insertion of a temporary pervenous demand pacemaker (Table 1). This was performed at the bedside using a Flexon steel (platinum-tipped electrode) wire introduced through a central venous pressure catheter and positioned in the right ventricle by observation of the intracardiac ECG. Satisfactory pacing with this electrode is obtained only when it is in contact with the myocardium, although an intracardiac ECG occurs even when the tip is floating free in the right ventricle. In 22 patients the intermittent arrhythmias were independent of myocardial infarction. Two patients required temporary pervenous pacers several days preoperatively for repeated attacks of sinus arrest. In the remaining cases, isoproterenol (Isuprel), administered intravenously, controlled the occasional prolonged ventricular asystole that occurred during permanent catheter insertion. If a suitable external jugular vein or tributary is not available, the stimulating bipolar electrode is placed directly into the internal jugular vein and passed, under fluoroscopic control, to the apex of the right ventricle. If the heart is not captured From the Division of Thoracic Surgery, University of British Columbia and Vancouver General Hospital, and the Department of Cardiology, Shaughnessy Hospital (Department of Veterans Affairs), Vancouver, B.C., Canada. Presented at the Fifth Annual Meeting of The Society of Thoracic Surgeons, San Diego, Calif., Jan , Address reprint requests to Dr. Allen, 808 Fairmont Medical Building, 750 West Broadway, Vancouver 9, B.C., Canada. 146 THE ANNALS OF THORACIC SURGERY

2 Demand Pacing in Cardiac Arrhythmias TABLE 1. Permanent INDICATIONS FOR DEMAND PACING Temporary Intermittent 3" heart block Acute A-V conduction disturbances Sinus rhythm predominant with myocardial infarction 3 O block predominant ' Sinus bradycardia below 45 beats Periodic sinus arrest per minute 2" heart block with irregular ventric- 2" and 3" heart block ular response at 1 to 1% ma., applied from an external source, the electrode tip is repositioned to a more responsive area of the myocardium. Particular attention is paid to the angle of the electrode in the right atrium to prevent subsequent perforation in the anterior wall of the right ventricle. The projecting end of the electrode is passed deep to the clavicle and attached to the demand pulse generator placed subcutaneously or in the fascia1 space between the pectoralis major and minor. The pacemaker" used in this series has a fixed pulse amplitude of 11.2 ma. and a pulse stimulation of 1.7 msec. The pulse generator has a sensing circuit that inhibits cardiac stimulation by QRS potentials as low as 1.5 mv. received at the electrode terminal. The inhibitory signal strength can be verified with an external, battery-powered demand pacemaker. If the QRS impulse does not occur within a preset period, usually 1 second or less, the pulse generator activates the heart and continues until further intrinsic QRS signals arrive at the electrode. A disadvantage of the demand pacemaker is the occasional difficulty encountered in determining its function. In some cases carotid sinus massage will slow the heart rate sufficiently to trigger the demand pacer. If this technique fails, a quick method is to accelerate the heart by an External Rate Controlt placed over the demand power unit for 2 to 3 minutes. When the Control is stopped, a period of ventricular asystole greater than 1 second usually occurs (Fig. I). The period is sufficient to activate the demand pacer and confirm its function by ECG tracing. RESULTS Of the 26 patients with postinfarction arrhythmias treated by demand pacers, 4 died (15%). Three of the deaths resulted from cardiogenic shock and one from uncontrolled ventricular tachycardia that was unresponsive to repeated electrical countershock. Of the surviving 22 postinfarction patients, 21 required temporary demand pacing for 2 to 5 days. The pacer electrode was removed RATE CONTROL ONl ASISTOLE I -NORMAL SINUS RHYTHM f t t t f FIG. 1. ECG strip demonstrating demand pacing following External Rate Control. *Model 5841, Medtronics, Inc., Minneapolis, Minn. TMedtronics, Inc., Minneapolis, Minn. VOL. 8, NO. 2, AUGUST,

3 ALLEN AND ROTEM 48 hours after stable sinus rhythm was restored. One patient, however, remained in 3" heart block, and after 28 days a permanent fixed-rate pacer was inserted. Of the 22 noninfarction patients, 17 were male. The age range was 40 to 82 years, with 12 patients 70 years of age or older. Fifteen patients in this group had periodic 2" and 3" heart block with Stokes-Adams attacks. Fourteen are active and asymptomatic 6 to 24 months following implantation of a pervenous demand pacemaker. One patient, however, lost response to demand pacing after 8 months. A I-cm. withdrawal of the electrode restored cardiac response, but during the following months the patient was increasingly dependent upon the pacemaker, and the preset rate of 60 became almost constant. Short periods of pacemaker failure recurred and produced Stokes-Adams attacks. Because of increased pacemaker dependency and recurring loss of pervenous cardiac capture, a transthoracic epicardial fixed-rate pacemaker was inserted. At operation, the tip of the demand electrode was found to have penetrated the pericardial cavity. Response to fixed-rate pacing has been excellent. Three patients in the noninfarction group had attacks of sinus arrest which responded well to demand pacing. Two other patients had had fixed-rate pacemakers inserted previously for established 3" heart block, but periodic return of sinus rhythm 9 and 12 months later produced bizarre arrhythmias of which the patients were acutely aware. In one of these 2 patients, stable rhythm was restored following replacement of the fixed-rate pacemaker with a demand unit. The other patient, while improved with standby pacing, continues to be limited because of paroxysmal atrial tachycardia. Among the 22 noninfarction patients, two deaths occurred. One patient had periodic 3" heart block and congestive failure. The arrhythmia responded well to demand pacing, but failure remained intractable and the patient died 3 months later. The second death occurred in a patient severely disabled from periodic sinus arrest. He was asymptomatic following insertion of a demand pacemaker but died 2 months later. The cause of death remained unexplained at postmortem examination. Structural failure of electrodes and powerpacks did not occur in these 22 patients. COMMENT About 7% of patients with acute myocardial infarction develop varying degrees of heart block during the first 72 hours. Intermittent 2" block is most frequent, but this commonly progresses to 3",block and sudden death. The value of temporary demand pacing in these patients with block is demonstrated by a reduction in mortality from 40 to 67% in nonpaced patients to 10 to 15% in patients supported by pacing [4, 51. The temporary nature of postinfarction block is shown in our series of 22 surviving patients in which 21 eventually regained sinus rhythm. In the noninfarction patient with intermittent 2" and 3" heart block, sinus arrest, or sinus bradycardia, demand pacing has proved most successful and is the treatment of choice (Table 1). This is exemplified by the group of 22 noninfarction patients, 21 of whom were restored to full activity as far as arrhythmias correctable by pacemaker were concerned. Patients with long-established 3 " heart block continue to,be satisfactorily treated by fixed-rate pacers; consequently, the authors have 148 THE ANNALS OF THORACIC SURGERY

4 Demand Pacing in Cardiac Arrhythmias not converted these patients to demand pacers when powerpack changes are required. In our series of 160 patients with established 3" heart block treated with fixed-rate pacemakers, only 2 developed arrhythmia for which a demand pacer was used subsequently [l]. Improvements in the design of pacemaking equipment, and surgical experience gained by the authors in a series'of pervenous fixedrate pacemakers, have been responsible for the absence of complications in this series. If problems are to be avoided, however, attention to the following details is still mandatory. 1. Perforation of the right ventricle can be avoided by close attention to the correct angle of the catheter electrode in the right heart. In a study,by the authors of patients experiencing catheter perforation of the right ventricle, the catheter angle in the right atrium was noted to be critical. To avoid this complication, the angle of catheter passage from right atrium to ventricle must be obtuse. It must never be at a right angle (Fig. 2). The obtuse angle allows free catheter movement in ventricular systole and avoids repeated resistance from contact with the right atrium. 2. Erosion and ulceration over the powerpack in the chest wall are complications arising from excessive tension on the overlying skin flaps. This can be avoided by placing the powerpack in the medial half of the fascia1 space between the pectoralis major and minor in thin people. The subcutaneous site should be used only in patients with sufficient adipose tissue, to avoid tension of the suture line or necrosis of overlying skin (Fig. 3). 3. Retraction of the catheter tip from the apex of the right ventricle is a complication arising, in part, from traction on the subcutaneous catheter by the clavicle when the arm is elevated. This is an early complication and can be avoided by passing the catheter sub- b : CORRECT FLUOROSCOPIC POSITION OF PERVENOUS PACEMAKER CATHETER FIG. 2. Correct and incorrect catheter angles in the right heart. VOL. 8, NO. 2, AUGUST,

5 ALLEN AND ROTEM FIG. 3. Skin ulceration of subcutaneously placed pace+ in a thin patient. cluviculurly. It is important, however, to pass the catheter through the lateral half of the subclavicular space to avoid perforating the subclavicular vein. 4. Loss of cardiac capture can occur with the customary increase of threshold current in the postoperative period. To avoid this, measurement of current for capture is absolutely necessary at the time of electrode placement in the right ventricle. If capture is not obtained at less than 1.5 ma., the tip must be repositioned until response is obtained at that current. SUMMARY The indications for demand pacing in postinfarction and noninfarction arrhythmias are presented and exemplified by a series of 48 patients. A quick and accurate method of demonstrating function of the Medtronics demand pacer is outlined. It has been successful in all patients of this series. Techniques to prevent common causes of loss of pacing also are discussed. REFERENCES 1. Allen, P., Robertson, R., and Trapp, W. G. Indications for treatment of complete atrioventricular dissociation. Canad. Med. Ass. J. 91 :547, Chardack, W. M., Gage, A. A., Federico, A. J., Schimert, G., and Greatbatch, W. The longterm treatment of heart block. Progr. Cardiovasc. Dis. 9:105, Lemberg, L., Castellanos, A., and Berkovits, B. V. Pacing on demand in A.-V. block. J.A.M.A. 191:106, Sowton, E. Clinical application of demand pacemakers. Brit. Med. J. 3:576, THE ANNALS OF THORACIC SURGERY

6 Demand Pacing in Cardiac Arrhythmias 5. Sowton, E. Cardiac pacemakers and pacing. Mod. Conc. Cardiovasc. Dis. 36:31, Zuckerman, W., Zaroff, L. I., Berkovits, E. V., MatlofE, J. M., and Harken, D. E. Clinical experiences with a new implantable demand pacemaker. Amer. J. Cardiol. 20:232, DISCUSSION DR. JOHN H. KENNEDY (Cleveland, Ohio): My associate, Dr. Otto Heiderer, has recently reviewed our own experience with implantable pacemakers, a sum total of 444 patient-months of pacing. A prototype demand pacemaker unit was first placed at our disposal through the kindness of Dr. Chardack at a time when we had a patient with fixed bigeminus and bradycardia. Fixed-rate pacing, of course, was unsuitable in this case. Since this time we have tended to put demand pacemakers in all patients. I support the suggestion of the essayists that, indeed, demand pacing must be considered useful for specific indications, since in 4 of our patients there was competition, so to speak, or intrinsic inhibition of the demand system by premature ventricular contractions, which of course were interpreted by the demand pacemaker as a stimulus that would bias the gate of the pulse generator. Only 1 of 4 patients required replacement of the demand pacemaker by a fixedrate unit. In the other 3 it was possible to control this troublesome complication by increasing the rate of the implanted demand unit. NOTICE FROM THE SOCIETY OF THORACIC SURGEONS Abstracts for papers to be presented at the 1970 Annual Meeting of The Society of Thoracic Surgeons are now being accepted. The meeting is to be held at the Regency Hyatt House, Atlanta, Georgia, January 12-14, The deadline for receipt of abstracts is September 15, An original and eight copies should be submitted to John C. Callaghan, M.D., Chairman, Program Committee, The Society of Thoracic Surgeons, 339 North Michigan Ave., Chicago, Ill Abstracts must summarize an original contribution not presented or submitted elsewhere. It must not exceed 200 words in length. Abstracts received after the deadline or exceeding 200 words will not be considered. The program committee reserves the right to select papers for either regular or forum-type presentations. Essayists are reminded that the complete manuscript must be submitted in duplicate either to the Editor of The Annals of Thoracic Surgery before the meeting or to the Secretary of the Society at the meeting, immediately prior to presentation. RALPH D. ALLEY, M.D. Secretary VOL. 8, NO. 2, AUGUST,