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With increasing use of artificial cardiac pacing, criteria for selection of patients have been refined. In general, the most important indication for pacing is the presence and severity of symptoms due to bradyarrhythmias. Use of pacing in acute myocardial infarction remains controversial, but some guidelines are presented here.
Following insertion or implantation of an artificial cardiac pacemaker, both physician and patient are involved in aftercare to monitor the patient's cardiac status, the condition of the implantation site, and the function of the pacemaker. Among the complications that may occur are pacemaker malfunction and perforation of the ventricles. The physician and patient must also be alert to the possibility of electrical interference and to the physiologic factors that can modify pacemaker function.
This study presents a beat-to-beat analysis of digital arterial pulse volume (DAPA), left ventricular end-diastolic diameter (LVEDD), and stroke volume (SV) and their correlation to PQ interval in ten patients with complete heart block and artificial cardiac pacing. DAPA was measured by strain-gauge plethysmography and LVEDD/SV by echocardiography. A close relationship was found between SV and DAPA (R = 0.83-0.97) in seven patients, who all drew considerable benefit from atrial contraction as regards SV and DAPA (increase with 35-94%). The optimal PQ interval was calculated to approximately 240 msec for DAPA and 180 msec for LVEDD and SV. It may be concluded that the present study demonstrates a close relationship between beat-to-beat variations of SV measured by echocardiography and plethysmographically recorded digital arterial pulse volume. These variables may be useful in clinical practice for assessing the hemodynamic effect of atrial contribution in patients with various forms of cardiac conduction disturbances. The two methods may, for instance, be useful for screening in order to pick out patients who may benefit from AV synchronous rather than ventricular pacing.
A new balloon-tipped ventricular endocardial electrode for permanent artificial cardiac pacing is described. Following transvenous insertion of the electrode to the right ventricular apex, the distal balloon is inflated with contrast material in order to wedge the electrode tip between or beneath trabeculae and prevent displacement. fifty-nine electrodes were implanted, including a second generation type incorporating a wedge tip as well as the balloon. The incidence of displacement was 17% with 10% of cases being early, and 7% late. Early in the series, 50% Urografin was used to inflate the balloon and this resulted in premature deflation and early electrode displacement in two of the nine patients. When the concentration of Urografin was reduced, the balloon remained inflated for a longer period and the incidence of early displacement was reduced to 8%. However, there was still a late displacement of 8%. Only one wedge-tipped balloon electrode displaced. This electrode had a faulty sealing mechanism and the balloon could not be adequately inflated. There was a 3% incidence of early and a 3% incidence of late threshold problems with the electrode. However, name of the wedge-tipped balloon electrodes exhibited this problem. It was concluded that this new electrode did not fulfill its objectives. The total electrode failure rate, including displacements and episodes of high threshold was approximately 24%.
A three-year experiences with the treatment by artificial pacing of the cardiac rhythm anomalies after open-heart surgery, at the Institute of Surgery of the Heart and Great Vessels, Ist School of Medicine, University of Naples, are reported. The most frequent arrhythmias occurring during or soon after open-heart surgery and the main aetiologic factors are examined. The surgical techniques for pacing and their indications are considered. Thereafter some particularly interesting cases are reported.
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The basic electrophysiology of temporary and permanent cardiac pacing is reviewed, as are the indications, the types of pacing systems, and the methods of implantation. Recent developments in power sources and leads are described. The mercury-zinc battery is now obsolete and is being replaced by lithium, rechargeable, and isotopic power systems. While ventricular pacing continues to be the standard, a brief review of atrial programmed systems is given, including atrial pacing and atrioventricular synchronized and atrioventricular sequential pacing. Conventional pacing is aimed at the control of symptomatic bradycardia. Brief reference is made to experimental pacing systems designed to control ventricular or supraventricular tachyarrhythmias.
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The acute and chronic electrophysiological effects of a cryolesion produced in the left ventricle were studied in six dogs. All dogs had frequent ventricular premature beats (VPB) and five of six dogs had ventricular tachycardia during the first 4 days after the cryolesion; only one of the six dogs continued to have VPBs after 1 week, and this dog had identical VPBs before the creation of the cryolesion. Neither control dog had VPBs. Two additional dogs underwent epicardial and transmural mapping studies immediately after production of a cryolesion. VPBs in these animals were shown to originate at the border of the cryolesion. Epicardial activation sequence during normal sinus rhythm was not altered by the chronic cryolesion. The border zone of the chronic cryolesion was sharply demarcated with normal potentials recorded outside of the lesion and "extrinsic" potentials recorded within.
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The effect of atrial, ventricular, and atrioventricular (A-V) sequential pacing on cardiac output (CO) was evaluated in patients within 24 hours after cardiac surgery. In patients with normal sinus rhythm, ventricular pacing reduced CO by as much as 42% (average, 14%), whereas atrial and A-V sequential pacing at the same rate increased CO by averages of 13% and 19%, respectively. In patients with junctional rhythm, increase of the heart rate by ventricular pacing produced an increase in CO, however, and an additional 25% increase in CO could be obtained by atrial or A-V sequential pacing at the same rate. Atrial or A-V sequential pacing was superior to ventricular pacing at the same rate and they are the preferred methods for temporary carciac pacing in the postoperative period. In suitable cases elective A-V sequential pacing is an effective method for increasing CO after cardiac surgery.
The direct relationship between graft flow and regional midwall myocardial function has not been documented in patients. Therefore, the present study was designed to quantitate the effects of coronary artery bypass grafting on regional myocardial mechanics distal to a coronary artery obstruction. Twenty-one patients with subtotal or total occlusion of the left anterior descending (LAD) coronary artery underwent coronary artery bypass grafting. Following completion of the aortic and coronary anastomoses, two miniature ultrasonic dimension transducers (2.5 mm. diameter) were positioned within the minor axis of the anterior left ventricular free wall and were allowed complete freedom of movement. The transducers were placed at midwall depth, and areas of clinically apparent myocardial fibrosis were not utilized as sites of implantation. During control, 30 minutes following the termination of cardiopulmonary bypass, regional myocardial dimensions, pulmonary artery diastolic pressure, arterial pressure, and heart rate were recorded with all saphenous vein grafts open and after 30 seconds of single vein graft occlusion. These measurements were repeated during atrial pacing at a rate of 128 +/- 4 beats per minute. Data are mean +/- the standard error of the mean. During control, graft occlusion resulted in a regional decrease in systolic excursion from 1.3 +/- 0.1 to 1.0 +/- 0.2 mm. (p less than 0.01), as well as a decrease in the rate of shortening from 8.7 +/- 0.2 to 6.2 +/- 1.1 mm. per second (p less than 0.05); heart rate, mean arterial pressure, and diastolic pulmonary artery pressure remained unchanged. Graft occlusion with atrial pacing resulted in an exaggerated decrease in both regional systolic excursion, from 1.2 +/- 0.2 to 0.6 +/- 0.2 mm. (p less than 0.01), and rate of shortening, from 9.4 +/- 1.5 to 4.4 +/- 0.2 mm. per second (p less than 0.01). For the group of patients studied, end-diastolic lengths were unchanged with graft occlusion during control and atrial pacing. Moreover, with graft occlusion, isolated patients demonstrated regional dyskinesia as evidenced by holosystolic bulging. These studies in patients have documented for the first time that, despite a constant preload, afterload, and heart rate, regional myocardial function following coronary artery bypass grafting is dependent upon adequate graft flow, especially during stress.
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