THE MANAGEMENT OF HEART BLOCK

Ventricular tachyarrhythmias in the long QT syndromes

Marked prolongation of the electrocardiographic QT interval often is associated with a distinctive form of ventricular tachycardia characterized by the gradual oscillation around the baseline of the peaks of successive QRS complexes. This was named torsades de pointes, or "twisting of the points." This form of ventricular tachycardia tends to be rapid and self-terminating and often occurs in clusters, leading afflicted patients to present with recurrent dizziness and syncope. Ventricular fibrillation and sudden death are common.

Prognosis of patients paced for chronic atrioventricular block

Between the years 1960 and 1974, 839 patients were paced for chronic complete atrioventricular block. Analysis of survival compared with the general population showed that 170 deaths were expected according to standard mortality tables and 288 actually occurred, giving a ratio of actual to expected deaths of 1.7:1. Patients with a definite history of myocardial infarction showed a higher than average mortality when paced. Mortality was not influenced whether heart was constant or intermittent, whether the ventricular rate was below or above 40/minutes, or whether QRS duration was greater or less than 0.1 second. Analysis of the age groups paced disclosed the most important correlations. Between the ages of 80 and 89 years paced patients could expect to survive as long as other of the same age without heart block. There was, however, a very high ratio of 4.5:1 for 90 patients in the age group 50 to 59 years. The reason for the high mortality ratio was uncertain but it may have been the result of a greater incidence of underlying coronary artery disease.

Cardiac pacing

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.

Hemodynamic changes during ventricular pacing in patients with complete heart block and aortic and mitral valvular heart disease

Increasing the heart rate to near normal in patients with complete heart block (CHB) and slow ventricular rates may lead to greater improvement in ventricular function than when the heart rate is increased from normal to more rapid heart rates. Improvement in ventricular function is usually manifested by a decrease in left ventricular end-diastolic pressure (LVEDP) and volume and by an increase in contractility. In patients with both CHB and valvular heart disease improvement in ventricular function during pacing may be modified by the nature of the valvular disease. Hemodynamic data from six patients with both valvular heart disease and CHB were compared with those from ten patients with CHB and normal cardiac valves. Hemodynamic studies were performed at slow or idioventricular rates and again after increasing the heart rate to more nearly normal levels by ventricular pacing. When obstruction to left ventricular inflow (mitral stenosis) co-existed with CHB, increasing the heart rate resulted in a reduction of an elevated LVEDP to normal. This resulted in only a small increase in left atrial pressure in spite of a striking increase in the mean left atrial-ventricular gradient. When obstruction to left ventricular outflow prevailed (aortic stenosis), improvement in cardiac function was manifested mainly by a decrease in LVEDP and was accompanied by a decrease in left ventricular stroke work. When a large regurgitant volume (aortic insufficiency) was added to a ventricle which has enlarged subsequent to CHB, there was striking elevation in ventricular filling pressures which returned to more nearly normal levels when the heart rate was increased. This was accompanied by a reduction in regurgitant stroke volume in the patient in whom it was measured. Thus, an increase in heart rate may be especially beneficial to those patients with CHB who also have valvular lesions which contribute to an increase in LVEDP and end-diastolic volume. Careful hemodynamic evaluation is helpful in determining appropriate therapy in these patients.

Adams-Stokes seizures due to ventricular tachydysrhythmias in patients with heart block: prevalence and problems of management

One hundred and twelve patients with heart block and chronic tendency to syncope were ECG-monitored during syncope. Ventricular tachycardia and/or fibrillation (VT-VF) was observed as the cause of syncope in 11 patients: in 6 of 20 patients with chronic third degree A-V block, in 3 of 65 with paroxysmal A-V block and in 2 of 27 with S-A block. The R-R interval preceding the escape beat which initiated VT-VF varied between 1.2 and 2.2 seconds. The cerebral attacks were amenable to long-term pacemaker treatment. However, relapses of VT-VF were observed during pacing with a low rate of 55 per minute and during short interruptions in pacing, as produced by intermittent pacemaker failure or threshold determination. In one patient, supplementary treatment with a beta-blocking agent had to be given to suppress exercise-induced attacks of VT-VF after pacemaker implantation.

Management of infected transvenous permanent pacemakers

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Implanted-pacemaker-induced dysrhythmia and its management

Five cases of implanted-pacemaker-induced dysrhythmia are described and factors precipitating such dysrhythmias are discussed.

The efficacy of practolol in the treatment of such dysrhythmias is shown and its use as a prophylactic antidysrhythmic agent has been suggested.

Atrioventricular conduction defects in patients presenting with syncope and normal PR interval

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The Birmingham (Lucas) pacemaker. An appraisal of its use

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Aspects of the psychological status of patients treated with cardiac pacemakers

An initial clinical observation that patients with externally located cardiac pacemakers are more distressed and depressed than those with internally sited pacemakers has been confirmed. The total patient group is also characterized by its tendency to report that it does not worry about getting an incurable illness. At the same time, it is evident to others that it does have such an illness. Those patients who acknowledge that they did worry in this way were found to score significantly higher on several scales of a standardized psychoneurotic index than did the overall ‘pacemaker’ population.

Possible reasons for the greater psychological distress displayed by the group of patients with external pacemakers are discussed.

Aetiology of chronic heart block. A clinico-pathological correlation in 65 cases

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Perforation of the right ventricle by electrode catheters: a review and report of nine cases

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Permanently implanted transvenous pacemakers. Electrical measurements of function

Three patients with complete heart block had a high resistance to electrical stimulation of the endocardium through transvenous pacemaker systems. One patient died; one needed reoperation for implantation of epicardial electrodes; and the third required a generator of higher current. The present enthusiasm for permanent transvenous implantation of pacemakers must be tempered somewhat by the knowledge that high endocardial resistance to pacing represents another cause of failure. Simple and rapid methods of determining the current necessary to stimulate the endocardium are available and should be used prior to permanent implantation of the generator. If a substantial margin of safety does not exist, one should consider substituting a pulse generator with greater output or an epicardial electrode system.