Alberto Benchimol

Medical and physiological considerations in the use of artificial cardiac pacing. Part I

Abstract This review has been concerned with medical and physiological considerations in the clinical use of cardiac pacing. Certain problems were selected for discussion and the relevant pathology and pathophysiology treated in some depth. Particular attention was given to the Stokes-Adams syndrome, heart block complicating acute myocardial infarction, the electrophysiological complications of pacing, the appropriate roles of synchronous vis-a-vis-fixed-rate pacemakers, and the nature and possible applications of coupled and paired pacing. The importance of hemodynamic and electrophysiologic studies during a preliminary period of temporary pacing in establishing the optimal mode and rate of permanent pacing was stressed. The review was confined to clinical material and no attempt was made to discuss purely experimental and investigative uses of pacing.

Contribution of atrial systole to the cardiac function at a fixed and at a variable ventricular rate

Abstract 1. 1. The contribution of atrial systole to cardiovascular dynamics was described in 21 patients with complete heart block at a fixed and at a variable ventricular rate. 2. 2. It was demonstrated that a properly timed atrial systole significantly improves cardiac function in patients with complete heart block. The optimal P-R interval was found to occur between 1 and 300 msec. For this range there were 13, 14, 6, 12, 14 and 33 per cent increases in ejection time, mechanical systole, isometric contraction time, systemic pressure, peak derivative of brachial artery pressure and tensiontime index, respectively, as compared with figures obtained when atrial systole occurred during ventricular systole. 3. 3. It was also found that the contribution of atrial systole to cardiac function occurs in all ranges of ventricular rates studied (20 to 125 beats/min.). However, the maximal beneficial effect of atrial systole was found to occur for the ventricular rate in the range of 51 to 80 beats/min. 4. 4. Very short or very long P-R intervals resulted in minor changes in the measured parameters, and the figures obtained closely approach the ones determined when atrial systole occurred during ventricular systole. 5. 5. It is, therefore, concluded that atrial systole significantly improves cardiac function in man under the conditions of our study.

Cardiovascular Dynamics in Complete Heart Block at Various Heart Rates Effect of Exercise at a Fixed Heart Rate

Thirteen patients with complete atrioventricular block resulting from coronary disease were studied. In seven the diagnosis of coronary disease was established by the presence of typical history and electrocardiographic and enzymatic findings compatible with an acute infarction. Of the remaining six cases, three had a typical history of angina pectoris. In three cases there was no history of myocardial infarction or angina pectoris, and the diagnosis of coronary disease was suspected by the appearance of heart block above age 60 in the absence of any other possible etiologic factor that might be responsible for the establishment of the block. Exercise studies were performed in eight cases. Right heart catheterization was performed under local anesthesia prior to implantation of a permanent cardiac pacemaker. A no.-6 bipolar electrode catheter * 1 was introduced into the antecubital vein and advanced to the apex of the right ventricle. Another no.-7 Lehman catheter was introduced into the cephalic vein and advanced to the right atrium and right ventricle. Cardiac output was determined by the indicator-dilution technic with indocyanine t (Cardio-

A study of the period of isovolumic relaxation in normal subjects and in patients with heart disease

Abstract 1. 1. Measurements of isovolumic relaxation time from simultaneous recording of the apex cardiogram, carotid tracing and phonocardiogram were obtained in 64 normal subjects and in 60 patients with compensated heart disease. This time interval was measured from the second heart sound of the phonocardiogram to the O point of the apex cardiogram. The range for normal values was 50 to 140 milliseconds, with a mean of 103 ± 22 milliseconds. In the patients with compensated heart disease this interval ranged from 58 to 175, with a mean of 102 ± 26 milliseconds. The standard error of the measurement was 4 per cent of the mean. 2. 2. Age itself did not influence the duration of isovolumic relaxation time. Heart rate, exercise and the administration of isoproterenol significantly decreased the isovolumic relaxation time. 3. 3. Digitalis significantly increased the duration of the isovolumic relaxation time, which may prove to be the basis for a useful and simple method of evaluating digitalization in man. 4. 4. Since this period of the cardiac cycle may be altered by pharmacologic means and by disease states, it may be a useful avenue to the study of the condition of ventricular function in man.

Effect of Heart Rate, Exercise, and Nitroglycerin on the Cardiac Dynamics in Complete Heart Block

THE PRESENCE of complete heart block offers a good opportunity to study cardiovascular functions, since one of the major variables of cardiac activity, i.e., heart rate, is maintained constant.113 In addition, if a cardiac pacemaker is implanted in a heart for treatment of complete heart block,14-20 total control of the cardiac rate is achieved, thereby providing an excellent opportunity for studying cardiovascular hemodvnamics under a variety of fixed rates. The present study was unidertaken (1) to attempt to establish the most appropriate heart rate for permanent pacing; (2) to ascertain the hemodynamic consequences of complete heart block at a fixed slow heart rate, and the effect of increasing heart rate; (3) to determine the effects of exercise and nitroglycerin on the cardiac dynamics at various fixed heart rates. A patient with complete heart block resulting from coronary artery disease was studied.

Clinical experience with the use of computers for calculation of cardiac output

Abstract 1. 1. One hundred and seventeen cardiac output determinations were obtained in 12 patients with normal and abnormal cardiovascular systems. The dye curves were calculated by the hand method of Hamilton and with the use of a dye-dilution analog computer. 2. 2. There was a good agreement between the two methods with an average of the percentage difference of 8 per cent and with a standard deviation of 4.2 per cent. In curves with prolonged clearance time and low peak concentration, the average difference was 25.2 per cent with a standard deviation of 11.0 per cent. 3. 3. Changes in the cardiac output provoked by exercise, change in heart rate and by administration of drugs were adequately detected by the computer technic. 4. 4. It was found that the cardiac output computer is a time-saving, reliable and reproducible instrument in the calculation of the cardiac output. 5. 5. The computer should not be used in cases with low peak concentration, prolonged clearance time and in cases with any form of intracardiac shunt.

The carotid tracing and apexcardiogram in subaortic stenosis and idiopathic myocardial hypertrophy

I N a PREVIOUS paper’ we reported abnormalities of the indirect carotid tracing in patients with aortic valvular stenosis, and we confirmed some of the findings previously described in the literature.2-12 The described findings, consistently present in all patients with this valvular lesion, consisted of prolonged total ejection time and upstroke time, carotid shudder, low anacrotic notch and an inconspicuous dicrotic notch. At that time we also indicated that 2 of our cases with subaortic stenosis presented distinct characteristics in the carotid tracing which were quite different from those in the cases with the valvular type of aortic obstruction. The purpose of this present report is to analyze in more detail the abnormalities of the carotid tracings in patients with subaortic stenosis and in cases of idiopathic myocardial hypertrophy.

CARDIOVASCULAR RESPONSE TO EXERCISE DURING ATRIAL FIBRILLATION AND AFTER CONVERSION TO SINUS RHYTHM.

Abstract Cardiovascular dynamics were studied at rest and during and after exercise in 8 patients with atrial fibrillation who were successfully converted to a sinus rhythm with a DC defibrillator. The study demonstrated an improvement in cardiac efficiency following conversion to normal sinus rhythm as evidenced by increases of 6 per cent in the cardiac index, 22 in the stroke index, 18 in the work index and 13 in the stroke power and decreases of 16 per cent in the pulse rate, 12 in peripheral resistance, 10 in the mean arterial pressure and 58 in the tension-time index. The improvement in cardiac function was more evident during exercise but did not approach the values obtained in experimental studies conducted with essentially normal hearts.

Cardiovascular Hemodynamics and the Internally Placed Cardiac Pacemaker

Abstract 1. 1. Cardiovascular hemodynamics were studied in a patient with complete heart block and an indwelling cardiac pacemaker having an external induction-coil control unit. 2. 2. Determinations at varying heart rates demonstrated a system capable of increasing its cardiac output by increasing the heart rate at the expense of a fall in stroke volume. 3. 3. An implanted cardiac pacemaker with an external control unit offers an excellent bioelectric system for the study of the effects of physical activity on the heart as well as the nonchronotropic effects of cardiovascular drugs, since a major variable of cardiac function, i.e., heart rate, can be held constant .

Rapidly repeated determinations of the cardiac output with the indicator-dilution technic

T HE indicator-dilution technic has been extensively used in the study of the circulation under a variety of conditions.1-10 Although it has been in use for a relatively long time, only a few have attempted to employ it in man for rapidly repeated determinations of cardiac output.“-I4 In these previous reports the time intervals between injections were kept above 5 minutes. Determination of cardiac output by the Fick principle does not allow sequential observations at short time intervals. However, moment-to-moment changes may occur, as, for example, in response to short periods of exercise, during administration of short-acting cardiac drugs or during various states such as experimental shock and acute hypervolemia. In these instances rapidly repeated serial determinations of cardiac output in man or in intact experimental animals are highly desirable. The present study was undertaken (a) to verify the random, systematic variability of rapidly repeated determinations of the cardiac output in man by the dye-dilution technic, and (b) to determine its possible usefulness in studying circulatory changes over a short period of time during a variety of conditions.