Abnormalities of left ventricular function associated with the anginal state

Importance of considering ventricular function when prescribing exercise after acute myocardial infarction

This investigation was undertaken in patients who had an acute myocardial infarction 12.6 +/- 0.4 months earlier to determine, using conventional methods, the nature of stroke volume changes during training regimens. Twenty-seven patients (mean age 52 +/- 2 years; rest ejection fraction 49 +/- 2%; New York Heart Association functional class I or II) and 9 normal, age-matched sedentary control subjects (mean age 50 +/- 1 years) exercised in the upright position on a bicycle ergometer. Stroke volume was measured by impedance cardiography at rest and after each workload. Ten patients (group A) had a stroke volume response similar to that of the normal sedentary subjects. In 8 patients (group B) the stroke volume increased initially, then decreased (more than 15%) at heart rates (HRs) greater than 100 to 105 beats/min. Nine patients (group C) had a flattened stroke volume response throughout exercise. Training HR determined by conventional methods corresponded to a maximal stroke volume in the normal subjects. Training HR in group A corresponded to a stroke volume that was maximal or near-maximal. Training HR in group B corresponded to a maximal or diminishing stroke volume. In group C, the training HR corresponded to a stroke volume no different from that at rest. Thus, training HR determined by conventional methods based solely on the chronotropic responses to exercise may place patients who have abnormal stroke volume responses to upright exercise in a situation during training sessions in which an inappropriately high HR, excessive fatigue or silent ischemia may develop.

On the mode of action of antianginal drugs

The antianginal action of coronary dilating drugs seems to be related at least partly to their effect of improving the blood supply of the ischemic myocardium. No correlation was found between coronary dilating action of these drugs in the normal myocardium and in the ischemic area, however. It has been shown that coronary dilator drugs are able to produce a further dilatation of the vascular bed which is already in maximum hypoxic dilatation. The antianginal effect of adrenergic beta receptor blockade cannot be explained solely by its negative chronotropic and inotropic action. It involves a favourable redistribution of the coronary flow which is increased in the ischemic area. In addition, there is evidence for a direct cardiac metabolic effect of beta blockade which reduces the myocardial oxygen requirement and moderates the ischemic diminution of the myocardial lactate uptake independently of its action on the autonomic nervous control and other extracardiac factors as well as on contractility, heart rate and myocardial blood supply.

Systolic time intervals before and after maximal exercise treadmill testing for evaluation of chest pain

The change in systolic time intervals from before exercise to three to four minutes following a maximal-exercise treadmill test was measured to eveluate chest pain in 110 fasting supine subjects. Forty-six (85 percent) of 54 patients with chest pain and with abnormal findings on coronary arteriograms were found to have at least a 10-msec prolongation in the left ventricular ejection time index (LVETI), whereas only two (8 percent) of 25 subjects without heart disease and 5 (16 percent) of 31 subjects with chest pain but with normal findings on coronary arteriograms had 10 msec or more of prolongation of the LVETI after exercise. The change in the other systolic time intervals (total electromechanical systole, preejection phase [PEP], and PEP/LVET) were less reliable in detecting the presence or absence of coronary disease. We conclude that determination of LVETI before and after maximal-exercise treadmill testing is a clinically useful noninvasive disgnostic test for obstructive coronary disease in patients with chest pain.

Left ventricular compliance: mechanisms and clinical implications

Left ventricular diastolic compliance is determined by the level of operating pressure and the diastolic pressure-volume relation. This relation is curvillinear and the slope of a tangent (operative chamber stiffness) to the pressure-volume curve increases as the chamber progressively fills. Such preload-dependent changes in compliance occur during any acute alteration in ventricular volume. At a given diastolic pressure, operative chamber stiffness (or its reciprocal, operative chamber compliance) is determined by the relative values for ventricular volume and muscle mass and by the stiffness of a unit of myocardium. Thus, there may be a leftward shift of the diastolic pressure-volume curve (increase in the modulus of chamber stiffness) as a consequence of ventricular hypertrophy or an increase in the stiffness of heart muscle itself (increase in modulus of muscle stiffness). To distinguish between hypertrophy and stiff muscle, it is useful to examine the modulus of chamber stiffness, derived from pressure-volume data, together with the volume/mass ratio of the ventricle. In this fashion, changes in the modulus of chamber stiffness that are inappropriate for a given volume/mass ratio may be attributed to changes in the material properties of the heart muscle. Examples of clinical and experimental pressure-volume studies are presented to illustrate the variety of mechanisms by which acute and chronic changes in ventricular chamber compliance evolve during the course of clinical heart disease. The pathophysiology of pulmonary congestion is best understood by considering the factors responsible for producing changes in chamber stiffness of the ventricle, whereas an examination of muscle stiffness is likely to provide more insight into the extent of irreversible functional and structural defects of the myocardium.

Left ventricular dyskinesia in infarction and angina

In 29 patients, the site and extent of coronary artery obstruction were related to the position and area of abnormally contracting segments of the left ventricle, both in patients with a history of angina without myocardial infarction (group I) and in patients with prior documented myocardial infarction (group II). The degree of coronary artery obstructive disease was estimated in the standard manner and also by a coronary artery index which considered not only the degree of obstruction but also the total length of the obstructed segment. A kinetic or dyskinetic segments were present in 22 of the 29 patients. An abnormally contracting segment was present in 12 or 18 patients without prior myocardial infarction in comparison with 10 of the 11 patients with prior infarction. Complete obstruction of a coronary vessel and resultant dyskinesia were more frequent in the right coronary artery than in either the left anterior descending or the circumflex artery. There was a significant correlation between total per cent of vessel obstruction and degree of ventricular asynergy in both groups; consideration of length of obstructed segment did not improve this correlation.

Prinzmetal's variant angina: hemodynamic and angiographic observations during pain

Hemodynamic and angiographic data obtained during pain from four patients with Prinzmetal's variant angina are reported. The left ventricular pressure-time index did not increase before or during attacks of angina in three of the four patients; left ventricular systolic performance was impaired during pain in all three. In one of these three patients left ventricular pressure-volume data obtained during angina suggested a reduction in diastolic compliance; in another, pain and S-T segment elevation were present during coronary arterial spasm. The fourth patient had an increase in both arterial blood pressure and heart rate before an attack; in this patient coronary arterial spasm could not be demonstrated during the period of pain and S-T elevation. The data presented suggest that hemodynamic factors that increase the myocardial oxygen requirements are absent and that coronary arterial spasm is present in some, but not all, patients with variant angina.

Central haemodynamics during oxygen breathing in angina pectoris

Lecerof, H. (1974).Thorax, 29, 673-677. Central haemodynamics during oxygen breathing in angina pectoris. The haemodynamic effects of breathing 100% oxygen have been studied by right heart catheterization at rest and during bicycle exercise in nine male patients with coronary heart disease. Oxygen breathing produced no significant haemodynamic benefit during angina pectoris induced by physical exercise, although at rest a reduction in heart rate and cardiac index was evident. The favourable effects of 100% oxygen breathing described in pacing-induced angina pectoris cannot therefore be transferred to exercise-induced angina probably because the myocardial blood flow during the latter condition is hampered by an increased left ventricular end-diastolic pressure.

Effects of catecholamines, exercise, and nitroglycerin on the normal and ischemic myocardium in conscious dogs

The effects of isoproterenol, norepinephrine, dobutamine, exercise, and nitroglycerin on left ventricular diameter, pressure, velocity of shortening, dP/dt, dP/dt/P, arterial pressure, left circumflex coronary blood flow, and coronary vascular resistance were examined in healthy conscious dogs with normal coronary perfusion and in the same animals after moderate global ischemia had been induced by partial occlusion of the left main coronary artery. In the normal nonischemic heart, all interventions improved left ventricular performance, as evidenced by increases in dP/dt/P and velocity at the same or lower left ventricular end-diastolic diameter. Interventions, which in the normal heart caused large increases in heart rate and myocardial contractility, e.g. isoproterenol and exercise, or which decreased coronary perfusion pressure, e.g. nitroglycerin or isoproterenol, elicited paradoxical responses in moderate global ischemia, i.e., left ventricular enddiastolic diameter and pressure rose, and dP/dt/P and velocity fell substantially. On the other hand, norepinephrine, which increased coronary perfusion pressure along with myocardial contractility but did not increase heart rate, improved left ventricular function. Dobutamine, which did not alter heart rate or arterial pressure substantially while improving myocardial contractility, produced an intermediate response between that of norepinephrine and isoproterenol in the presence of moderate global myocardial ischemia. Thus, interventions that increase myocardial O(2) requirements, by increasing heart rate and myocardial contractility without augmenting coronary perfusion pressure, can produce a paradoxical depression of ventricular function in the presence of global myocardial ischemia.