Effects of propranolol and timolol on left ventricular volumes during exercise in patients with coronary artery disease

Exercise release of cardiac natriuretic peptides is markedly enhanced when patients with coronary artery disease are treated medically by beta-blockers

OBJECTIVES

This study sought to identify determinants of the exercise rise in plasma levels of cardiac natriuretic peptides (NPs) in patients with coronary artery disease (CAD).

BACKGROUND

During stress, there is a variable rise in the plasma level of NPs, but this rise frequently reaches levels that are known to lower the cardiac load and that thus might be beneficial to CAD patients.

METHODS

Plasma venous concentrations of atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) were determined at rest and peak exercise in 104 patients with chronic CAD who were referred to exercise thallium-201 ((201)Tl) single-photon emission computed tomography (SPECT) and radionuclide angiography.

RESULTS

The extent of scarred myocardium by (201)Tl-SPECT and patient age were the best independent predictors of NP concentrations at rest, but also of increases in NP concentration during exercise (all p < 0.001). Moreover, beta-blocking treatment was an additional and strong independent predictor of the increase in NP concentrations at exercise (p < 0.001 for ANP; p = 0.001 for BNP). On average, exercise increases in NP concentrations were more than twice as high in patients with (n = 55) than in those without (n = 49) beta-blocker treatment (ANP: +49 +/- 63 vs. +22 +/- 25 ng/l, p = 0.01; BNP: +24 +/- 5 vs. +11 +/- 15 ng/l, p = 0.04), whereas NP concentrations at rest were equivalent in the two groups (ANP: 34 +/- 34 vs. 30 +/- 33 ng/l, p = NS; BNP: 85 +/- 152 vs. 57 +/- 101 ng/l, p = NS).

CONCLUSIONS

Patients with chronic CAD exhibit much higher exercise releases of ANP and BNP when they are treated with beta-blockers. This enhanced secretion of potent vasodilating and natriuretic agents constitutes an original therapeutic mechanism for further protecting diseased hearts against stress.

The physiology behind exercise testing

Despite significant advances in related technologies, the exercise test remains a useful clinical tool. It can define the limits of performance in an athlete or the functional capabilities of the patient with heart disease. Although virtually all of the body's physiologic and metabolic systems interact in a coordinated fashion to perform a single bout of exhaustive exercise, a major burden falls on the cardiopulmonary system. A good understanding of the basic physiologic responses to acute exercise can assist the clinician in applying the information gained from the test. These responses are influenced by state of health and fitness, age, gender, type of exercise, exercise position, and the environment. This article provides an overview of the physiologic responses to acute exercise, and discusses the many factors that influence these responses.

Effects of atropine on left ventricular volumes and ejection and filling rates at rest and during exercise

1. The influence of the parasympathetic nervous system on left ventricular function including ejection and filling rates was studied by radionuclide cardiography in eight healthy young men at rest and during upright exercise. 2. After parasympathetic blockade induced by atropine, the mean heart rate (HR) at upright rest increased from 67 to 114 beats min-1, cardiac output (CO) from 4.05 to 5.17 1 min-1 (both P less than 0.001), and the diastolic blood pressure by 13 mm Hg (P less than 0.01). 3. Stroke volume (SV), left ventricular end diastolic and end systolic volume all decreased significantly after atropine. The relative ejection time increased from 0.33 to 0.51 of the cardiac cycle length (P less than 0.001), and the appropriate ejection and filling rates increased by 13% (P less than 0.05) and 147% (P less than 0.001), respectively. Haemodynamic changes in the supine position were virtually the same. 4. During exercise atropine increased HR from 115 to 146 beats min-1 (P less than 0.001) and CO by 12% (P less than 0.05), whereas SV decreased by 12% (P less than 0.05) and the systolic blood pressure by 16 mm Hg (P less than 0.001). Changes in ejection and filling rate of the left ventricle were of the same nature as those found at rest. 5. Thus apart from its HR limiting properties, secondary effects of parasympathetic nervous tone are dilatation of the left ventricle and enhancement of ejection, effects that are counteracted by atropine.

Effect of beta-blockade on low heart rate-related ischemia during mental stress

To explore the effect of beta-adrenergic blockade on low heart rate-related (mental stress) ischemia, 19 patients with coronary artery disease were randomized into a double-blind crossover trial of metoprolol, 100 mg twice daily, and underwent serial mental stress/bicycle exercise studies. Mental stress-induced wall motion abnormalities occurred at a lower heart rate than exercise-induced wall motion abnormalities during placebo administration (81 +/- 16 vs. 123 +/- 20 beats/min, p less than 0.05). Metoprolol reduced the mean magnitude of exercise-induced wall motion abnormalities (2.8 +/- 2.0 vs. 1.6 +/- 2.4, p = 0.003); improvement was related to the magnitude of hemodynamic beta-blockade effect. Metoprolol did not significantly reduce the mean magnitude of mental stress-induced wall motion abnormalities (3.0 +/- 2.2 vs. 2.6 +/- 2.2), although individual responses predominantly either improved (50%) or worsened (29%). Unlike exercise, the magnitude of hemodynamic beta-blockade did not predict mental stress response and metoprolol did not block mental stress-induced blood pressure elevations. Patients with abolition of exercise-induced ischemia were more likely to have reduction of mental stress-induced ischemia. Patients whose ischemia worsened with metoprolol during mental stress had more easily inducible ischemia, as assessed by exercise-induced placebo wall motion abnormality, chest pain and prior myocardial infarction. Beta-blockade was associated with a lowering of ischemia-related hemodynamic thresholds compared with placebo. These results suggest that beta-blockade has a variable effect on low heart rate-related ischemia that may be due to a lack of effect on mental stress-induced blood pressure elevation in patients with easily induced ischemia or to effects on coronary vasomotor tone, or both.

Acute effects of alcohol and food intake on cardiac performance

Alcohol and food intake induce changes in LV performance which can be evaluated by radionuclide cardiographic methods. Alcohol probably exerts its effects by a direct action of ethanol in the blood on the myocardium, while the postprandial hemodynamic changes are related to the effects of food in the intestine. Alcohol intoxication causes a dose-dependent impairment of LV emptying at rest, whereas compensatory mechanisms other than an increased sympathetic nervous activity counterbalance this effect during exercise. In patients with coronary artery disease, alcohol induces only small changes in LV volumes at rest, possibly because of a concomitant vasodilation. Food intake seems to have a considerable influence on central hemodynamics leading to an increase in cardiac output both in healthy subjects and in patients with coronary artery disease. In healthy subjects an increase is recorded in the LVEDV and LVESV after a meal. The autonomic nervous system is probably responsible for most of the hemodynamic changes.

Effect of beta blockade on silent regional left ventricular wall motion abnormalities

The effect of beta-adrenergic blockade on regional left ventricular wall motion abnormalities was studied in 11 patients with coronary artery disease and silent myocardial ischemia during exercise testing. Four patients were asymptomatic; 7 were asymptomatic after a myocardial infarction. Left ventricular wall motion abnormalities were characterized by reduced regional ejection fraction (EF) during exercise determined by gated left anterior oblique images of the cardiac blood pool. In the 11 patients, 10 anteroseptal and 8 inferoposterior regions were subserved by stenotic coronary arteries. Before beta blockade, regional EF decreased in 15 of 18 regions. After beta blockade, this occurred in only 6 of 18 regions (p less than 0.05); the other 12 regions showed no change or an actual increase in regional EF. Thus, beta-adrenergic blockade effectively improved the reduction in exercise regional EF usually seen in patients with coronary artery disease with silent myocardial ischemia. One probable mechanism of action is a reduction in myocardial oxygen requirement at peak exercise.

Effects of intravenous infusion of esmolol and propranolol on biventricular performance at rest and during exercise as assessed by quantitative radionuclide angiography

This double-blind, randomized, crossover study examined the effects of intravenous infusion of esmolol (a new ultra-short-acting beta-receptor blocking agent) and propranolol on cardiovascular performance at rest and during peak upright exercise in 15 patients. Biventricular function was assessed by means of first-pass radionuclide ventriculography with a computerized multicrystal camera. At rest, significant treatment differences between esmolol and propranolol vs baseline were found for the heart rate, systolic blood pressure, double product, left ventricular ejection fraction (EF), systolic blood pressure to end-systolic volume ratio, cardiac index and right ventricular EF. During exercise, significant treatment differences were also found for the heart rate, systolic blood pressure, double product, right ventricular EF and cardiac index. The mean baseline measurements were higher than the mean treatment measurements, but no significant differences were found between mean esmolol and mean propranolol measurements at rest and during exercise except for the exercise systolic blood pressure, which was lower during esmolol infusion. The magnitude of drug effect was greater at the time of exercise than at rest. The blood level of esmolol decreased markedly by 30 minutes after infusion. Esmolol was well tolerated, with no important local, systemic or laboratory abnormalities. Thus, the effects of esmolol on cardiovascular performance at rest and exercise are similar to those of propranolol.

Exercise training during chronic beta blockade in cardiovascular disease

To determine whether cardioselective and nonselective beta-blocking agents impair exercise training effects in patients with cardiovascular disease, 50 subjects were evaluated. All were in a 3-times-weekly medically supervised outpatient exercise program for 3 months or longer. Treadmill exercise tests were done initially and at 3-month intervals. Eight patients were receiving atenolol, 23 propranolol, 3 timolol, 6 metoprolol, and 8 nadolol and 1 patient receiving timolol changed to atenolol and 1 receiving nadolol changed to propranolol. Treadmill test duration increased significantly (p less than 0.05), from 7.5 +/- 2.5 to 9.9 +/- 2.3 minutes, with exercise training. In 35 of the 50 subjects heart rate at rest decreased significantly (p less than 0.05) from 67.5 +/- 11.7 to 60.4 +/- 10.5 beats/min. The other 15 subjects were excluded from heart rate analysis because beta blockade was begun 1 to 2 weeks after the initial exercise test. It is concluded that exercise training effects (increase in exercise test duration and decrease in resting heart rate) can be achieved in patients with cardiovascular disease in the presence of both cardioselective and nonselective beta-blocking agents.