Differences in haemodynamic response to beta-blocking drugs between stable coronary artery disease and acute myocardial infarction

Exploring Sex Differences of Beta-Blockers in the Treatment of Hypertension: A Systematic Review and Meta-Analysis

AIMS

In the prevention of cardiovascular morbidity and mortality, early recognition and adequate treatment of hypertension are of leading importance. However, the efficacy of antihypertensives may be depending on sex disparities. Our objective was to evaluate and quantify the sex-diverse effects of beta-blockers (BB) on hypertension and cardiac function. We focussed on comparing hypertensive female versus male individuals.

METHODS AND RESULTS

A systematic search was performed for studies on BBs from inception to May 2020. A total of 66 studies were included that contained baseline and follow up measurements on blood pressure (BP), heart rate (HR), and cardiac function. Data also had to be stratified for sex. Mean differences were calculated using a random-effects model. In females as compared to males, BB treatment decreased systolic BP 11.1 mmHg (95% CI, -14.5; -7.8) vs. 11.1 mmHg (95% CI, -14.0; -8.2), diastolic BP 8.0 mmHg (95% CI, -10.6; -5.3) vs. 8.0 mmHg (95% CI, -10.1; -6.0), and HR 10.8 beats per minute (bpm) (95% CI, -17.4; -4.2) vs. 9.8 bpm (95% CI, -11.1; -8.4)), respectively, in both sexes' absolute and relative changes comparably. Left ventricular ejection fraction increased only in males (3.7% (95% CI, 0.6; 6.9)). Changes in left ventricular mass and cardiac output (CO) were only reported in males and changed -20.6 g (95% CI, -56.3; 15.1) and -0.1 L (95% CI, -0.5; 0.2), respectively.

CONCLUSIONS

BBs comparably lowered BP and HR in both sexes. The lack of change in CO in males suggests that the reduction in BP is primarily due to a decrease in vascular resistance. Furthermore, females were underrepresented compared to males. We recommend that future research should include more females and sex-stratified data when researching the treatment effects of antihypertensives.

Effects of xamoterol in acute myocardial infarction: blood pressure, heart rate, arrhythmias and early clinical course

Xamoterol is a novel partial agonist of beta 1 adrenoceptors that reduces myocardial ischaemia and improves ventricular function in patients with mild to moderate heart failure. In a double blind, randomised, placebo controlled study, the effects of xamoterol given in a dose of 200 mg twice daily were studied in 51 consecutive patients with acute myocardial infarction, including 17 receiving diuretics for left ventricular failure. Treatment was started on the third day of admission and continued for 7 days. Blood pressure was recorded at 0900 daily, and 24 hour ambulatory electrocardiogram monitoring was commenced at this time on days 1 (pre-treatment), 4, 6 and 9 of admission. Additional drug therapy was recorded daily throughout the study. One patient died prior to randomisation and three were withdrawn (1 placebo, 2 xamoterol) with ventricular arrhythmias and/or disturbances of conduction. Compared to placebo, xamoterol had no effect on the rate of ventricular premature beats or ventricular tachycardia. Xamoterol increased nocturnal heart rate (0000-0600 hrs 79 +/- 2; placebo 72 +/- beats/min; P less than 0.03) but did not change blood pressure. Three patients receiving xamoterol, and 7 on placebo, required new (after randomisation) antianginal therapy. One patient treated with placebo developed new heart failure. These results show that xamoterol can be administered safely to selected patients following myocardial infarction, including those treated for mild heart failure.

Measurement and cardiovascular relevance of partial agonist activity (PAA) involving beta 1- and beta 2-adrenoceptors

In the normal heart the ratio of beta 1/beta 2-receptors in both atria and ventricles is about 75:25; in the failing heart the ratio is about 60:40. Stimulation of either beta 1- or beta 2-receptors results in a positive chronotropic and inotropic response. In the periphery, with the exception of lipolysis, renin release, control of intraocular pressure and intestinal relaxation, beta 2-related activity predominates. The nature of the beta 2-receptor is being unravelled and it has now been cloned. The beta-receptor antagonist is 'anchored' via disulfide bonding. Subsequent events involve the regulatory protein guanine nucleotide which couples the receptor to adenylate cyclase. beta-receptor density may by up- or down-regulated. beta-stimulation down-regulates (uncouples and internalizes or sequestrates) and beta-antagonism up-regulates beta-receptor numbers, but the functional implications of such changes are not always clear. A partial agonist occupies a receptor site and competitively inhibits the full agonist (e.g. noradrenaline). A partial agonist differs from a full agonist in that maximal response of a tissue is less. When background sympathetic activity is absent or very low a partial agonist will act as an agonist, e.g. increase heart rate, but when background tone is high the partial agonist will behave functionally as an antagonist, e.g. decrease heart rate. In animals partial agonist activity (PAA) can be assessed in many ways. In the catecholamine-depleted (reserpine or syrosingopine), vagotomized or pithed, intact animal beta-activity can be assessed via changes in heart rate, cardiac contractility and atrioventricular conduction. Isolated organs can also be used such as atria, papillary muscle, tracheal, mesenteric artery and uterine preparations. The choice of animal is important as marked species differences in response can occur. In man assessing PAA is difficult due to the presence of an intact sympathetic system: the problem can be overcome by autonomic blockade of constrictor and vagal reflexes with prazosin, clonidine and atropine but leaving the beta-receptor mediated responses unimpaired. beta 1- and beta 2-selective PAA can also be gauged via an increased sleeping heart rate (basal sympathetic tone) in the presence and absence of a beta 1- and beta 2-selective antagonist. beta 1-selective PAA can also cause an increase in resting systolic blood pressure, beta 2-selective PAA may be further assessed by a fall in DBP, increased blood flow, fall in peripheral resistance or increased finger tremor.(ABSTRACT TRUNCATED AT 400 WORDS)