Is reduced cardiac performance the only mechanism for myocardial infarct size reduction during beta adrenergic blockade?

Feasibility and First Results of Heart Failure Monitoring Using the Wearable Cardioverter-Defibrillator in Newly Diagnosed Heart Failure with Reduced Ejection Fraction

The wearable cardioverter–defibrillator (WCD) is used in patients with newly diagnosed heart failure and reduced ejection fraction (HFrEF). In addition to arrhythmic events, the WCD provides near-continuous telemetric heart failure monitoring. The purpose of this study was to evaluate the clinical relevance of additionally recorded parameters, such as heart rate or step count. We included patients with newly diagnosed HFrEF prescribed with a WCD. Via the WCD, step count and heart rate were acquired, and an approximate for heart rate variability (HRV5) was calculated. Multivariate analysis was performed to analyze predictors for an improvement in left ventricular ejection fraction (LVEF). Two hundred and seventy-six patients (31.9% female) were included. Mean LVEF was 25.3 ± 8.5%. Between the first and last seven days of usage, median heart rate fell significantly (p < 0.001), while median step count and HRV5 significantly increased (p < 0.001). In a multivariate analysis, a delta of HRV5 > 23 ms was an independent predictor for LVEF improvement of ≥10% between prescription and 3-month follow-up. Patients with newly diagnosed HFrEF showed significant changes in heart rate, step count, and HRV5 between the beginning and end of WCD prescription time. HRV5 was an independent predictor for LVEF improvement and could serve as an early indicator of treatment response.

Bradycardia Induces Angiogenesis, Increases Coronary Reserve, and Preserves Function of the Postinfarcted Heart

Background— We tested the hypothesis that induction of chronic bradycardia would trigger an upregulation of key growth factors and receptors, which would then lead to angiogenesis and improve coronary reserve in the left ventricle after myocardial infarction.

Methods and Results— Bradycardia was induced in rats by administering alinidine via osmotic pumps beginning 1 day after coronary artery ligation. Echocardiographic analysis was conducted before and after treatment. Morphometric analysis was used in perfusion-fixed hearts to document arteriolar and capillary growth. Western blots were used to evaluate growth factor and receptor changes. During the first week of treatment, vascular endothelial growth factor (VEGF), VEGF receptor 1 (Flt-1), and basic fibroblast growth factor proteins were higher in the treated group, whereas VEGF receptor 2 (Flk-1), angiopoietin-1, and angiopoietin-2 were not affected by treatment. After 3 weeks, VEGF protein remained elevated, and bradycardia was associated with a higher capillary length density in the border (40%) and remote (14%) regions and a higher arteriolar length density in the septum (62%), despite a greater increase in left ventricular mass. Although arteriolar length density increased in all size classes, the greatest increase occurred in the smallest (terminal) arterioles. This vascular growth was associated with a 23% greater coronary reserve. Echocardiography revealed a smaller increase in ventricular volume and a greater preservation of ejection fraction in rats treated with bradycardia.

Conclusions— Pharmacologic induction of bradycardia enhances vascularity and coronary reserve, preserves function of surviving myocardium, and therefore, is a noninvasive, therapeutic avenue that provides an alternative to gene therapy.

Modulation of beta-adrenergic receptor subtype activities in perioperative medicine: mechanisms and sites of action

This review focuses on the mechanisms and sites of action underlying beta-adrenergic antagonism in perioperative medicine. A large body of knowledge has recently emerged from basic and clinical research concerning the mechanisms of the life-saving effects of beta-adrenergic antagonists (beta-AAs) in high-risk cardiac patients. This article re-emphasizes the mechanisms underlying beta-adrenergic antagonism and also illuminates novel rationales behind the use of perioperative beta-AAs from a biological point of view. Particularly, it delineates new concepts of beta-adrenergic signal transduction emerging from transgenic animal models. The role of the different characteristics of various beta-AAs is discussed, and evidence will be presented for the selection of one specific agent over another on the basis of individual drug profiles in defined clinical situations. The salutary effects of beta-AAs on the cardiovascular system will be described at the cellular and molecular levels. Beta-AAs exhibit many effects beyond a reduction in heart rate, which are less known by perioperative physicians but equally desirable in the perioperative care of high-risk cardiac patients. These include effects on core components of an anaesthetic regimen, such as analgesia, hypnosis, and memory function. Despite overwhelming evidence of benefit, beta-AAs are currently under-utilized in the perioperative period because of concerns of potential adverse effects and toxicity. The effects of acute administration of beta-AAs on cardiac function in the compromised patient and strategies to counteract potential adverse effects will be discussed in detail. This may help to overcome barriers to the initiation of perioperative treatment with beta-AAs in a larger number of high-risk cardiac patients undergoing surgery.

Effects of beta-adrenoceptor agonists and antagonists on heart-rate variability in normal subjects assessed using summary statistics and nonlinear procedures

The influence of celiprolol (beta1- and beta2-adrenoceptor partial agonist), propranolol (beta1- and beta2-adrenoceptor antagonist), and atenolol (beta1-adrenoceptor antagonist) on heart-rate variability (HRV) was assessed from Holter records in 12 normal volunteers. A combination of summary statistics and nonlinear procedures was used to assess HRV and autonomic balance. Under double-blind and randomised conditions (Latin-square design), subjects received placebo, celiprolol (200 and 800 mg), propranolol (160 mg), atenolol (50 mg), and combinations of these agents. Single oral doses of medication (at weekly intervals) were administered at 22:30 h with sleeping heart rates (HRs) recorded overnight. Compared with placebo, celiprolol (200 and 800 mg) increased the sleeping HR, the HR effect of celiprolol was different from the bradycardia after propranolol, 160 mg, and atenolol, 50 mg. Dose-response effects on HR with celiprolol were evident in the presence of atenolol, unlike those with propranolol that abolished the HR increase between celiprolol, 200 mg and 800 mg. These data were consistent with beta1-selective adrenoceptor agonism with 200 mg but agonism at both the beta1- and beta2-adrenoceptor with celiprolol, 800 mg. The action of the drugs on short-term HRV indices (rMSSD and pNN50) closely followed their effects on HR. The longer-term HRV indices (global SD, SDANN) were reduced by celiprolol but increased by propranolol and atenolol. At a fixed HR, the data dispersion (SDNN5) was higher with propranolol compared with celiprolol; however, the dispersion was not merely an HR-dependent phenomenon. A novel nonlinear approach (quadrant analysis) revealed the sequencing of cardiac accelerations and decelerations after the high correlation between adjacent intervals had been removed. Celiprolol increased the frequency of consecutive cardiac accelerations; the duration between and variance of these beat-to-beat differences shortened after celiprolol but lengthened with increased variance after propranolol and atenolol. These results demonstrated reduced HRV indices and a shift toward sympathetic dominance after the beta-adrenoceptor agonist celiprolol contrasting with increased HRV indices and parasympathetic dominance after the beta-adrenoceptor antagonists propranolol and atenolol. The implications of these findings for the treatment of patients with cardiovascular disease warrant further study.

Infarct size in rabbits: a modified method illustrated by the effects of propranolol and trimetazidine

Following a 45-min period of coronary occlusion the myocardial infarct that developed after 24 h of blood reperfusion in the rabbit heart was studied in three groups of animals: controls (n = 7), and those pretreated with 3 mg.kg-1 of the piperazine derivative, trimetazidine (n = 7) or propranolol at 0.3 mg.kg-1 (n = 6). Twenty-four hours after coronary artery ligation for 45 min infarct size was measured in myocardial slices using trinitrophenyl-tetrazolium staining, and the "area at risk" was determined by injection of zinc/cadmium particles and delineated by imaging under fluorescent light the areas of tissue that did not fluoresce. The range of "area at risk" was similar in all of the groups. There was a significant reduction in the size of infarct that developed in the trimetazidine treated group when compared with the controls. In the propranolol treated group there was a slight reduction in infarct size when compared to control, but this was less than in the trimetazidine treated group and did not reach statistical significance. It is concluded that pretreatment with trimetazidine in the blood perfused rabbit heart is effective in reducing myocardial infarct size.

Beta-adrenergic blockade improves uniformity of local contraction in the anterior wall of feline left ventricles

Uniformity of myocardial contraction has been put forward as an important regulatory mechanism of myocardial contraction, and we have previously demonstrated reduced uniformity of local myocardial contraction in the midwall of left ventricles during preload reduction combined with increased inotropy. The aim of the present study was to explore the isolated inotropic influence on uniformity of contraction, keeping loading conditions constant. Segment performance was measured by implanted piezo-electric crystals in ten open-chest, anaesthetized cats. One crystal pair, circumferential segment, aligned with midwall and epicardial fibres, whereas another perpendicular segment, longitudinal, ran close to endocardial fibre direction. Maximal systolic shortening of longitudinal segments remained unchanged following inotropic interventions, isoprenaline and timolol, whereas circumferential segments revealed reduced performance with timolol (8.4 +/- 1.0% compared with 14.0 +/- 1.3% during control; P < 0.001). In the control state the longitudinal-to-circumferential ratio (LONG/CIRC) a quantitative measure of uniformity, was 0.32 +/- 0.08. No change in uniformity occurred during isoprenaline infusion (0.32 +/- 0.11) but during beta-adrenergic blockade with timolol a clearly higher LONG/CIRC ratio was observed (0.56 +/- 0.06, P < 0.005). Myocardial tissue blood flow measurement by radioactive microspheres showed a shift in transmural distribution with interventions so that subepicardial blood flow was markedly reduced during beta-adrenergic blockade. The direction of subepicardial fibres approximates our circumferential segments. Thus, there may well exist a relationship between segmental shortening and perfusion. In conclusion, circumferential segments were most influenced by changes in inotropy in contrast to previous observations where pronounced changes in longitudinal segments with loading occur. Furthermore, this study demonstrates that reduced inotropy with timolol helped uniform local contraction as estimated by the increased LONG/CIRC ratio, a transition that could improve contraction efficacy.

Myocardial adenine nucleotide depletion within 1 h of acute coronary artery occlusion

In anaesthetized open-chest casts with occlusion of the left anterior descending coronary artery (LAD), adenine nucleotides and degradation products were studied in small myocardial tissue samples (10-20 mg) with high-pressure liquid chromatography, and tissue blood flow was measured with radioactive microspheres 5, 10, 20, 40, and 60 min after LAD occlusion. There was a rapid and parallel decrease of myocardial ATP and accumulation of adenosine, inosine, hypoxanthine, and xanthine both in epicardial and endocardial half-layers of the ischaemic myocardium within the first 20 min of coronary occlusion. After 40 and 60 min, myocardial ATP content decreased and degradation products accumulated further in the endocardium but stabilized epicardially. Analysis of covariance showed that the slightly higher blood flow in ischaemic epicardial layers, did not explain the transmural difference in ATP content after 40 and 60 min. Adenosine decreased after 40 min of ischaemia in both wall layers reaching negligible amounts after 60 min. It is concluded that breakdown of energy stores is less severe in epicardial than in endocardial wall layers during the first hour after acute coronary occlusion in the cat heart. This transmural difference cannot be explained entirely by less severe epicardial ischaemia. Therefore, transmural heterogeneity in metabolic function during severe ischaemia may also be important.

Management of acute myocardial infarction in the very elderly

Coronary artery disease is highly prevalent among the elderly, and the incidence of myocardial infarction (MI) is high. Still, the notion of optimal treatment for the elderly patient with MI remains unclear. This review will first discuss some of the characteristics of the aging myocardium that impact on the care of elderly cardiac patients. Next, the therapeutic options and their appropriateness for the aged patient are presented. Thrombolytic and beta-blocker therapies are reviewed extensively since they remain among the controversial issues in geriatric cardiology. Other well-known as well as experimental therapies are also discussed.

Influence of heart rate on mortality after acute myocardial infarction

Elevated heart rate (HR) during hospitalization and after discharge has been predictive of death in patients with acute myocardial infarction (AMI), but whether this association is primarily due to associated cardiac failure is unknown. The major purpose of this study was to characterize in 1,807 patients with AMI admitted into a multicenter study the relation of HR to in-hospital, after discharge and total mortality from day 2 to 1 year in patients with and without heart failure. HR was examined on admission at maximum level in the coronary care unit, and at hospital discharge. Both in-hospital and postdischarge mortality increased with increasing admission HR, and total mortality (day 2 to 1 year) was 15% for patients with an admission HR between 50 and 60 beats/min, 41% for HR greater than 90 beats/min and 48% for HR greater than or equal to 110 beats/min. Mortality from hospital discharge to 1 year was similarly related to maximal HR in the coronary care unit and to HR at discharge. In patients with severe heart failure (grade 3 or 4 pulmonary congestion on chest x-ray, or shock), cumulative mortality was high regardless of the level of admission HR (range 61 to 68%). However, in patients with pulmonary venous congestion of grade 2, cumulative mortality for patients with admission HR greater than or equal to 90 beats/min was over twice as high as that in patients with admission HR less than 90 beats/min (39 vs 18%, respectively); the same trend was evident in patients with absent to mild heart failure (mortality 18 vs 10%, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacology of acute effort angina

From the pharmacologic point of view, each of the major types of antianginal agents--calcium antagonists, beta-blockers, and nitrates--seem to act at least in part by an improvement of the myocardial blood supply. The recently elucidated mechanism of action of nitrates, acting on a common pathway with the endothelium-derived relaxation factor (EDRF), suggests an important role for guanylate cyclase and cyclic GMP in maintaining coronary artery patency in patients with coronary atheroma. The efficacy of calcium antagonists, even in effort-induced angina, is in accord with a current hypothesis that physical exercise in the presence of coronary stenosis can cause relative coronary vasoconstriction, or at the least, failure of full dilation. Therefore, calcium antagonists all act, at least in part, on the "supply" side of the supply-demand equation. Beta-adrenergic blockers appear to have as their major mode of action a reduction of heart rate, which not only reduces the oxygen demand but, through an anti-ischemic effect, also appears to improve the endocardial blood supply (in relation to the heart rate). Thus beta-blockade indirectly enhances the supply side of the equation. The intriguing situation arises whereby all three major types of antianginal compounds may also act by a common mechanism of anginal relief, namely, improvement in the coronary blood supply, in addition to the diverse mechanisms specific to each type of compound. That conclusion does not mean the the "demand" side of the equation can be ignored. Rather, the critical importance of a reduced myocardial blood supply in the production of anginal syndromes is highlighted.

Effects of alinidine on survival and infarct size in rats with coronary artery occlusion

Ligation of the left anterior descending coronary artery was performed in open-chest anaesthetized rats. One group had coronary occlusion for 3 h while ligation lasted for 30 min in a second group and was followed by a 150-min reperfusion period. The area at risk and area of infarction were determined immediately after premature death or 3 h after the ligature was set, by means of Evans blue and triphenyltetrazoliumchloride staining and subsequent photometric quantification. Saline or alinidine (5 mg/kg i.v.) was administered 15 min prior to ligation. The alinidine groups received a further 0.5 mg/kg i.v. 1 and 2 h after ligation. A large number of animals in the control groups died during the first 30 min. The animals that survived 3 h had a smaller area at risk than those dying prematurely and about 100% of the area at risk became infarcted. All animals in the two alinidine groups survived the first 30 min. All these animals survived with a larger area at risk than the control groups. The area of infarction in relation to the area at risk was significantly smaller than in the control groups. The cardioprotective effects of alinidine may be explained by a reduction in heart rate and a slight reduction in blood pressure.

Protective effects of long-term bradycardial pacing against catecholamine-induced myocardial damage in rabbit hearts

A high intravenous dose of norepinephrine (4 micrograms/kg/min for 60 minutes) to New Zealand Red rabbits produced patchy subendocardial damage (estimated stereologically in frozen sections) of about 5% of the heart volume 2 days after application. The damaged areas showed loss of staining for alkaline phosphatase, an enzyme present in normal capillary endothelium. Heart performance (cardiac output index, cardiac work [i.e., cardiac output X mean blood pressure], and dP/dtmax) were significantly lower than in control hearts. Capillary density distribution estimated in nondamaged areas of the left ventricular free wall was inhomogeneous favoring subepicardial regions, while homogeneous transmural distribution was found in control hearts. Bradycardial pacing (reduction of heart rate to 50% of normal) performed for 3-4 weeks prior to norepinephrine administration showed a protective effect against catecholamine damage manifested in a smaller extent of necrosis, in the maintenance of homogeneous transmural capillary distribution in nondamaged areas, and, most importantly, in the maintenance of normal cardiac pump performance at rest and during maximal work in response to acutely administered norepinephrine.