Haemodynamic and metabolic effects of timolol (Blocadren) on ischaemic myocardium

Metabolic Approaches for the Treatment of Dilated Cardiomyopathy

In dilated cardiomyopathy (DCM), where the heart muscle becomes stretched and thin, heart failure (HF) occurs, and the cardiomyocytes suffer from an energetic inefficiency caused by an abnormal cardiac metabolism. Although underappreciated as a potential therapeutic target, the optimal metabolic milieu of a failing heart is still largely unknown and subject to debate. Because glucose naturally has a lower P/O ratio (the ATP yield per oxygen atom), the previous studies using this strategy to increase glucose oxidation have produced some intriguing findings. In reality, the vast majority of small-scale pilot trials using trimetazidine, ranolazine, perhexiline, and etomoxir have demonstrated enhanced left ventricular (LV) function and, in some circumstances, myocardial energetics in chronic ischemic and non-ischemic HF with a reduced ejection fraction (EF). However, for unidentified reasons, none of these drugs has ever been tested in a clinical trial of sufficient size. Other pilot studies came to the conclusion that because the heart in severe dilated cardiomyopathy appears to be metabolically flexible and not limited by oxygen, the current rationale for increasing glucose oxidation as a therapeutic target is contradicted and increasing fatty acid oxidation is supported. As a result, treating metabolic dysfunction in HF may benefit from raising ketone body levels. Interestingly, treatment with sodium-glucose cotransporter-2 inhibitors (SGLT2i) improves cardiac function and outcomes in HF patients with or without type 2 diabetes mellitus (T2DM) through a variety of pleiotropic effects, such as elevated ketone body levels. The improvement in overall cardiac function seen in patients receiving SGLT2i could be explained by this increase, which appears to be a reflection of an adaptive process that optimizes cardiac energy metabolism. This review aims to identify the best metabolic therapeutic approach for DCM patients, to examine the drugs that directly affect cardiac metabolism, and to outline all the potential ancillary metabolic effects of the guideline-directed medical therapy. In addition, a special focus is placed on SGLT2i, which were first studied and prescribed to diabetic patients before being successfully incorporated into the pharmacological arsenal for HF patients.

Harnessing multimodal data integration to advance precision oncology

Advances in quantitative biomarker development have accelerated new forms of data-driven insights for patients with cancer. However, most approaches are limited to a single mode of data, leaving integrated approaches across modalities relatively underdeveloped. Multimodal integration of advanced molecular diagnostics, radiological and histological imaging, and codified clinical data presents opportunities to advance precision oncology beyond genomics and standard molecular techniques. However, most medical datasets are still too sparse to be useful for the training of modern machine learning techniques, and significant challenges remain before this is remedied. Combined efforts of data engineering, computational methods for analysis of heterogeneous data and instantiation of synergistic data models in biomedical research are required for success. In this Perspective, we offer our opinions on synthesizing complementary modalities of data with emerging multimodal artificial intelligence methods. Advancing along this direction will result in a reimagined class of multimodal biomarkers to propel the field of precision oncology in the coming decade.

AI in health and medicine

Artificial intelligence (AI) is poised to broadly reshape medicine, potentially improving the experiences of both clinicians and patients. We discuss key findings from a 2-year weekly effort to track and share key developments in medical AI. We cover prospective studies and advances in medical image analysis, which have reduced the gap between research and deployment. We also address several promising avenues for novel medical AI research, including non-image data sources, unconventional problem formulations and human-AI collaboration. Finally, we consider serious technical and ethical challenges in issues spanning from data scarcity to racial bias. As these challenges are addressed, AI's potential may be realized, making healthcare more accurate, efficient and accessible for patients worldwide.

Reduction of resting heart rate with antianginal drugs: review and meta-analysis

The benefit of heart rate (HR) reduction in patients with stable coronary artery disease is well demonstrated for symptom prevention and relief, and benefits on outcomes are being actively investigated. We aimed to quantify the reduction in resting HR induced by 5 antianginal drugs frequently used for symptom prevention (diltiazem, verapamil, atenolol, metoprolol, and ivabradine) in stable angina pectoris. We identified studies published between 1966 and 2007 in PubMed, Embase, and the Cochrane database and reviewed the bibliographies to locate additional studies. Eligible studies were double-blind, randomized, placebo-controlled trials in patients with stable angina. Trials were combined using weighted mean difference and fixed-effect model meta-analysis. The main outcome measure was resting HR at the study end. For diltiazem, resting HR reduction versus placebo ranged from -0.08 beats per minute (bpm) [95% confidence interval (CI) -1.5 to +1.4] for 120 mg/d to -8.0 bpm (95% CI, -11.1 to -5.0) with 360 mg/d. For sustained-release diltiazem, there was a reduction in resting HR of -4.5 bpm (95% CI, -6.4 to -2.5), with no dose-response relationship (heterogeneity P = 0.62). Resting HR reductions for the other agents were -3.2 bpm (95% CI, -5.1 to -1.3) for verapamil (with no dose-response relationship, heterogeneity P = 0.87); -19.0 bpm (95% CI, -20.4 to -17.6) for atenolol; -13.2 bpm (95% CI, -14.7 to -11.7) for metoprolol (with greater reductions for 150 mg/d and long-acting 190 mg/d); and between -9.3 bpm (95% CI, -13.8 to -4.8) and -19.6 bpm (95% CI, -23.8 to -15.4) for ivabradine. Ivabradine, atenolol, and metoprolol give similar reductions in resting HR (-10 to -20 bpm), whereas verapamil and diltiazem produce only marginal reductions (<10 bpm).

Heart rate: a forgotten link in coronary artery disease?

A considerable body of evidence indicates that elevated resting heart rate is an independent, modifiable risk factor for cardiovascular events and mortality in patients with coronary artery disease. Elevated heart rate can produce adverse effects in several ways. Firstly, myocardial oxygen consumption is increased at high heart rates, but the time available for myocardial perfusion is reduced, increasing the likelihood of myocardial ischemia. Secondly, exposure of the large elastic arteries to cyclical stretch is increased at high heart rates. This effect can increase the rate at which components of the arterial wall deteriorate. Elastin fibers, which have an extremely slow rate of turnover in adult life, might be particularly vulnerable. Thirdly, elevated heart rate can predispose the myocardium to arrhythmias, and favor the development and progression of coronary atherosclerosis, by adversely affecting the balance between systolic and diastolic flow. Comparisons of the effects of the specific heart-rate-lowering drug ivabradine with those of β-blockers could help clarify the pathophysiological effects of elevated heart rate. Effective heart rate control among patients with coronary artery disease is uncommon in clinical practice, representing a missed therapeutic opportunity.

Elevated heart rate in cardiovascular diseases: a target for treatment?

Heart rate is a major determinant of myocardial oxygen consumption and of cardiac work, and thus reduction of heart rate may represent an important strategy for the treatment of patients with a wide range of cardiac disorders. In addition, several experimental lines of research point to high heart rate as an important risk factor for atherosclerosis and, thus, pharmacologic heart rate reduction could prevent or retard the development of atherosclerotic plaques and increase survival. Today, in patients with acute or chronic coronary syndromes or with congestive heart failure, reducing heart rate is a generally accepted treatment modality. Up to now, no human study has been performed to demonstrate the efficacy and the risk-benefit ratio of cardiac slowing in patients without cardiac disorders. However, recent retrospective analyses of the INternational VErapamil-SR/trandolapril STudy and the Paris Prospective Study 1 provided promising results. Treatment of high heart rate in healthy subjects appears to be premature, but in clinical conditions such as hypertension or diabetes, the reduction of elevated heart rate appears a desirable additional goal of therapy.

Resting heart rate in cardiovascular disease

The importance of resting heart rate (HR) as a prognostic factor and potential therapeutic target is not yet generally accepted. Recent large epidemiologic studies have confirmed earlier studies that showed resting HR to be an independent predictor of cardiovascular and all-cause mortality in men and women with and without diagnosed cardiovascular disease. Clinical trial data suggest that HR reduction itself is an important mechanism of benefit of beta-blockers and other heart-rate lowering drugs used after acute myocardial infarction, in chronic heart failure, and in stable angina pectoris. Pathophysiological studies indicate that a relatively high HR has direct detrimental effects on the progression of coronary atherosclerosis, on the occurrence of myocardial ischemia and ventricular arrhythmias, and on left ventricular function. Studies have found a continuous increase in risk with HR above 60 beats/min. Although it may be difficult to define an optimal HR for a given individual, it seems desirable to maintain resting HR substantially below the traditionally defined tachycardia threshold of 90 or 100 beats/min. These findings suggest that the potential role of HR and its modulation should be considered in future cardiovascular guidance documents.

Heart Rate Lowering by Specific and Selective If Current Inhibition with Ivabradine

Resting heart rate is associated with cardiovascular and all-cause mortality, and the mortality benefit of some cardiovascular drugs seems to be related in part to their heart rate-lowering effects. Since it is difficult to separate the benefit of heart rate lowering from other actions with currently available drugs, a 'pure' heart rate-lowering drug would be of great interest in establishing the benefit of heart rate reduction per se. Heart rate is determined by spontaneous electrical pacemaker activity in the sinoatrial node. Cardiac pacemaker cells generate the spontaneous slow diastolic depolarisation that drives the membrane voltage away from a hyperpolarised level towards the threshold level for initiating a subsequent action potential, generating rhythmic action potentials that propagate through the heart and trigger myocardial contraction. The I(f) current is an ionic current that determines the slope of the diastolic depolarisation, which in turn controls the heart beating rate. Ivabradine is the first specific heart rate-lowering agent to have completed clinical development for stable angina pectoris. Ivabradine specifically blocks cardiac pacemaker cell f-channels by entering and binding to a site in the channel pore from the intracellular side. Ivabradine is selective for the I(f) current and exerts significant inhibition of this current and heart rate reduction at concentrations that do not affect other cardiac ionic currents. This activity translates into specific heart rate reduction, which reduces myocardial oxygen demand and simultaneously improves oxygen supply, by prolonging diastole and thus allowing increased coronary flow and myocardial perfusion. Ivabradine lowers heart rate without any negative inotropic or lusitropic effect, thus preserving ventricular contractility. Ivabradine was shown to reduce resting heart rate without modifying any major electrophysiological parameters not related to heart rate. In patients with left ventricular dysfunction, ivabradine reduced resting heart rate without altering myocardial contractility. Thus, pure heart rate lowering can be achieved in the clinic as a result of specific and selective I(f) current inhibition. Two randomised clinical studies have shown that ivabradine is an effective anti-ischaemic agent that reduces heart rate and improves exercise capacity in patients with stable angina. Ivabradine was shown to be superior to placebo in improving exercise tolerance test (ETT) criteria (n = 360) and, in a 4-month, double-blind, controlled study (n = 939), ivabradine 5 and 7.5mg twice daily were shown to be at least as effective as atenolol 50 and 100mg once daily, respectively, in improving total exercise duration and other ETT criteria, and reducing the number of angina attacks. Experimental data indicate a potential role of pure heart rate lowering in other cardiovascular conditions, such as heart failure.

Effects of epanolol, a selective beta1-blocker with intrinsic sympathomimetic activity, in patients with ischemic left ventricular dysfunction

Recently, different beta-blockers have been shown to be effective in the treatment of chronic heart failure (CHF), but the importance of their ancillary properties is not clear. Epanolol is a selective beta1-blocker with intrinsic sympathomimetic activity, which has been shown useful in angina pectoris, but its value in patients with left ventricular (LV) dysfunction and CHF is unknown. We examined the effects of epanolol in patients with LV dysfunction (n = 8; mean LV ejection fraction, 0.33 +/- 0.08) and compared them with patients with normal LV function (n = 8; mean LV ejection fraction, 0.52 +/- 0.04). Measurement of invasive hemodynamics and neurohormones was performed at rest and during myocardial ischemia, which was induced by atrial pacing. All measurements were performed before and after epanolol. Before epanolol, pacing-induced ischemia led to a similar increase in norepinephrine and coronary sinus blood flow in both groups. After epanolol, the increase in neurohormones was more pronounced in the group with LV dysfunction (norepinephrine, 1,130 +/- 164 pg/ml for patients with LV dysfunction vs. 637 +/- 41 pg/ml for normal subjects; p < 0.05). A similar effect was observed for angiotensin II. Further, in the LV-dysfunction group, coronary sinus blood flow increased less, and coronary vascular resistance decreased less (both values, p < 0.05). Despite the fact that the increase in double product was decreased to a similar extent in both groups, ischemia was reduced only in normal LV function (p < 0.05). In ischemic LV dysfunction, neurohumoral activation after epanolol may impair adequate coronary flow response, and this may limit its antiischemic properties. Because of the small size of the study, no definitive inference on the clinical benefit of epanolol in patients with ischemic LV function can be made from this study.

Influence of beta 1-blockade on myocardial substrates early after a coronary operation

A high adrenergic strain during reperfusion after ischemia impedes functional recovery. Conversely, adrenergic blockade may be beneficial during reperfusion. This study was undertaken to find out if early postoperative high-dose infusion of the selective beta 1-blocking agent metoprolol tartrate has additional effects on metabolic variables related to myocardial energy supply/demand balance compared with those obtained with a late preoperative oral dose. The study included 21 male patients undergoing coronary bypass grafting. All patients received an oral dose of metoprolol before the operation. After the operation, patients were randomized to a control group or a group receiving intravenous infusion of metoprolol. Myocardial uptake of oxygen and substrates was determined before and during atrial pacing. Metoprolol reduced arterial concentrations of free fatty acids, reduced myocardial uptake of free fatty acids, and enhanced myocardial uptake of lactate. During paced tachycardia, the metoprolol concentration correlated negatively with myocardial uptake of free fatty acids (r = -0.80; p < 0.001) and positively with myocardial uptake of lactate (r = 0.53; p < 0.05). It is concluded that postoperative infusion of metoprolol induces myocardial metabolic changes compatible with an improved energy supply/demand balance.

Exercise hemodynamics and myocardial metabolism during long-term beta-adrenergic blockade in severe heart failure

Hemodynamics and myocardial metabolism at rest and during exercise were investigated in 21 patients with heart failure. The patients were evaluated before and after long-term treatment (14 +/- 7 months) with the beta-adrenergic blocking agent metoprolol. Clinical improvement with increased functional capacity occurred during treatment. Maximal work load increased by 25% (104 to 130 W; p less than 0.001). Hemodynamic data showed an increased cardiac index (3.8 to 4.6 liters/min per m2; p less than 0.02) during exercise. Pulmonary capillary wedge pressure decreased at rest (20 to 13 mm Hg; p less than 0.01) and during exercise (32 to 28 mm Hg; p = NS). Stroke volume index (30 to 39 g.m/m2; p less than 0.006) and stroke work index (28 to 46 g.m/m2; p less than 0.006) increased during exercise and long-term metoprolol treatment. The arterial norepinephrine concentration decreased at rest (3.72 to 2.19 nmol/liter; p less than 0.02) but not during exercise (13.2 to 11.1 nmol/liter; p = NS). The arterial-coronary sinus norepinephrine difference suggested a decrease in myocardial spillover during metoprolol treatment (-0.28 to -0.13 nmol/liter; p = NS at rest and -1.13 to -0.27 nmol/liter; p less than 0.05 during exercise). Coronary sinus blood flow was unchanged during treatment. Four patients produced myocardial lactate before the study, but none produced lactate after beta-blockade (p less than 0.05). There was no obvious improvement in a subgroup of patients with ischemic cardiomyopathy. In summary, there were signs of increased myocardial work load without higher metabolic costs after treatment with metoprolol.

Effect of timolol on mortality and reinfarction after acute myocardial infarction: prognostic importance of heart rate at rest

Long-term timolol treatment after acute myocardial infarction is associated with a significant reduction in mortality and nonfatal reinfarction. To evaluate whether the reduction in mortality and morbidity is exclusively or partly dependent on a reduction in heart rate (HR), cardiac events in the Norwegian Timolol Multicenter Study were analyzed according to resting HR at baseline and at 1 month of follow-up Resting HR at baseline was a significant predictor of total death and all events (total death plus nonfatal reinfarction) both in placebo- and in timolol-treated patients. In the placebo group the median resting HR was unchanged from baseline to 1 month control (72 beats/min), but was reduced from 72 beats/min to 56 beats/min in the timolol group. Resting HR during follow-up remained a significant predictor of total death. Further, mortality at a given HR during treatment was not markedly different whether the HR was spontaneous or caused by timolol. Timolol treatment was related to a significant reduction in mortality, and this study suggests that the major effect of timolol treatment on mortality after acute myocardial infarction may be attributed to the reduction in HR. Timolol treatment was also associated with an overall reduction in nonfatal reinfarction. However, nonfatal reinfarction was inversely related to resting HR during follow-up, indicating that although coronary artery occlusion in low-risk patients may cause nonfatal reinfarction, the outcome in high-risk patients is more likely to be death. When analyzing mortality and nonfatal reinfarction combined, timolol treatment was related to a reduction in cardiac events at any given HR, suggesting that factors in addition to HR reduction are important in the protective effects of timolol.

Importance of heart rate in determining beta-blocker efficacy in acute and long-term acute myocardial infarction intervention trials

Heart rate after an acute myocardial infarction (AMI) is an index of late mortality. The hypothesis--that the potential beneficial effect of beta-blocking drugs after an AMI is quantitatively dependent on the reduction of heart rate obtained by such treatment--was examined by reviewing available data from acute and long-term intervention trials. Only properly randomized and double-blind trials were considered. In acute intervention trials only patients who received treatment within 12 hours after onset of pain were included. In early intervention trials there was a close relation between the reduction in heart rate and infarct size as determined by accumulated creatine kinase release (r = 0.97, p less than 0.001). A reduction in heart rate of at least 15 beats/min during infarct evolution was associated with a reduction of infarct size between 25 and 30%. The data suggest that a reduction in heart rate less than 8 beats/min has no effect or may actually increase infarct size. Comparison of post-AMI trials indicated a relation between the actual reduction of resting heart rate and percentage of reduction in mortality obtained in each trial (r = 0.60, p less than 0.05). An almost similar relation was demonstrated between the reduction in resting heart rate and nonfatal reinfarctions (r = 0.59, p less than 0.05). Confounding properties of a beta blocker, such as intrinsic sympathomimetic activity or prolongation of the QT interval, may reduce its efficacy. These results strongly suggest that the beneficial effect of beta blockers is related to a quantitative reduction in heart rate, probably indicating an antiischemic effect. However, the data do not exclude the possibility that other protective mechanisms may be operative.

Improved myocardial lactate extraction after propranolol in coronary artery disease: effected by peripheral glutamate and free fatty acid metabolism

Ten patients with chronic effort angina and coronary artery disease (luminal diameter reduction greater than 75%) were stressed by atrial pacing (140 beats/minutes) before and 15 minutes after intravenous propranolol (mean dose 7.4 mg). Myocardial substrate exchange of oxygen, blood lactate, plasma free fatty acids, citrate, glucose, glutamate, and alanine as well as coronary sinus blood flow were measured. Coronary sinus blood flow, oxygen consumption, and systemic haemodynamics did not change after propranolol. Propranolol did not influence arterial lactate concentration, and it reduced the arterial concentration of free fatty acid by 37% and increased that of glutamate by 21%. During pacing myocardial lactate extraction increased in all 10 patients; in two lactate release was converted to lactate uptake. Propranolol reduced free fatty acid uptake and increased glutamate uptake during pacing. For both substances the changes in aortocoronary sinus differences or in uptake or both correlated positively with the changes in their delivery to the heart from extracardial sources (arterial concentrations/loads). In the unstressed state before pacing, aortocoronary sinus lactate differences correlated inversely with free fatty acid differences and positively with those of glutamate. During pacing the relation between lactate and glutamate differences remained positive while the inverse correlation between lactate and free fatty acid differences was lost. Myocardial citrate release was halved during pacing and recovery. Propranolol did not influence alanine or glucose exchanges. An improved myocardial lactate extraction after propranolol administration may be secondary to decreased free fatty acid uptake or increased glutamate uptake or both. In the unstressed state both mechanisms may be of importance. During pacing induced ischaemia, increased glutamate uptake is more likely than reduced free fatty acid uptake to be the mechanism responsible for the improvement in myocardial lactate extraction. The propranolol mediated alterations in myocardial substrate exchanges may reflect the extracardial effects of the drug.