Nitric oxide synthase inhibitor (MTR-105) during open-heart surgery. A pilot double-blind placebo-controlled study of hemodynamic effects and safety

OBJECTIVES

Hypotension is common immediately following cardiopulmonary bypass. Experimentally, MTR-105 (S-ethylisothiuronium diethylphosphate), a fast-acting synthetic nitric oxide synthase inhibitor, rapidly increases blood pressure. The purpose of the current study was to assess the influence of MTR-105 on hemodynamics early after cardiopulmonary bypass in patients undergoing open-heart surgery.

METHODS

Thirty-six patients with an ejection fraction >50% undergoing open-heart surgery were randomly assigned to either 50 microg kg(-1) min(-1) MTR-105 (M50, n = 12), 10 microg kg(-1) min(-1) MTR-105 (M10, n = 12) or buffered phosphate solution (placebo control, n = 12). Half suffered from atrial fibrillation and 75% had severe tricuspid regurgitation. Patients received the drug for 6 h after cross-clamp removal. Hemodynamic variables were measured before drug administration until 24 h after operation. Adverse events were recorded from study drug initiation through 30 days after the operation.

RESULTS

Compared with control, both MTR-105 doses were associated with an immediate increase in systemic blood pressure (16%) and systemic vascular resistance and a decrease in cardiac index. Half-life time of MTR-105 was calculated to be 4.1 +/- 0.8 h (M10) and 4.45 +/- 0.92 h (M50). Three patients died during hospitalization, unrelated to the study medication.

CONCLUSIONS

At the doses employed, MTR-105 appears hemodynamically active in increasing both blood pressures.

The funny current: cellular basis for the control of heart rate

The 'funny' (pacemaker, I(f)) current, first described almost 30 years ago in sinoatrial node (SAN) myocytes, is a mixed sodium/potassium inward current, activated on hyperpolarisation in the diastolic range of voltages. 'Funny' (f) channels are activated by intracellular cyclic adenosine monophosphate (cAMP) concentrations according to a mechanism mediating regulation of heart rate by the autonomic nervous system, as well as by voltage hyperpolarisation. Structural subunits of native f-channels are the hyperpolarisation-activated cyclic nucleotide-gated (HCN) channels; of the four HCN isoforms known, HCN4 is the most highly expressed in SAN tissue. The I(f) current is a natural target in the search for drugs aimed specifically at affecting heart rate, given its function in pacemaking. Increased heart rate has a negative influence on clinical outcome in patients with cardiovascular disease, and indeed is also an established risk factor for cardiovascular and all-cause mortality in the general population. Clearly, therefore, independent reduction of heart rate, through inhibition of the I(f) current, appears to be a suitable therapeutic option for patients with ischaemic heart disease.beta-Adrenoceptor antagonists (beta-blockers) reduce intracellular cAMP levels, and a substantial part of their negative chronotropic effect is therefore attributable to a reduction of the I(f) current. However, neither beta-blockers nor Ca(2+) channel antagonists, both of which have traditionally been used to reduce myocardial ischaemia, are 'pure' heart rate-lowering drugs. These agents may, in fact, have adverse cardiovascular and noncardiovascular effects.Conversely, the novel heart rate-reducing agent ivabradine is a specific blocker of f-channels, hence a selective inhibitor of the pacemaker I(f) current in the SAN. Ivabradine slows heart rate by reducing the I(f) current-regulated steepness of the diastolic depolarisation in SAN myocytes, thereby increasing diastolic duration, without altering action potential duration or causing negative inotropy. As such, ivabradine is particularly useful in patients with chronic stable angina pectoris. Further clinical studies are ongoing to evaluate the efficacy of ivabradine in patients with coronary heart disease, left ventricular dysfunction and heart failure. This short article reviews the current state of knowledge of the properties of the 'funny' current in relation to exploitation of the I(f) function in pacemaking generation and modulation for the pharmacological control of heart rate.

Similarities and differences in design considerations for cell therapy and pharmacologic cardiovascular clinical trials

Cell therapies hold the potential for suppression, modification, or cure of disease. Several unique challenges have been recognized as this field has developed. Many of these involve considerations of trial design. This paper summarizes the discussion and suggestions constructed during the 8th Cardiovascular Clinical Trialists Workshop, a meeting involving cardiovascular clinical trialists, biostatisticians, National Institutes of Health scientists, European and United States regulators, and pharmaceutical industry scientists. Investigators must adapt research methods to accommodate the scientific advances associated with cell therapy. Safety and efficacy of cell therapy for cardiovascular indications should be evaluated with the same degree of scientific rigor required of pharmacologic agents, and the same fundamental regulatory requirements and scientific processes apply to both. Clinical trials for these indications should also meet standards similar to those set for drug therapies. Safety should be determined throughout development, dose responsiveness should be established and, while surrogate endpoints are important development tools, the ultimate demonstration of efficacy must rely on clinical benefit. The establishment of a global safety database for cell therapy would significantly advance the field. Efforts to discover innovative therapies must be balanced by a commitment to comprehensively evaluate the safety and efficacy of the new treatments.

Prognostic value of exercise tolerance testing in asymptomatic chronic nonischemic mitral regurgitation

In many heart diseases, exercise tolerance testing (ETT) has useful functional correlates and/or prognostic value. However, its predictive value in mitral regurgitation (MR) is undefined. To determine whether ETT descriptors predict death or indications for mitral valve surgery in patients with MR, we prospectively followed, for 7 +/- 3 end-point-free years, a cohort of 38 patients with chronic severe nonischemic MR who underwent modified Bruce ETT; all lacked surgical indications at study entry. Their baseline exercise descriptors were also compared with those from 46 patients with severe MR who, at entry, already had reached surgical indications. End points during follow-up in the cohort included sudden death (n = 1), heart failure symptoms (n = 2), atrial fibrillation (n = 4), left ventricular (LV) ejection fraction <60% (n = 2), LV systolic dimensions > or =45 mm (n = 12) and >40 mm (n = 11), LV ejection fraction <60% plus LV systolic dimensions > or =45 mm (n = 3), and heart failure plus LV systolic dimensions > or =45 mm plus LV ejection fraction <60% (n = 1). In univariate analysis, exercise duration (p = 0.004), chronotropic response (p = 0.007), percent predicted peak heart rate (p = 0.01), and heart rate recovery (p <0.02) predicted events; in multivariate analysis, only exercise duration was predictive (p <0.02). Average annual event risk was fivefold lower (4.62%) with an exercise duration > or =15 versus <15 minutes (average annual risk 23.48%, p = 0.004). Relative risks in patients with and without exercise-inducible ST-segment depression were comparable (< or =1.3, p = NS) whether defined at entry and/or during follow-up. Exercise duration, but not prevalence of exercise-inducible ST-segment depression, was lower (p <0.001) in patients with surgical indications at entry versus initially end-point-free patients. In conclusion, in asymptomatic patients with chronic severe nonischemic MR and no objective criteria for operation, progression to surgical indications generally is rapid. However, those with excellent exercise tolerance have a relatively benign course. Exercise-inducible ST-segment depression has no prognostic value in this population.

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.

Cardiovascular safety of drugs not intended for cardiovascular use: need for a new conceptual basis for assessment and approval

Recently, several drugs for non-cardiovascular diseases have ceased marketing because of cardiovascular risk, highlighting the importance of evaluating the cardiovascular safety of new drugs even if not intended for cardiovascular diseases. Assessing and ensuring acceptable cardiovascular safety of non-cardiovascular drugs is difficult; nonetheless, governmental regulatory agencies are likely to change the requirements for drug safety information. This article explores our recommendations for rethinking current regulatory policies, emphasizing the need for mandatory post-marketing surveillance registries and highlighting the exposures necessary to subserve the need for greater assessment of safety issues.

Teaching clinical research methodology to the academic medical community: a fifteen-year retrospective of a comprehensive curriculum

BACKGROUND

Due to inadequate preparation, many medical professionals are unable to critically evaluate published research articles or properly design, execute and present their own research.

AIMS

To increase exposure among physicians, medical students, and allied health professionals to diverse methodological issues involved in performing research.

METHOD

A comprehensive course on research methodology was newly designed for physicians and other members of an academic medical community, and has been successfully implemented beginning 1991. The role of the study hypothesis is highlighted; interactive pedagogical techniques are employed to promote audience engagement. Participants complete an annual evaluation to assess course quality and perceived outcomes. Outcomes also are assessed qualitatively by faculty.

RESULTS

More than 500 physicians/other professionals have participated. Ratings have been consistently high. Topics deemed most valuable are investigational planning, hypothesis construction and study designs. An enhancement of capacity to define hypotheses and apply methodological concepts in the criticism of scientific papers and development of protocols/manuscripts has been observed. Participants and faculty believe the course improves critical appraisal skills and ability to conduct research.

CONCLUSIONS

Our experience shows it is feasible to accomplish these objectives, with a high level of satisfaction, through a didactic program targeted to the general academic community.

Risk of cardiovascular events in patients receiving celecoxib: a meta-analysis of randomized clinical trials

Some nonsteroidal anti-inflammatory drugs (NSAIDs), including cyclooxygenase-2 selective inhibitors, have been associated with increased cardiovascular (CV) events in recent clinical trials or observational studies. To determine whether the cyclooxygenase-2 selective inhibitor celecoxib affects CV risk, the incidence of CV events was analyzed in patients treated with celecoxib, placebo, or nonselective NSAIDs in the clinical trial database for celecoxib using defined Antiplatelet Trialists' Collaboration end points of nonfatal myocardial infarction, nonfatal stroke, and CV death. Patient data were derived from studies in osteoarthritis, rheumatoid arthritis, ankylosing spondylitis, low back pain, and Alzheimer's disease. This meta-analysis included (1) 7,462 patients exposed to celecoxib 200 to 800 mg/day for 1,268 patient-years compared with 4,057 patients treated with placebo for 585 patient-years, and (2) 19,773 patients treated with celecoxib 200 to 800 mg/day for 5,651 patient-years compared with 13,990 patients treated with nonselective NSAIDs (diclofenac, ibuprofen, naproxen, ketoprofen, and loxoprofen) for 4,386 patient-years. CV events were adjudicated by a 3-member expert end point committee (WBW, JSB, PBG) blinded to treatment group and study. The incidence rates of the combined CV events were not significantly different between patients treated with celecoxib and placebo or between those treated with celecoxib and nonselective NSAIDs. Event rates were similar for adjudicated and nonadjudicated data. Dose of celecoxib, the use of aspirin, or the presence of CV risk factors did not alter these results. In conclusion, these analyses failed to demonstrate an increased CV risk with celecoxib relative to placebo and demonstrated a comparable rate of CV events with celecoxib treatment compared with nonselective NSAIDs.

Cyclooxygenase inhibition: what should we do to resolve the confusion? An American perspective

Recent placebo-controlled clinical trials suggest excessive adverse cardiovascular (CV) events associated with cyclooxygenase (COX)-2 selective nonsteroidal anti-inflammatory drugs (NSAIDs), developed to reduce gastrointestinal irritation associated with nonselective NSAIDs. Subsequent retrospective analyses of observational series and non-CV clinical trials suggest that CV events may occur with modest excess with all NSAIDs, nonselective and COX-2 selective, compared with nonuse of these drugs, may be dose related, and do not differ substantially in frequency among various NSAIDs. However, inadequacy of study designs, controls, and events has precluded definition of the risk-benefit relationship of COX-2 selective and nonselective NSAIDs. Resolution of this problem requires several different types of studies, necessarily including appropriately designed randomized, controlled trials comparing commonly employed nonselective and COX-2 selective NSAIDs in patients expected to benefit (ie, those with symptomatically severe arthritis) who also have coronary occlusive disease so that achievable noninferiority trial size has power sufficient to resolve relatively small differences in adverse CV (and gastrointestinal) event rates. This article explores the goals and possible designs of trials appropriate for defining risk-benefit relationship that must be known for optimal application of NSAID therapy.

Clinical effect of 'pure' heart rate slowing with a prototype If current inhibitor: placebo-controlled experience with ivabradine

Heart rate slowing is generally accepted as effective for angina prevention but this approach has not been rigorously evaluated as no pure heart rate slowing treatment has been available. With the identification of the I(f) current, the primary modulator of heart rate, and use of this as a target for drug development, the role of isolated heart rate slowing can be elucidated. More than 4,000 patients now have been studied in angina prevention trials with ivabradine, a prototype I(f) current inhibitor devoid of other cardiovascular effects. These studies demonstrate the efficacy of isolated heart rate slowing for angina prevention. Indeed, in one direct comparison with atenolol involving 939 patients, ivabradine not only was non inferior to the Beta-blocker but nominally appeared to be more efficient in angina prevention. Moreover, since ivabradine is devoid of most of the adverse effects of beta-blockers (and of calcium channel blockers), it is a suitable alternative when these established drugs are not adequately tolerated. Additional studies now must assess other potential actions in patients with coronary disease.

Should angiotensin-converting enzyme-inhibitors be used to improve outcome in patients with coronary artery disease and 'preserved' left ventricular function?

Early clinical studies investigating the role of angiotensin-converting enzyme (ACE) inhibitors in the treatment of heart failure unexpectedly demonstrated a possible reduction in coronary heart disease endpoints. Two large scale clinical trials, HOPE and EUROPA, both studies in patients with coronary artery disease (CAD) but without clinical evidence of heart failure, showed a highly significant improvement in coronary heart disease outcomes on treatment with ramipril and perindopril, respectively, in contrast, in a similar population, PEACE was unable to demonstrate such benefit with trandolapril. Meta-analyses of all trials involving ACE-inhibitors showed a highly significant improvement in coronary heart disease endpoints. Current ESC guidelines recommend ACE-inhibitor therapy in CAD patients with co-existing indications for ACE-inhibitors, such as hypertension, heart failure, left ventricular dysfunction, prior MI was left ventricular dysfunction, or diabetes (class I, level of evidence A). These guidelines also recommend ACE-inhibitor therapy in all patients with angina and proven coronary disease (class IIa, level of evidence B). However, in angina patients without independent indication for ACE-inhibitor treatment, the anticipated benefit should be weighted against the costs and risks of side effects; in these patients, only agents and doses of proven efficacy for secondary prevention should be employed.

Therapeutic effects of If blockade: Evidence and perspective

Heart rate slowing has been accepted for decades as a primary therapeutic approach to prevention (and even to treatment) of angina pectoris. Pure heart rate slowing has not been achieved with previously available rate-slowing pharmacological agents (beta adrenergic blockers, certain calcium channel blockers), all of which have other pharmacological effects that may be beneficial but also may underlie adverse drug effects. Modulation of heart rate is a function of variation in the I(f) current, a sodium-potassium mediated membrane phenomenon that is active physiologically only in the heart's sinoatrial node. Though the current first was described more than 25 years ago, a practical pharmacological method for its inhibition only recently has been developed, tested and approved for use in Europe. The effective drug, ivabradine, has demonstrated anti-anginal, anti-ischemic efficacy and now is being tested for its effect on survival in patients with coronary artery disease and impaired left ventricular function, as well as for heart failure. The data supporting the use of the drug for angina prevention, and the potential for additional applications, are reviewed in this article.

Drug insight: If inhibitors as specific heart-rate-reducing agents

Heart rate is determined primarily by spontaneously repeating net inward current carried by sodium ions and potassium ions through hyperpolarization-activated cyclic-nucleotide-gated channels. Within the heart, these channels are found most abundantly in sinoatrial cardiomyocytes. The channels open in response to membrane hyperpolarization, modulated by local cAMP concentrations. They permit activation of the I(f) current, which can be blocked specifically by molecules characterized by linked benzazepinone and benzocyclobutane rings, and which are devoid of effects on cardiac conduction, inotropy or peripheral vascular tone. The resulting heart-rate reduction has been effective in angina prevention in clinical trials involving 4,000 patients, using the prototype I(f) inhibitor, ivabradine. No serious adverse events have been attributed to the treatment; the most prominent side-effect is dose-related, always reversible and often transient visual symptoms that seldom result in voluntary drug discontinuation.

Cellular Response of Human Cardiac Fibroblasts to Mechanically Simulated Aortic Regurgitation

Myocardial fibrosis has been identified in biopsy specimens from catheterization and valve replacement surgery in patients with severe chronic aortic regurgitation (AR). While characterization of these extracellular matrix (ECM) alterations has been incomplete in humans, fibrosis also has been identified in chronic severe experimentally created AR, in which ECM composition features abnormal fibronectin/glycoprotein production, with normal collagen content. Virtually identical ECM variations have been induced when normal rabbit cardiac fibroblasts (CF) are subjected in culture to cyclic mechanical strain mimicking that found in the left ventricle (LV) in severe AR. To determine whether the changes seen experimentally can be extrapolated to humans, we exposed normal human CF in culture to the mechanical strain employed in the experimental model to simulate severe AR (n=3 replications from 1 patient). CF were isolated from epicardial biopsy distant from diseased coronary arteries in a 38-year-old man with normal LV function and without prior myocardial infarction who was undergoing elective coronary artery bypass grafting. Gelatin Sepharose affinity chromatography (GSAC) and Western analysis were used to compare fibronectin expression in strained versus nonstrained normal human CF in tissue culture; Western analysis was used to compare type I collagen production. In AR-strained CF, fibronectin synthesis nominally increased [av 38% (Western) and 45% (GSAC)] relative to control; type I collagen synthesis was virtually unchanged. These results simulate those found experimentally and suggest that human CF, like rabbit CF, manifest abnormal compositional distribution of ECM proteins in AR.