Differential effects of diltiazem and nitroprusside on left ventricular function in experimental chronic volume overload

Management of Chronic Congestive Heart Failure Caused by Myxomatous Mitral Valve Disease in Dogs: A Narrative Review from 1970 to 2020

Simple Summary

Myxomatous mitral valve disease (MMVD) is the most common acquired cardiovascular disease in dogs. The progression of the disease and the increasing severity of valvular regurgitation cause a volume overload of the left heart, leading to left atrial and ventricular remodeling and congestive heart failure (CHF). The treatment of chronic CHF secondary to MMVD in dogs has not always been the same over time. In the last fifty years, the drugs utilized have considerably changed, as well as the therapeutic protocols. Some drugs have also changed their intended use. An analysis of the literature concerning the therapy of chronic heart failure in dogs affected by this widespread degenerative disease is not available; a synthesis of the published literature on this topic and a description of its current state of art are needed. To the authors’ knowledge, a review of this topic has never been published in veterinary medicine; therefore, the aim of this study is to overview the treatments of chronic CHF secondary to MMVD in dogs from 1970 to 2020 using the general framework of narrative reviews.

Abstract

The treatment of chronic congestive heart failure (CHF), secondary to myxomatous mitral valve disease (MMVD) in dogs, has considerably changed in the last fifty years. An analysis of the literature concerning the therapy of chronic CHF in dogs affected by MMVD is not available, and it is needed. Narrative reviews (NRs) are aimed at identifying and summarizing what has been previously published, avoiding duplications, and seeking new study areas that have not yet been addressed. The most accessible open-access databases, PubMed, Embase, and Google Scholar, were chosen, and the searching time frame was set in five decades, from 1970 to 2020. The 384 selected studies were classified into categories depending on the aim of the study, the population target, the pathogenesis of MMVD (natural/induced), and the resulting CHF. Over the years, the types of studies have increased considerably in veterinary medicine. In particular, there have been 43 (24.29%) clinical trials, 41 (23.16%) randomized controlled trials, 10 (5.65%) cross-over trials, 40 (22.60%) reviews, 5 (2.82%) comparative studies, 17 (9.60%) case-control studies, 2 (1.13%) cohort studies, 2 (1.13%) experimental studies, 2 (1.13%) questionnaires, 6 (3.40%) case-reports, 7 (3.95%) retrospective studies, and 2 (1.13%) guidelines. The experimental studies on dogs with an induced form of the disease were less numerous (49–27.68%) than the studies on dogs affected by spontaneous MMVD (128–72.32%). The therapy of chronic CHF in dogs has considerably changed in the last fifty years: in the last century, some of the currently prescribed drugs did not exist yet, while others had different indications.

Current animal models for the study of congestion in heart failure: an overview

Congestion (i.e., backward failure) is an important culprit mechanism driving disease progression in heart failure. Nevertheless, congestion remains often underappreciated and clinicians underestimate the importance of congestion on the pathophysiology of decompensation in heart failure. In patients, it is however difficult to study how isolated congestion contributes to organ dysfunction, since heart failure and chronic kidney disease very often coexist in the so-called cardiorenal syndrome. Here, we review the existing relevant and suitable backward heart failure animal models to induce congestion, induced in the left- (i.e., myocardial infarction, rapid ventricular pacing) or right-sided heart (i.e., aorta-caval shunt, mitral valve regurgitation, and monocrotaline), and more specific animal models of congestion, induced by saline infusion or inferior vena cava constriction. Next, we examine critically how representative they are for the clinical situation. After all, a relevant animal model of isolated congestion offers the unique possibility of studying the effects of congestion in heart failure and the cardiorenal syndrome, separately from forward failure (i.e., impaired cardiac output). In this respect, new treatment options can be discovered.

Rodent models of heart failure: an updated review

Heart failure (HF) is one of the major health and economic burdens worldwide, and its prevalence is continuously increasing. The study of HF requires reliable animal models to study the chronic changes and pharmacologic interventions in myocardial structure and function and to follow its progression toward HF. Indeed, during the past 40 years, basic and translational scientists have used small animal models to understand the pathophysiology of HF and find more efficient ways of preventing and managing patients suffering from congestive HF (CHF). Each species and each animal model has advantages and disadvantages, and the choice of one model over another should take them into account for a good experimental design. The aim of this review is to describe and highlight the advantages and drawbacks of some commonly used HF rodents models, including both non-genetically and genetically engineered models, with a specific subchapter concerning diastolic HF models.

Left ventricular response to sustained volume overload from chronic aortic valve regurgitation in rats

OBJECTIVES

Aortic regurgitation (AR) induces left ventricular (LV) eccentric hypertrophy in response to chronic volume overload. Patients suffering from this disease often remain asymptomatic for decades before progressive LV dysfunction develops silently. Because of this slow evolution, large clinical trials with long-term follow-up on subjects with chronic AR are hard to perform. To overcome this problem, animal models have been developed in the past but results were very heterogeneous.

METHODS

Helped by echocardiography, we refined a known technique to induce homogeneous degrees of severe AR in Wistar-Kyoto rats. The effects on LV function without treatment and with nifedipine (25 mg/kg daily) (a drug currently recommended in humans with chronic AR) were evaluated by echocardiography.

RESULTS

Over 6 months, nontreated animals developed progressive LV dilatation and eccentric hypertrophy, characteristic of chronic LV volume overload. The animals also developed progressive LV systolic dysfunction, mimicking closely the evolution of the disease in humans. Abnormal filling parameters were also detected in the majority of animals. Systolic and diastolic abnormalities were prevented but only partially in the group treated with nifedipine.

CONCLUSION

This model can be used to study chronic AR and LV dysfunction associated with the disease. Nifedipine seems to protect the LV against chronic volume overload but only partially. Treatment strategies currently used in humans deserve further investigation.

Effects of acute dynamic cardiomyoplasty in a goat model of chronic ventricular dilatation: part 1

BACKGROUND

The acute effects of cardiomyoplasty in an experimental model of chronic dilated heart have not been thoroughly investigated. Therefore, a model of chronic left ventricular (LV) dilatation was created to accurately determine actual changes shortly after passive and active wrapped skeletal muscle.

METHODS

A carotid-jugular shunt model in 8 goats was used to induce progressive dilatation of the cardiac ventricles. Geometric modifications induced by the arteriovenous shunt were monitored by transthoracic echocardiography. After 8 weeks, cardiomyoplasty was performed, and the acute hemodynamic changes obtained with static cardiomyoplasty soon after the wrapping procedure were determined. Hence, hemodynamic variables recorded during assisted cardiac beats were then compared with data collected with unassisted cardiac beats using the conductance catheter method to generate pressure-volume loops.

RESULTS

During electrical stimulation of the unconditioned skeletal muscle wrapped around the dilated left ventricle, a significant increase in stroke volume (117 +/- 48 mL versus 87 +/- 38 mL; p < 0.05) was observed. Early wrapped latissimus dorsi muscle activation also induced a reduction in LV end-systolic volume (from 51 +/- 28 mL to 27 +/- 14 mL; p < 0.05) when compared with unassisted LV contraction.

CONCLUSIONS

In a chronic model of cardiac dilatation, acute dynamic cardiomyoplasty was shown to increase LV contractile performance and reduce LV volume. Further evaluation is necessary to show the effects of a conditioned wrapped muscle on LV systolic function and dimensions in the long-term.

Perioperative hemodynamic and geometric changes of the left ventricle during cardiomyoplasty in goats with dilated left ventricle

OBJECTIVE

Clinical data have suggested the occurrence of temporary short-term deterioration of the heart following cardiomyoplasty. The purpose of this study was to monitor the short-term hemodynamic effects of cardiomyoplasty in a goat model of a dilated left ventricle, using conductance catheters (ie, pressure-volume loops) and cardiac output measurements.

METHODS

Eight female goats underwent acute cardiomyoplasty 8 to 12 weeks after left ventricular (LV) dilatation was induced by a carotid jugular arteriovenous shunt. The cardiomyoplasty procedure was monitored using a Swan-Ganz catheter for cardiac output measurements and a 12-electrode (dual-field) conductance catheter to LV pressure-volume loops.

RESULTS

After wrapping the heart with the latissimus dorsi muscle, there was a significant reduction in both cardiac output and LV end-diastolic volume (LVEDV) at 10 min. Partial recovery was observed 45 min later.

CONCLUSION

A decrease in both cardiac output and LVEDV was observed following myocardial wrapping. This may explain some of the perioperative and postoperative morbidity and mortality observed following cardiomyoplasty.

Calcium channel blockade limits cardiac remodeling and improves cardiac function in myocardial infarction-induced heart failure in rats

Calcium channel antagonists (CCAs) have been proposed to prevent cardiac events after myocardial infarction (MI). However, unwanted effects, such as negative inotropy, limit their use in many cases. The aim of this study was to compare the effects of long-term treatment with the CCAs, mibefradil, verapamil, and amlodipine, administered before and after chronic MI on myocardial remodeling and cardiac function. MI was induced by permanent ligation of the left coronary artery in male Wistar rats. Infarcted animals were treated with placebo, mibefradil (10 mg/kg/d po), verapamil (8 mg/kg bid po), or amlodipine (4 mg/kg/d po). Treatment was started 7 days before or 3 h after MI induction. Six weeks after MI, mean arterial blood pressure (MAP), heart rate (HR), left ventricular end diastolic pressure (LVEDP), and cardiac contractility (dP/dt(max)) were measured. Morphometric parameters such as infarct size (IS), left ventricular dilation (LVD), septal thickness (ST), and cardiac fibrosis were determined in picrosirius red-stained hearts. Six weeks after MI, MAP and dP/dt(max) were decreased, whereas LVEDP and HR were increased in placebo-treated controls. The hearts featured an IS of 45%, left ventricular dilation, cardiac fibrosis, and septal thinning. MAP of all CCA-treated animals was increased, whereas LVEDP was decreased and dP/dt(max) increased 7-day pre- and 3-h post-MI started in mibefradil- and amlodipine-treated animals, but not in verapamil-treated animals. In contrast to amlodipine treatment, before and after MI started mibefradil and verapamil treatment decreased HR. Pretreatment with all CCA reduced IS and increased ST, whereas only mibefradil and amlodipine pretreatment prevented LVD and cardiac fibrosis. After MI started treatment with mibefradil and amlodipine reduced IS and cardiac fibrosis, and increased ST. Long-term treatment with the CCAs mibefradil, verapamil, and amlodipine reduced myocardial remodeling and improved cardiac function in MI-induced heart failure in rats.

Effects of the calcium channel antagonist mibefradil on haemodynamic and morphological parameters in myocardial infarction-induced cardiac failure in rats

OBJECTIVE

Calcium channel antagonists (CCA) have been proposed for the prevention of cardiac events after myocardial infarction (MI). Mibefradil is a CCA featuring a selective blockade of T-type Ca2(+)-channels. The aim of the study was to characterize the effects of mibefradil on haemodynamic and morphological parameters in a model of postMI chronic heart failure and to establish the "therapeutic window" for the start of therapy.

METHODS

MI was induced by permanent ligation of the left coronary artery in male normotensive Wistar rats. Animals were assigned to placebo- or mibefradil-treated (10 mg/kg/day p.o.) groups as follows: (1) sham operation; (2) MI placebo treatment; (3) 7 days preMI start of treatment; (4) 3 h postMI start of treatment; (5) 24 h postMI start of treatment; (6) 3 days postMI start of treatment; (7) 7 days postMI start of treatment. Treatment was continued for 6 weeks postMI. At this time point, mean arterial blood pressure (MAP), heart rate, left ventricular enddiastolic pressure (LVEDP) and contraction force (dP/dtmax) were measured in conscious rats at baseline and after methoxamine (MEX; 0.5-1.0 mg/h i.v.) stimulation to increase afterload. The hearts were subjected to histological determination of infarct size (IS), infarct length (IL), noninfarcted length (NL), left ventricular circumference (LVC), inner LV-diameter (LVD) and septal thickness (ST).

RESULTS

Six weeks after MI, MAP was lowered, LVEDP increased and dP/dtmax reduced. Mibefradil treatment increased basal MAP in groups 3-5 compared to the placebo-treated MI group. Under mibefradil, LVEDP was reduced at baseline in groups 3-6 and, after MEX, in all groups. dP/dtmax was increased in groups 3-4 at baseline and after MEX. In the placebo-treated MI group, the infarcted area was 39% of the LV and heart weight, LVD and LVC were increased. Heart weights of mibefradil-treated rats (groups 3-6) did not differ from those of the placebo-treated group. Early onset of treatment with mibefradil reduced IS and IL and increased NL in groups 3-4. LVD and LVC were decreased in group 3 only. ST was increased in groups 3-5.

CONCLUSION

Chronic treatment with mibefradil exerts beneficial actions on cardiac structure and performance in postMI cardiac failure in rats, especially when the onset of treatment is either prior to or within hours after the acute ischemic event.

Impaired coronary sensitivity to diltiazem in experimental heart failure: involvement of the cyclooxygenase but not the nitric oxide-synthase pathway

Because controversies surround the increased negative inotropic effects of calcium antagonists in heart failure, other mechanisms may explain their lack of efficacy in this condition. We hypothesized that altered coronary sensitivity through endothelial dysfunctions may be involved. Our goal was to evaluate the effects of heart failure on coronary and cardiac sensitivity to the calcium antagonist diltiazem. Left ventricular developed pressure (LVP) and coronary flow (CF) were assessed in isovolumetrically beating, perfused, failing hearts from cardiomyopathic hamsters (UM-X7.1) and hearts from normal hamsters. Diltiazem concentration-response curves for both coronary dilation and its negative inotropic effects were charted under control conditions and in the presence of the specific nitric oxide (NO) synthase inhibitor, NG-nitro-L-arginine methyl ester (L-NAME, 30 microM), and the cyclooxygenase inhibitor, indomethacin (10 microM). Diltiazem concentration-response curves for its negative inotropic action were similar in normal and failing hearts (IC50 1.2 and 2.3 microM, respectively). In contrast, the coronary dilator effects of diltiazem were impaired in failing hearts (EC50 for diltiazem-induced coronary dilation increased from 90 nM in normal hearts to 1.1 microM in failing hearts, p < 0.01). The involvement of endothelial dysfunctions in the observed coronary "desensitization" to diltiazem in heart failure was evaluated through the NO-synthase and cyclooxygenase pathways. Diltiazem concentration-response curves from failing hearts were not modified in the presence of L-NAME, whereas indomethacin normalized the coronary response to diltiazem in heart failure. These findings suggest that coronary "desensitization" to diltiazem occurs through parallel production and/or release of a vasoconstricting factor or factors originating from the cyclooxygenase pathway. Heart failure was not associated with increased cardiac sensitivity to diltiazem but rather with altered coronary sensitivity. These findings suggest that coronary desensitization may play a role in the lack of efficacy of diltiazem in heart failure and provide a better understanding of factors modulating the effects of calcium antagonists in heart failure.

A physical analog of the failing left ventricle for in vitro studies of mechanical wall actuation

Mechanical repowering of a failing heart with devices or skeletal muscle could circumvent blood-pump lining problems. Requirements are complex: indefinite support with preservation of valve competence and coronary flow, avoidance of wall coaptation, and allowance of both rapid low impedance refilling and independent left and right pressures. An accurate in vitro physical failing-heart analog could facilitate the choice and screening of surgical and engineering approaches in mock circulation experiments. Prosthetic models, transplant recipient hearts, normal animal hearts, existing in vivo animal failure models, and failing cadaver hearts all have serious limitations. One hundred and four excised porcine hearts were dilated and fixed by three iterative protocols. Geometric and passive mechanical parameters were assessed and compared with targets expected for an end-stage failing heart. For Protocol 3, Subgroup 2 (reinforcing valve support, dilatation by compliant ventricular balloon, and ethyl alcohol fixation), the left ventricular shape and capacity (ellipsoid, 201-377 ml/500 g of heart weight), passive valve function, wall flexural rigidity (Et3 range 0.101-0.331 Nm), and refilling mechanics (99 +/- 17.46 ml during 200-400 ms at < or = 10 mm Hg transmural gradient) were all within goal criteria.

Effects of the calcium channel blockers, diltiazem and Ro 40-5967, on systemic haemodynamics and plasma noradrenaline levels in conscious dogs with pacing-induced heart failure

1. Calcium channel blockers increase cardiovascular morbidity and mortality in patients with left ventricular dysfunction. These adverse effects are probably related to the negative inotropic effect of calcium channel blockers and/or a neurohormonal activation. 2. The present study was designed to examine, in conscious dogs, the acute haemodynamic and sympathetic effects of diltiazem and Ro 40-5967 (a novel calcium channel blocker) in the control state and in heart failure. 3. Thirteen dogs were instrumented with a micromanometer and an aortic catheter. After completion of experiments in the control state, heart failure was induced by right ventricular pacing (250 beats min-1, 3 weeks). Diltiazem and Ro 40-5967 were given intravenously (0.8 mg kg-1 and 1.0 mg kg-1 respectively). Cardiac output was measured by a thermodilution technique. 4. In the control state, both agents decreased similarly mean aortic pressure with significant increases in heart rate, cardiac output (both +1.0 l min-1 and P < 0.001) and plasma noradrenaline (both +55%) without changes in left ventricular dP/dtmax. In heart failure, for matched decreases in mean aortic pressure, neither diltiazem nor Ro 40-5967 changed heart rate significantly; diltiazem decreased cardiac output (-0.3 l min-1, P < 0.02) and dP/dtmax (-14%, P < 0.001) while Ro 40-5967 still increased cardiac output (+0.3 l min-1, P < 0.02) although the increased amount was smaller than in the control state. Plasma noradrenaline level was increased more during diltiazem infusion (+120%) than during Ro 40-5967 infusion (+38%, P < 0.001). 5. Diltiazem and Ro 40-5967 have similar haemodynamic and sympathetic effects in the control state.Heart failure alters haemodynamic and sympathetic responses to both calcium channel blockers but the magnitude of the alteration appears to be different. Diltiazem exerts a depressant effect on cardiac function which cannot be overcome by its vasodilator effect and sympathetic stimulation, while Ro 40-5967 has little effect on cardiac function. These data suggest that novel calcium channel blockers with less depressant effect may not be detrimental in heart failure.

Improvement of relaxation velocity parameters by calcium channel blockers in the aging rabbit myocardium

Normal aging in man is known to be associated with a reduction in left-ventricular diastolic function, including the rates of relaxation and filling. Calcium channel blockers have been reported to improve left-ventricular diastolic function in patients with various forms of heart disease. Clinically, the action of calcium channel blockers may be related to either a direct myocardial effect or may be secondary to the peripheral or coronary vasodilation effects. The purpose of this study is to investigate a possible direct effect of calcium channel blockers on modulation of the reported age-related reduction in myocardial relaxation. The direct effects on myocardial relaxation of the dihydropyridine calcium channel blocker, nifedipine, were studied in isolated, perfused interventricular septa and left-ventricular wall from eight young (ages 9 to 18 months) and 14 old (ages 3 to 5 years) rabbits. Septa were perfused with oxygenated Ringer's solution and paced at 48 beats/min. Maximum relaxation velocity per unit of developed tension [-dT/dt]/T, and relaxation time per unit of developed tension tR/T were continuously measured before and after infusion of calcium channel blockers. In absence of drugs, the older rabbits demonstrated a mean [-dT/dt]/T which was 32% lower (p < 0.003) and a mean tR/T which was 45% higher (p < 0.005) than the younger rabbits. When nifedipine was introduced at concentrations > 10(-8) M equivalent to doses above the therapeutic free-plasma concentration in humans, all contraction and relaxation parameters were depressed. However, at lower doses, equivalent to doses in the clinical therapeutic range, [-dT/dt]/T was increased in the older rabbit septa by 18% in the presence of nifedipine. tR/T was shortened in the older rabbit septa by 17% in the presence of nifedipine. Myocardial relaxation in older rabbits after drug infusion approximated these parameters in the younger rabbits prior to drug infusion (P = NS). Calcium channel blockers had similar beneficial effects on the relaxation properties of the myocardium in younger rabbits. All beneficial effects were observed at concentrations of calcium channel blockers which were within and below the clinically therapeutic range of plasma free drug concentration, i.e., 5 x 10(-9) to 4 x 10(-8) M. Potential differences in relaxation effects related to different segments of the myocardium and different mechanical recording vectors were evaluated. Isolated left ventricle preparations from aging rabbits demonstrated improvements in tR/T and [-dT/dt]/T similar to those observed in the septum. Furthermore, improvement in mechanical function along the y-axis and x-axis vectors of the septum was similar.(ABSTRACT TRUNCATED AT 400 WORDS)

Use of intravenous diltiazem in patients with acute coronary artery disease

The use of calcium antagonists for the treatment of patients with unstable angina and acute myocardial infarction has been a promising area of both basic and clinical research. Despite consistently beneficial effects experimentally, the clinical extrapolation of these results has been less than ideal, especially in patients with evolving myocardial infarction. Calcium antagonists have in some instances failed to manifest benefit and at times have been shown to have negative effects. One reason for this could be the use of oral or sublingual preparations, which result in variable absorption, variable volumes of distribution, and variable clearance. For this reason, an intravenous preparation of one of the calcium antagonists, diltiazem, may be more beneficial. Such a preparation has been developed and its safety confirmed in patients without cardiovascular disease and in patients with acute infarction. Substantial benefit has been documented in patients with stable angina and during noncardiac surgery. Preliminary data in patients with unstable angina suggest that the drug is effective, although studies comparing intravenous diltiazem with other agents or with the oral preparation of diltiazem have not yet been reported. Experimental data in animals with acute infarction have demonstrated that administration of intravenous diltiazem after occlusion, but prior to reperfusion, elicits a marked increase in the degree of myocardial salvage induced by thrombolysis. This appears to be due to the inhibition of lipid peroxidation rather than alterations in coronary perfusion. Thus, it appears that the intravenous preparation may permit the more effective use of diltiazem in patients with acute coronary artery disease.

Inotropic effect of nicardipine in patients with heart failure: assessment by left ventricular end-systolic pressure-volume analysis

Nicardipine, a new dihydropyridine calcium channel blocker, has been investigated for the treatment of coronary artery disease and heart failure. To assess the inotropic effect of nicardipine in humans independent of its vasodilator effect, equihypotensive doses of intravenous nitroprusside (mean infusion rate 65 +/- 13 micrograms/min) and nicardipine (mean dose 5.2 +/- 0.4 mg) were administered to 15 patients with heart failure (New York Heart Association functional classes II to IV, radionuclide left ventricular ejection fraction 0.15 +/- 0.02). Left ventricular micromanometer pressure and simultaneous radionuclide left ventricular volume were obtained at baseline, during nitroprusside infusion, during a second baseline period and during nicardipine infusion. Heart rate did not change significantly with either nitroprusside or nicardipine. Mean systemic arterial pressure decreased by an average of 21 mm Hg with both drugs. A greater decrease in left ventricular end-diastolic pressure occurred with nitroprusside (27 +/- 2 to 14 +/- 2 mm Hg, p less than 0.01) than with nicardipine (27 +/- 2 to 23 +/- 3 mm Hg, p less than 0.05), and pulmonary capillary wedge pressure decreased significantly only with nitroprusside. Cardiac index increased from 1.8 +/- 0.1 to 2.1 +/- 0.1 liters/min per m2 (p less than 0.05) with nitroprusside and to a greater extent from 1.7 +/- 0.1 to 2.4 +/- 0.1 liters/min per m2 (p less than 0.01) with nicardipine. Left ventricular ejection fraction increased with nicardipine (0.15 +/- 0.01 to 0.19 +/- 0.01, p less than 0.01), but not with nitroprusside. Peak positive first derivative of left ventricular pressure (dP/dt) decreased by 9% with both agents.(ABSTRACT TRUNCATED AT 250 WORDS)

Diltiazem attenuates the inotropic and peripheral vascular effects of cardiac glycosides

The influence of diltiazem on the hemodynamic effects of ouabain in 10 preinstrumented awake dogs was studied. Mean aortic pressure increased from 102 to 119 mm Hg with ouabain (p less than 0.05), an effect that was attenuated by pretreatment with diltiazem. The increase in systemic vascular resistance of 30% with ouabain was ablated by prior diltiazem. Heart rate did not significantly change with ouabain or with diltiazem plus ouabain, but intravenous diltiazem alone produced a reflex increase in heart rate of 26%. Left ventricular (LV) end-diastolic dimension was significantly greater with ouabain alone, but not with ouabain after pretreatment with diltiazem. LV dP/dt max increased by 40% with ouabain alone, but by only 23% (p less than 0.001) after pretreatment with diltiazem plus ouabain. When observed at matched preload and heart rate, diltiazem markedly attenuates the positive inotropic and peripheral arterial constrictive effects of acute ouabain administration in the conscious animal with normal LV function.

Linearity of the left ventricular end-systolic pressure-volume relation in patients with severe heart failure

The left ventricular end-systolic pressure-volume relation is a relatively load-independent measure of left ventricular contractile function. Linearity of the relation derived from full left ventricular pressure-volume loops has not previously been demonstrated for patients with severe heart failure. Therefore, nine patients with markedly depressed left ventricular systolic function (ejection fraction 0.14 +/- 0.08) were studied with micromanometer left ventricular pressure measurement and simultaneous radionuclide ventriculography. Afterload was reduced with graded infusions of nitroprusside, allowing construction of pressure-volume loops under four afterload conditions in four patients and three afterload conditions in the other five patients. The end-systolic pressure-volume relation derived from the pressure-volume loops was found to be linear for the range of pressures and volumes examined, with correlation coefficients in individual patients ranging from 0.936 to 0.999 (mean 0.981). The mean slope of the relation (or end-systolic elastance) was 0.71 mm Hg/ml (range 0.42 to 1.52), and the extrapolated volume intercept at zero pressure was positive in all patients. An exponential relation between end-systolic elastance and ejection fraction was demonstrated for this group of patients. Approximations of end-systolic elastance obtained from measurements other than the full pressure-volume loops correlated variably with "true" elastance obtained from the pressure-volume loops. The relation between stroke work and end-diastolic volume was nonlinear in most patients. Thus, the end-systolic pressure-volume relation is linear in the "physiologic" range in patients with severe heart failure. This finding should permit construction of the relation from two loading conditions in clinical studies, facilitating its use as an index of contractile function in patients with heart failure.

The effect of diltiazem on mortality and reinfarction after myocardial infarction

We studied the effect of diltiazem on mortality and reinfarction in 2466 patients with previous infarction from 38 hospitals in the United States and Canada. The patients were randomly assigned to receive diltiazem (240 mg per day, n = 1234) or placebo (n = 1232) and followed for 12 to 52 months (mean, 25). Total mortality rates were nearly identical among the two treatment groups (167 and 166, respectively), as were cumulative mortality rates. There were 11 percent fewer first recurrent cardiac events (death from cardiac causes or nonfatal reinfarction) in the diltiazem group than in the placebo group (202 vs. 226; Cox hazard ratio, 0.90; 95 percent confidence limits, 0.74 and 1.08). A significant (P = 0.0042) bidirectional interaction between diltiazem and pulmonary congestion was observed on x-ray examination. In 1909 patients without pulmonary congestion, diltiazem was associated with a reduced number of cardiac events (hazard ratio, 0.77; 95 percent confidence limits, 0.61 and 0.98); in 490 patients with pulmonary congestion, diltiazem was associated with an increased number of cardiac events (hazard ratio, 1.41; 95 percent confidence limits, 1.01 and 1.96). A similar pattern was observed with respect to the ejection fraction, which was dichotomized at 0.40. Thus, diltiazem exerted no overall effect on mortality or cardiac events in this population of patients with previous infarction. This neutral effect reflected a diltiazem-related reduction in cardiac events in the majority of patients without left ventricular dysfunction and an increase in such events in the minority of patients with left ventricular dysfunction.

Calcium channel antagonists. Part III: Use and comparative efficacy in hypertension and supraventricular arrhythmias. Minor indications

The major antihypertensive mechanism of calcium antagonists is by decreasing the systemic vascular resistance, modified by the counter-regulatory responses of the baroreflexes and the renin-angiotensin-aldosterone system. In severe hypertension, the concept that calcium overload of the vascular myocyte could precipitate or aggravate peripheral vasoconstriction provides a logical basis for the use of these agents as first choice therapy; nifedipine, especially, has been well tested. As monotherapy for mild to moderate hypertension each of the three first-generation agents compares well with beta-blockers. Calcium antagonists may have a special role in the therapy of certain patient groups (elderly, black) or in those subjects whose life style involves intense physical or mental exertion (hemodynamics better maintained than with beta-blockade) or in patients with early end-organ damage such as left ventricular hypertrophy or renal insufficiency. However, the goal blood pressure may not be reached during monotherapy so that drug combinations may be required. Further indications for these compounds are as follows. Verapamil and diltiazem are frequently used in supraventricular tachycardias including acute and chronic atrial fibrillation. In the arrhythmias of the Wolff-Parkinson-White syndrome, there is the potential danger of provocation of anterograde conduction. Further indications for calcium antagonists, still under evaluation, include congestive heart failure (controversial), hypertrophic cardiomyopathy (verapamil), primary pulmonary hypertension (high doses required), Raynaud's phenomenon (nifedipine and diltiazem effective), peripheral vascular disease (proof not yet documented), cerebral insufficiency and subarachnoid hemorrhage (nimodipine promising), migraine, exertional bronchospasm, renal disease, atherosclerosis (experimental), and primary aldosteronism (nifedipine inhibits aldosterone release). Second-generation agents include dihydropyridines, such as nitrendipine, nicardipine, felodipine, amlodipine, nisoldipine, nimodipine, and isradipine. From these will be selected agents that are longer acting and provide higher vascular selectivity. New preparations of existing agents include slow-release formulations of nifedipine, verapamil, and diltiazem. Minor side effects include those caused by vasodilation (flushing and headaches), constipation (verapamil), and ankle edema. Serious side effects are rare and result from improper use of these agents, as when intravenous verapamil is given to patients with sinus or atrioventricular nodal depression from drugs or disease, or nifedipine to patients with aortic stenosis. The potential of a marked negative inotropic effect is usually offset by afterload reduction, especially in the case of nifedipine. Yet caution is required when calcium antagonists, especially verapamil, are given to patients with myocardial failure unless caused by hypertensive heart disease. Drug interactions of calcium antagonists occur with other cardiovascular agents such as alpha-adrenergic blockers, beta-adrenergic blockers, digoxin, quinidine, and disopyramide.(ABSTRACT TRUNCATED AT 400 WORDS)

Prognostic importance of the immediate hemodynamic response to nifedipine in patients with severe left ventricular dysfunction

To determine the clinical significance of the occurrence of hemodynamic deterioration after the administration of calcium channel blocking drugs, nifedipine (20 mg orally) was administered to 29 patients with severe left ventricular dysfunction. Thirteen patients showed hemodynamic improvement with the drug (Group 1), as shown by a notable increase in cardiac index associated with a modest decrease in mean arterial pressure. The other 16 patients exhibited hemodynamic deterioration after nifedipine (Group 2), as reflected by a decline in right and left ventricular stroke work indexes accompanied by a marked hypotensive response. These differences were not related to differences in the peripheral vascular response to nifedipine, because both groups showed similar decreases in systemic and pulmonary vascular resistances. Groups 1 (hemodynamic improvement) and 2 (hemodynamic deterioration) were similar with respect to all demographic variables and pretreatment left ventricular performance (cardiac index, left ventricular filling pressure and systemic vascular resistance). Yet, the 1 year actuarial survival in patients in Group 1 was substantially better than that in patients in Group 2 (67 versus 23%, p = 0.009). Group 2, however, had higher values for plasma renin activity (17.7 +/- 6.0 versus 4.3 +/- 1.4 mg/ml per h, p less than 0.05), lower values for serum sodium concentration (134.6 +/- 1.2 versus 139.2 +/- 0.6 mEq/liter, p less than 0.05) and higher values for mean right atrial pressure (15.8 +/- 2.0 versus 7.9 +/- 1.4 mm Hg, p less than 0.01) than did patients in Group 1.(ABSTRACT TRUNCATED AT 250 WORDS)

Calcium channel antagonists, Part I: Fundamental properties: mechanisms, classification, sites of action

Ca2+ channel antagonists are agents that interact with the voltage-dependent Ca2+ channel in a highly specific way. The prototype agents of cardiovascular importance are verapamil, nifedipine, and diltiazem, in historical order of appearance. These agents all have different molecular structures and bind separately with receptor sites located in or near the calcium channel, at molecular sites still to be fully identified. There are probably three distinct receptor sites (V, N, D) which stand in relation to the "gate" of the long-acting "L" calcium channel. There is probably overlap among the receptor sites, especially between the V and D sites to explain their common properties. All three agents inhibit the voltage-dependent calcium channel in vascular smooth muscle and also myocardial slow calcium channels. The ratio of the arterial to the myocardial effect is an index of the arterial selectivity, generally held to be a desirable property because the negative inotropic effect is usually a liability. The general clinical impression that nifedipine is the agent most active in vascular tissue in relation to the myocardial effect is supported by data on the relative potencies of these three agents on blood perfused dog preparations and by a comparison of the potency on rat vascular (portal vein) versus myocardial effects. Nonetheless all three agents are highly active in the inhibition of K(+)-induced vascular contractions (nifedipine 10(-9) M to 10(-8) M; verapamil 10(-7) M to 10(-6) M; and diltiazem 5 x 10(-7) M to 10(-6) M; concentrations for 50% inhibition of K(+)-induced vascular contractions in rat or rabbit aorta; comparative data for resistance vessels not available). The clinical impression that verapamil and diltiazem are more active on nodal tissue is also supported by a comparison of potencies on blood perfused dog nodal preparations in comparison with effects on coronary flow, with verapamil and diltiazem being approximately 10x more potent on the AV node than increasing coronary blood flow, so that the nodal effect is first detected. These basic pharmacological properties explain why all these three agents have clinical effects relevant to inhibition of vascular contraction (antihypertensive and antianginal effects) and only verapamil and diltiazem have clinically relevant inhibitory effects on the AV node (inhibition of supraventricular tachycardias). The comparative potencies of verapamil, diltiazem, and nifedipine in angina and hypertension will be examined in Parts II and III of this review.

Experience with calcium antagonist drugs in congestive heart failure

Several clinical studies have demonstrated beneficial hemodynamic effects of calcium antagonist drugs when used as arterial vasodilators in the treatment of certain patients with moderate to severe congestive heart failure. These drugs usually decrease systemic vascular resistance and improve ejection phase indexes of left ventricular function in such patients. However, calcium antagonists have intrinsic negative inotropic effects and other vasodilators such as nitroprusside, hydralazine and captopril appear to be more beneficial when used in the treatment of severe congestive heart failure.

Usefulness of calcium antagonists for congestive heart failure

In patients with congestive heart failure (CHF) due to dilated cardiomyopathy, nifedipine, diltiazem and several of the newer calcium antagonists including nicardipine, nitrendipine, felodipine and PN 200-110 (isradipine) improve left ventricular function. Because of its relatively more pronounced negative inotropic and chronotropic actions, verapamil is generally not tolerated by patients with left ventricular failure. In addition, even relatively vascular-selective agents such as nifedipine can occasionally cause significant left ventricular depression, particularly if combined with beta-adrenergic blocking agents. Comparative studies using nitroprusside to cause an equivalent decrease in arterial pressure indicate that nifedipine acts predominantly on the arterial vasculature, and that a small but significant decrease in contractility occurs, apparently due to a direct myocardial action. Although diltiazem causes a depression in myocardial contractility in dogs with volume overload heart failure, limited data show no significant negative inotropic action in patients with heart failure. The negative inotropic effects, if any, of newer and possibly more vascular-selective agents are not yet known. Calcium antagonists appear to act predominantly on the limb and coronary vasculature, with relatively less effect on renal and hepatic vessels. In patients with CHF, nifedipine causes an increase in coronary blood flow and a decrease in the aorto-coronary sinus oxygen difference indicating an improvement in myocardial energetics. Although nifedipine causes an increase in cardiac index and decreases in systemic vascular resistance and pulmonary capillary wedge pressure during exercise, the limited data available fail to show a short- or long-term increase in exercise capacity. Nifedipine causes an increase in plasma renin activity, possibly due to a direct action on the kidney.(ABSTRACT TRUNCATED AT 250 WORDS)

[Calcium antagonists in heart failure?]

Although beneficial acute hemodynamic effects of calcium antagonists in heart failure have been reported, their use in this setting is still controversial because of the negative inotropic effects produced by these agents. The direct actions of calcium antagonists, that is direct depression of myocardial contractility and coronary and peripheral vasodilation, are modulated by systemic hypotension-induced baroreceptor activation of autonomic reflexes. Thus, at clinically relevant dosages, the baroreceptor-mediated cardiac stimulatory effects may counterbalance or override the direct negative-inotropic effects, as usually observed with nifedipine or diltiazem. By contrast, with verapamil significant depression of contractility may occur. Newer calcium antagonists with higher vasoselectivity such as nisoldipine or felodipine may be particularly interesting in the setting of congestive heart failure because of pronounced arterial vasodilatation and their additional effects on coronary blood flow, LV-regional wall motion and diastolic function and peripheral blood flow distribution with negligible myocardial effects. Due to their marked vasodilatating properties, newer derivatives may be advantageous in the treatment of heart failure due to coronary artery disease and hypertension. Although limited data concerning long-term efficacy are available, preliminary studies suggest long-term benefit in selected patients. It appears that verapamil should not be used for vasodilator therapy of severe heart failure, since deterioration of LV function may occur.

Advances in calcium blocker therapy

Calcium blockers are drugs that interfere with the entry of calcium ions into cells of a variety of tissues. Three calcium blockers, verapamil, nifedipine, and diltiazem, are currently approved for clinical use in the United States and many others are undergoing clinical trials. All calcium blockers share the effect of dilating blood vessels, although some agents are selective dilators of certain vascular beds, such as the coronary or cerebral circulation. There exist major differences among these drugs in their ability to depress myocardial contraction and inhibit cardiac impulse conduction, as well as other properties. The therapeutic actions of the agents in use, as well as the actions of the investigational calcium blockers, have been reviewed. Although calcium blockers are generally well tolerated and have fewer side effects than many alternative drugs, serious adverse effects are possible in certain clinical settings. The clinical indications for these drugs continue to expand and will likely find many uses in surgical patients, especially in the areas of cardiac surgery, neurosurgery, vascular surgery, and general surgery.

Improved myocardial oxygen utilization by diltiazem in patients

Calcium entry blocking drugs produce different effects on systemic and coronary hemodynamics and myocardial oxygen extraction. To examine the effects on myocardial oxygen extraction, intravenous diltiazem (100 micrograms/kg bolus with a continuous 10 micrograms/kg/min infusion) was administered to 11 patients at rest and during controlled heart rates (100 +/- 5 and 120 +/- 5 bpm). At rest, diltiazem decreased mean arterial pressure from 109 +/- 13 to 99 +/- 14 mm Hg (p less than 0.01), increased heart rate from 64 + 12 to 74 +/- 14 bpm (p less than 0.01), and decreased coronary sinus resistance (1.02 +/- .41 to 0.87 +/- .40 U, p less than 0.05). Myocardial oxygen extraction was significantly reduced since coronary sinus oxygen content increased (6.0 +/- 0.9 to 7.8 +/- 1.2 ml/dl, p less than 0.01) and the arterial-coronary sinus oxygen difference decreased (12.0 +/- 1.7 to 10.6 +/- 1.6 ml/dl, p less than 0.01). Similar changes occurred with heart rate held constant. There were no significant changes in absolute coronary sinus blood flow, calculated myocardial oxygen consumption, or left ventricular dP/dt. Diltiazem decreases mean arterial pressure while reducing both myocardial oxygen extraction and coronary arterial resistance, suggesting that a principal mechanism of a beneficial effect upon the coronary circulation appears to be an improvement in myocardial oxygen extraction relative to myocardial oxygen demand.

Hemodynamic effects of verapamil in left ventricular valvular volume overload

The hemodynamic consequences of aortic and mitral insufficiency may be influenced by the high systemic vascular resistance often seen in these patients. Since the calcium antagonists have been shown to reduce systemic vascular resistance, we evaluated the effects of intravenous verapamil in 23 patients. In 11 patients with aortic insufficiency, verapamil resulted in a 20% increase in cardiac index (p less than 0.001), 18% increase in forward stroke volume index (p less than 0.001), and a 24% decrease in regurgitant fraction (p less than 0.005). In the 12 patients with mitral insufficiency, verapamil resulted in a 19% increase in both cardiac index (p = 0.004), and forward stroke volume index (p less than 0.001), while there was a 19% decrease in regurgitant fraction (p less than 0.02). Left ventricular end-systolic stress decreased significantly in both groups as did end-diastolic stress in the mitral insufficiency group. There was no significant change in several measures of contractile performance, though the end-systolic stress-to-volume index ratio fell significantly (p less than 0.04) in the mitral insufficiency group. Our findings suggest that the vasodilatory effects of intravenous verapamil predominate over the negative inotropic effects in patients with aortic and mitral insufficiency. Verapamil may be of use in patients intolerant to other vasodilators, patients with concomitant ischemic heart disease, or those with supraventricular arrhythmias.

Direct and indirect effects of calcium entry blocking agents on isovolumic left ventricular relaxation in conscious dogs

To assess the direct and indirect effects of the commonly used calcium entry blockers (CEB) upon the major determinants of isovolumic left ventricular relaxation, we administered equidepressant intracoronary (IC, n = 7) and equihypotensive intravenous (n = 12) dosages of diltiazem (16 +/- 3 SE micrograms/kg IC and 63 +/- 9 micrograms/kg i.v.), verapamil (10 +/- 2 and 57 +/- 5 micrograms/kg), and nifedipine (1 +/- 0.1 and 8 +/- 0.3 micrograms/kg) to preinstrumented awake dogs with normal ventricular function. The time constant of left ventricle (LV) relaxation, analyzed by two methods (T1, from the linear relation of the natural logarithm of LV pressure and time; T2, from the linear relation of LV pressure and negative high fidelity LV pressure), was significantly and equivalently prolonged by IC diltiazem (T1 + 48%, P less than 0.02), verapamil (T1 + 43%, P less than 0.001), and nifedipine (T1 + 30%, P less than 0.03). Lesser amounts of each CEB that did not affect rate of LV pressure development or extent of shortening produced no change in T1 or T2. By contrast, intravenous calcium entry blockade either produced no significant change (diltiazem and verapamil) or shortened (nifedipine T1 - 18%, P less than 0.01) LV isovolumic relaxation. However, after beta adrenergic blockade with propranolol (2 mg/kg i.v., n = 6) no change in ventricular relaxation was observed during nifedipine and the time constant was significantly prolonged by verapamil (T1 + 15%, P less than 0.05). We conclude that calcium entry blockade directly impairs normal left ventricular relaxation: This effect is closely linked to the negative inotropic properties of these drugs. The prolongation of isovolumic relaxation produced by calcium blockade is attenuated or even reversed by reflex sympathetic stimulation and favorably altered loading conditions during systemic administration.

Inotropic, vascular and neuroendocrine effects of nifedipine in heart failure: comparison with nitroprusside

To evaluate the short-term hemodynamic and neuroendocrine effects of nifedipine in heart failure, it was compared with nitroprusside, a balanced vasodilator without known inotropic effect, in equihypotensive doses during right and left heart catheterization in nine patients with heart failure. Mean arterial pressure decreased from 89 +/- 12 to 76 +/- 14 mm Hg with nitroprusside, and from 90 +/- 12 to 75 +/- 13 mm Hg with sublingual nifedipine. Right atrial, pulmonary artery, pulmonary capillary wedge and left ventricular end-diastolic pressures decreased significantly with nitroprusside, but not with nifedipine. Cardiac index and stroke volume index increased to a similar extent with both drugs; in contrast, stroke work index increased significantly with nitroprusside, but not with nifedipine. Peak rate of left ventricular pressure development (dP/dt) (measured with a micromanometer-tipped catheter in seven patients) was unchanged with nitroprusside, but decreased significantly with nifedipine (747 +/- 292 to 639 +/- 238 mm Hg/s; p less than 0.002). There was no change in heart rate with either medication. Plasma norepinephrine and epinephrine concentrations were not altered significantly by either drug. Plasma renin activity was not changed by nitroprusside infusion, but was increased after the administration of nifedipine. Thus, in contrast to the balanced vasodilator action of nitroprusside, the effect of nifedipine is predominantly on the arterial circulation. In these patients with heart failure, reflex sympathetic stimulation did not occur in response to a decrease in systemic arterial pressure by either vasodilator. A negative inotropic effect occurred after the administration of nifedipine, but not nitroprusside.

Use of calcium antagonists in ventricular dysfunction

Calcium antagonists are now widely used in a variety of cardiocirculatory disorders, many of which are associated with varying levels of depressed myocardial function. Thus, the hemodynamic effects of calcium antagonists in patients with normal as well as depressed ventricular function are clinically relevant. None of the 3 agents verapamil, nifedipine or diltiazem exerts significant negative inotropic effects in patients with relatively normal myocardial function, although increases in left ventricular end-diastolic pressure may occur with verapamil and possibly diltiazem. In a setting in which ischemia, hypertension or arrhythmias contribute to cardiac failure, all 3 agents may ameliorate myocardial decompensation if they reverse the precipitating causes. In patients with depressed myocardial function, the effects of diltiazem are not known; verapamil may depress myocardial function, especially if the ventricular filling pressure is increased. Nifedipine generally has little depressant action in this setting and usually improves cardiac function, especially if the sympathetic reflexes are intact. However, hemodynamic deterioration after nifedipine administration has been reported. Thus, the available data do not support the use of calcium antagonists as afterload-reducing agents in heart failure and suggest caution in the use of these agents in patients with impaired ventricular performance.

Beneficial hemodynamic effects of intravenous and oral diltiazem in severe congestive heart failure

Concern persists about the potential negative inotropic effects of calcium channel blockers in patients with severely depressed myocardial function. Therefore, intravenous diltiazem (100 to 200 micrograms/kg per min infusion) was administered for 40 minutes followed by oral diltiazem (90 to 120 mg/8 hours) for 24 hours to patients with advanced congestive heart failure (New York Heart Association class III to IV, mean ejection fraction 26 +/- 4 [SD]). Intravenous diltiazem (eight patients) increased cardiac index 20% (2.05 +/- 0.8 to 2.47 +/- 0.8 liters/min per m2, p less than 0.01), stroke volume index 50% (22 +/- 9 to 33 +/- 12 ml/m2, p less than 0.001) and stroke work index 27% (19 +/- 10 to 24 +/- 10 g-m/m2, p less than 0.05); while reducing heart rate 23% (97 +/- 18 to 75 +/- 11 beats/min, p less than 0.01), mean arterial pressure 18% (95 +/- 13 to 78 +/- 7 mm Hg) and pulmonary wedge pressure 34% (29 +/- 9 to 19 +/- 7 mm Hg), without altering maximal first derivative of left ventricular pressure (dP/dtmax). Oral diltiazem (seven patients) produced equivalent hemodynamic effects. Transient junctional arrhythmias were observed in three of eight patients with intravenous diltiazem and one of seven patients with oral diltiazem. It is concluded that intravenous and short-term oral diltiazem improve left ventricular performance and reduce myocardial oxygen demand by heart rate and afterload reduction without significantly depressing contractile function in severe congestive heart failure. Caution should be exercised to avoid potential adverse, drug-induced electrophysiologic effects in such patients.

Calcium ions, drug action and the heart--with special reference to calcium antagonist drugs

Calcium antagonists, of which the best known are verapamil, nifedipine and diltiazem, are a powerful group of cardioactive agents with a clinical spectrum of indications rather similar to those of beta-adrenoceptor blockade, including angina of effort, angina at rest, hypertension and supraventricular tachycardias (nifedipine is ineffective for the latter). In angina caused by coronary spasm, calcium antagonists are preferred to beta-blockade. Calcium antagonists have a basically different mode of action from beta-adrenoceptor blockade, although both ultimately act on the free cytoplasmic calcium ion concentration. Critical differences between the calcium antagonists are dependent on the individual properties of the calcium antagonists concerned. Different binding sites on the sarcolemma have been identified for nifedipine-like agents and verapamil, but with a different interaction with the nifedipine site. None of these sites might be relevant to the binding of calcium antagonists to the tissue of their therapeutic site of action (arterial smooth muscle for all; atrioventricular node for verapamil and diltiazem). As a group, calcium antagonists cause vascular dilation and do not cause bronchial constriction, in contrast to the beta-adrenoceptor blocking agents. In many patients, these diverse properties allow safe combination of calcium antagonists and beta-adrenoceptor blockers if due care is observed, especially in the case of nifedipine. The clinical differences between the effects of various calcium antagonists reflect: (i) the greater vasodilator capacity of nifedipine, so that at a given concentration the afterload effect dominates over possible effects on the nodal or myocardial tissue; (ii) the greater inhibition of vagal tone by nifedipine than by verapamil or diltiazem; and (iii) the greater inhibition of the atrioventricular node by verapamil and diltiazem. In angina of effort, calcium antagonists are now becoming the agents of first choice in some centers. Experimental use of calcium antagonists include the possible prevention of ventricular fibrillation, the inhibition of ischemic injury, the prevention of catecholamine mediated injury to the myocardium and decreased arterial calcinosis.