Calcium entry blocking drugs: mechanisms of action, experimental studies and clinical uses

Treatment of Perioperative Myocardial Ischemia

Prevention and treatment of myocardial ischemia re mains a central focus of perioperative care. Myocardial ischemia is best understood in terms of myocardial oxygen supply and demand ratios. Conventional ther apy includes nitrates, β-blockers, and calcium channel blockers. In all 3 drug classes, ischemia is reduced by either improving supply, decreasing demand, or both. More recent investigation evaluates these medications either as prophylactic therapy or as a component of long-term risk reduction for cardiac morbid events. Newer therapies, including anticoagulation, pain ther apy, normothermia, central neuroaxial techniques, and other therapies, are reviewed.

Resting and end-diastolic [Ca2+]i measurements in the Langendorff-perfused ferret heart loaded with a 19F NMR indicator

Intracellular free calcium concentration ([Ca2+]i) was measured in Langendorff-perfused ferret hearts (30 degrees C, pH 7.4) by loading paced hearts with the 19F NMR calcium indicator, the 5,5'-difluoro derivative of 1,2-bis(o-aminophenoxy)ethane-N, N,N',N'-tetraacetic acid (5FBAPTA), to an initial cytosolic concentration of approximately 120 microM. Increasing the pacing frequency raised the end-diastolic [Ca2+]i from 299 +/- 44 nM (mean +/- SEM) at 0.2 Hz to 522 +/- 54 nM at 1.0 Hz and 691 +/- 166 nM at 2.0 Hz. Raising [Ca]o from 1.8 to 7.0 mM at a pacing frequency of 1.0 Hz increased end-diastolic [Ca2+]i to 625 +/- 39 nM. In unpaced hearts perfused with diltiazem (100 microM), [Ca2+]i fell rapidly to a steady-state value of < 100 nM after 60 min. Raising [Ca]o from 1.8 to 7.0 mM had no detectable effect on resting [Ca2+]i. The time course of the [Ca2+]i transient was measured in hearts paced at 1.1 Hz and perfused with 1.8 mM [Ca]o. The peak [Ca2+]i was approximately 2 microM at approximately 150 msec after the pacing pulse, and peak developed LVP occurred at 550 msec compared with 280 msec in control hearts not loaded with 5FBAPTA. Comparisons with data obtained by other techniques, including fluorescent [Ca2+]i indicators, imply that although the end-diastolic [Ca2+]i values obtained with 5FBAPTA in beating hearts are elevated by the concentrations of intracellular 5FBAPTA required for signal detection, the changes in [Ca2+]i observed in response to experimental interventions are qualitatively consistent with previous data.

The effects of nimodipine on cocaine toxicity

The response to nimodipine as an inhibitor of cocaine toxicity was investigated in pentobarbital-anesthetized dogs and in isolated dog heart preparations at constant heart rates. Nimodipine (10 micrograms/kg) markedly decreased peripheral and coronary vascular resistance and increased cardiac output, cardiac work, and coronary blood flow. When corrected for the change in afterload, nimodipine had a positive inotropic response, as measured by +/- maximal dP/dt, in the cocaine-depressed animal. Thus, cocaine toxicity was partially reversed by nimodipine. In the isolated heart preparation, nimodipine resulted in further cardiac depression similar to that seen with other calcium channel antagonists.

Calcium-channel blockers and anaesthesia

Verapamil was the first calcium-channel blocker (CCB). It has been used since 1962 in Europe then in Japan for its antiarrhythmic and coronary vasodilator effects. The CCB have become prominent cardiovascular drugs during the last 15 years. Many experimental and clinical studies have defined their mechanism of action, the effects of new drugs in this therapeutic class, and their indications and interactions with other drugs. Due to the large number of patients treated with CCB it is important for the anaesthetist to know the general and specific problems involved during the perioperative period, the interactions with anaesthetics and the practical use of these drugs.

The hibernating myocardium

The hibernating myocardium refers to resting LV dysfunction due to reduced coronary blood flow that can be partially or completely reversed by myocardial revascularization and/or by reducing myocardial oxygen demand. It is different from the stunned myocardium. Methods for its detection are not yet perfect. Hibernating myocardium has been demonstrated to be present in several clinical subgroups of patients; however, currently its full clinical presence and impact are not adequately defined.

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 blockers in systemic hypertension

Alterations in transmembrane flux of calcium ions may be playing a role in the pathophysiology of systemic hypertension. Calcium channel blockers have been shown to be effective antihypertensive drugs with excellent safety profiles. They are efficacious in the long term treatment of systemic hypertension in all population subgroups, and have special applicability for treating patients with hypertensive urgencies and individuals with concomitant diseases such as angina pectoris and arrhythmias.

Postinfarction angina

In conclusion, the PIA patient is at high risk, with higher early as well as late mortality. The pathophysiology of PIA is complex and may vary from patient to patient. The concepts of ischemia at a distance and ischemia in the infarct zone have led to a better understanding of early PIA. Coronary spasm may play an important role in most PIA patients as in the general population of patients with angina pectoris. Medical therapy is efficacious in many, although it may on rare occasion aggravate myocardial ischemia. Urgent coronary arteriography is generally safe and should be performed as soon as possible for medically refractory PIA. CABG appears to be safe in experienced hands, but its timing must be individualized. The IABP should be reserved for more unstable patients for fear of vascular complications. Randomized controlled trials such as the BARI Trial will further compare PTCA with CABG.

Prognostic significance and beneficial effect of diltiazem on the incidence of early recurrent ischemia after non-Q-wave myocardial infarction: results from the Multicenter Diltiazem Reinfarction Study

Of 576 patients with non-Q-wave acute myocardial infarction enrolled in the Diltiazem Reinfarction Study, 246 (43%) had 1 or more episodes of angina at rest or with minimal effort during 10.5 days of treatment with either diltiazem (90 mg every 6 hours) or placebo. Reinfarction (12.2% vs 3.6%, p less than 0.0001) or death (6.1% vs 1.5%, p = 0.003) was more likely to occur within 2 weeks of randomization in patients with postinfarction angina than in those without angina. Based on serial electrocardiographic data, 115 of the 246 patients with angina had transient ST-T changes and 131 did not. Comparison of the 14-day event rates in these 2 groups showed that the 115 patients with electrocardiographic evidence of ischemia had a higher frequency of reinfarction (20% vs 5.3%, p less than 0.001), more extensive damage as assessed by peak MB-creatine kinase levels (91 +/- 76 vs 37 +/- 19 IU/liter, p = 0.059 [Wilcoxon rank sum]) and a higher mortality rate (11.3% vs 1.5%, p = 0.001). Angina associated with transient ST-T changes occurred in 70 of the 289 patients in the placebo group but in only 45 of the 287 patients in the diltiazem group--a 28% reduction in cumulative life-table incidence (p = 0.0103 [2-tail, log rank]; 95% confidence interval, 9.3 to 53.8%). It is concluded that patients with early postinfarction angina are at increased risk of reinfarction and death, and angina associated with transient electrocardiographic changes identified a very high risk subset. This subset appeared to have a larger area of viable but jeopardized myocardium and benefited from prophylactic therapy with diltiazem.

Effect of a sustained release formulation of diltiazem on the development of atherosclerosis in cholesterol-fed rabbits

Cholesterol-fed rabbits were used to test potential anti-atherosclerotic effects of diltiazem, a calcium antagonist of the benzothiazepine type. Two groups of 7 rabbits each were fed standard laboratory chow supplemented with 1% cholesterol. One group received a 60 mg sustained release diltiazem capsule twice a day and the other group received a placebo capsule twice a day. A third group of control animals were fed an unmodified basal diet under conditions exactly the same as the experimental groups. All groups were studied over a period of 16 weeks. The cholesterol-fed animals showed a marked increase in plasma total cholesterol which was not significantly different for the diltiazem and placebo groups. Plasma calcium levels, blood pressure, and heart rate were also unchanged from the control animals. In the diltiazem-treated animals, 47.5 +/- 10.5% of the aortae showed atherosclerotic lesions; the value for the placebo group was 43.1 +/- 8.1%. Similar results were obtained for the coronary arteries. These results show that diltiazem treatment in the doses employed in this study had no effect on the reduction of atherosclerosis in this animal model.

Noncardiac surgery in the patient with heart disease

Optimal care of the patient with heart disease undergoing noncardiac surgery requires that the members of the surgical team, including anesthesiologist, internist-cardiologist, and surgeon, be familiar with the cardiovascular response to surgery, preoperative cardiac risk stratification, and the unique pathogenesis of cardiac complications that may occur in the perioperative period. Preoperative evaluation and computation of cardiac risk, anesthetic considerations, along with perioperative care of the patient with ischemic heart disease, valvular heart disease, congestive heart failure, arrhythmias and conduction disorders, and hypertension is discussed.

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.

Diltiazem and reinfarction in patients with non-Q-wave myocardial infarction. Results of a double-blind, randomized, multicenter trial

We performed a multicenter, double-blind, randomized study to evaluate the effect of diltiazem on reinfarction after a non-Q-wave myocardial infarction. Nine centers enrolled 576 patients: 287 received diltiazem (90 mg every six hours) and 289 received placebo. Treatment was initiated 24 to 72 hours after the onset of infarction and continued for up to 14 days. The primary end point, reinfarction, was defined as an abnormal reelevation of MB creatine kinase in plasma within 14 days. Reinfarction occurred in 27 patients in the placebo group (9.3 percent) and in 15 in the diltiazem group (5.2 percent)--a 51.2 percent reduction in cumulative life-table incidence (P = 0.0297; 90 percent confidence interval, 7 to 67 percent). Diltiazem reduced the frequency of refractory postinfarction angina (a secondary end point) by 49.7 percent (P = 0.0345; 90 percent confidence interval, 6 to 73 percent). Mortality was similar in the two groups (3.1 and 3.8 percent, respectively, in the placebo and diltiazem groups), but adverse drug reactions (most of which were mild) were more common in the diltiazem group. Nevertheless, the drug was well tolerated, despite concurrent treatment with beta-blockers in 61 percent of the patients. We conclude that diltiazem was effective in preventing early reinfarction and severe angina after non-Q-wave infarction and that it was also safe and generally well tolerated.

Immediate and short-term hemodynamic effects of diltiazem in patients with hypertension

The immediate effects of intravenous diltiazem effects and short-term (4 weeks) of the oral drug on systemic and regional hemodynamics, cardiac structure, and humoral responses were evaluated by previously reported methods in nine patients with mild-to-moderate essential hypertension and in one patient with primary aldosteronism. Diltiazem was first administered in three intravenous doses of 0.06, 0.06, and 0.12 mg/kg, respectively; patients were then treated for 4 weeks with daily doses ranging from 240 to 360 mg (average 300 mg). Intravenous diltiazem immediately reduced mean arterial pressure (from 115 +/- 3 to 96 +/- 3 mm Hg; p less than .01) through a fall in total peripheral resistance index (from 37 +/- 3 to 23 +/- 2 U/m2; p less than .01) that was associated with an increase in heart rate (from 66 +/- 2 to 77 +/- 3 beats/min; p less than .01) and cardiac index (from 3.3 +/- 0.3 to 4.3 +/- 0.4 liters/min/m2; p less than .01). These changes were not associated with changes in plasma levels of catecholamines or aldosterone or in plasma renin activity. After 4 weeks the significant decrease in mean arterial pressure persisted (104 +/- 3 mm Hg; p less than .01) and there were still no changes in the humoral substances or plasma volume. Renal blood flow index increased (from 368 +/- 52 to 462 +/- 57 ml/min/m2; p less than .01) and renal vascular resistance index decreased (from 0.37 +/- 0.06 to 0.26 +/- 0.04 U/m2; p less than .01), while splanchnic hemodynamics did not change.(ABSTRACT TRUNCATED AT 250 WORDS)

The mechanism of action of calcium antagonists relative to their clinical applications

As a class of therapeutic agents calcium antagonists have attracted increasing attention in recent years. Their major indications have been in the treatment of ischaemic myocardial syndromes, certain cardiac arrhythmias, hypertension, obstructive cardiomyopathies, and a number of lesser clinical disorders in which their role is less clearly defined. With the widening spectrum of therapeutic utility and an increasing plethora of newer agents under development, it is of importance to relate the overall pharmacodynamics of individual agents to their clinical effects. Calcium antagonists have a variable specificity for cardiac and peripheral activity. Based on such activity, it is useful to construct a classification of these compounds, new and old, into four categories. Type I agents, typified by verapamil and its congeners (tiapamil and gallopamil) and diltiazem, prolong AV nodal conduction and refractoriness with little effect on ventricular or atrial refractory period. These actions account for their direct antiarrhythmic properties. Type II agents include nifedipine and other dihydropyridines. In vivo, these agents are devoid of electrophysiologic effects in usual doses. They are potent peripheral vasodilators with some selectivity of action for different vascular beds; their overall haemodynamic effects are dominated by this peripheral vasodilatation and reflex augmentation of sympathetic reflexes. Type III agents include flunarizine and cinnarizine (piperazine derivatives), which, in vitro and in vivo, are potent dilators of peripheral vessels, with no corresponding calcium-blocking actions in the heart. Type IV agents are agents with a broader pharmacologic profile (perhexiline, lidoflazine and bepridil); they block calcium fluxes in the heart, in the peripheral vessels, or both. They may inhibit the fast channel in the heart and have other electrophysiologic actions. A clear understanding of the varied pharmacologic properties of the different classes of calcium antagonists is likely to provide a rational basis for the use of these agents in clinical therapeutics.