Myocardial protection through cold cardioplegia with potassium or diltiazem. Experimental evidence that diltiazem provides better protection even when coronary flow is impaired by a critical stenosis

Resistance of the failing dystrophic hamster heart to the cardioprotective effects of diltiazem and clentiazem: evidence of coronary vascular dysfunctions

Although hypothermia and cardioplegic cardiac arrest provide effective protection during cardiac surgery, ischemia of long duration, poor preoperative myocardial function, and ventricular hypertrophy may lead to heterogeneous delivery of cardioplegic solutions, incomplete protection, and impaired postischemic recovery. Calcium antagonists are potent cardioprotective agents, but their efficacy in the presence of cold cardioplegia is still controversial, especially in heart failure, since it is often believed that failing hearts are more sensitive to their negative inotropic and chronotropic actions. However, recent data have demonstrated that the benzothiazepine-like calcium antagonists diltiazem and clentiazem, in selected dose ranges, elicit significant cardioprotection independently of intrinsic cardiodepression, thus lending support to their use in cardioprotective maneuvers involving the failing heart. We therefore evaluated the cardioprotective interaction of diltiazem, clentiazem, and cold cardioplegia in both normal and failing ischemic hearts. Hearts were excised from 200- to 225-day-old cardiomyopathic hamsters (CMHs) of the UM-X7.1 line and age-matched normal healthy controls. Ex vivo perfusion was performed at a constant pressure (140 cmH2O; 1 cmH2O = 98.1 Pa) according to the method of Langendorff. Heart rate, left ventricular developed pressure (LVDP), and coronary flow were monitored throughout the study. Global ischemia was produced for 90 min by shutting down the perfusate flow, followed by reperfusion for 30 min. Normal and failing CMH hearts were either untreated (control) or perfused at the onset of global ischemia with one of the following combinations: cold cardioplegia alone (St. Thomas' Hospital cardioplegic solution, 4 degrees C, infused for 2 min), cold cardioplegia + 10 nM diltiazem, or cold cardioplegia + 10 nM clentiazem. The cardiac and coronary dilator properties of 10 nM diltiazem and 10 nM clentiazem alone were investigated in separate groups of isolated preparations. Failing CMH hearts had lower basal LVDP (42 +/- 2 vs. 77 +/- 2 mmHg (1 mmHg = 133.3 Pa) for normal hearts, p < 0.05), while coronary flow was only slightly reduced (5.6 +/- 0.2 vs. 6.2 +/- 0.2 mL/min for normal hearts). Following 90 min global ischemia, coronary flow was increased in both groups, but the peak hyperemic response declined only in failing CMH hearts (+50 +/- 17 vs. +82 +/- 17% in normal hearts). In normal hearts, LVDP virtually recovered within 5 min of reperfusion but steadily decreased thereafter (-37 +/- 4% at 30 min). In contrast, in failing CMH hearts, LVDP significantly decreased early during reperfusion but improved over time (-19 +/- 7% at 30 min). In normal hearts, the addition of diltiazem or clentiazem to cold cardioplegic solutions resulted in improved postischemic contractile function for the duration of reperfusion (85 +/- 4% vs. only 71 +/- 6% for cardioplegia, p < 0.05). The post-ischemic increase in coronary flow was similar in all groups. In failing CMH hearts, the addition of diltiazem or clentiazem afforded no significant contractile benefit at reperfusion. In nonischemic normal hearts, infusion of diltiazem or clentiazem (10 nM) alone increased coronary flow (+6 +/- 1% for diltiazem and +24 +/- 3% for clentiazem) without significant negative inotropic or chronotropic effects. In nonischemic failing CMH hearts, infusion of diltiazem or clentiazem did not elicit cardiodepression. In contrast their coronary dilator actions reverted to vasoconstriction (diltiazem) or were significantly attenuated (clentiazem). From these experiments we can conclude that, compared with the normal heart, the failing CMH heart adapted differently to global ischemia.

Reversal of the adverse cardiovascular effects of intravenous diltiazem in anesthetized dogs

Intravenous diltiazem can be used to treat myocardial ischemia, hypertension, and supraventricular dysrhythmias, but significant adverse effects including atrioventricular block and hypotension have been reported. At the present time, there is controversy as to which drug is most effective in reversing these sequelae. This study was designed to assess the effectiveness of calcium chloride v epinephrine in reversing these side effects. The hemodynamic and electrophysiologic effects of diltiazem infusion were investigated in eight dogs anesthetized with fentanyl and nitrous oxide/oxygen. This study confirmed that diltiazem infusions in high concentrations produced predominantly atrioventricular conduction depression followed by profound hypotension. Epinephrine infusion proved to be most effective in attenuating and eliminating each of these deleterious side effects. In contrast, calcium chloride did not significantly increase heart rate or blood pressure or reverse atrioventricular block. In two instances calcium chloride produced further depression of atrioventricular conduction, leading to severe bradycardia and sinus arrest. Although calcium chloride increased left ventricular contractile force (LV dP/ dt) and cardiac index (CI), mean arterial pressure was not affected and SVR was further decreased. This study indicates that calcium chloride should not be given to reverse the side effects of diltiazem in the presence of atrioventricular conduction block or profound hypotension. Calcium chloride is indicated only when isolated myocardial depression is present and after the calcium channels have been reopened by epinephrine.

Calcium channel blockers and cardiac surgery

Calcium channel blockers have an important role in the pharmacotherapy of cardiovascular disorders. These agents act by inhibiting the slow inward current into excitable cells, exert direct negative inotropic, chronotropic, and dromotropic activity, and are potent vasodilators. These direct effects are modified by reflex autonomic stimulation and by pathologic states. Serious adverse effects of the calcium channel blockers are most frequently observed in patients with ventricular dysfunction, conduction system disease, or concomitant beta blockade. Calcium channel blockers are indicated in the treatment of angina pectoris, supraventricular arrhythmias, and hypertension. The use of these agents in patients with hypertrophic cardiomyopathy, congestive heart failure, and pulmonary hypertension is investigational. The calcium channel blockers are gaining increased importance in the management of patients undergoing cardiac surgery. Verapamil is indicated for the treatment of post-cardiac-surgical atrial flutter and fibrillation; however, the calcium antagonists are not effective as prophylaxis against postoperative supraventricular arrhythmias. Laboratory studies have shown that drug interactions exist between calcium channel blockers and inhalational anesthetics and nondepolarizing neuromuscular blocking agents; clinical studies have demonstrated that these interactions are rarely significant. Perioperative coronary spasm can be effectively treated with the calcium channel blockers. The timing of calcium antagonist withdrawal prior to surgery is controversial, but continuation of therapy until surgery is usually safe. The clinical significance of platelet function inhibition by the calcium antagonists is unknown. Protection of ischemic myocardium by calcium channel blockers has been demonstrated. Important interactions between the calcium antagonists, hypothermia, and the ionic constituents of cardioplegia require further study before the role of these agents as adjuncts to clinical cardioplegia is defined. Expanded indications and the introduction of new calcium channel blockers will result in increased use of these agents in the future.

Temperature-specific effects of adjuvant diltiazem therapy on myocardial energetics following potassium cardioplegic arrest

Adjuvant slow calcium channel blockade theoretically minimizes the calcium influx attendant to potassium-induced cardioplegic arrest, particularly if clinically acceptable levels of cardiac hypothermia are not maintained. The present study assessed the efficacy of diltiazem therapy in ameliorating perturbations of myocardial oxygen consumption that could be attributable to postischemic intracellular calcium accumulation. In 30 canine hearts, myocardial oxygen consumption was determined during incremental isovolumic pressure-volume loading before and 30 minutes after 2 hours of either 20 or 28 degrees C potassium cardioplegic arrest. The intracoronary perfusate in randomized hearts was modified by the addition of diltiazem, 150 micrograms/kg. Although systolic performance (as defined by peak developed pressure as compared with balloon volume curves) was unchanged after 20 degrees C ischemia, adjuvant diltiazem therapy prevented the 44 +/- 2% (p less than .01) decrease in peak developed pressure after 28 degrees C arrest. Moreover, the 39% augmentation of postischemic myocardial oxygen consumption at specific peak developed pressure following both 20 and 28 degrees C ischemia was attenuated with diltiazem only after the warmer ischemic interval. This difference was characterized by a larger (35 +/- 2 vs. 26 +/- 2%; p less than .025) decrease in postischemic oxygen extraction despite a comparable hyperemia. These data suggest that adjuvant diltiazem therapy during potassium-induced cardioplegic arrest preserves energy-efficient pump function only after warmer ischemia, thereby limiting the clinical application of this myoprotective regimen.

Reduction of creatine kinase and creatine kinase-MB indexes of infarct size by intravenous verapamil

In a prospective, controlled study, 29 patients were randomly allocated to receive intravenous verapamil, 5 to 10 mg/hour, for 2 days starting at a mean of 8 hours after the onset of myocardial infarction. Twenty-five patients received no specific treatment and served as control subjects. Left ventricular (LV) filling pressure in all patients was initially less than 15 mm Hg. Age, infarct localization and hemodynamic values on admission (Swan-Ganz catheter) were comparable in both groups. Maximal creatine kinase (CK) and creatine kinase-MB (CK-MB) values were markedly lower in the verapamil group than in the control group (CK 547 vs 703 U/liter, p less than 0.05; CK-MB 51 vs 68 U/liter, p less than 0.025), as was infarct weight (48 vs 65 g-Eq, p less than 0.03; CK-MB 31 vs 49 g-Eq, p less than 0.005). Arterial blood pressure was 10% lower in the verapamil group than in the control group. Systemic vascular resistance and LV filling pressure remained unchanged. Verapamil reduced myocardial infarction size by about 30% in patients without LV failure and the arterial pressure was reduced.

Promising uses of calcium-channel blocking agents

It is not surprising that calcium-channel blocking agents, which have numerous effects on various physiologic systems, have been employed for several "unapproved" uses. This manuscript reviews reports that have appeared within the last two years describing unapproved cardiovascular and noncardiovascular uses of the three available calcium-channel blocking agents. The cardiovascular uses discussed include hypertensive emergencies, pulmonary hypertension, congestive heart failure, aortic insufficiency, Raynaud's phenomenon, migraine headaches, antiplatelet effects and cardiac surgery. Areas of noncardiovascular use include muscular dystrophy, achalasia, esophageal spasm, dysmenorrhea, preterm labor, asthma, hyperuricemia, mania and depression and endocrinologic and oncologic conditions. While some of the data appear promising, other reports are conflicting and contradictory. Furthermore, because much of the information comes from poorly controlled trials or anecdotal reports, even the more promising uses must be studied further and compared with conventional therapy.

Calcium-channel blockade as an adjunct to heterogeneous delivery of cardioplegia

The clinical situation of heterogeneous cardioplegia was simulated in a canine model by temporary ligation of the circumflex coronary artery during a three-hour interval of cardioplegic arrest. Nifedipine and lidoflazine, administered prior to aortic clamping, were evaluated as adjuncts to cold (2 degrees C) crystalloid cardioplegia. Assessment was made of regional function (sonomicrometer systolic shortening) and of global function by measuring left atrial (LA) pressure at constant cardiac output (CO), aortic pressure, and heart rate, and by measuring stroke work at constant LA pressure, aortic pressure, and heart rate. Among 14 control dogs, only 7 could achieve a CO of 5 liters per minute following cardioplegic arrest. Left anterior descending coronary arterial systolic shortening recovered to only 86% of prearrest values (p less than 0.05), circumflex coronary arterial systolic shortening recovered only 28% (p less than 0.01), stroke work recovered 59% (p less than 0.01), and LA pressure was 6.7 mm Hg higher (p less than 0.01) than prior to cardioplegic arrest. Lidoflazine provided no statistically significant benefit in these animals (N = 4). However, dogs given nifedipine (N = 6) had very little change in left anterior descending coronary arterial systolic shortening (99% recovery), stroke work (93% recovery), and LA pressure (delta = 0.4 mm Hg). None of these changes was statistically significant. There was some deterioration in circumflex coronary arterial systolic shortening (56% recovery; p less than 0.05). All 6 dogs given nifedipine achieved a CO of 5 L/min following cardioplegic arrest. Clinical cardioplegia is typically heterogeneous cardioplegia. Calcium-channel blockade appears to be useful in this situation.

Clinical value of calcium antagonists in treatment of cardiovascular disorders

All calcium antagonists have the ability to decrease the symptoms and signs in some patients with ischemic heart disease and help lower the blood pressure in hypertensive persons, but in clinical doses nifedipine does not exhibit antiarrhythmic properties, although these are an important part of the action of verapamil, diltiazem and some substances with a similar chemical structure. In certain disorders beta-adrenergic blocking drugs are useful adjuncts, and under some circumstances, particularly variant angina and supraventricular arrhythmias, specific calcium antagonists are the drugs of choice. More data are needed to define the role of calcium antagonists during cardiopulmonary bypass, in the protection of the ischemic myocardium, in the management of hypertrophic cardiomyopathy and in specific cases of primary pulmonary hypertension. When used with an appropriate sense of perspective and careful observation, calcium antagonists provide useful additional means of helping selected patients suffering from particular cardiovascular diseases.

Clinical applications of slow channel blocking compounds

The slow-channel blockers constitute a structurally diverse group of drugs with varying mechanisms of action, propensities for site of greatest cardiovascular activity, and clinical efficacy. They share however the property of blocking the slow inward channel in heart muscle and of inhibiting calcium fluxes in smooth muscle. Their in vivo and in vitro actions must be distinguished. The overall actions represent a balance of direct and autonomically-mediated reflex actions interacting with the compounds' varying degrees of intrinsic non-competitive sympathetic antagonism. A knowledge of the pharmacodynamic differences between these drugs allows the physician to select the most appropriate agent for a given clinical situation. The central role of calcium in the cellular processes in the heart and the vascular system forms the basis for the utility of this class of drugs in a wide variety of cardiovascular disorders. Current intensive experimental and clinical investigations are likely to further define the roles of nifedipine, verapamil and diltiazem and their congeners in cardiovascular therapeutics. The prospect of development of newer compounds with greater selectivity of action is real. As pointed out by Braunwald (1982 a,b), with further clarification of the mechanisms of actions of these compounds and elucidation of the role of calcium fluxes throughout the body, more specific and potent agents may be developed. The apparent efficacy of the nifedipine congener nimodipine, in the treatment of cerebral vasospasm associated with subarachnoid hemorrhage (Allen et al., 1983) may simply be the first of a large number of 'specific' or targeted slow channel blockers. The development of such compounds may offer further therapeutic possibilities in the control of a variety of cardiocirculatory diseases.