The effect of verapamil on myocardial ultrastructure during and following release of coronary artery occlusion

Management of No-Reflow Phenomenon in the Catheterization Laboratory

At the conclusion of a primary percutaneous coronary intervention for ST-segment elevation myocardial infarction, and after the cardiologist makes certain that there is no residual stenosis following stenting, assessment of coronary flow becomes the top priority. The presence of no-reflow is a serious prognostic sign. No-reflow can result in poor healing of the infarct and adverse left ventricular remodeling, increasing the risk for major adverse cardiac events, including congestive heart failure and death. To achieve normal flow, features associated with a high incidence of no-reflow must be anticipated, and measures must be undertaken to prevent its occurrence. In this review, the authors discuss various preventive strategies for no-reflow as well as pharmacological and nonpharmacological interventions that improve coronary blood flow, such as intracoronary adenosine and nitroprusside. Nonpharmacological therapies, such as induced hypothermia, were successful in animal studies, but their effectiveness in reducing no-reflow in humans remains to be determined.

Evaluation of the protective effect of verapamil on reperfusion injury by 111In anticardiac myosin antibody in canine myocardial infarction

We quantitated the protective effect of verapamil on reperfusion injury in canine myocardial infarct using 111In-anticardiac myosin antibody and correlated to the electronmicroscopic findings. Experimental myocardial infarction was performed by one hour occlusion of the anterior descending coronary artery and followed by reperfusion. Saline or verapamil (0.6 mg/kg/hr) was started at 40 minutes after coronary artery occlusion and continued throughout the experiment. There was an inverse exponential relationship between anticardiac myosin uptake and regional coronary blood flow in both the control (r = -0.86) and the verapamil treated (r = -0.71) groups. Less uptake of 111In-anticardiac myosin antibody was observed in the verapamil treated group than in the control group of the regions where blood flow was lower than 30% of normal. In the control group, the myocardium showed signs of the typical contraction band necrosis. In the verapamil treated group, however, the myocardium contained fewer electron dense granules and mild degree of contraction bands.

Progress in cardioprotection: the role of calcium antagonists

Calcium antagonists are now widely used for the treatment of clinical hypertension and angina pectoris. They are efficacious for the treatment of vasospastic, fixed atherosclerotic and mixed angina; they reduce the incidence of silent ischemia; and they have been shown to reduce postmyocardial infarct angina. Experimental data suggest that they may have certain cardioprotective properties in cases of acute myocardial ischemia and infarction, stunned myocardium, diastolic dysfunction, left ventricular hypertrophy and atherosclerosis. Moreover, they have been shown to improve exercise performance, as well as the diastolic abnormalities in patients with hypertrophic cardiomyopathy. In animals, they may delay or reduce the extent of myocardial necrosis after coronary occlusion or coronary occlusion followed by reperfusion, and in low doses that do not alter the hemodynamic profile, they have been shown to enhance the return of ventricular function in animals with stunned myocardium. However, the early first-generation calcium antagonists (nifedipine, verapamil, diltiazem) have not been shown to reduce myocardial infarct size or to enhance survival in patients with acute myocardial infarction. There now are clinical studies that suggest that, unlike beta blockers or nitrates, nifedipine may slow the development of atherosclerotic progression in humans over a 2-year period, and it seems likely that in the 1990s there will be further expansion of the use of calcium antagonists for not only angina and hypertension but also for aspects of cardioprotection. That calcium antagonists may delay, prevent or possibly regress atherosclerotic lesions is an exciting possibility.

Effects of diltiazem on phosphate metabolism in ischemic and reperfused myocardium using phosphorus31 nuclear magnetic resonance spectroscopy in vivo

Diltiazem may provide a protective effect to ischemic and reperfused myocardium through preservation of high-energy phosphate metabolism. To test this hypothesis, rabbits had a 1.3 cm solenoidal coil placed over the myocardium to be rendered ischemic. Data were acquired with a 22 cm bore nuclear magnetic resonance spectrometer at 2.0 T. Animals were treated with diltiazem (200 micrograms/kg intravenous bolus of drug followed by a 15 micrograms/kg/min continuous intravenous infusion, n = 10) or by an equal volume of saline (n = 6). The left circumflex artery was occluded and reperfused using a reversible snare while electrocardiogram-gated spectra were accumulated. Levels of phosphocreatine were decreased during occlusion in both groups; however, this decrease was attenuated in the diltiazem treated animals compared to control (in relative percent area: 7.8 +/- 1.0 to 2.5 +/- 0.5, p less than 0.01). Levels of phosphocreatine promptly returned to baseline following reperfusion and there was no difference between the two groups. The inorganic phosphate metabolites of high-energy phosphate consumption increased with occlusion, though more so in the control group compared with the diltiazem-treated rabbits (in relative percent area: 72.5 +/- 0.9 to 55.4 +/- 1.3, p less than 0.01). With reperfusion, levels of inorganic phosphates returned toward baseline in both groups; however, the diltiazem group had a more complete recovery relative to control (in relative percent area: 38.8 +/- 2.1 to 47.6 +/- 2.7, p less than 0.05). Levels of adenosine triphosphate decreased in both groups relative to baseline; however, the amount of decrease was similar in the two groups. With reperfusion there was a definite though incomplete recovery of levels of adenosine triphosphate in the diltiazem-treated group (in relative percent area: 10.7 +/- 1.0 at occlusion, 12.3 +/- 0.4 during reperfusion, p less than 0.05), but in the control group levels of adenosine triphosphate remained depressed (in relative percent area: 9.8 +/- 0.6 at occlusion, 9.8 +/- 0.8 during reperfusion, p = NS). During ischemia there was a trend toward attenuation of intracellular acidosis in the diltiazem group; however, this trend did not reach statistical significance. These data indicate that diltiazem provides a protective effect on myocardial high-energy phosphate metabolism during regional ischemia and reperfusion in the intact animal.

Protection of rat atrial myocardium against electrical, mechanical and structural aspects of injury caused by exposure in vitro to conditions of simulated ischaemia

1. Rat isolated and superfused atria were exposed for varying periods to a solution simulating the composition of extracellular fluid during myocardial ischaemia (SI). 2. Atria subjected to SI showed a loss of systolic contractile tension, a rise in diastolic tension, a shortening of electrical refractory periods, a slowing of action potential conduction velocity and disruption of the mitochondrial ultrastructure. All these features were reversible when the muscle was returned to normal superfusate. 3. Atria pretreated with a superfusate containing a calcium channel antagonist, a calmodulin inhibitor or an intracellular calcium antagonist showed fewer features of the response to SI than did controls. 4. Atria pretreated with a superfusate containing various non-steroidal anti-inflammatory agents did not show identical responses to SI. Sulphinpyrazone protected against all features of the response to SI but ibuprofen, flurbiprofen and GP25671 (a metabolite of sulphinpyrazone) had little effect. Flufenamate, phenylbutazone and salicylate enhanced the responses to SI.

Effects of calcium channel blocker on responses of blood flow, function, arrhythmias, and extent of infarction following reperfusion in conscious baboons

Two groups of chronically instrumented, conscious baboons were studied. The effects of coronary artery occlusion for 3 hours and reperfusion for 1 week were examined on measurements of left ventricular function, ischemic-zone wall thickness, regional myocardial blood flow, arrhythmias, and extent of necrosis. The experimental group of animals (n = 7) was treated with the calcium channel blocker nisoldipine (0.1 microgram/kg/min) from 1 hour after coronary occlusion to 3 hours after coronary reperfusion. The control group (n = 6) received the vehicle (n = 4) or saline (n = 2). The effects of coronary artery occlusion and reperfusion on arterial pressure, left ventricular systolic pressure, heart rate, and left ventricular dP/dt were similar in both groups. Systolic wall thickening was reversed to paradoxical wall thinning during occlusion in both groups, and there was no recovery to systolic wall thickening over the 1-week period in either group. There were differences in regional blood flow; during coronary artery occlusion, nisoldipine increased blood flow significantly in the endocardium and epicardium of nonischemic and ischemic zones. There was a major difference in the number of arrhythmic beats per minute on reperfusion; during reperfusion, the number of arrhythmias rose markedly in the vehicle-treated group but actually fell in the nisoldipine-treated group. The size of areas at risk, infarcts, infarcts related to the area at risk, and amount of total creatine kinase (CK) and MB-CK appearing in blood were not significantly different in the two groups. Thus, in the conscious baboon, nisoldipine administered 1 hour after coronary artery occlusion exerted a marked effect in diminishing reperfusion-induced arrhythmias and improved blood flow to the ischemic zone during occlusion but did not salvage ischemic tissue.

Effects of verapamil and timolol on cellular morphometric changes in cat hearts with regional ischaemia

In twenty-one anaesthetized open chest cats the left anterior descending coronary artery (LAD) was occluded for three hours. Seven cats were pretreated with a bolus injection of Verapamil, followed by a continuous infusion of Verapamil during the ischaemic period. Seven cats were pretreated with a bolus injection of Timolol to a heart rate reduction of 20 beats/min or more and seven cats were given saline. In the latter two groups the cats received a continuous infusion of saline during the period of coronary occlusion. Biopsies were taken from the mid-myocardium of the normal, border and ischaemic zones, as defined by fluorescein staining, and verified by blood flow measurements with radiolabelled microspheres. Standard point counting techniques were used for calculations of fractional volumes of mitochondria, cytoplasm and myofibrils as well as of mitochondrial surface density and surface to volume ratio. We observed a cytoplasmic oedema in the border and ischaemic zones, that was not altered by medical treatment. In the border zone of the control cats there is greater mitochondrial swelling than in the ischaemic zone. This particular swelling is not seen in the treatment groups. However, in the normal and border zones of the verapamil group the mitochondria are smaller when compared with the respective zones in the two other groups, but increases relatively more in size in the border and ischaemic zones. Furthermore, we measured the water content, sarcomere length and per cent heavily damaged cells. These variables were not altered by Verapamil or Timolol in any zone when compared with the respective zones in the control group.

Protection by verapamil of mitochondrial glutathione equilibrium and phospholipid changes during reperfusion of ischemic canine myocardium

Pretreatment of the ischemic myocardium with verapamil protects against mitochondrial respiratory depression observed during ischemic arrest as well as during reperfusion. Since ischemic mitochondrial function appears not to be altered further by reperfusion, the purpose of this study is to identify a biochemical event affecting mitochondria that is specifically associated with reperfusion injury. It has been proposed that increased cellular Ca2+ influx and oxygen toxicity may result from reintroduction of coronary flow. Increased cytosolic Ca2+ is transmitted to the mitochondria with subsequent activation of Ca2+-dependent events, including phospholipase A2. Net production of lysophospholipids (and loss of total diacylphospholipids from the mitochondria) will proceed when reacylation mechanisms are inhibited. Since acyl-CoA:lysophospholipid acyltransferase is a sulfhydryl-sensitive enzyme and since increased activity of glutathione peroxidase shifts the levels of the mitochondrial sulfhydryl buffer, glutathione, towards oxidation, levels of glutathione and its oxidation state were measured during reperfusion in the absence or presence of verapamil pretreatment. Ischemia lowers total glutathione and reduces the redox ratio (reduced glutathione: oxidized glutathione) by 85%. Reperfusion partially returns the redox ratio to control by causing oxidized glutathione to disappear from the matrix. Verapamil maintains both the concentration and the redox potential of glutathione at control levels. Concomitant with alterations in reduced glutathione:oxidized glutathione is a decrease in ischemic mitochondrial phospholipid content. During reperfusion, phosphatidylethanolamine and its major constituent fatty acids (C 18:0 and C 20:4) are specifically lost from the mitochondrial membrane. Accompanying the significant loss of arachidonic acid during reperfusion is the decreased content of 11-OH, 12-OH, and 15-OH arachidonate. These lipid peroxidation products are not increased in ischemia. It is proposed that oxidation of matrix glutathione to glutathione disulfide during ischemia results in formation of glutathione-protein mixed disulfides and inhibition of sulfhydryl-sensitive proteins, including acyl-CoA lysophosphatide acyltransferase. Thus, metabolic events occurring within the ischemic period set the stage for prolonged dysfunction during reperfusion.

Effects of calcium antagonists on infarcting myocardium

Numerous studies have been conducted over the past 10 years on the effects of calcium antagonists on regional myocardial ischemia and infarct size. Verapamil, for example, reduced the degree of adenosine triphosphate degradation during 15 minutes of coronary occlusion followed by reperfusion in an anesthetized canine preparation. It also preserved the ultrastructural appearance of mitochondria in myocardium subjected to 1 hour of ischemia. Using an 8-hour permanent coronary artery occlusion model in which risk zone was assessed with radioactive microspheres and infarct size determined by tetrazolium staining, verapamil, administered 1 hour after occlusion, resulted in a modest decrease in infarct size. In a reperfusion model in which anesthetized dogs were subjected to 3 hours of coronary artery occlusion followed by 3 hours of reperfusion, verapamil decreased infarct size when it was administered during the period of ischemia, but failed to decrease infarct size when administered only during the reperfusion phase, i.e., after 3 hours of ischemia. Although verapamil is known to have negative inotropic effects, the newer calcium antagonist agent nisoldipine is less negatively inotropic, and might therefore be preferable in the situation of compromised hemodynamics. In a 6-hour permanent coronary artery occlusion model, nisoldipine decreased infarct size without decreasing left ventricular contractility. Most published reports support the concept that calcium antagonists decrease infarct size in models of experimental infarction. Of 4 major clinical studies, only 1 has shown that calcium antagonists are capable of reducing infarct size in man. However, in most of these studies, drug therapy commenced relatively late--4 or more hours after symptoms. In order for these drugs to demonstrate beneficial effects, the risk zone may have to be small and the degree of collateral flow adequate, the drug may have to be given very early or even before coronary occlusion (in a prophylactic fashion) and administration of the drug may have to be coupled to early coronary reperfusion.

Effect of intracoronary verapamil on infarct size in the ischemic, reperfused canine heart: critical importance of the timing of treatment

In an effort to determine whether the beneficial effect of calcium blocking drugs occurs only during ischemia or during reperfusion as well, anesthetized dogs were subjected to 3 hours of occlusion of the left anterior descending coronary artery followed by 3 hours of reperfusion. In protocol A, intracoronary verapamil (0.01 mg/kg/min) was begun 90 minutes after coronary occlusion and continued for 1 hour into the reperfusion phase (n = 6) while a control group received an infusion of saline solution (n = 6). In vivo area at risk determined by dye injection was 29 +/- 3% of the left ventricle (+/- standard error of the mean) in the control group and 30 +/- 3% in the verapamil group (difference not significant [NS]), whereas the area of necrosis determined by triphenyltetrazolium staining and expressed as a percent of area at risk was smaller in the verapamil group (29 +/- 8%) than in the control group (57 +/- 8%, p less than 0.05). In protocol B, verapamil infusion into the left anterior descending coronary was begun 5 minutes before blood reperfusion and continued throughout the 3-hour reperfusion phase. Area at risk was similar in both groups (control, 25 +/- 1%, n = 8; verapamil, 28 +/- 2%, n = 8, NS); area of necrosis expressed as a percentage of area at risk was 49 +/- 6% in the control group and 45 +/- 10% in the verapamil group (NS). Therefore, calcium blockade of ischemic myocytes delays death and enhances salvage produced by reperfusion. However, calcium blockade begun after prolonged coronary occlusion does not enhance reperfusion-induced myocardial salvage.

Preservation of high-energy phosphates by verapamil in reperfused myocardium

To determine whether verapamil prevents depletion of adenine nucleotides during and after severe myocardial ischemia, dogs were subjected to 15 min occlusions of the left anterior descending coronary artery followed by 240 min of reperfusion. One hour before occlusion, dogs were randomly assigned to a treatment group (n = 10) to which an infusion of intravenous verapamil was given until the onset of reperfusion or to an untreated saline group (n = 9). Verapamil reduced mean aortic pressure and heart rate. After 15 min of ischemia, endocardial adenosine triphosphate (ATP) level, determined by needle biopsy, decreased in the untreated group from 34.7 +/- 2.0 to 24.4 +/- 2.7 nmol X mg protein-1 (p less than .005 vs preocclusion) and in the verapamil group from 32.8 +/- 1.5 to 30.3 +/- 1.5 nmol X mg protein-1 (NS vs preocclusion). Dogs receiving verapamil had significantly higher ATP levels than untreated animals after 90 and 240 min of reperfusion. In untreated animals the sum of inosine and hypoxanthine levels increased during occlusion from very low levels to 4.6 +/- 1.1 nmol X mg protein-1 in the epicardium and to 6.8 +/- 1.5 nmol X mg protein-1 in the endocardium (p less than .05 compared with preocclusion values). In verapamil-treated dogs inosine and hypoxanthine levels increased to only 1.2 +/- 0.3 (epicardium) and 1.9 +/- 0.6 nmol X mg protein-1 (endocardium) (both NS compared with preocclusion values). After 90 min of reperfusion the sum of ATP, adenosine diphosphate, adenosine monophosphate, inosine, and hypoxanthine levels was decreased in the endocardium by 10.2 nmol X mg protein-1 in the untreated group, but no change was observed in verapamil-treated animals. We conclude that breakdown of ATP to inosine and hypoxanthine during severe ischemia is reduced by verapamil, resulting in higher ATP concentrations during occlusion and reperfusion and decreased washout of the diffusible purines inosine and hypoxanthine during reperfusion.

Blood flow to infarct and surviving myocardium: implications regarding the action of verapamil on the acutely ischemic dog heart

After coronary occlusion, myocardium originally supplied by the occluded vessel ultimately separates into infarct and surviving muscle. To clarify this process, evolution of collateral blood flow to infarct and to surviving myocardium was retrospectively analyzed after permanent left anterior descending occlusion in 24 closed chest dogs. Microspheres were injected before occlusion and 5 and 20 minutes and 4 hours after occlusion. Ten minutes after occlusion, dogs received either verapamil, 0.4 mg/kg, followed by 0.6 mg/kg per hour for 6 hours (n = 10) or equivalent saline solution (n = 14). These dogs were sacrificed 3 days later, the distribution of the occluded artery was defined by dye perfusion and infarcted myocardium was determined by triphenyltetrazolium staining of heart slices. Surviving muscle within the distribution of the occluded artery was divided into medial regions adjacent to the infarct (medial adjacent) and remote from the infarct (medial remote) and lateral regions adjacent to infarct (lateral adjacent) and remote from the infarct (lateral remote). In both control and verapamil groups, collateral flows in all regions increased significantly by 140 to 400% over 4 hours. However, the relative magnitude of collateral flow to different regions showed a consistent order: infarct less than medial adjacent less than medial remote less than lateral remote. There were no significant differences in regionally matched flows or size of infarction between control and verapamil-treated groups. Collateral perfusion begins to show distinctive patterns of change in infarct and surviving muscle very soon after coronary occlusion. Collateral flow within subdivisions of the occluded coronary artery bed increases as distance from the infarct increases, with lateral segments having higher flows than medial segments. This relation persists during the first 4 hours after occlusion. In this study, verapamil neither increased collateral flow to the occluded bed nor altered minimal flow requirements for myocardial survival.