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Dive into the research topics where Kevin J. Alker is active.

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Featured researches published by Kevin J. Alker.


Circulation | 1992

The effects of acute and chronic cocaine use on the heart.

Robert A. Kloner; Sharon L. Hale; Kevin J. Alker; Shereif H. Rezkalla

It is clear that cocaine has cardiotoxic effects. Acute doses of cocaine suppress myocardial contractility, reduce coronary caliber and coronary blood flow, induce electrical abnormalities in the heart, and in conscious preparations increase heart rate and blood pressure. These effects will decrease myocardial oxygen supply and may increase demand (if heart rate and blood pressure rise). Thus, myocardial ischemia and/or infarction may occur, the latter leading to large areas of confluent necrosis. Increased platelet aggregability may contribute to ischemia and/or infarction. Young patients who present with acute myocardial infarction, especially without other risk factors, should be questioned regarding use of cocaine. As recently pointed out by Cregler, cocaine is a new and sometimes unrecognized risk factor for heart disease. Acute depression of LV function by cocaine may lead to the presence of a transient cardiomyopathic presentation. Chronic cocaine use can lead to the above problems as well as to acceleration of atherosclerosis. Direct toxic effects on the myocardium have been suggested, including scattered foci of myocyte necrosis (and in some but not all studies, contraction band necrosis), myocarditis, and foci of myocyte fibrosis. These abnormalities may lead to cases of cardiomyopathy. Left ventricular hypertrophy associated with chronic cocaine recently has been described. Arrhythmias and sudden death may be observed in acute or chronic use of cocaine. Miscellaneous cardiovascular abnormalities include ruptured aorta and endocarditis. Most of the cardiac toxicity with cocaine can be traced to two basic mechanisms: one is its ability to block sodium channels, leading to a local anesthetic or membrane-stabilizing effect; the second is its ability to block reuptake of catecholamines in the presynaptic neurons in the central and peripheral nervous system, resulting in increased sympathetic output and increased catecholamines. Other potential mechanisms of cocaine cardiotoxicity include a possible direct calcium effect leading to contraction of vessels and contraction bands in myocytes, hypersensitivity, and increased platelet aggregation (which may be related to increased catecholamine). The correct therapy for cocaine cardiotoxicity is not known. Calcium blockers, alpha-blockers, nitrates, and thrombolytic therapy show some promise for acute toxicity. Beta-Blockade is controversial and may worsen coronary blood flow. In patients who develop cardiomyopathy, the usual therapy for this entity is appropriate.


Circulation | 1984

Preservation of high-energy phosphates by verapamil in reperfused myocardium.

Rüdiger Lange; Joanne S. Ingwall; Sharon L. Hale; Kevin J. Alker; Eugene Braunwald; Robert A. Kloner

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.


Circulation | 1991

Nifedipine protects the heart from the acute deleterious effects of cocaine if administered before but not after cocaine.

Sharon L. Hale; Kevin J. Alker; Shereif H. Rezkalla; Andrew C. Eisenhauer; Robert A. Kloner

BackgroundWe tested the hypothesis that nifedipine, a calcium channel blocker, could ameliorate the toxic effects of cocaine on the myocardium. Methods and ResultsIn an initial protocol, anesthetized dogs were pretreated with nifedipine or saline and then administered cocaine (10 mg/kg, i.v. bolus). Coronary blood flow, heart rate, mean arterial pressure, and the first derivation of left ventricular pressure (dP/dt) were measured at baseline, 2 minutes, and 15 minutes after cocaine administration. Nifedipine pretreatment prevented the early cocaine-induced decrease in coronary blood flow and improved left ventricular dP/dt compared with untreated control animals. After cocaine, ejection fraction fell in the saline group to 37 + 3% but increased in the nifedipine group to 59 ±4% (p < 0.05). In a second protocol, vehicle or intravenous nifedipine was administered after an infusion of cocaine (10 mg/kg). In contrast to pretreatment, there was no significant improvement in left ventricular function or coronary blood flow in nifedipine-treated versus control animals. Data from the study also suggested that cocaine acts directly on the myocardium. Within seconds of cocaine bolus administration, coronary blood flow in control animals increased to a peak level 59±14% higher than before cocaine and left ventricular dP/dt decreased by 23 ± 5%, providing evidence that cocaine causes direct depression of myocardial function independent of a decrease in myocardial blood flow. ConclusionsWe conclude that nifedipine administered as a pretreatment protects against the depression of myocardial function and decrease in coronary blood flow caused by acute cocaine administration. However, when nifedipine is given after cocaine, no improvement is seen. Cocaine has a direct negative inotropic effect on the heart that is independent of a decrease in coronary blood flow.


Basic Research in Cardiology | 1984

Effects of recurrent ischemia on myocardial high energy phosphate content in canine hearts.

Rüdiger Lange; Joanne S. Ingwall; Sharon L. Hale; Kevin J. Alker; Robert A. Kloner

SummarySuccessive ischemic episodes are commonly seen in clinical and experimental cardiology. Although prolonged abnormalities of the canine myocardium have been described following a single ischemic episode, it is not known whether myocardial injury is cumulative following multiple ischemic episodes. Dogs were subjected to three 15-min left anterior descending coronary artery occlusions, each followed by 30 min of reperfusion.In vivo biopsies were obtained for biochemical analysis before and during the first occlusion and 30 min into each reperfusion period. ATP and creatine phosphate (CP) fell in the endocardium during occlusion by 24% and by 69% respectively (both p<.0001). While CP recovered during each reperfusion period, ATP remained significantly depressed. Loss of membrane-permeable purine nucleotide synthesis precursors occurred with the first reperfusion period but not with the second and third reperfusion periods. Therefore, reperfusion following one 15-min coronary occlusion is associated with severe depression of myocardial high energy phosphates; however, two additional occlusions do not cause a further decrease of these substances when intermittent reperfusion is allowed for 30 min.


Journal of the American College of Cardiology | 1986

Effect of verapamil on infarct size in dogs subjected to coronary artery occlusion with transient reperfusion

Colin A. Campbell; Robert A. Kloner; Kevin J. Alker; Eugene Braunwald

Reocclusion after successful coronary reperfusion occurs in 15 to 35% of patients receiving thrombolytic therapy for acute myocardial infarction. The present study was designed to simulate the clinical situation of reocclusion and determine whether verapamil might be effective in reducing myocardial necrosis and preserving high energy phosphates in this setting. Pentobarbital-anesthetized, open chest dogs underwent occlusion of the left anterior descending coronary artery for 2 hours followed by 1 hour of reperfusion and a further 4 hours of coronary artery occlusion. Treatment with verapamil (intravenous bolus dose of 0.2 mg/kg body weight followed by infusion of 0.56 +/- 0.14 mg/kg per h) was begun 1 hour after occlusion and infusion was continued for the remainder of the experiment. The dose of verapamil was adjusted to lower mean arterial pressure to approximately 90 mm Hg. The area at risk was determined by intraatrial injection of monastral blue dye and the area of necrosis was assessed by triphenyltetrazolium chloride staining. In vivo myocardial needle biopsy for determination of adenosine triphosphate and creatine phosphate was performed at the end of the experiment. The area of the left ventricle at risk was similar in both groups (control [n = 8], 20.2 +/- 1.6% versus verapamil-treated [n = 9], 23.1 +/- 2.9%; p = NS). The area of necrosis expressed as a percent of the area at risk was reduced in the verapamil-treated group compared with the control group (43.3 +/- 5.0% versus 63.1 +/- 6.8%, p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)


American Journal of Cardiology | 1985

Effects of transient increased afterload during experimentally induced acute myocardial infarction in dogs

Haim Hammerman; Robert A. Kloner; Kevin J. Alker; Frederick J. Schoen; Eugene Braunwald

Alterations in afterload may occur during acute myocardial infarction (AMI), but it is unknown whether such alterations cause long-term changes in the left ventricular topography or alter healing of the AMI. AMI was produced by ligation of the left anterior descending coronary artery in open-chest dogs. Eight dogs were randomized to a methoxamine group with an infusion dose of 30 micrograms/kg/min starting 1 hour after ligation for 4 hours to increase systemic systolic pressure by 40 to 50 mm Hg, and 8 were randomized to a saline control group (n = 8). Seven days later the dogs were killed and the hearts examined. The ratio of infarct wall thickness to noninfarct wall thickness was 1.13 +/- 0.03 (mean +/- standard error of the mean) in control dogs and was 0.98 +/- 0.03 in the dogs treated with methoxamine (p less than 0.005). An expansion index was determined as previously reported and expansion was considered to have occurred if this index exceeded 1.09. The expansion index was 0.98 +/- 0.06 in the control group and 1.18 +/- 0.07 in the methoxamine group (p less than 0.05). Histologic analysis suggested a lag in the healing rate in the methoxamine-treated dogs. Thus, early, brief increases in afterload cause infarct expansion and thinning and appears to slow the early healing phase of AMI in dogs.


American Journal of Cardiology | 1984

Correlates of reperfusion ventricular fibrillation in dogs

Sharon L. Hale; Rüdiger Lange; Kevin J. Alker; Robert A. Kloner

To elucidate determinants of reperfusion ventricular fibrillation (VF), regional myocardial blood flow, ATP, creatine phosphate (CP), heart rate and blood pressure were compared in 2 groups of anesthetized dogs: those that fibrillated spontaneously upon release of a 15-minute coronary artery occlusion (VF group, n = 8) and those that did not fibrillate when reperfused (No VF group, n = 27). Arterial pressure and heart rate before and during coronary artery occlusion were similar in both groups. Ischemic endo- and epicardial ATP values, measured at the end of the occlusion period, were reduced approximately 20% of nonischemic values in both groups. In contrast, CP (nmol . mg protein-1) within the ischemic zone was significantly lower in the VF group in both the epicardium (14.3 +/- 1.6 in the VF group vs 22.8 +/- 2.5 in the No VF group, p less than 0.01) and the endocardium (9.0 +/- 2.0 in the VF group vs 18.7 +/- 1.8 in the No VF group, p less than 0.01). Furthermore, epi- and endocardial regional myocardial blood flow in the center of the ischemic zone during occlusion was significantly lower in VF dogs than in No VF dogs. Epicardial flow was 0.06 +/- 0.03 ml X min-1 X g-1 in VF dogs vs 0.44 +/- 0.06 in No VF dogs (p less than 0.001) and endocardial flow was 0.03 +/- 0.02 ml X min-1 X g-1 in VF dogs vs 0.23 +/- 0.04 ml X min-1 X g-1 in No VF dogs (p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)


American Heart Journal | 1994

Acute cocaine administration induces ventricular regional wall motion and ultrastructural abnormalities in an anesthetized rabbit model

Julius M. Gardin; Nathan D. Wong; Kevin J. Alker; Sharon L. Hale; James Paynter; Margaret Knoll; Beverly Jamison; Michael Patterson; Robert A. Kloner

Whether acute doses of cocaine can induce left ventricular (LV) regional wall motion abnormalities in animals with otherwise normal coronary arteries is unknown. We studied rabbits receiving constant cocaine infusions (group I: 0.025 to 1.5 mg/kg/min, n = 10), multiple cocaine boluses (group II: 3-5 mg/kg each bolus, n = 10), or saline (group III; n = 8). In group I rabbits, short-axis LV area and diameter increased by 15% to 40% at 60 minutes compared to baseline and to controls (p < 0.01), but percentage of global area fractional shortening was unchanged. Eight rabbits in each of groups I and II, but no controls, developed LV regional wall motion abnormalities as detected by echocardiography: 15 (7 hypokinesis and 8 akinesis or dyskinesis) in the anteroseptal and 2 (hypokinesis) in the posterior LV wall. Among rabbits showing LV wall motion abnormalities, anteroseptal fractional shortening and % area reduction averaged > 20% less (p = 0.03 for area reduction) at 30 minutes versus controls. Only 50% of group I or II rabbits with LV anteroseptal wall motion abnormalities had intraventricular conduction disturbances. Radioactive microsphere flow studies (n = 6) 1 minute after a 4 mg/kg cocaine bolus revealed an equivalent decrease (10% to 20%, average) in septal and LV free wall perfusion (p value not significant). Electron microscopy revealed myocardial cell contraction band necrosis in 3 and sarcoplasmic reticular edema in 7 of 10 cocaine rabbits (unrelated to dose). We conclude that acute cocaine administration in rabbits frequently produces LV anteroseptal wall motion abnormalities even in the absence of differentially decreased perfusion or intraventricular conduction disturbances and produces ultrastructural abnormalities of the myocytes. These findings suggest a direct, nonuniform effect of cocaine on the LV myocardium.


Journal of Cardiovascular Pharmacology | 1992

Absence of hemodynamic deterioration in the presence of amlodipine following experimental myocardial infarction.

Robert A. Kloner; Sharon L. Hale; Kevin J. Alker

Summary: In general, calcium channel blockers have not been used in patients during acute myocardial infarction as they may exacerbate heart failure, possibly by neurohumoral stimulation. Amlodipine, a new dihydropyridine calcium channel blocker without neurohumoral stimulation, was tested in an experimental model of acute myocardial infarction with assessment of hemodynamics, left ventricular (LV) function, and infarct size. Anesthetized dogs were subjected to 3 h of coronary artery occlusion followed by 3 h of reperfusion. At 2 h of occlusion, they were randomized to receive either amlodipine (250 (µg/kg, n = 11) or saline (n = 11). Before treatment, all variables were similar in both groups. The diastolic pressure was unchanged following saline, but was reduced following amlodipine by 1 h after therapy (from 94 ± 5 to 71 ± 3 mm Hg, p < 0.0001 vs. saline) and for the duration of the protocol. Indices of left ventricular (LV) function did not deteriorate with amlodipine treatment compared with saline. After 3 h of reperfusion, the LV dP/dt was 1,720 ± 114 mm Hg/s in the saline group and 1,958 ± 167 mm Hg/s with amlodipine (p = ns). The area ejection fraction, assessed by echocardiography, was similar in both groups (43 ± 5%, saline; 45 ± 3%, amlodipine; p = ns), as was the LV end-diastolic pressure (8 ± 1 mm Hg, saline; 7 ± 1 mm Hg, amlodipine; p = ns). Subendocardial regional myocardial blood flow, measured by radioactive microspheres, was 0.75 ± 0.08 ml/min/g with saline and 1.34 ± 0.33 ml/min/g with amlodipine in the previously ischemic reperfused subendocardium (p = 0.1). The infarct size, expressed as a % of the risk region, was not changed by amlodipine treatment: 31 ± 6% with amlodipine vs. 41 ± 6% with saline (p = ns). We conclude that amlodipine in the setting of acute myocardial infarction and reperfusion does not cause a deterioration of LV function


American Journal of Cardiology | 1984

Morphologic and functional effects of piroxicam on myocardial scar formation after coronary occlusion in dogs

Haim Hammerman; Kevin J. Alker; Frederick J. Schoen; Robert A. Kloner

To determine whether piroxicam, a widely used, long-acting anti-inflammatory agent, causes scar thinning after acute myocardial infarction (MI), MI was produced in 16 anesthetized, open-chest dogs by ligation of the proximal left anterior descending coronary artery. The dogs were randomized into 2 groups and treated in a blinded fashion, 8 with piroxicam, 1 mg/kg i.v. at 15 minutes and at 3 hours after ligation (Group 1) and 8 with saline solution (Group 2). Two-dimensional echocardiograms were performed 7 days and 6 weeks after ligation. At 6 weeks, the dogs were killed and the hearts examined. Scar thickness was 7.1 +/- 0.3 mm in control dogs and 5.2 +/- 0.4 mm in piroxicam-treated dogs (p less than 0.01). The ratio of scar thickness to noninfarcted wall thickness was 0.87 +/- 0.03 (mean +/- standard error of the mean) in the control group, and was significantly lower (0.62 +/- 0.04) in the piroxicam-treated group (p less than 0.001). Regional function, expressed as the percent change in the area of the left ventricular cavity (% delta A) from short-axis 2-dimensional echocardiograms, was 42 +/- 3% 7 days after occlusion in the control group and was not significantly different in the treated group (34 +/- 5%). At the end of 6 weeks % delta A had improved in the piroxicam-treated group to 44 +/- 3% (p less than 0.05 compared with the value after 7 days), and was similar to % delta A of the control group at 6 weeks (43 +/- 3%). Thus, clinical doses of piroxicam administered early after MI caused moderate scar thinning, which was not associated with impairment of regional left ventricular function 6 weeks later.

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Robert A. Kloner

Huntington Medical Research Institutes

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Eugene Braunwald

Brigham and Women's Hospital

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Joanne S. Ingwall

Brigham and Women's Hospital

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Andrew C. Eisenhauer

Brigham and Women's Hospital

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Frederick J. Schoen

Brigham and Women's Hospital

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Rüdiger Lange

Technische Universität München

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Haim Hammerman

Technion – Israel Institute of Technology

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