Diabetes mellitus and risk of idiopathic dilated cardiomyopathy. The Washington, DC Dilated Cardiomyopathy Study

An epidemiologic study was carried out to examine the possible role of diabetes mellitus and other factors in the development of idiopathic dilated cardiomyopathy. Possible associations with diabetes and other factors were examined by comparing newly diagnosed case patients (n = 129) ascertained from five Washington, DC area hospitals with neighborhood control subjects (n = 258) identified using a random-digit dialing technique. The case patients and control subjects were matched by sex and 5-year age intervals and were compared in the analysis using conditional logistic regression methods. A statistically significant association was observed between idiopathic dilated cardiomyopathy and history of diabetes (relative odds = 2.2; 95% confidence interval: 1.5 to 3.3). The association with diabetes was not explained by race, income, cigarette usage, or hypertension. A total of 28.7% (37/129) of the case patients had a reported history of diabetes, as compared with 13.6% (35/258) of the control subjects (P < 0.05). A possible interactive effect was also observed between diabetes and history of hypertension (P > 0.05). These findings support the view that diabetics, particularly those with a history of hypertension, may be at increased risk of idiopathic dilated cardiomyopathy.

Double-blind, placebo-controlled study of the efficacy of flosequinan in patients with chronic heart failure. Principal Investigators of the REFLECT Study

OBJECTIVES

The aim of this study was to assess the efficacy of flosequinan in chronic heart failure.

BACKGROUND

Flosequinan is a new vasodilator drug that acts by interfering with the inositol-triphosphate/protein kinase C pathway, an important mechanism of vasoconstriction. The drug dilates both peripheral arteries and veins, is orally active and has a long duration of action that permits once-daily dosing. Previous studies have shown that flosequinan produces sustained hemodynamic benefits in heart failure, but large scale studies evaluating its clinical efficacy have not been reported.

METHODS

One hundred ninety-three patients with chronic heart failure (New York Heart Association functional class II or III and left ventricular ejection fraction < 40%) receiving digoxin and diuretic drugs were randomly assigned (double-blind) to the addition of flosequinan (100 mg once daily, n = 93) or placebo (n = 100) for 3 months. The clinical status and exercise tolerance of each patient was evaluated at the start of the study and every 2 to 4 weeks during the trial while background therapy remained constant.

RESULTS

After 12 weeks, maximal treadmill exercise time increased by 96 s in the flosequinan group but by only 47 s in the placebo group (p = 0.022 for the difference between groups). Maximal oxygen consumption increased by 1.7 ml/kg per min in the flosequinan group (n = 17) but by only 0.6 ml/kg per min in the placebo group (n = 23), p = 0.05 between the groups. Symptomatically, 55% of patients receiving flosequinan but only 36% of patients receiving placebo benefited from treatment (p = 0.018). In addition, fewer patients treated with flosequinan had sufficiently severe worsening of heart failure to require a change in medication or withdrawal from the study (p = 0.07). By intention to treat, seven patients in the flosequinan group and two patients in the placebo group died.

CONCLUSIONS

These findings indicate that flosequinan is an effective drug for patients with chronic heart failure who remain symptomatic despite treatment with digoxin and diuretic drugs. The effect of the drug on survival remains to be determined.

Pharmacologic management of ischemic heart disease with beta-blockers and calcium channel blockers

In myocardial ischemia beta-blockers reduce myocardial oxygen demand, improve flow toward ischemic regions, and have mild antiplatelet and antiarrhythmic effects. These agents are effective in chronic stable angina and unstable angina. In chronic myocardial ischemia, the beta-blockers timolol, metoprolol, atenolol, and propranolol have cardioprotective effects, reducing overall mortality and the incidence of recurrent myocardial infarction. Calcium channel blockers, which reduce myocardial oxygen demand and improve oxygen supply, are effective in the treatment of chronic stable angina, vasospastic angina, and unstable angina. Although calcium channel blockers generally have no effect or adverse effects when used as primary therapy for acute myocardial infarction, diltiazem (when used concomitantly with nitrates or beta-blockers) has been shown to reduce the incidence of reinfarction in patients after non-Q wave myocardial infarction.

Liposomal amphotericin B for treatment of pulmonary aspergillosis in a heart transplant patient

Pulmonary aspergillosis developed in a 52-year-old man 2 months after heart transplantation for ischemic cardiomyopathy. Conventional amphotericin B therapy caused marked deterioration of his already compromised kidney function after only 10% of the projected total dose. Conversion to liposomal encapsulated amphotericin B was associated with reversal of the kidney dysfunction and clearing of the pulmonary infiltrate. It is now 16 months since completion of therapy, and there is no evidence of recurrent infection.

Reduction in coronary heart disease: clinical and anatomical considerations

Coronary artery bypass surgery, percutaneous transluminal coronary angioplasty and thrombolytic therapy in acute myocardial infarction have relieved symptoms, preserved myocardium, and prolonged life but have not modified the progression of atherosclerosis in the coronary arteries. In the last 10 years, however, progress has been made in establishing the cholesterol-atherogenesis hypothesis. Epidemiologic studies have demonstrated that the higher the total plasma cholesterol and low density lipoprotein cholesterol (LDL-C), the greater the risk that coronary artery disease will develop. Recently, clinical trials including the Coronary Drug Project, the Lipid Research Clinics Coronary Primary Prevention Trial (LRC-CPPT), and the Helsinki Heart Study provided evidence that lowering cholesterol reduces the frequency of fatal and nonfatal coronary events. In addition, the National Heart, Lung, and Blood Institute (NHLBI) Type II Coronary Intervention Study and the Cholesterol Lowering Atherosclerosis Study demonstrated that lowering of cholesterol was associated with a decreased incidence of progression of coronary disease, as well as with the potential for reduction in the atherosclerotic plaque. Beneficial effects of diet and lifestyle changes also have an important effect on atherosclerosis. The impact of lowering cholesterol has been limited primarily by pharmacologic programs which lower cholesterol only 10-20% and are associated with a high incidence of intolerable side effects. With the recent introduction of the HmG co-A reductase inhibitors and their more profound effect on serum lipids, it may be possible to further promote plaque regression. The future of all these interventions, however, must still be assessed by overall mortality; studies to date have demonstrated beneficial effects on cardiovascular mortality but age-adjusted total mortality has remained unchanged. Future management of patients with acute and chronic coronary artery disease will involve a collaboration of cardiologists, endocrinologists, and epidemiologists to coordinate screening, recognition, and treatment of this disease.

Calcium antagonists in acute myocardial infarction

Calcium antagonists have proved effective in stable angina, unstable angina and vasospastic angina. However, despite a strong theoretical rationale for their use and promising experimental data, these agents have not reduced infarct size in acute myocardial infarction (AMI) in the large clinical trials performed to date. Their role as adjunctive therapy in combination with reperfusion needs to be examined. Diltiazem has been demonstrated to reduce angina and reinfarction in the 2-week period after AMI in patients receiving multidrug therapy. Results of the single large trial of a calcium antagonist (verapamil) for secondary prevention after AMI were negative; however, several well-designed studies are currently ongoing.

Changes in drug prescribing patterns related to commercial company funding of continuing medical education

In order to determine the impact of commercial company funding of continuing medical education (CME) courses, a survey was undertaken. Drug prescribing rates for drugs related to course content were determined by self-report survey of physician attendees (374 in number) for three different CME courses. The survey was performed immediately before and six months after the courses. A single, though different, drug company provided the majority of the funding for each course. Courses I and III were related to calcium channel blockers and Course II to beta blockers. The return rate before Course I was 73.0 percent; after, 54.0 percent (unmatched). The return rate for Course II was 49.4 percent before and 42.9 percent after (unmatched). There were 121 (61.4%) matched returns for Course III. While the rates for prescribing some of the related drugs increased after the courses, overall the sponsoring drug company's products were favored. Although physicians attending CME and accredited sponsors of CME need to be aware of this potential influence, the final burden of adequate evaluation of drugs remains with the physician prescriber. Further studies should be done to substantiate the findings and elucidate the mechanism(s) of the increase in sponsoring company's drug prescriptions.

Late angiographic follow-up after successful coronary arterial thrombolysis and angioplasty during acute myocardial infarction

Emergency percutaneous transluminal coronary angioplasty (PTCA) is accepted as an important reperfusion intervention for acute myocardial infarction (AMI). Although its primary success rate is well documented, the frequency of restenosis after this procedure is unclear. The frequency of restenosis was determined in patients undergoing emergency PTCA at least 6 months after PTCA was performed during AMI. Of 66 consecutive patients undergoing emergency PTCA, 25 had a second, elective catheterization at an average of 22 months after AMI and 6 underwent repeat catheterization because of recurrent chest pain. Restenosis of the PTCA site was found in 10 of the 31 patients (32%) restudied. Also, 14 (45%) of these 31 patients showed progression of narrowing in the non-infarct-related coronary arteries. In summary, patients in whom AMI is treated by PTCA are at risk for restenosis and for progressive narrowing of the non-infarct artery.

Metabolic support during coronary reperfusion

The limitation of infarct size by thrombolysis could potentially be improved by an early metabolic intervention. We therefore evaluated the effects of a 48-hour infusion of glucose-insulin-potassium (GIK) in patients with anterior infarctions. Seventeen patients were randomized to receive intravenous GIK (n = 10) or placebo (n = 7). All patients additionally received streptokinase. Changes in left ventricular function were assessed by comparing the global ejection fractions and the regional infarct area ejection fractions of the first ventriculogram with the 10-day second ventriculogram. There was a significantly greater improvement in the global ejection fraction of patients receiving GIK (increases 0.07 +/- 0.04) than in those randomized to placebo (decreases 0.08 +/- 0.04) (p less than 0.02). There was also a much greater improvement in the area ejection fractions of the group receiving GIK vs the group receiving placebo in the anterolateral (increases 0.24 +/- 0.07 vs decreases 0.02 +/- 0.04 [p less than 0.02]) and diaphragmatic (increases 0.08 +/- 0.08 vs decreases 0.17 +/- 0.05 [p less than 0.005]) segments. Thus in patients with anterior infarctions receiving streptokinase, GIK improves ventricular function and reduces the size of the segmental wall motion abnormality.

Assessment of residual coronary arterial stenosis after thrombolytic therapy during acute myocardial infarction

Maximal myocardial salvage appears to be related to the severity of residual coronary arterial stenosis after thrombolysis. The degree of residual infarct vessel stenosis was assessed in 119 consecutive patients with patent arteries who received streptokinase during acute myocardial infarction. After administration of streptokinase, 99 of 119 patients (83%) had a residual stenosis 70% or more in diameter. Assuming that a residual diameter stenosis of at least 70% is flow limiting, the feasibility for percutaneous transluminal coronary angioplasty (PTCA) was determined by the following criteria: length less than 10 mm, no significant distal narrowing or left main stenosis, and an adequate-sized distal artery. In 81 of 99 patients (82%), arterial anatomy was suitable for PTCA. Thus, after therapy with streptokinase for acute myocardial infarction, most patients have a significant infarct arterial residual stenosis and are candidates for PTCA.

Determinants of cardiac failure after coronary bypass surgery within 30 days of acute myocardial infarction

Timing of coronary artery bypass grafting after acute myocardial infarction (MI) is controversial, especially if myocardial function is depressed. Early coronary artery bypass grafting may result in reperfusion injury causing cardiac failure. Delay, however, may risk a second ischemic event. This study was performed to determine if four preoperative factors--time after MI, ejection fraction, ischemia (need for intravenous administration of nitroglycerin), and failure (need for inotropic support)--independently predict postoperative cardiac failure. Postoperative failure was defined as the need for inotropic support or intraaortic balloon pumping. The study group consisted of 145 patients who underwent isolated coronary artery bypass grafting between January, 1980, and July, 1985, within 4 weeks of an acute MI. Postoperatively 38 patients (26%) had cardiac failure. Five patients, all of whom had postoperative cardiac failure, died. Univariate and stepwise logistic regression analyses showed preoperative failure (p = .0001), ejection fraction less than 45% (p = .002), and preoperative ischemia (p = .02) were predictors of postoperative cardiac failure. Time after MI was not found to be an independent predictor (p = .96). We conclude that if ischemia or threatening coronary anatomy is present early after MI and clinical improvement is not occurring, operative intervention should be strongly considered at that time, as it does not appear that delay itself reduces the risk of cardiac failure and may risk a second ischemic event.

Ventricular arrhythmias during reperfusion

Accelerated idioventricular rhythm has been used as a marker for coronary reperfusion. The incidence of accelerated idioventricular rhythm and ventricular tachycardia was evaluated in 52 consecutive patients undergoing thrombolysis with intracoronary streptokinase during acute myocardial infarction. Complete 12-hour Holter recordings during and after intracoronary streptokinase were obtained in 39 patients. Reperfusion was documented in 17 patients (44%), no reperfusion in 14 (36%), and subtotal occlusion in eight (20%). Accelerated idioventricular rhythm occurred in 83%, 57%, and 63% of patients by group, respectively (p greater than 0.05). Ventricular tachycardia occurred in 100%, 71%, and 100% of patients by group, respectively (p less than 0.05). These data demonstrate that accelerated idioventricular rhythm is not specific for reperfusion and cannot be used as a marker for this event, and that ventricular tachycardia is more common with reperfusion and subtotal occlusion.

The assessment of contractile reserve after thrombolytic therapy for acute myocardial infarction

"Stunned" myocardium prevents the assessment of myocardial salvage after streptokinase. In order to unmask "stunning," we sought to evaluate left ventricular inotropic contractile reserve of patients after streptokinase. Radionuclide ventriculograms were obtained in 75 consecutive patients 2 weeks after myocardial infarction, at rest and during intravenous isoproterenol infusion. Resting and isoproterenol-stressed ejection fractions were compared in the patent and closed-infarct vessel groups. Although there was no difference in the resting ejection fractions between the patent group (0.48 +/- 0.02) and the closed group (0.48 +/- 0.02), isoproterenol increased the ejection fractions in the patent group (increase 0.14 +/- 0.01) significantly more than in the closed group (increase 0.06 +/- 0.01) (p less than 0.0001). Thus, despite identical resting ventricular function, the greater inotropic contractile reserve in the patent infarct vessel group suggests that restoration of blood flow in acute myocardial infarction salvages myocardium.

Noninvasive detection of coronary artery patency using continuous ST-segment monitoring

Continuous ST-segment Holter recordings were analyzed from 46 patients with acute myocardial infarction (AMI) receiving intracoronary streptokinase (SK) during the first 48 hours of hospitalization. Changes in ST deviation and the time periods of these changes were quantitated and correlated with angiographic evidence of reperfusion. Thirty-six patients had total occlusion of the infarct vessel and 10 had subtotal occlusion. Of the 36 vessels that were totally occluded, 19 were reperfused and 17 were not. In patients in whom reperfusion was successful, an ST steady state was achieved 55 +/- 32 minutes after SK administration. In patients in whom it was not successful, a steady state was achieved in 219 +/- 141 minutes (p less than 0.001). Achievement of steady state within 100 minutes after SK reperfusion indicated successful reperfusion with 89% sensitivity and 82% specificity. All patients with subtotal occlusion achieved an ST steady state before SK infusion. No patient with total occlusion achieved a steady state before SK. Achievement of ST steady state before SK infusion was 100% sensitive and 100% specific for subtotal occlusion at initial angiography. Continuous, quantitative ST-segment analysis is a sensitive and specific noninvasive technique for following coronary artery patency during AMI.

Inhibition of a physiologic pacing system due to its anti-pacemaker-mediated tachycardia mode

Newer programmable DDD pacemakers prevent pacemaker-mediated tachycardia by automatic extension of the atrial refractory period after a detected premature ventricular contraction. We present an example in which the automatic extension of the atrial refractory period resulted in pacemaker inhibition, which should not automatically be assumed to represent pacemaker malfunction. A careful understanding of pacemaker timing intervals may allow for identification and correction of this problem.

Ischemia during angioplasty after streptokinase: a marker of myocardial salvage

Although thrombolytic therapy can result in lysis of a coronary artery thrombus, salvage of myocardium as measured by enzymatic, electrocardiographic and regional wall motion evaluation has not been clearly documented. Many patients after successful reperfusion continue to experience recurrent chest pain. The presence of recurrent chest pain suggests salvaged myocardium. Controlled reocclusion of the infarct vessel with the use of coronary angioplasty may support evidence for myocardial salvage. Experience in 50 patients who underwent angioplasty was reviewed retrospectively. Sixteen of the 50 patients had electrocardiographic or clinical evidence of ischemia at the time of balloon inflation. Prospectively, all patients who underwent angioplasty after they had received streptokinase were evaluated, and 5 of 5 patients had chest pain and ST-segment elevation during balloon inflation. The development of ischemic changes during balloon catheter inflation suggests the presence of persistently viable, salvaged myocardium after successful thrombolysis.

Nifedipine in acute myocardial infarction

Preliminary experimental and clinical data suggest that nifedipine can abort early acute myocardial infarction (AMI) or decrease infarct size by reversal of coronary artery spasm, improved coronary flow to the ischemic zone, reduction in myocardial oxygen demand or protection of ischemic cells. The first large clinical trial testing the ability of nifedipine to reduce infarct size, the Nifedipine Angina Myocardial Infarction Study, was recently reported. Nifedipine treatment failed to prevent progression of threatened infarction to AMI or to reduce infarct size in patients with AMI. The study suggested an increased early mortality rate in patients with AMI treated with nifedipine, but this finding should be interpreted with caution pending the results of similar trials now in progress.

Nifedipine therapy for patients with threatened and acute myocardial infarction: a randomized, double-blind, placebo-controlled comparison

Preliminary clinical and laboratory observations suggest that nifedipine might prevent progression of threatened myocardial infarction by reversing coronary spasm or might limit necrosis during the course of acute myocardial infarction. We screened 3143 patients with ischemic pain of greater than 45 min duration and randomly assigned 105 eligible patients with threatened myocardial infarction and 66 with acute myocardial infarction to receive nifedipine (20 mg orally every 4 hr for 14 days) or placebo plus standard care. Treatment was started 4.6 +/- 0.1 hr after the onset of pain. Infarct size index was calculated by the MB-creatine kinase (CK) method and expressed as CK-geq/m2 +/- SE. The incidence of progression to infarction among patients with threatened myocardial infarction was not significantly altered by nifedipine (36 of 48 [75%] for placebo-treated and 43 of 57 [75%] for nifedipine-treated patients). Furthermore, infarct size index was similar among placebo- and nifedipine-treated patients (16.9 +/- 1.5 MB-CK-geq/m2, n = 65, and 17.0 +/- 1.5 MB-CK-geq/m2, n = 68, respectively) with threatened myocardial infarction who exhibited infarction and for those with acute myocardial infarction. Among the 171 eligible patients randomly assigned to drug or placebo, 6 month mortality did not differ significantly (8.5% for placebo vs 10.1% for nifedipine, NS), but mortality in the 2 weeks after randomization was significantly higher for nifedipine-treated patients (0% for placebo compared with 7.9% for nifedipine, p = .018).(ABSTRACT TRUNCATED AT 250 WORDS)

Nifedipine and conventional therapy for unstable angina pectoris: a randomized, double-blind comparison

To characterize the potential of nifedipine in the therapy of unstable angina pectoris we implemented a blinded, randomly assigned, titrated schedule of conventional therapy (propranolol, if not contraindicated, and isosorbide dinitrate) or nifedipine for 14 days in 126 patients hospitalized in a coronary care unit for ischemic chest pain of less than 45 min duration. There were no significant differences between conventionally and nifedipine-treated patients with regard to (1) the time to relief of pain as judged by life table analysis, (2) the decrease in anginal attacks per 24 hr from day 0 to day 2 (-2.5 +/- 0.4 for conventional therapy vs; -2.8 +/- 0.3 for nifedipine), (3) the decrease in the number of nitroglycerin tablets consumed per 24 hr (-2.0 +/- 0.5 for conventional vs -2.1 +/- 0.4 for nifedipine therapy), (4) the percentage of patients requiring morphine on day 1 (13% for conventional vs 21% for nifedipine therapy), or (5) the percentage of patients who developed infarction (14% in both groups). Among the 27 patients who did not respond to initial conventional (n = 13) or nifedipine therapy (n = 14), five in each group became pain free when the opposite therapy (either nifedipine or conventional therapy) was added. In the subgroup of 67 patients who were receiving propranolol before randomization, addition of nifedipine was more effective in controlling pain than was an increase in conventional therapy (p = .026). In the subgroup of 59 patients not receiving prior propranolol, initiation of conventional therapy produced more rapid pain relief than initiation of nifedipine therapy alone (p less than .001), which tended to increase heart rate. Thus, for the study population as a whole therapy with nifedipine alone was equivalent to conventional therapy for unstable angina, although this overall equivalence may result from a combination of superiority of nifedipine therapy in patients previously receiving beta-blocker therapy and superiority of beta-blocker therapy in patients not previously receiving beta-blockers.

Comparative vagolytic effects of procainamide and N-acetylprocainamide in the dog

Procainamide exerts vagolytic effects which are deleterious in clinical therapy for supraventricular arrhythmias. The purpose of the present study was to determine if N-acetylprocainamide (NAPA), an active metabolite of procainamide which has been proposed as an effective and less toxic alternative, would exert an equivalent degree of vagal blockade. In anesthetized dogs, the right cervical vagus nerve was electrically stimulated at supramaximal voltage using frequencies from 0.5 to 20 Hz to slow the sinus rate. The ability of NAPA and procainamide to block this response was tested with infusion of equimolar doses (1.0 and 0.87 mg/kg/min i.v., respectively) continuously over a period of 40-78 min. Both drugs exerted statistically significant vagolytic effects at the higher frequencies of stimulation. Although the vagolytic effect appeared to be more pronounced with procainamide, this could not be demonstrated by statistical analysis of the data.

Coronary spasm produced by picrotoxin in cats

Picrotoxin (2 mg/kg i.v.) was administered to 6 vagotomized chloralose-anesthetized cats while monitoring coronary blood flow (electromagnetic flow probe), blood pressure and ECG. Coronary constriction occurred in each animal as measured by an increase in coronary vascular resistance (CVR) (mean = 25.2 +/- 7.5%, P less than 0.05) followed by ST segment elevation (0.30 +/- 0.06 mV, P less than 0.05). Pretreatment with phentolamine prevented the increase in CVR and the elevation in ST segment. These results demonstrate that picrotoxin produces alpha-receptor mediated coronary spasm.

The natural history of aortic stenosis in adults

Accepted clinical views about the natural history of aortic stenosis are based on surprisingly little hemodynamically documented data, and further information in unlikely to be forthcoming in the modern surgical era. Therefore, follow-up data were obtained on 42 adult patients with isolated valvular aortic stenosis catheterized at Georgetown University Hospital who did not undergo early valve replacement. Of 32 symptomatic patients, 23 had moderate or severe stenosis and were followed until death or for an average of 64.4 months after catheterization. The prognosis was more ominous than previously reported. Mortality rates from onset of symptoms were 26% at one year, 48% at two years, and 57% at three years. Fifty-six % of deaths occurred suddenly, within hours of new symptoms. Asymptomatic patients with moderate or severe stenosis did not share the high mortality rate of those with symptoms. Eight such patients were followed for an average of 69.8 months, and none died.

Superiority of practolol versus propranolol in protection against ventricular fibrillation induced by coronary occlusion

The ability of practolol and propranolol of prevent ventricular fibrillation in experimental anterior myocardial infarction was compared in dogs subjected to ligation of the left anterior descending and first septal coronary arteries. This procedure, which causes ventricular fibrillation in 90 percent of animals within 30 minutes, was performed in control dogs and in dogs pretreated with propranolol (0.5 mg/kg body weight) or with practolol (1.5 to 2.5 mg/kg). These doses produced nearly equivalent shifts in isoproterenol-induced chronotropic dose-response curves, indicating equivalent degrees of beta adrenergic blockade. In 21 dogs with confirmed ligation, cardiogenic shock did not develop. Six of seven control dogs died with ventricular fibrillation. Six of seven dogs pretreated with propranolol also had fibrillation, whereas only one of the seven dogs pretreated with practolol manifested ventricular fibrillation during the 45 minute postligation observation period. Practolol afforded significant protection compared with no treatment or treatment with propranolol (P less than 0.05).

Coronary occlusion site as a determinant of the cardiac rhythm effects of atropine and vagotomy

We have previously demonstrated that atropine pretreatment increases the incidence of fatal ventricular arrhythmias induced by left anterior descending coronary artery (LAD) occlusion. The purpose of the present study was to determine whether the deleterious effect of atropine also applies to arrhythmias induced by right coronary artery (RCA) occlsusion. Occlusion of the RCA resulted in ventricular arrhythmias in all 20 animals studied, followed by ventricular fibrillation in three animals (15 per cent). Right coronary occlusion also resulted in bradycardia (-30.3 +/- 5.1 beats per minute) and hypotension (-23.1 +/- 4.9 mm. Hg). Pretreatment of 15 animals with atropine caused no significant increase in the incidence of ventricular fibrillation (i.e., 20 per cent). In addition, atropine pretreatment had no effect on the fall in heart rate and hypotension associated with RCA ligation. Sectioning the vagus nerves produced results similar to atropine pretreatment with the exception that a significant portion of the bradycardia was prevented. These results indicate that the increase in deaths after atropine observed in animals undergoing experimental LAD occlusion in not demonstrated with RCA occlusion. The results also indicate that the potential for deleterious effects of atropine in acute infarction might depend on the anatomic location of the involved myocardium.

Site of myocardial infarction. A determinant of the cardiovascular changes induced in the cat by coronary occlusion

The influence of site of acute myocardial infarction on heart rate, blood pressure, cardiac output, total peripheral resistance (TPR), cardiac rhythm, and mortality was determined in 58 anesthetized cats by occlusion of either the left anterior descending (LAD), left circumflex or right coronary artery. LAD occlusion resulted in immediate decrease in cardiac output, heart rate, and blood pressure, an increase in TPR, and cardiac rhythm changes including premature ventricular beats, ventricular tachycardia, and occasionally ventricular fibrillation. The decrease in cardiac output and increase in TPR persisted in the cats surviving a ventricular arrhythmia. In contrast, right coronary occlusion resulted in a considerably smaller decrease in cardiac output. TPR did not increase, atrioventricular condition disturbances were common, and sinus bradycardia and hypotension persisted in the cats recovering from an arrhythmia. Left circumflex ligation resulted in cardiovascular changes intermediate between those produced by occlusion of the LAD or the right coronary artery. Mortality was similar in each of the three groups. We studied the coronary artery anatomy in 12 cats. In 10, the blood supply to the sinus node was from the right coronary artery and in 2, from the left circumflex coronary artery. The atrioventricular node artery arose from the right in 9 cats, and from the left circumflex in 3. The right coronary artery was dominant in 9 cats and the left in 3. In conclusion, the site of experimental coronary occlusion in cats is a major determinant of the hemodynamic and cardiac rhythm changes occurring after acute myocardial infarction. The cardiovascular responses evoked by ligation are related in part to the anatomical distribution of the occluded artery.

Role of the nervous system in experimentally induced arrhythmias

The purpose of our studies was to examine the role of the nervous system in arrhythmias produced by digitalis overdose and coronary artery occlusion in the cat. This was done by observing the effect of these arrhythmogenic procedures on cardiac efferent neural activity and then determining whether any observed alteration in neural activity contributed to the cardiac rhythm disturbances evoked by digitalis and coronary artery occlusion. Our data indicate that both procedures used to evoke arrhythmias activate each division of the autonomic nervous system. Activation of the sympathetic nervous system resulted in a deleterious effect on cardiac rhythm whereas activation of the parasympathetic nervous system, in general, resulted in a beneficial effect on cardiac rhythm. With coronary occlusion, the role exerted by the nervous system depended on the anatomic location of the involved myocardium. Studies directed at elucidating the mechanisms whereby the nervous system caused cardiac rhythm disturbances indicated that there may be an important difference between the antiarrhythmic efficacy of beta-adrenergic blockade and bilateral stellate ganglionectomy. The latter procedure proved to be a more effective way of removing deleterious sympathetic neural effects on the heart. In conclusion, our findings suggest that the development of new drugs for treating arrhythmias resulting from digitalis and coronary occlusion should be aimed at finding drugs that act to either depress central sympathetic outflow or enhance parasympathetic effects on the ventricle.

Failure of beta-adrenergic receptor blockade to prevent arrhythmias induced by sympathetic nerve stimulation

Cardiac arrhythmias produced by electrical stimulation of the ventrolateral cardiac sympathetic nerve in dogs were not blocked by the combined administration of propranolol and practolol in amounts that completely blocked cardiac beta-adrenergic receptors. Blockade of cardiac alpha-adrenergic receptors, as well as cardiac cholinergic receptors, also had no influence on the arrhythmias. These results suggest that the adrenergic neuroeffector junction is fundamentally different from any hitherto described, differing perhaps in the neurotransmitter involved or in the nature of the receptor.