Prophylactic antiarrhythmic therapy in acute myocardial infarction

Anion manipulation: a new antiarrhythmic approach. Action of substitution of chloride with nitrate on ischemia- and reperfusion-induced ventricular fibrillation and contractile function

The role of anions in the initiation of ischemia- and reperfusion-induced arrhythmias is unknown. We examined the antiarrhythmic effects of isotonic substitution of extracellular Cl- with NO3- by using the rat Langendorff preparation (n = 12 per group). During 30 minutes of regional ischemia, the incidence of ventricular fibrillation (VF) was reduced from 50% in hearts perfused with control solution (containing a Cl-:NO3- ratio of 100:0) to 25%, 0% (p less than 0.05), 0% (p less than 0.05), and 0% (p less than 0.05) by perfusion with solution containing Cl-:NO3- ratios of 75:25, 50:50, 25:75, and 0:100, respectively. The incidence of reperfusion-induced VF was also reduced from 58% to 25%, 8% (p less than 0.05), 8% (p less than 0.05), and 0% (p less than 0.05), respectively. Similar effects were produced in hearts reperfused after briefer durations of ischemia (10 or 15 minutes). Substitution of NO3- for Cl- also facilitated spontaneous termination of VF. Heart rate and occluded zone size were not affected by anion manipulation. Coronary flow was affected by NO3-, but changes did not correlate with arrhythmias. During ischemia, electrocardiographic changes indicative of class III activity (widening of the ventricular complex) were produced by anion substitution. These changes occurred selectively in the ischemic tissue with no significant influence before ischemia onset. However, the relation between this effect and arrhythmia reduction was not linear and a cause-effect relation is therefore unlikely. In separate groups of hearts (n = 12 per group), switching from 100:0 to 0:100 Cl-:NO3- solution or vice versa 10 seconds after coronary occlusion or just before reperfusion demonstrated that 1) protection against ischemia-induced VF resulted partly from an action in the ischemic zone and partly from an action in the nonischemic zone, and 2) protection against reperfusion-induced VF resulted principally from an action occurring during reperfusion and within the reperfused tissue. To assess whether benefit was offset by deleterious effects on contractile function in nonischemic tissue, we constructed Starling curves in isolated rate hearts. The 0:100 Cl-:NO3- solution had no effect on compliance or contractility at physiological end-diastolic pressures but reduced the slope of the peak systolic pressure-volume relation by approximately 20% as end-diastolic pressure was increased above 10 mm Hg. In conclusion, anions appear to play a hitherto unrecognized role in arrhythmogenesis in ischemia and reperfusion. Manipulation of anion homeostasis may represent a novel target for antiarrhythmic drug development.

Incidence and prognosis of secondary ventricular fibrillation in acute myocardial infarction. Evidence for a protective effect of thrombolytic therapy. GISSI Investigators

The multicenter randomized study of the Gruppo Italiano per lo Studio della Streptochinasi nell'Infarto Miocardico has provided the opportunity to analyze the impact of thrombolytic treatment on secondary ventricular fibrillation incidence in a large population of patients (11,712) with acute myocardial infarction. A reduction of about 20% in the frequency of secondary ventricular fibrillation was observed among patients allocated to thrombolytic treatment (streptokinase, 2.4% versus control, 2.9%; relative risk, 0.80; 95% confidence interval, 0.64-1.00). Streptokinase appeared to exert its protective effect specifically in patients treated within 3 hours of onset of symptoms (streptokinase, 2.6% versus control, 3.7%; relative risk, 0.71; 95% confidence interval, 0.53-0.95). This protection was essentially due to a reduced incidence of late ventricular fibrillation occurring after the first day of hospitalization. The 311 patients with secondary ventricular fibrillation represented an overall incidence of 2.7%. Such incidence was not related to infarct location or sex but was significantly more common in patients older than 65 years (3.3% versus 2.3% in younger patients). A significant excess of in-hospital deaths was found in patients with secondary ventricular fibrillation compared with those in the reference group (38% versus 24%; relative risk, 1.98; 95% confidence interval, 1.56-2.52). Conversely, secondary ventricular fibrillation was not a predictor of 1-year mortality for hospital survivors. Thrombolytic treatment with intravenous streptokinase affords protection against secondary ventricular fibrillation most probably by a limitation of infarct size. When the arrhythmia complicates the course of infarction, it is associated with an adverse short-term outcome, whereas the long-term prognosis is not influenced.

Lidocaine improves survival rate in diabetic rats submitted to acute left coronary artery ligation

This study was designed to evaluate whether the decreased early survival rate of diabetic rats submitted to acute experimental myocardial infarction can be improved by pretreatment with lidocaine. Male Wistar rats (+/- 210 g) were rendered diabetic with i.v. injection of streptozotocin (50 mg/kg), and only those presenting 1 week later a tail-blood glucose value between 250-400 mg/dl were retained in the protocol. Eleven weeks after induction of diabetes, a bolus of lidocaine (2 mg/kg) was administered i.v. about 6 min prior to ligation of the left coronary artery under ether anesthesia in control (n = 54) and diabetic (n = 48) rats; similar studies were conducted in 53 control and 55 diabetic rats without lidocaine pretreatment. Adequate occlusion was confirmed by an elevation of plasma CK-MB levels 4 h later or by a toluidine blue injection technique in rats which died earlier. Rats were followed over 48 h and comparison in the survival rate in each group established with the Fisher's exact test. Early survival rate (measured after 20 min) was significantly decreased in diabetic rats (27% vs 45%; p = 0.04). This was greatly improved by lidocaine pretreatment in diabetic (60% vs 27%; p = 0.0013), but not in control animals (50% vs 45%; p = 0.348). Furthermore, the beneficial effect of prophylactic lidocaine observed early after coronary ligation in diabetic rats was maintained throughout the period of observation (48 h). These data suggest that the prophylactic use of lidocaine is able to reverse the increased incidence of sudden death following experimental myocardial infarction in chronically diabetic rats.

Arrhythmia prophylaxis after acute myocardial infarction: a decade of controversy

Primary ventricular fibrillation continues to be a major complication of acute myocardial infarction occurring in 5-9% of patients in the coronary care unit and in a higher percentage of pre-hospital admissions. Prophylactic anti-arrhythmic drugs can prevent primary ventricular fibrillation. Lidocaine has been used for this purpose and can be administered safely and effectively in most patients by following well-established programs based on pharmacokinetic and pharmacodynamic data. The in-hospital mortality for patients with primary ventricular fibrillation exceeds that of matched controls not having the arrhythmia, and many studies show a higher 1-, 3-, and 5-year mortality. Other studies have failed to confirm these long-term results and have produced controversy among cardiologists. I continue to recommend prophylactic antiarrhythmic drugs for all patients with acute infarction, especially in those undergoing early interventional therapy.

Reduction of ventricular arrhythmias by phosphocreatine (Neoton) in patients with acute myocardial infarction

On the basis of the positive results of recent experimental research, a clinical trial of phosphocreatine (Neoton) was carried out in 60 randomized patients with acute myocardial infarction (30 patients in the Neoton group and 30 patients in the control group). Neoton was given intravenously not later than 6 hours after the onset of symptoms, in a dose of 2 gm as a bolus injection, followed by a 2-hour infusion at the rate of 4 gm/hr. Holter monitoring for 24 hours showed a significant decrease in the frequency of ventricular premature beats: in the Neoton-treated group the total number of ventricular premature beats for 24 hours was 690 +/- 179 vs 2468 +/- 737 in the control group (p less than 0.02). During this period of time the number of ventricular tachycardia paroxysms was 6 +/- 2 in the treated group and 97 +/- 35 in the control group (p less than 0.01). No side effects or complications were found after administration of phosphocreatine. It is concluded that phosphocreatine may be a potentially important antiarrhythmic drug for treatment of patients with acute myocardial infarction.

In-hospital prognosis of patients with acute myocardial infarction complicated by primary ventricular fibrillation

The in-hospital prognosis of patients with acute myocardial infarction complicated by primary ventricular fibrillation has not been satisfactorily defined. We addressed this question by studying patients with primary ventricular fibrillation derived from a large study (11,712 patients) of intravenous streptokinase in the treatment of acute myocardial infarction. Ventricular fibrillation was considered to be primary when it complicated a first myocardial infarction not associated with heart failure or shock and occurred within 48 hours of hospital admission. The 332 patients with primary ventricular fibrillation represented an overall incidence of 2.8 percent. A significant excess of in-hospital deaths was found in the patients with primary ventricular fibrillation as compared with those in the reference group (10.8 percent vs. 5.9 percent; relative risk, 1.94; 95 percent confidence interval, 1.35 to 2.78). Thrombolytic treatment with intravenous streptokinase did not afford protection against primary ventricular fibrillation. We observed that being over 65 years old had a protective effect against primary ventricular fibrillation (relative risk, 0.6; 95 percent confidence interval, 0.45 to 0.80). Our data do not indicate whether primary ventricular fibrillation is simply a marker for patients at increased risk of death or a direct cause of the increase in mortality. Our results do show, however, that primary ventricular fibrillation occurring in a coronary care unit is a negative predictor of short-term survival in patients with acute myocardial infarction.

BW A256C, a chemically novel class 1 antiarrhythmic agent. A comparison of in vitro and in vivo activity with other class 1 antiarrhythmic agents

BW A256C (5(3)-amino-6-(2,3-dichlorophenyl)-2,3(2,5)-dihydro-3(5)-imino-2 -isopropyl-1,2,4-triazine) is a novel class 1 antiarrhythmic agent designed to combine the features of potency with reduced central nervous system penetration. BW A256C reduced the maximum rate of depolarization of guinea-pig ventricle and dog Purkinje fibres in vitro (EC50, 2.2 X 10(-6) M and 1.8 X 10(-6) M, respectively), being significantly more potent than quinidine, lidocaine, disopyramide and flecainide. BW A256C was also more potent than these agents at inhibiting aconitine-induced arrhythmias in anaesthetized rats; however, unlike these agents, BW A256C was devoid of hypotensive activity at antiarrhythmic doses. In anaesthetized dogs, intravenous administration of BW A256C (0.25-1 mg kg-1) caused a dose-dependent suppression of ventricular arrhythmias that occurred on reperfusion of an occluded coronary artery. In conscious dogs, intravenous infusion (total dose, 1.5 mg kg-1) or oral administration of BW A256C (1.25-5 mg kg-1) caused dose-dependent suppression of the ventricular ectopic activity that occurred following 20-24 h of permanent coronary artery ligation. In the conscious dog, BW A256C was approximately 7 times more potent and was also longer acting than flecainide. Administration of BW A256C was not associated with any evidence of peripheral or CNS toxicity. However, plasma levels 3-4 times greater than the antiarrhythmic levels were associated with a proarrhythmic activity.