Anti-arrhythmic efficacy of beta-adrenergic blockade during acute ischemia in myocardium with scar

Neurohormonal intervention to reduce sudden cardiac death in heart failure: what is the optimal pharmacologic strategy?

Sudden cardiac death (SCD) accounts for up to 50% of deaths in patients with heart failure (HF), depending on severity of symptomatic impairment and left ventricular dysfunction. Neurohormonal therapy directed at the renin-angiotensin-aldosterone system may reduce the propensity to SCD through improved hemodynamic responsiveness, reduced sympathetic tone in the myocardium and inhibition of cardiac remodelling. Angiotensin converting enzyme (ACE) inhibitors reduce overall mortality in chronic HF, the greatest benefit appearing to arises from reduction of HF progression rather than SCD. In HF patients who experience myocardial infarction (MI) reduced incidence in SCD may make a more marked contribution to the mortality benefits of ACE inhibition. Addition of beta-blocker therapy to ACE inhibition has consistently resulted in a reduction in SCD in patients with either mild-to-moderate or severe HF, and in the presence or absence of MI; the reduction in SCD is of the order of one-third versus placebo. Aldosterone blockade reduces the risk of SCD in advanced chronic heart failure (when added to ACE inhibitor) and in HF associated with acute MI (when given in addition to both ACE inhibitor and beta blocker). The evidence base suggests that for maximal SCD risk reduction in HF, beta-blocker therapy is advisable in combination with standard ACE inhibitor therapy, with addition of aldosterone blockade to this regimen for particular groups of heart failure patients.

Nonplatelet effects of aspirin during acute coronary occlusion: electrophysiologic and cation alterations in ischemic myocardium

BACKGROUND

Mortality after acute myocardial ischemia has been reduced by aspirin (ASA) but mechanisms other than the antiplatelet effect have not been established. This article evaluates an antiarrhythmic action during sympathetic stimulation in the intact anesthetized dog with and without ischemia.

METHODS AND RESULTS

The ventricular fibrillation threshold (VFT) was examined before and after epinephrine (E) in normals (group I). A VFT reduction during E was normalized after 1 week of ASA (P<.01). Regional myocardial ischemia for 1 hour resulted in similar hypoperfusion in controls of group II and after ASA. Action potential responses in isolated superfused ischemic tissue showed prolonged repolarization (APD90) in response to E, which was normalized after ASA (P<.01). To assess the antiarrhythmic role of the anion in group III, Na salicylate was given. During 1 hour of ischemia, the VF incidence was reduced and cation abnormalities diminished in ischemic myocardium compared with untreated ischemia.

CONCLUSIONS

ASA antagonizes the reduction of the VFT induced by catecholamine in normals as well as the repolarization abnormality elicited by E during acute ischemia. The salicylate anion appears to be the active component in view of the efficacy in preventing VF during the early ischemic period.

Beta blockers: evidence versus wishful thinking

Catecholamines and ischemia play an important role in the induction of ventricular tachyarrhythmias. Beta blockers antagonize the effect of catecholamines and have anti-ischemic properties. Several controlled studies performed in the early 1980s in patients after myocardial infarction have shown that beta-blocker therapy clearly decreases sudden and nonsudden cardiac death. Despite the lack of recent randomized trials, data from uncontrolled studies suggest that the beneficial effect of beta blockers is still present in the thrombolytic era. Thus, it is incomprehensible that today in the United States and in most parts of Europe, < 40% of post-myocardial infarction patients are treated with beta blockers. Even in patients with documented sustained ventricular tachycardias (VTs) or ventricular fibrillation (VF), clinical studies indicate that beta blockers improve survival. Thus, even in the thrombolytic era, beta blockers should be used as a basic therapy in patients who are at risk of sudden cardiac death.