The recent Electrophysiologic Study Versus Electrocardiographic Monitoring (ESVEM) trial examined this question in patients with VT. Holter monitoring predicted efficacy in 77% of cases; PES, in only 45%. In addition Holter monitoring required only about one-half the number of hospital days. Thus PES offers no advantage over Holter monitoring in accurate evaluation of drug efficacy. The negative predictive value of PES is good (approximately 90%), but the positive predictive value is weak (25%). Therefore Holter monitoring may offer an alternative to PES in evaluation of antiarrhythmic agents.
Are antiarrhythmic drugs still classified according to their electrophysiologic effects?
The Vaughn Williams classification of antiarrhythmic agents is still used despite multiple attempts to develop more clinically oriented system, based, for example, on channels, pumps, and receptors. The Vaughn Williams system serves as a useful means of communication:
Class 1â”local membrane-stabilizing activity; blocks the fast sodium channel
Class 2â”blocks the beta-adrenergic receptors
Class 3â”prolongs duration of cardiac action potential and repolarization; blocks potassium channels
Class 4â”blocks the slow calcium channel.
This classification is based on the repolarization/depolarization curve of the action potential.
Should lidocaine be initiated in all patients with acute myocardial infarction (AMI)?
Although some data suggest that lidocaine decreases VF in patients admitted within 6 hours of onset of AMI symptoms, the untreated group had no increased risk of death, and all patients were resuscitated. Likewise, two meta-analyses in over 9,000 patients showed a reduction in primary VF but no benefit in survival, perhaps because the toxic effects of lidocaine produce conduction abnormalities and increased asystole, which negate the benefit of decreased VF.
No evidence suggests that routine or prophylactic use of lidocaine in AMI is beneficial. Use of lidocaine in AMI is recommended (1) for frequent, multiform ventricular ectopy, especially R-on-T phenomenon, or short runs of nonsustained VT; (2) after an episode of VT or VF requiring electrical conversion or after cardiopulmonary resuscitation; and (3) for ventricular ectopy so frequent or so timed that it significantly impairs hemodynamics. Treatment of left ventricular failure is essential in the treatment of arrhythmias in patients with AMI. Ischemia, which also may contribute to ectopy, should be aggressively treated. The possibility of drug-induced VT or hypokalemia should always be considered.