Pre-Tachyarrhythmia Practice Exam

Class IC antiarrhythmics slow conduction very strongly by blocking sodium channels. In hearts with structural disease—scar tissue from a prior heart attack, cardiomyopathy, or other remodeling—this marked slowing can create or worsen reentrant circuits and provoke dangerous ventricular arrhythmias. The classic evidence comes from the CAST trial, where flecainide (and encainide) increased mortality in patients after myocardial infarction with structural damage. Propafenone is in the same Class IC category and carries similar proarrhythmic concerns in structurally abnormal hearts, so both are avoided in this setting. The other options include drugs from different classes and do not carry the same level of risk for proarrhythmia in structural heart disease. Thus the pair to avoid is flecainide and propafenone.