Differentiating SVT from VT--a personal viewpoint.

There are two situations in which it may be difficult to differentiate supraventricular tachycardia from ventricular tachycardia via the surface 12 lead electrocardiogram: (1) when supraventricular tachycardia is conducted to the ventricles with aberration, and (2) when ventricular preexcitation is present. In both cases, the physician in faced with a tachycardia with wide (> = 0.12 s) QRS complexes. In order to avoid improper or delayed therapy the physician should keep in mind simple facts. Ventricular tachycardia is far more common than supraventricular with aberrant conduction, as it accounts for more than 80% of tachycardia with wide QRS complexes. The first step is to determine the tolerance of the tachycardia and therefore whether prompt termination is required. If the tachycardia is associated with syncope, cardiac arrest, severe hypotension or angina, DC cardioversion is necessary. Diagnosis should be delayed until after termination of the tachycardia. If tachycardia is well tolerated, the bedside diagnosis should take into account the clinical context: age of the patient, history or presence of heart disease and patient medications. In an adult patient with a history of myocardial infarction, the most likely diagnosis is ventricular tachycardia. The second step is to exclude or ascertain the presence of preexcitation. If this is suspected in young adults or children an ECG in sinus rhythm should indicate overt preexcitation. The physician should be aware of the various mechanisms of tachycardia with preexcited QRS complexes, all of which have a common denominator: anterograde conduction through the accessory pathway.(ABSTRACT TRUNCATED AT 250 WORDS)