Portal de Periódicos da CAPES

Differentiating SVT from VT-- a Personal Viewpoint

1994; Oxford University Press; Volume: 15; Issue: suppl A Linguagem: Inglês

10.1093/eurheartj/15.suppl_a.31

1522-9645

Samuel Lévy,

Cardiac pacing and defibrillation studies

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 hypotention or angina, DC cardioversion is necessary. Diagnosis should be delayed until afier 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. The exact mechanism will most often require expert electrophysiological evaluation. If anterograde preexcitation during tachycardia is excluded, the site of origin may be recognized by a process of deduction. However, it should be stressed that symptoms associated with tachycardia are not helpful in determining the site of origin. One should look for the P waves and their relationship with QRS complexes. The presence of AV dissociation is diagnostic of ventricular tachycardia, but although specific, this criterion is not sensitive. If the P waves are absent or not identified on the surface ECG an oesophageal or right atrial recording may be useful, although it would be even better to have a His bundle recording. Capture of fusion beats are also diagnostic of ventricular tachycardia, but these are present in only a minority of cases of VT, mainly with long cycle lengths. Wellens et al. have described a number of helpful criteria, taking into account the axis, the width and the morphology of the QRS complex in the precordial leads. Using the clinical context, the step-by-step approach and the criteria dominated by AV dissociation, it is possible to distinguish SVT from VT in 90% of cases In the remaining 10% it is difficult to diagnose the site of origin from the 12 lead ECG, and the tachycardia should be treated as VT An electrophysiological study will subsequently ascertain the exact diagnosis.