ESSENTIALS OF DIAGNOSIS
Nonsustained: three or more consecutive QRS complexes of uniform configuration of ventricular origin at a rate of more than 100 bpm.
Sustained: lasts more than 30 seconds; requires intervention for termination.
Monomorphic ventricular tachycardia.
Polymorphic ventricular tachycardia: beat-to-beat variation in QRS configuration.
The magnitude of ventricular tachycardia (VT), one of the most common health problems encountered in clinical practice, can best be appreciated in terms of its various clinical manifestations, which include ventricular fibrillation (sudden cardiac death [SCD]), syncope or near syncope, and wide QRS tachycardia.
The most serious is its degeneration into ventricular fibrillation, producing cardiac arrest and SCD that accounts for 200,000 deaths a year. The second most serious clinical presentation is syncope. Although the overall prevalence of VT-related syncope is unclear, it is estimated to be frequent because inducible VT (via electrical stimulation) is the most common arrhythmia detected in patients with unexplained syncope. A high prevalence of SCD (> 20% incidence within the ensuing 12 months) is noted in patients with syncope from cardiovascular causes, suggesting that undiagnosed VT may be an underlying cause of sudden death in patients with unexplained syncope. The third most significant clinical manifestation of VT is a wide QRS complex tachycardia that is often hemodynamically well tolerated.
VT as a cause of morbidity and mortality is grossly underdiagnosed, potentially leading to mismanagement. This may be particularly true when the clinical presentation is unexplained syncope because no concomitant electrocardiographic (ECG) documentation is available. In the case of cardiac arrest or SCD, acute myocardial infarction rather than an arrhythmic problem is often assumed to be responsible. Most persons who have suffered sudden death have no evidence of acute myocardial necrosis, even though the episode often occurs in patients with underlying coronary artery disease. Managing the underlying coronary artery disease with no regard to treating the concomitant VT is inadequate.
If a patient with a wide complex tachycardia is hemodynamically stable, it is often erroneously assumed that the rhythm must be a supraventricular tachycardia (SVT) with aberrant conduction rather than VT. In reality, the clinical presentation of VT can be quite variable, and the rate as well as the hemodynamic tolerance in a patient depends on many factors, including concomitant coronary artery disease, heart failure, the presence of cardioactive drugs, and even the patient’s posture at the time of onset. Therefore, it is prudent not to exclude the diagnosis of VT on the basis of hemodynamic tolerance alone. Approximately 80% of the patients with sustained wide QRS tachycardia have VT. To avoid misdiagnosis, clinicians in emergency settings must become familiar with established ECG criteria (discussed in the next section) that distinguish VT from SVT with aberrant conduction. When there is uncertainty, it is best to simply assume that the rhythm ...