Ventricular tachycardias evaluation and treatment are complicated because it often occurs in life-threatening situations that dictate rapid diagnosis and treatment.
Ventricular tachycardia is defined as three or more beats of ventricular origin (lower chamber of the heart) in succession at a rate greater than 100 beats/minute. The rhythm is usually regular, but may be slightly irregular. It may be well-tolerated, but may also be associated with grave, life-threatening compromise.
Ventricular tachycardia can be referred to as sustained, lasting at least 30 seconds, or nonsustained. Sustained generally requires termination by antiarrhythmia drugs, antitachycardia pacing techniques or electrical cardioversion. Nonsustained ventricular tachycardia ia short (three beats or longer) and terminate spontaneously.
In general, ventricular tachycardia affects the diseased heart, although it has been described in patients with apparently normal hearts. It is usually associated with coronary artery disease. Patients who have ventricular tachycardia in the absence of coronary artery disease have other cardiac abnormalities, including cardiomyopathy, mitral valve prolapse, valvular heart disease, QT interval prolongation and, in an otherwise normal heart, an abnormality described as primary electrical instability. Other causes of ventricular tachycardia include sarcoidosis, beginning treatment in patients with myxedema and drugs such as digitalis, and other antiarrhythmia agents. Occasional runs of tachycardia are initiated by a change in posture, exercise, emotional excitement or vagal stimulation.
Ventricular tachycardia when sustained but stable is initially treated with medications; however, ventricular tachycardia that is unstable should be treated as a life threatening condition.