Non-Sustained Ventricular Tachycardia - NSVT

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Ventricular tachycardia that stops by itself within 30 seconds is called non-sustained ventricular tachycardia (NSVT). Since ventricular tachycardia is at least potentially a dangerous cardiac arrhythmia, the longer it lasts the worse it tends to be. So NSVT is substantially less dangerous than ventricular tachycardia that persists longer. Still, it can cause important symptoms, and can certainly indicate increased cardiac risk.

 

What Is NSVT?

The formal definition of NSVT is: an episode of ventricular tachycardia with a heart rate of at least 120 beats per minute, lasting for at least three beats and persisting less than 30 seconds. 

Most often, NSVT either does not cause any symptoms at all, or it may just cause palpitations. Occasionally, however, NSVT can produce lightheadednessdizziness, or, more rarely, syncope (loss of consciousness).

Because NSVT usually does not produce alarming symptoms, it is typically discovered incidentally, while recording an electrocardiogram (ECG) or during some other form of cardiac monitoring.

Why Is NSVT Important?

There are three reasons NSVT is important. First, the NSVT itself may produce troublesome symptoms. Second, it may indicate the presence of previously unknown underlying heart disease. Finally, the presence of NSVT may indicate an electrical instability that threatens to become worse, perhaps leading to even more dangerous arrhythmias such as ventricular fibrillation.

How Should NSVT Be Evaluated?

If you are diagnosed with NSVT, it is particularly important for your doctor to do a cardiac evaluation to look for underlying heart disease.

The kinds of heart disease most commonly associated with NSVT are coronary artery disease (CAD) and heart failure due to dilated cardiomyopathy.

NSVT is also seen with hypertrophic cardiomyopathy and heart valve diseae (especially aortic stenosis and mitral regurgitation)..

Most of these conditions can be ruled out with an echocardiogram, but a stress thallium test may also be useful if you have risk factors for CAD.

Sometimes, NSVT is caused by cardiac conditions that are not associated with structural heart disease (that is, heart disease that does not alter the anatomy of the heart). The most common of these conditions is repetitive monomorphic ventricular tachycardia (RMVT). RMVT is an uncommon congenital disorder involving the heart's electrical system, which produces no structural changes that are detectable with an echocardiogram. Disorders like this that produce NSVT are usually diagnosed when a doctor notices particular characteristics of the arrhythmia on the ECG.

What Is the Treatment For a Patient With NSVT?

In most cases, NSVT is significant mainly as an indicator that underlying heart disease may be present. If heart disease is subsequently discovered, treatment should be directed toward that. If no underlying heart disease is found, in general the NSVT does not measurably increase the risk of cardiac arrest, and from a strictly medical standpoint it is often the case that no treatment is necessary.

Not infrequently, the underlying heart disease itself poses a significant risk for sudden death from heart arrhythmias. This is especially true for CAD and heart failure. In these conditions, the risk for cardiac arrest is related much more to the left ventricular ejection fraction than it is to the presence or absence of NSVT. To reduce that risk, when the ejection fraction is significantly reduced, an implantable defibrillator should be strongly considered.

In people who have hypertrophic cardiomyopathy, the presence of NSVT indicates a somewhat elevated risk of sudden death.

So in these individuals having NSVT would make the cardiologist lean in the direction of an implantable defibrillator, especially if there is a history of sudden death from hypertrophic cardiomyopathy in the family. 

Having NSVT does not change the prognosis of valvular heart disease, including mitral valve prolapse, and in these conditions should not be a factor in making treatment decisions.

Young people with a lot of NSVT and no structural heart disease should be referred to a cardiac electrophysiologist (a heart rhythm specialist) to be evaluated for RMVT and other congenital conditions that can produce this arrhythmia. These kinds of arrhythmias can often be treated with ablation therapy.

What About Treating the NSVT With Medication?

If it were easy and/or safe to get rid of NSVT with drug therapy, this would not be a difficult question. Unfortunately, the antiarrhythmic drugs that can be used to treat NSVT are often not very effective, and tend to produce a lot of very nasty side effects.

If drug therapy is used, most doctors will begin by using beta blockers, and then calcium channel blockers, since these drugs can occasionally reduce the symptoms, and are relatively safe. However, if real antiarrhythmic drugs are being considered, their usage should almost always be directed by a cardiac electrophysiologist. 

The bottom line is that the importance of NSVT is often not about the NSVT itself. Instead, it’s often about the fact that the NSVT can be a clue to an underlying cardiac problem that needs to be evaluated and treated.

Sources:

Marine JE, Shetty V, Chow GV, et al. Prevalence and Prognostic Significance of Exercise-induced Nonsustained Ventricular Tachycardia in Asymptomatic Volunteers: BLSA (Baltimore Longitudinal Study of Aging). J Am Coll Cardiol 2013; 62:595.

Zipes, DP, Camm, AJ, Borggrefe, M, et al. ACC/AHA/ESC 2006 Guidelines for Management of Patients With Ventricular Arrhythmias and the Prevention of Sudden Cardiac Death-Executive Summary A Report of the American College of Cardiology/American Heart Association Task Force and the European Society of Cardiology Committee for Practice Guidelines (Writing Committee to Develop Guidelines for Management of Patients With Ventricular Arrhythmias and the Prevention of Sudden Cardiac Death). J Am Coll Cardiol 2006; 48:1064.

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