Non-Sustained Ventricular Tachycardia (NSVT)

Tachycardia is a term used to describe an abnormally fast heartbeat caused by irregular electrical impulses to the chambers of the heart. When it occurs in the lower chambers of the heart (the ventricles), it is referred to as ventricular tachycardia. Ventricular tachycardia that stops by itself within 30 seconds is called non-sustained ventricular tachycardia (or NSVT). Any ventricular tachycardia is considered, at least potentially, a dangerous cardiac arrhythmia.

Because NSVT does not persist, it is substantially less dangerous than a sustained ventricular tachycardia (SVT) and may turn out to be completely benign. Still, NSVT can cause potentially worrisome symptoms and may indicate an increased cardiac risk.

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 lightheadedness, dizziness, or, more rarely, syncope(loss of consciousness).

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

There are three reasons NSVT is important:

• Firstly, the NSVT itself may produce troublesome symptoms.
• Secondly, it may indicate the presence of previously unknown underlying heart disease.
• Thirdly, the presence of NSVT may indicate an electrical instability that may become worse, leading to even more dangerous arrhythmias such as ventricular fibrillation.

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 disease (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.

In most cases, NSVT is significant mainly as an indicator that underlying heart disease may be present. If a 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.

With that being said, the risk is related more to the reduced flow of the blood from the left ventricle (called the ejection fraction than it is to the presence of NSVT. To reduce the risk, an implantable defibrillator is strongly recommended.

Having NSVT does not change the prognosis of valvular heart disease, including mitral valve prolapse, and in these conditions, it generally 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.

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. This means that anyone who is found to have NSVT needs to have at least a baseline cardiac assessment to look for potential underlying causes.