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What’s Up Doc column: What is ventricular tachycardia?

Dr. Jeff Hersh
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Q: I was feeling lightheaded and having palpitations, went to the ER and was admitted to the ICU. They said I had a run of ventricular tachycardia. What is this?

A: The heartbeat is controlled by electrical signals (giving rise to those “blips” on an electrocardiogram (ECG)) that tell the heart cells when they should squeeze, and coordinates the opening/closing of the heart’s valves. Normally the electrical signal begins in the sinoatrial (SA) node by the top of the heart. It then propagates through the atria (the top smaller chambers of the heart), then through the atrioventricular (AV) node and on to the ventricles (the big chambers of the heart, the right ventricle pumping blood to the lungs and the left ventricle to the entire body). This orchestrated flow of electricity (called normal sinus rhythm) is responsible for the carefully synchronized mechanics of the heart that makes it such a reliable and amazing pump.

In case something happens to the SA node, the heart has a “back-up plan” where every cell in the heart can initiate electrical signals. When an electrical signal is initiated in a cell in the ventricles it is called a premature (prior to the SA node signal) ventricular contraction (PVC). Over three-quarters of people have at least one PVC per day. If PVCs do not occur frequently and/or with multiple in a row they are usually not of clinical concern.

Three or more PVCs in a row at what would be a rate of over 100 beats per minute is called ventricular tachycardia (V-tach).

*It is important to differentiate whether the V-tach is monomorphic or polymorphic (the first being a more ‘organized’ rhythm).
*V-tach that lasts for 30 seconds or less and stops without treatment is called non-sustained V-tach (NSVT, also referred to as “a run of V-tach”).
*A run that continues for over 30 seconds, but with the heart still able to pump adequate blood during the episode, is called sustained V-tach. Sustained V-tach may degenerate into unstable V-tach.
*Unstable V-tach is when a sustained episode of V-tach occurs but during the episode, the heart is not able to pump sufficient blood; it is a life-threatening emergency.

Patients with unstable V-tach experience “sudden death.” They will have no palpable pulse and need immediate resuscitation with electrical cardioversion (a type of “shock” treatment shown on many TV shows); unstable V-tach and ventricular fibrillation (V-fib, a similar heart arrhythmia but with “quivering”/less defined electrical activity) are the most common causes of sudden cardiac death.

Symptoms of stable V-tach include palpitations, light-headedness, fainting, chest pain and/or a feeling of anxiety. Most patients with sustained V-tach will have symptoms. If their V-tach continues when they are medically evaluated they should be treated immediately, possibly using medications to “convert” them back to normal sinus rhythm or with cardioversion (as with unstable V-tach, although the sustained but stable V-tach patients will usually be sedated before “being shocked”). Many patients with NSVT have no symptoms, their run(s) of V-tach incidentally found if they happen to have it when they are on a heart monitor or have an ECG done for whatever reason.

There are many possible causes/contributing factors to V-tach. These include damage to some ventricular heart cells from some cardiac condition (such as a cardiac ischemia from a heart attack which is the most common cause, or from cardiomyopathy or other heart diseases, including some congenital conditions), certain abnormal blood electrolyte levels (such as abnormal potassium, calcium and/or magnesium levels, for whatever reason, may be causing them), toxicity from certain drugs or medications, or from other causes. Hence evaluation of a patient with V-tach will include an ECG, blood tests (to look for electrolyte levels, a possible heart attack, certain medication levels if indicated, tests for drug toxicities, other tests), tests of their heart (which will often include an echocardiogram, a heart catheterization, and/or possible evaluation in an electrophysiology lab, and/or other possible tests), and tests for any underlying conditions that may be suspected.

The different types of V-tach require different treatments:
*All unstable V-tach requires emergency resuscitation.
*Patients with V-tach require treatment for any underlying condition (treating electrolyte abnormalities and their cause, treating any underlying heart condition, etc.), healthy lifestyle reinforcement and other treatments. For example, some patients may benefit from medications to minimize the recurrence of their V-tach, such as certain anti-arrhythmic medications (although the overall efficacy of these is somewhat limited), beta-blocker medications, and/or others. Some patients may benefit from radiofrequency (RF) ablation (a specialized procedure to identify the area of the heart responsible for inappropriately initiating the ventricular electrical activity and destroying the cells responsible for it).
*Patients with sustained V-tach and survivors of resuscitation for unstable V-tach may require an automated implantable cardiac defibrillator (AICD) to automatically administer a “shock” if they have a recurrence. Patients with NSVT that have structurally normal hearts have a low risk of sudden cardiac death so they may not require an AICD.
All patients diagnosed with V-tach should be evaluated by a cardiologist and an electrophysiologist to determine the specifics of their condition, including identifying any underlying causes and contributing factors. The best treatment for each patient needs to be personalized depending on the specifics of their condition.

Jeff Hersh, Ph.D., M.D., can be reached at DrHersh@juno.com.