Ventricular Tachycardia
Ventricular tachycardia (sometimes referred to as "VT" or "V-Tach") is a potentially life-threatening rhythm disturbance. It occurs when rapid, abnormal electrical impulses arise from the ventricles. It can result in heart rates of up to 300 beats per minute! When VT occurs for only a few seconds and then stops on its own, it is called "non-sustained" VT. Non-sustained VT can cause palpitations, lightheadedness, and even fainting. "Sustained" VT is ventricular tachycardia that does not stop without medical intervention. It is most often caused by reentry within the ventricular heart muscle, and is almost always associated with underlying heart disease. Most commonly, a patient with VT has had a heart attack in the past and the tachycardia arises from the edge of the scar tissue left behind from the heart attack. The continuous rapid heart beat that results impedes the ventricles from filling properly, and so effective pumping is terribly reduced (even though the ventricles are contracting rapidly). This causes the cardiac output (and the blood pressure) to decrease dramatically, which can in some cases cause collapse and sudden cardiac death. Rarely, sustained VT will be slow enough for the heart to maintain an adequate cardiac output, and will only result in weakness, lightheadedness, and palpitations.
If a patient with VT does not collapse immediately, they can be treated emergently by paramedics or brought to an emergency room. If a person with VT remains awake, medications can be given intravenously to stop the arrhythmia. However, patients with sustained VT often go into Cardiac Arrest (a life-threatening condition of unconsciousness associated with no detectable pulse or blood pressure). In this case, electrical cardioversion (a shock delivered to the chest) is necessary to stop the abnormal electrical signals and rapidly restore a normal rhythm to save the person's life.
Intensive medical treatment is usually necessary to prevent recurrent sustained VT. Rarely, sustained VT is due to acute ischemia of the heart muscle from an occluded coronary artery (heart attack). Those patients need to have an acute intervention, usually cardiac catheterization and direct opening up the occluded artery, usually with a coronary stent to keep it open. If sustained VT occurs in the absence of an acute heart attack, most patients will undergo surgical insertion of an Implantable Cardioverter-Defibrillator or "ICD." An ICD is an electrical device (like a pacemaker) that can automatically restore a normal heart rhythm if the VT recurs. It can work by automatically shocking the heart, but more often the device is able to painlessly stimulate the ventricle rapidly ("anti-tachycardia pacing") to stop the VT quickly without a shock. ICDs have been in use since 1985 and has saved the lives of countless people who would otherwise have died from cardiac arrest. ICDs are more effective than medical therapy in nearly all cases of life-threatening ventricular arrhythmias. Invasive testing of the electrical system of the heart by a cardiac electrophysiologist (an Electrophysiologic Study) is usually performed in cases of sustained VT. In patients who have recurrent episodes of sustained VT, especially if they have received multiple ICD shocks, the short circuit in the heart muscle may be modified or eliminated completely by an invasive procedure called catheter ablation. Electrophysiologists are trained to perform catheter ablation for VT when patients have recurrent problems with this arrhythmia.
Rarely, VT can occur in the absence of underlying heart disease. This condition is often called "Idiopathic Ventricular Tachycardia." It includes several unusual electrical disturbances that, in general, are less severe than the VT that occurs in the setting of underlying heart disease. Idiopathic VT can be exercise-induced, or it may occur anytime. This arrhythmia may require medical therapy to prevent recurrent symptoms, but usually is not life-threatening. Often, idiopathic ventricular tachycardia can be cured with catheter ablation.