Ventricular arrhythmias can be either deadly or innocuous, depending on their type and persistence and whether the person's heart function is already compromised. The most common type of ventricular arrhythmia in both healthy and diseased individuals is the ventricular premature beat. The incidence of this condition increases with age.
A premature beat occurs when there is an extra contraction of the ventricles midway between two normal contractions or shortly after a normal contraction. In the latter case, they can delay the next heartbeat prompted by the natural pacemaker.
Ventricular premature beats often do not prompt symptoms, but they may be perceived as skipped beats or fluttering or thumping in the chest known as heart palpitations, and they may cause dizziness or weakness. Probably everyone develops ventricular premature beats at one time or another, according to the American Heart Association. This type of arrhythmia is commonly encountered in cardiac monitoring, even in healthy individuals.
Ventricular premature beats are not by themselves harmful, but they can be a precursor to two more serious types of ventricular arrhythmias: ventricular tachycardia and ventricular fibrillation.
Ventricular tachycardia is rapid heartbeat that arises from the lower chambers of the heart and is usually much faster than the normal heart rate of 60 to 100 times per minute. Ventricular tachycardia is considered "nonsustained" if it lasts only seconds or "sustained" if it lasts for more than 30 seconds. Like ventricular premature beats, ventricular tachycardias commonly occur in healthy people, particularly those who are frightened or excited.
Ventricular tachycardias prevent ventricles from properly filling with blood. This reduces pumping efficiency, which can be made worse if there are underlying heart muscle abnormalities.
Nonsustained ventricular tachycardias may cause no noticeable symptoms, or they may be felt as palpitations. When sustained, however, tachycardias often cause palpitations, as well as weakness, dizziness, chest pain, and breathing difficulties. Particularly rapid or long-lasting ventricular tachycardias or sustained tachycardias in people whose heart function is already compromised by disease can cause loss of consciousness or lead to fatal cardiac arrest.
A ventricular tachycardia can degenerate into ventricular fibrillation, which is an extremely rapid, chaotic rhythm that starts in the ventricles and causes the heart to quiver. Such quivering prevents the heart from pumping blood to the rest of the body. The onset of a ventricular fibrillation is dramatic: People suddenly lose consciousness and collapse in a shock-like state. Their pulse, heartbeat and blood pressure cannot be detected, and death occurs in minutes without effective treatment. A common cause of ventricular fibrillation is a heart attack.
Emergency Care
Patients with ventricular fibrillation must be treated immediately with one or more electric shocks to the heart, which are transmitted externally with defibrillator paddles placed on the chest. Severe ventricular tachycardias also must often be treated with defibrillators.
Defibrillators tend to synchronize the heart's electrical system. "By giving a shock you start things from scratch again and organize a disorganized rhythm," said Andrew Epstein, M.D., of the University of Alabama at Birmingham.
Defibrillators may become more readily available as a result of FDA's approval in September 1996 of a smaller portable version that may be particularly beneficial to police officers, firefighters, flight attendants, and others who may be the first to respond to cardiac emergencies and can now equip their vehicles with the compact units.
Once the heartbeat has been restored, patients usually are given lidocaine hydrochloride (Xylocaine) or bretylium tosylate (Bretylol) intravenously to stabilize their heart rhythm.
