Ventricular Arrhythmias or Irregular Heartbeats

by Food and Drug Administration (FDA)

Two-time Olympic gold-medalist skater Sergei Grinkov shocked the world in fall 1995, when he collapsed on the ice rink and died hours later at the young age of 28. A blood clot that blocked blood flow to his heart triggered it to quiver instead of beat. Medical technicians were unable to restore a normal heart rhythm, and by the time he reached a hospital, Grinkov's heart had stopped beating altogether.

Grinkov suffered what is known as ventricular fibrillation. This inefficient and deadly quivering of the heart is one of several types of irregular heartbeats, or arrhythmias, that afflict the lower chambers, called the ventricles, of the heart. Not all arrhythmias are ventricular; some, for example, arise from the upper chambers of the heart.

Ventricular arrhythmias often occur in people with various forms of heart disease and, according to the American Heart Association, cause most cases of sudden cardiac death. But new drugs and devices show promise in curbing the number of deaths from this condition. These new treatments, approved by the Food and Drug Administration, include a longer-acting form of an antiarrhythmia drug, a wide availability of portable and implantable electrical devices that can spark a return to normal heart rhythm, and techniques for destroying heart tissue that triggers ventricular arrhythmias.

Heart of the Matter

Not much bigger than a fist, the human heart beats 100,000 times each day, sending about 2,000 gallons of blood coursing through vessels, which, laid end-to-end, would be long enough to circle the earth more than twice.

To carry out the vital task of pumping blood, the electrical timing of millions of heart cells must be exquisitely coordinated. Their timing sparks the heart to pump in a rhythmic, efficient fashion. When that coordination is disrupted, life-threatening ventricular arrhythmias result.

Each heartbeat normally starts in the upper right chamber of the heart, or right atrium. Here, a specialized bunch of cells called the sinus node, or pacemaker, sends an electrical signal. The signal spreads throughout the right and left atria and then travels along specific pathways to the lower chambers or ventricles. As the signal travels, the heart muscle contracts. First the atria (the upper right and left chambers) contract, pumping blood into the ventricles. A fraction of a second later, the ventricles contract in a squeezing motion, sending blood throughout the body. Each contraction is a heartbeat.

Ventricular arrhythmias occur when a group of heart cells in the ventricles triggers contractions out of sync with the normal rhythm established by the sinus node. A number of factors can prompt a ventricular arrhythmia, including stress, exercise, caffeine, tobacco, alcohol, amphetamines, tricyclic antidepressant drugs, and cough and cold medicines containing pseudoephedrine, as well as several drugs (such as diuretics and digitalis) used to treat various heart conditions.

Many types of heart disease also are associated with ventricular arrhythmias. Atherosclerosis, the buildup of plaque on artery walls, can reduce blood flow to heart tissue. That, in turn, can impede the transmission of electrical signals governing heart contractions. This can prompt groups of ventricle cells to generate their own "back-up" rhythm. In the extreme case of a heart attack, blood flow to specific parts of the heart muscle is completely blocked, and that heart tissue dies. If the affected area includes cells in the electrical pathways of the heart, arrhythmias ensue.

People with enlarged hearts or faulty heart valves also are prone to experiencing ventricular arrhythmias. Ventricular arrhythmias also commonly occur after heart attacks, heart infections, or heart surgery, or when the body is under severe physical stress from, for example, lack of oxygen, very low blood pressure, or major blood loss. They also are triggered by heart failure, surgery, and other conditions that cause abnormal blood and tissue concentrations of potassium, magnesium, sodium, or calcium. These minerals play key roles in triggering and conducting electrical impulses in the heart.

Harmless or Deadly Beats

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.

About the Author

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