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.
