A ventricular depolarization that occurs earlier than expected. It appears on the electrocardiogram as an early, wide QRS complex without a preceding related P wave. They may be idiopathic or caused by stress,
electrolyte imbalance, ischemia, hypoxemia, hypercapnia, ventricular by enlargement,
or a toxic reaction to drugs. They may occur occasionally, in a regular pattern, or as several in sequence. Occasional they are not clinically significant in healthy individuals, but they may produce decreased cardiac output in people with heart disease. If these happen frequently, they may be a precursor of ventricular tachycardia or fibrillation. What is this abnormal heart rhythm called?