Fundamentals of the electrocardiogram and common cardiac arrhythmias

The electrocardiogram (ECG) is an integral part of the diagnostic process for a wide variety of cardiac conditions. It consists of six limb and six precordial leads which record the electrical activity of the heart in the frontal and horizontal planes respectively. The standard ECG waves include the P wave which represents atrial depolarization, the QRS complex generated by depolarization of the ventricular myocardium and the T wave which reflects ventricular repolarization. According to the site of origin, cardiac arrhythmias can be classified as supraventricular or ventricular tachycardias. The most common supraventricular tachycardias are sinus tachycardia, atrial tachycardia, atrioventricular nodal re-entrant tachycardia, atrioventricular re-entrant tachycardia, atrial flutter and atrial fibrillation. Ventricular tachycardias originate in the ventricles and can be potentially life-threatening.