Arrhythmias are often categorized by the origin of the pacemaker impulse. These pacemakers are sinus (sinoatrial node), atrial (atrioventricular node), junctional, or ventricular. The usual pacemaker of the heart (see Part 1) is the SA node, which results in a normal sinus rhythm. 

Normal ECG patterns vary from patient to patient and can change in an instant due to certain conditions or illnesses. Therefore, it is important to use a systematic approach when interpreting ECGs.

Related Video – Introduction to ECG Interpretation