Sinus rhythm: physiology, ECG criteria & clinical implications

Sinus rhythm: physiology, ECG criteria & clinical implications

Sinus rhythm: the normal rhythm of the heart A  rhythm  is defined as three consecutive heart beats with identical waveforms on the  ECG . The similarity of the waveforms indicates that the origin of the impulse is the same. The  sinoatrial (SA) node  is the heart’s pacemaker under normal circumstances and the rhythm is referred to as  sinus rhythm . Hence, sinus rhythm is the normal rhythm of the heart. The  physiology of the SA node  and  pacemaker cells  in the heart have been discussed previously. This article deals mainly with ECG features of sinus rhythm. Definition (criteria) for sinus rhythm Regular rhythm with ventricular rate between 50 and 100 beats/min. P-wave with constant morphology preceding every QRS complex. The P-wave is positive in lead II. Figure 1  (below) shows normal sinus rhythm at paper speed 25 mm/s. Figure 1. Sinus rhythm. Paper speed 25 mm/s. Figure 2  (below) shows the exact same ECG at 50 mm/s. Figure 2. Sinus rhythm. Paper speed 50 mm/s.

Continue reading...