Coronary sinus rhythm arises from the the area of atrioventricular junction near the coronary sinus ostium
The impulse activates the atria retrogradely, hence a typical morphology of P waves in limb leads - negative in leads II, III and aVF
ECG characteristics
negative P waves in leads II, III and aVF
narrow QRS complex
normal PR interval
slightly slower rate than sinus rhythm
ECG 1 Coronary sinus rhythm with a rate of 48/min, narrow QRS complexes, negative P wave in II, III and a VF - best visible in lead III, 1st degree AV block is present with PR interval of 232ms
References
Čihalík, Čestmír, and Miloš Táborský. 2013. Ekg V Klinické Praxi. Meduca. Olomouc: Solen, Medical education.