Case Presentation
A 41 years old lady presented to us with drug refractory narrow QRS tachycardia. Echocardiography revealed normal left ventricular systolic function. 12 lead electrocardiography (ECG) showed long RP (RP>PR) narrow QRS tachycardia. Radiofrequency catheter ablation was performed after obtaining informed consent. Intracardiac electrograms and 12 lead ECG were continuously monitored using Workmate Claris system (Abbott, Plymouth, MN). Upper limb Venous angiography showed dilated coronary sinus with left sided superior vena cava. Basal AH and HV intervals were 85ms and 44ms respectively. Patient had spontaneously inducible tachycardia (Fig 1B) which could be terminated by intravenous adenosine. ECG showed narrow QRS tachycardia with variation in both atrial and ventricular cycle length (Fig 1A). Intracardiac electrogram during tachycardia showed variation in H-H, A-A, V-V and HA intervals (Fig 2)
  1. What is the mechanism of the tachycardia onset?
  2. What is the substrate for re-entry?
  3. What could be the reason for the variation in A-A, H-H, H-A and V-V intervals?