An Ectopic Primary Pacemaker in Association with Isolated Persistent Left Superior Vena Cava.

We are reporting a case of a young Nepalese man, who was not known to have any past medical history, and who presented with palpitations. An electrocardiogram showed negative P-waves atrial rhythm in II, III, arteriovenous fistula, and V3-V6 with a variable block at 90-130 bpm. No positive "normal" P-waves were demonstrated in any tracing. He was found to have a congenital absence of the right superior vena cava (RSVC) along with persistent left superior vena cava (PLSVC) a condition also called isolated PLSVC (IPLSC). He underwent a treadmill stress test for further evaluation which showed a normal chronotropic response and the same persistent negative P-waves morphology. An invasive electroanatomical and activation mapping showed an absence of RSVC, the earliest atrial activation site in the anterior side of the inferior vena cava (IVC), and the absence of normal (positive) P-waves/normal sinus node (SN) activation. Considering all the available clinical data together, we believe that the patient was living with an ectopic pacemaker node that acts as a primary node and originated in the IVC/right atrium instead of the normal expected SN position. Given the high risk of complete sinoatrial nodal block in case of radiofrequency ablation, the patient was kept on medical treatment with a beta-blocker which was effective in controlling his symptoms and atrial arrhythmia.