Abstract
BACKGROUND: Long RP supraventricular tachycardia poses a significant diagnostic challenge because of overlapping electrophysiological features among differential diagnoses. Detailed evaluation with an electrophysiological study is essential for accurate diagnosis and effective management, particularly when initial ablation attempts fail to eliminate inducibility. CASE PRESENTATION: A 40-year-old Southeast Asian male with a 5-year history of recurrent palpitations was referred for evaluation. Baseline echocardiography was normal. During symptomatic episodes, electrocardiography demonstrated long RP tachycardia. Electrophysiology study revealed eccentric atrial activation with decremental conduction, with the earliest A recorded at DD 9-10 (coronary sinus ostium/left posteroseptal region). Tachycardia cycle length was 410 ms, with a VA interval of 215 ms, AH interval of 93 ms, HA interval of 332 ms (AH/HA < 1), a VAV response during ventricular entrainment, PPI-TCL of 225 ms, and SA-VA of 194 ms. Ventricular reset did not terminate the arrhythmia and showed no atrial delay or advancement. Ablation at the coronary sinus ostium terminated the tachycardia but did not prevent reinduction. A subsequent slow pathway ablation was performed, during which slow junctional rhythm was observed. Post-ablation testing demonstrated crossover at 320 ms, while supraventricular tachycardia remained easily inducible with atrial S1 pacing at 400 ms. Given persistent inducibility, medical therapy was optimized and the patient was scheduled for advanced three-dimensional mapping and ablation. The leading differential diagnoses were atypical atrioventricular nodal reentrant tachycardia (fast-slow variant) with a bystander accessory pathway and permanent junctional reciprocating tachycardia with coexisting dual AV nodal physiology. CONCLUSION: This case illustrates the diagnostic complexity and management challenges of long RP supraventricular tachycardia, particularly in distinguishing atypical atrioventricular nodal reentrant tachycardia from permanent junctional reciprocating tachycardia. When initial ablation does not achieve full arrhythmia control, a stepwise strategy involving detailed electrophysiological evaluation, cautious ablation, and advanced mapping may be required to guide definitive therapy.