71-year - old female presented to the electrophysiology laboratory for an elective electrophysiology study ( eps ) and radiofrequency ablation for recurrent supraventricular tachycardia ( svt ) resulting in inappropriate icd shocks . her past medical history is remarkable for non - ischemic cardiomyopathy , aortic valve replacement done twice ( mechanical followed by tissue bioprosthesis for hemolysis ) , implantable cardioverter defibrillator ( icd ) placed for primary prevention in march 2012 . she presents initially in september and then again in december 2012 for multiple icd shocks . icd interrogation ( boston scientific ) confirmed it to be secondary to a svt at the rate of 170  bpm . during electrophysiology study , a narrow complex tachycardia was easily induced at a cycle length of 340 msec . using entrainment and 3-d mapping ( esi ) subsequent to a successful ablation of both the arrhythmias , the icd was re - interrogated . from top to bottom , patient s native electrocardiogram , atrial and ventricular electrograms , rv to svc coil ( far field ) and marker channels are shown . as seen in fig . different diagnosis at this stage included a possible atrial lead dislodgement or possible junctional rhythm . however a quick fluoroscopy confirmed an intact atrial lead position and a closer look at the surface electrocardiogram ( fig .  1 ) , confirmed presence of an atrial mechanism ( ruling out a junctional rhythm ) . furthermore , atrial capture threshold confirmed appropriate atrial pacing and ventricular sensing ( fig .  2 ) . the explanation of this lies in analyzing the coronary sinus ( cs ) electrograms during her native rhythm ( fig . extensive scarring from the two previous cardiac surgeries resulted in a significant delay from the left atrial site of origin to the high right atrial sensing lead . this delay resulted in a simultaneous sensing of the rv activation and the hra by the respective leads . an additional clue lies in comparing the far field ventricular sensing during atrial pacing ( fig . 2 ) and the terminal portion of the  apparent  ( or fused ) atrial electrogram during the native rhythm ( fig .  1 ) , which appears to be identical . the conduction delays that sometimes occur as a result can cause a variety of electrophysiological mirages . our case demonstrates the need to be aware of these phenomena to avoid misdiagnosis in interpretation of icd electrograms .
we present a case of a patient with significant structural heart disease from previous cardiac surgeries who presented for an electrophysiology study and radiofrequency ablation . 
 the case highlights the significance of intra - atrial conduction delays in such patients and potential pitfalls it can present while interpreting intra - cardiac electrograms especially during implantable cardioverter defibrillator ( icd ) interrogations .