A 68-yr-old lady underwent a VVI pacemaker implantation 10 years back for infra-hisian complete heart block. Now she presents with 3 episodes of syncope within the last 2 months. Detailed neurological evaluation and pacemaker checkup was initially unremarkable. Real time electrograms during device interrogation were suspicious of lead noise resulting in oversensing. She became alright when the pacing mode was made VOO immediately. After discussion with patient relatives she underwent ventricular lead replacement and upgradation to a dual chamber pacemaker. However, in the immediate post-operative period she became unresponsive requiring immediate resuscitation. Monitor suggested short runs of polymorphic VT which was reproducibly suppressed with higher rate obligatory pacing @ 110 bpm. The runs of VT resurfaced immediately as the rate was lower than 90. She was managed by overdrive pacing at a lower rate of 110 bpm. Over the next 2 months the lower rate was brought down to 70 bpm in a stepwise manner. A retrospective analysis of her initial stored device electrogram suggested that it was all PMVT and no noise at all. The cause of her polymorphic VT is not clear. Relative hypomagnesemia, late presenting long QT syndrome and long term VVI pacing in isolation or combination remain the probable offender. She is presently doing well on oral propranolol.

A 50-year-old lady with dilated cardiomyopathy and scar VT underwent single chamber implantable cardioverter-defibrillator (ICD, Medtronic Ltd, Evera XT VR, DVBB2D1) implantation 2 months back. A Sprint Quattro secure 6947 DF1 dual coil lead was placed at RV apex. Now, she presents with an episode of ICD shock while having breakfast. The device interrogation shows a 36 J shock in VF zone (Fig 1A). However, the stored electrograms (EGM) reveal distinct QRS complexes in the far-field EGM; hence, suggesting the shock is related to oversensing. Fig 1B shows 2 panels of another recent episode. Fortunately, there was aborted therapy as there was intermittent resolution of the oversensing. The lead impedance was normal but threshold was high. Is it possible to predict the reason for the oversensing from the EGM and how to troubleshoot?

Title: Paradoxical response during a Para-Hisian pacing in a case with fasciculo-ventricular pathway.Short title : Para-Hisian pacing in fasciculo-ventricular pathway

Case A 40-year-old gentleman underwent electrophysiology study for WPW syndrome with recurrent orthodromic atrioventricular reentrant tachycardia (AVRT). He had a right anterior accessory pathway (AP) which was ablated closer to the septum anterior to His catheter, ablation-distal (ABL) not recording any His signal during and after ablation (Appendix 1ABC). During the study, parahisian pacing (PHP) was performed before and after ablation as a routine protocol to determine the route of VA conduction (VAC). During the study 4 catheters were used: one quadripolar catheter for His region, One roving ablation catheter [for RV pacing/ mapping (MAP)/ablation], 2 decapolar catheters for coronary sinus (CS) and right atrium (RA). During PHP, both the His and MAP/ABL catheters were placed at His region. The CS catheter could not be placed fully deep inside, hence CS-12 was located near middle CS whereas the CS-34 was 2-3 cm inside proximal CS (Appendix 1BC). The decapolar catheter, placed in RA, was on the atrial aspect of tricuspid annulus, with RA-5 bipole near high right atrium (HRA). Pacing was performed at 600 ms cycle length (PCL) as her sinus CL was 700-750 ms. Starting at 20 mA current @ 2 ms pulse width and keeping the PCL and catheter position fixed, the current output was gradually reduced in a stepwise manner when various responses were noted. What are the responses observed in Fig.1 and Fig. 2?

TITLE PAGETitle: Interesting changeover from short VA to long VA tachycardia with single atrial premature depolarisation: What is the mechanism?Short title: Concomitant AVNRT and atrial tachycardia: Killing two birds with one stone.

Title pageTitle : Long VA tachycardia after slow pathway modification for slow-fast atrioventricular nodal reentrant tachycardia : Insights about the mechanism from intriguing electrogram and polarity reversal.Short Title: Mechanism of long VA tachycardia after slow pathway modification.