Analysis of intracardiac electrocardiogram during ill-sustained tachycardia - Door to a successful troubleshooting of 'unnecessary' defibrillator discharge.

A 50-year-old gentleman with old anterior wall myocardial infarction with implantable cardioverter defibrillator (ICD, Abbott Medical, Fortify ST VR 1235-40) presented with recurrent appropriate ICD shock. The ICD stored EGM indicated a possibility of supraventricular tachycardia (SVT) rather than ventricular tachycardia (VT) when the morphology match was found high. Bundle brunch re-entry (BBR) VT was another differential. An EP study conducted on antiarrhythmic drugs (AAD) induced reproducible but only ill-sustained tachycardia too short to perform any SVT maneuvers during tachycardia. However, critical analysis of the tachycardia electrograms suggested atypical AVNRT as the most likely mechanism. The other differentials were atrial tachycardia (AT) and BBR VT. Manoeuvres during sinus rhythm and ventricular pacing excluded other diagnosis. A single point radiofrequency ablation (RFA) near the SP region cured the arrhythmia. The reason for misclassification of SVT as VT was also sought for. It was found that the shocks were received due to fulfilment of 2/3 criteria (sudden onset and regular tachycardia). Hence, he received therapy despite an appropriate morphology match favouring SVT. This is one of the known limitations of ICDs where regular SVTs (AVNRT/AVRT or AT) may receive inappropriate ICD therapies. After slow pathway modification there was no further recurrence of either SVT or VT; hence, a substrate modification was deferred.

Endless loop tachycardia among patients with devices having advanced preventive algorithms: A case series and brief review.

BACKGROUND: Endless loop tachycardia (ELT) is the commonest pacemaker mediated tachycardia (PMT) encountered among patients with cardiac implantable electronic devices (CIEDs). Despite being enabled with various preventive algorithms, we encountered several cases having recurrent, long, and symptomatic ELT. MATERIALS AND METHODS: We retrospectively analyzed consecutive device checkups at device clinic at a single center of eastern India between January 2019 to March 2023. RESULTS: There were 20 cases of confirmed and sustained ELT among 4520 device checks. Although mostly benign, in two cases ELT led to clinical worsening in patients having left ventricular (LV) systolic dysfunction. Even with good ventricular function, ELT resulted in improper atrioventricular (AV) synchrony leading to disabling symptom in one case. The differentiation of ELT from sinus tachycardia and atrial tachycardia (AT) was not always easy. Magnet application is certainly useful to differentiate. The situations that provoked ELT in this study were-long AV delays, VIP (ventricular intrinsic preferences)/MVP (managed ventricular pacing), atrial non-capture, atrial under/over sensing, premature ventricular contractions (PVCs)/couplets, premature atrial contractions (PAC) and slower ventriculo-atrial (VA) conduction. Rate responsive shortening of post-ventricular atrial refractory period (PVARP) also promoted its occurrence and hindered troubleshooting. When ELT occurred despite post-PVC extension of PVARP, lowering the atrial sensitivity, switching to bipolar sensing and manual setting of longer PVARP after measuring VA conduction time were useful. "Rate responsive PVARP" had to be turned off in a few cases to prevent ELT. On the contrary, an over aggressive prolongation of PVARP led to repetitive non-reentrant ventriculo-atrial synchrony (RNRVAS) in two cases. Checking VA conduction during implantation and noninvasive program stimulation (NIPS) during follow up were useful to check the tendency for ELT. CONCLUSION: Clinically significant ELT is rare but not uncommon among devices having in-built preventive algorithms. Manual adjustments are often useful to troubleshoot the same.

Retrograde ventriculoatrial jump-What is the mechanism?

During ventricular extra stimuli(VES) protocol a VA jump was noted. In upper panel with VES @ 500/270 ms (Fig A) the His signal appeared after the A-EGM, ruling out pure nodal VA conduction and confirming presence of an accessory pathway (AP). The H signal was delayed due to probable retrograde RBBB. The atrium was already depolarised via AP and the VA traversing via left bundle-His-node got blocked with a H signal. In the lower panel with VES of 500/260 ms the retrograde AP conduction reached the effective refractory period and pure nodal VA conduction took place along with retrograde RBBB. The retrograde VA jump was hence due to a jump from AP to AV node.

Inappropriate ventricular fibrillation annotation and defibrillator discharge despite the same tachycardia cycle length in ventricular tachycardia-1 zone in an Abbott defibrillator - What is the mechanism?

Newer devices incorporate advanced algorithms to have more accurate delivery of implantable cardioverter-defibrillator (ICD) therapy. Newer models of Abbott Implantable cardioverter-defibrillators like Gallant and Entrant have a new ventricular fibrillation (VF) therapy assurance algorithm. This algorithm has a proven role in avoiding under-detection of VF where some of the smaller electrograms are under-sensed. We report a case of ventricular fibrillation therapy assurance (VFTA) algorithm malfunction in a 48-year-old lady having single chamber Entrant Implantable cardioverter-defibrillator, where the patient received inappropriate therapies. The VFTA algorithm eventually had to be turned off.

Change in the H-V Interval Without a Change in QRS Morphology During Atrial Pacing in a Case of Wolff-Parkinson-White Syndrome-What is the Mechanism?

In the background of an accessory pathway (AP), the H-V interval can vary during atrial/coronary sinus pacing, but only with a concomitant change in the QRS morphology and the degree of pre-excitation. In an interesting case of a 62-year-old woman, the H-V interval varied during coronary sinus pacing despite a fixed pre-excitation. This appears to have happened due to infra-Hisian complete atrioventricular dissociation, which resulted from iatrogenic mechanical bumping of the left anterior fascicle in the background of right bundle branch block and left posterior hemiblock.

Inappropriately long post-ventricular atrial blanking leading to 'unnecessary' defibrillator discharge.

A 55-year-old lady with non-ischemic cardiomyopathy (NICM) was referred for multiple implantable cardioverter defibrillator (ICD) shocks. Stored electrograms (EGM) revealed atrial flutter (AFL) with A > V. Morphology match was good and RR-intervals were irregular. Despite all these, the dual-chamber-ICD (Abbott medical) classified this as ventricular tachycardia (VT-2) via V > A algorithm where it did not analyze morphology/stability and delivered therapy. Anti-tachycardia-pacing (ATP) was delivered which induced a true VT (rate in VF-zone) and immediate shock was delivered. It was hence appropriate but an 'unnecessary' shock. The offender was found to be an inappropriately programmed long post-ventricular atrial-blanking (PVAB) of 200 ms which led to undersensing of several atrial electrograms, falsely making V > A during a clear AFL.

Positive QRS complex in limb lead 2 with negative QRS in lead 3 on surface electrocardiogram: A novel predictor for anterior location of right-sided accessory pathways (10-1 o'clock on tricuspid annulus).

BACKGROUND: Localization of atrioventricular accessory pathways (AP) from Electrocardiogram (ECG) is crucial for successful ablation. We analyzed the value of limb lead 2 versus 3 QRS vector discordance on surface ECG among right-sided pathways. METHODS: Data from consecutive patients undergoing successful ablation of manifest AP were analyzed. They were categorized into two groups-Gr I: Endocardial ablation from anterior and anterolateral tricuspid annulus (TA, 10-1 o'clock, right anterolateral [RAL]); Gr II: Ablation outside this region (1-10 o'clock of TA). Inferior lead discordance (ILD) was defined as positive QRS complex (monophasic R, Rs) in lead 2 with negative/equiphasic QRS vector in lead 3 (rS, S, RS). Maximally pre-excited ECGs during electrophysiology study were compared for presence of ILD. RESULT: Among total 22 cases (Age 36 ± 18 years, 12 males), ILD was noted in 4/4 cases of Gr I. It was absent among 17/18 cases of right-sided AP in Gr II. The only case in Gr II having ILD was ablated near 8 o'clock (posterolateral). In contrast to the other four cases, aVF was negative, along with lead 3. A close differential was mid-septal AP (MSAP). However, the MSAP had absence of r in V1 and lead 2 having rS/RS complex in contrast to strongly positive QRS in RAL pathways. The sensitivity and specificity of ILD for RAL are 100% and 95%, respectively. The positive, negative predictive value, and accuracy are 80%, 100%, and 95%, respectively. CONCLUSION: Positive QRS complex in lead 2 with negative QRS in lead 3 in maximally pre-excited ECG is often predictive of anterior and anterolateral location among right-sided pathways.

Unmasking of infra-Hisian conduction abnormality by intravenous isoproterenol during electrophysiology study for syncope.

Recurrent unexplained syncope in the background of bundle branch block (BBB) often requires a pacemaker. But the decision-making for pacemaker is difficult in case of single episode of syncope with intermittent bundle branch block. We encountered one such case with intermittent LBBB, where the results of invasive EP study were even normal, until intravenous isoproterenol unmasked the infra-Hisian disease during decremental atrial pacing.

Change in VA interval by a single atrial premature depolarization - What is the mechanism?

A long VA tachycardia during a typical atrioventricular nodal reentrant tachycardia (AVNRT) can be a concomitant atypical AVNRT, atrial tachycardia or rarely atrio-ventricular reentrant tachycardia (AVRT). There are reported associations of AVNRT with other tachycardia substrates. Maneuvers are useful for differentiating the mechanism of the second tachycardia. Atrial tachycardia (AT) is one common association. When the AT originates from the lower triangle of Koch/near coronary sinus ostium, it can mimic slow-slow/fast-slow AVNRT. We encountered an interesting case where a longer VA tachycardia got reproducibly induced when a critically timed atrial premature depolarisation was delivered on typical AVNRT. It was proved to be an AT. A slow pathway modification in the lower TOK was successful to eliminate both the tachycardia substrate.

Inhibition of ventricular output in a dual chamber pacemaker with normal pacing and sensing parameters: What is the mechanism?

A 65-year-old gentleman with dual chamber pacemaker presented with presyncope. The ECG raised concerns of oversensing which was confirmed by magnet response. The device interrogation revealed noise in ventricular channel temporally associated with P wave. The pacing thresholds were normal. Although the ventricular lead impedance was within normal limit the impedance trend suggested 100 Ω decline over last 1 year. RV lead insulation failure was speculated and supported by the bipolar and unipolar intracardiac electrogram. Device was programmed to DOO temporarily. He underwent RV lead replacement uneventfully.

Varying VA intervals during Para-Hisian pacing maneuver-What is the mechanism?

Inadvertent direct atrial capture and pure his capture can result in variable findings during parahis pacing manoeuvre (PHP). Understanding the results and positioning the pacing bipole towards ventricular aspect (distal his region) is helpful to avoid ambiguous results during PHP.

Unusually short VA time during Para-His pacing maneuver: Is it a simultaneous atrial capture?

Although a very VA interval (<60 ms in proximal CS) is suggestive of simultaneous atrial capture, rarely it can have exception. A very short VA shall not be discarded without analysing the electro grams.

Pitfalls and Nuances of Parahisian pacing: A revisit through an interesting case.

Parahisian pacing (PHP) is a useful maneuver during electrophysiology study of supraventricular tachycardia (SVT) especially when the tachycardia is non-sustained. Various responses during PHP can differentiate between the routes of VA conduction (VAC). In a case of WPW syndrome with orthodromic re-entrant tachycardia, we encountered various responses which one must be cognizant about to avoid erroneous conclusions. Along with para-hisian capture and only ventricular capture, simultaneous atrial capture (SAC) and pure His capture were also noted. Moreover, during pure-His capture underlying distal antegrade right bundle branch block (RBBB) was encountered making it an intriguing case.

Ventricular tachyarrhythmia after single chamber pacemaker programming - what is the mechanism?

Pacemaker can be life-saving in high grade atrioventricular (AV) blocks. But this reality is occasionally challenged by arrhythmias induced by ventricular pacing. Some of the events are related to automated pacemaker algorithms. Managed ventricular pacing (MVP) is one such example which has delivered benefits but has also been associated with ventricular tachyarrhythmias (VT). Our case is possibly the first report of hysteresis induced symptomatic VT.

Unexplained syncope during pacemaker interrogation: Wand, AutoCapture, or lead-Which one is the elusive culprit?

A 65-year-old gentleman underwent dual chamber pacemaker implantation (DDDR, St Jude Medical) 7 years back for infra-hisian complete heart block. He was completely asymptomatic and came for his annual routine check-up. After undergoing ECG with and without magnet, he was prepared for device evaluation. After placing the programmer wand over the chest as soon as the ";interrogate" button on the programmer screen was pressed, the patient immediately experienced pre-syncope but recovered instantly as the wand was promptly withdrawn. After taking him to the casualty room with all resuscitation measures in hand, a repeat attempt of interrogation was made after connecting ECG, which revealed reproducible loss of capture (LOC), exclusively during wand placement. A differential diagnosis of lead failure, battery depletion, or wand related issues were considered. However, serial ECGs recorded without wand raised the possibility of AutoCapture malfunction. With all precautions, the device was programmed to fixed ventricular output mode after which interrogation could be performed safely. There was a remaining battery longevity of 2 years with acceptable lead parameters and stable threshold. He continues to be asymptomatic at 10 months of follow up.

Arrhythmogenicity of radiofrequency ablation: Symptomatic non-sustained ventricular tachycardia and frequent premature ventricular ectopics after accessory pathway ablation.

Radiofrequency ablation (RFA) has emerged as the preferred treatment modality with high success rate in cases with WPW syndrome. Arrhythmogenic complications are rarely reported after RFA, except for early or late recurrence of accessory pathway (AP) conduction. We present a unique case where the AP was successfully ablated, however, a new monomorphic PVC of similar morphology to the pre-excited beats developed within 30 min of RFA. She required medical management with sotalol to overcome her worsening symptom on follow-up. The ectopics resolved after 4 months.