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.

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.

Inappropriate defibrillator shock due to EMI despite noise reversion and SecureSense - What is the mechanism?

Implantable cardioverter defibrillator (ICD) shocks are always a matter of anxiety and concern for both patient and clinician. We report a case of ischemic cardiomyopathy who reported to us after receiving two shocks within 48 hours. The therapy was inappropriate as noted from device logs. EMI was identified as the incriminating cause. We discuss the reasons why he received the therapy despite active 'Noise reversion' and 'SecureSense' algorithms to avoid noise /EMI related oversensing.

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.

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.

Reappraisal of resetting response to locate the antegrade pathway in slow-fast atrio-ventricular nodal re-entrant tachycardia.

Typical atrio-ventricular nodal re-entrant tachycardia (AVNRT) can occasionally remain easily inducible after slow pathway (SP) modification in lower Triangle of Koch (TOK). Analysis of resetting response by delivering atrial premature depolarizations (APD) from various sites (TOK, right atrium, coronary sinus and left atrium) can pin-point the culprit SP serving as the antegrade limb of the tachycardia circuit. However, the maneuver is under-utilized by most centers. We describe a case where anatomical SP modification in TOK failed to cure the arrhythmia. The resetting maneuver performed subsequently, helped us to rule out leftward inferior extension of SP and suggested right inferior SP as essential part of AVNRT circuit. Further ablation was performed at M1-M2 region (on the right side) to achieve success.

Comparing effectiveness of high-dose Atorvastatin and Rosuvastatin among patients undergone Percutaneous Coronary Interventions: A non-concurrent cohort study in India.

INTRODUCTION: Atorvastatin-80mg/day and Rosuvastatin-40mg/day are the commonest high-dose statin (3-hydroxy-3-methylglutaryl coenzyme-A reductase inhibitors) regimes for post-PCI (Percutaneous Coronary Interventions) patients to lower (by ≥50%) blood low-density-lipoprotein cholesterol (LDL-C). Dearth of conclusive evidence from developing world, regarding overall safety, tolerability and comparative effectiveness (outcome/safety/tolerability/endothelial inflammation control) of Rosuvastatin over Atorvastatin in high-dose, given its higher cost, called for an overall and comparative assessment among post-PCI patients in a tertiary cardiac-care hospital of Kolkata, India. METHODS: A record-based non-concurrent cohort study was conducted involving 942 post-PCI patients, aged 18-75 years, on high-dose statin for three months and followed up for ≥one year. Those on Atorvastatin-80mg (n = 321) and Rosuvastatin-40mg (n = 621) were compared regarding outcome (death/non-fatal myocardial infarction: MI/repeated hospitalization/target-vessel revascularisation/control of LDL and high-sensitivity C-reactive protein: hsCRP), safety (transaminitis/myopathy/myalgia/myositis/rhabdomyolysis), tolerability (gastroesophageal reflux disease: GERD/gastritis) and inflammation control adjusting for socio-demographics, tobacco-use, medications and comorbidities using SAS-9.4. RESULTS: Groups varied minimally regarding distribution of age/gender/tobacco-use/medication/comorbidity/baseline (pre-PCI) LDL and hs-CRP level. During one-year post-PCI follow up, none died. One acute MI and two target vessel revascularizations occurred per group. Repeated hospitalization for angina/stroke was 2.18% in Atorvastatin group vs. 2.90% in Rosuvastatin group. At three-months follow up, GERD/Gastritis (2.18% vs 4.83%), uncontrolled hs-CRP (22.74% vs 31.08%) and overall non-tolerability (4.67% vs. 8.21%) were lower for Atorvastatin group. Multiple logistic regression did show that compared to Atorvastatin-80mg, Rosuvastatin-40mg regime had poorer control of hs-CRP (A3OR = 1.45,p = 0.0202), higher (A3OR = 2.07) adverse effects, poorer safety profile (A3OR = 1.23), higher GERD/Gastritis (A3OR = 1.50) and poorer overall tolerability (A3OR = 1.50). CONCLUSION: Post-PCI high dose statins were effective, safe and well-tolerated. High dose Rosuvastatin as compared to high dose Atorvastatin were similar in their clinical efficacy. Patients treated with Atrovastatin had significantly lower number of patients with hs-CRP (high-sensitivity C-reactive protein)/C-reactive protein (CRP) level beyond comparable safe limit and relatively better tolerated as opposed to Rosuvastatin-40mg.Thus given the lower price, Atorvastatin 80mg/day appeared to be more cost-effective. A head-to-head cost-effectiveness as well as efficacy trial may be the need of the hour.

Acute encephalitis syndrome following scrub typhus infection.

OBJECTIVE: The aim was to find the incidence of acute encephalitis syndrome (AES) secondary to scrub infection and to observe the clinical, biochemical, radiological profile, and outcomes in these patients. MATERIALS AND METHODS: A total of 20 consecutive patients of AES were evaluated for scrub infection using scrub typhus immunoglobulin M enzyme linked immuno-sorbant assay positivity along with the presence or absence of an eschar. Clinical profile, routine laboratory tests, cerebrospinal fluid (CSF) analysis, and neuroimaging were analyzed. Patients were treated with doxycycline and followed-up. RESULTS: Among 20 consecutive patients with AES, 6 (30%) were due to scrub infection. They presented with acute onset fever, altered sensorium, seizures. Eschar was seen in 50% of patients. CSF done in two of them was similar to consistent with viral meningitis. Magnetic resonance imaging brain revealed cerebral edema, bright lesions in the putamen and the thalamus on T2-weighted and fluid-attenuated inversion recovery sequences. Renal involvement was seen in all patients. All patients responded well to oral doxycycline. CONCLUSION: AES is not an uncommon neurological presentation following scrub typhus infection. It should be suspected in all patients with fever, altered sensorium, and renal involvement. Oral doxycycline should be started as early as possible for better outcomes.

Tailoring the surface properties and carrier dynamics in SnO2 nanowires.

We report a study of the role of mid-gap defect levels due to surface states in SnO(2) nanowires on carrier trapping. Ultrafast pump-probe spectroscopy provides carrier relaxation time constants that reveal the nature and positions of various defect levels due to the surface states which in turn provide details on how the carriers relax after their injection. The effect of oxygen annealing on carrier concentration is also studied through XPS valence band photoemission spectroscopy, a sensitive non-contact surface characterization technique. These measurements show that charge transfer associated with chemisorption of oxygen in different forms produces an upward band bending and leads to an increase in the depletion layer width by approximately 70 nm, thereby decreasing surface conductivity and forming the basis for the molecular sensing capability of the nanowires.

Investigation of Nucleation Mechanism and Tapering Observed in ZnO Nanowire Growth by Carbothermal Reduction Technique.

ZnO nanowire nucleation mechanism and initial stages of nanowire growth using the carbothermal reduction technique are studied confirming the involvement of the catalyst at the tip in the growth process. Role of the Au catalyst is further confirmed when the tapering observed in the nanowires can be explained by the change in the shape of the catalyst causing a variation of the contact area at the liquid-solid interface of the nanowires. The rate of decrease in nanowire diameter with length on the average is found to be 0.36 nm/s and this rate is larger near the base. Variation in the ZnO nanowire diameter with length is further explained on the basis of the rate at which Zn atoms are supplied as well as the droplet stability at the high flow rates and temperature. Further, saw-tooth faceting is noticed in tapered nanowires, and the formation is analyzed crystallographically.

Rapid thermal annealing effects on tin oxide nanowires prepared by vapor-liquid-solid technique.

Tin oxide nanowires have been grown on p-type silicon substrates using a gold-catalyst-assisted vapor-liquid-solid growth process. The nanowires were annealed in the presence of oxygen at 700 degrees C for different time intervals. The changes in material properties of the nanowires after annealing were investigated using various characterization techniques. Annealing improves the crystal quality of the nanowires as seen from Raman spectroscopy analysis. Photoluminescence (PL) data indicates a decrease in the oxygen vacancies and defects after annealing, affecting the luminescence from the nanowires. In addition, x-ray photoelectron spectroscopy (XPS) was used to obtain the changes in the tin and oxygen atomic concentrations before and after annealing, from which the stoichiometry was calculated.