Right atrial collision time (RACT): A novel marker of propensity for typical atrial flutter.

INTRODUCTION: The risk of typical atrial flutter (AFL) is increased proportionately to right atrial (RA) size or right atrial scarring that results in reduced conduction velocity. These characteristics result in propagation of a flutter wave by ensuring the macro re-entrant wave front does not meet its refractory tail. The time taken to traverse the circuit would take account of both of these characteristics and may provide a novel marker of propensity to develop AFL. Our goal was to investigate right atrial collision time (RACT) as a marker of existing typical AFL. METHODS: This single-centre, prospective study recruited consecutive typical AFL ablation patients that were in sinus rhythm. Controls were consecutive electrophysiology study patients >18 years of age. While pacing the coronary sinus (CS) ostium at 600 ms, a local activation time map was created to locate the latest collision point on the anterolateral right atrial wall. This RACT is a measure of conduction velocity and distance from CS to a collision point on the lateral right atrial wall. RESULTS: Ninety-eight patients were included in the analysis, 41 with atrial flutter and 57 controls. Patients with atrial flutter were older, 64.7 ± 9.7 versus 52.4 ± 16.8 years (<.001), and more often male (34/41 vs. 31/57 [.003]). The AFL group mean RACT (132.6 ± 17.3 ms) was significantly longer than that of controls (99.1 ± 11.6 ms) (p < .001). A RACT cut-off of 115.5 ms had a sensitivity and specificity of 92.7% and 93.0%, respectively for diagnosis of atrial flutter. A ROC curve indicated an AUC of 0.96 (95% CI: 0.93-1.0, p < .01). CONCLUSION: RACT is a novel and promising marker of propensity for typical AFL. This data will inform larger prospective studies.

The evidence for the implantable loop recorder in patients with inherited arrhythmia syndromes: a review of the literature.

Risk stratification of patients with inherited arrhythmia syndromes (IASs) can be challenging. Recent guidelines acknowledge a place for considering the implantable loop recorder (ILR) to outrule malignant arrhythmia as a cause of syncope in certain inherited arrhythmia patients who are at low risk of sudden cardiac death. In this comprehensive literature review, we evaluate the available evidence for the use of the ILR in the IASs and in relatives of victims of sudden arrhythmic death syndrome.

Close-coupled pacing to identify the "functional" substrate of ventricular tachycardia: Long-term outcomes of the paced electrogram feature analysis technique.

BACKGROUND: The conduction delay and block that compose the critical isthmus of macroreentrant ventricular tachycardia (VT) is partly "functional" in that they only occur at faster cycle lengths. Close-coupled pacing stresses the myocardium's conduction capacity and may reveal late potentials (LPs) and fractionation. Interest has emerged in targeting this functional substrate. OBJECTIVE: The purpose of this study was to assess the feasibility and efficacy of a functional substrate VT ablation strategy. METHODS: Patients with scar-related VT undergoing their first ablation were recruited. A closely coupled extrastimulus (ventricular effective refractory period + 30 ms) was delivered at the right ventricular apex while mapping with a high-density catheter. Sites of functional impaired conduction exhibited increased electrogram duration due to LPs/fractionation. The time to last deflection was annotated on an electroanatomic map, readily identifying ablation targets. RESULTS: A total of 40 patients were recruited (34 [85%] ischemic). Median procedure duration was 330 minutes (interquartile range [IQR] 300-369), and ablation time was 49.4 minutes (IQR 33.8-48.3). Median functional substrate area was 41.9 cm2 (IQR 22.1-73.9). It was similarly distributed across bipolar voltage zones. Noninducibility was achieved in 34 of 40 patients (85%). Median follow-up was 711 days (IQR 255.5-972.8), during which 35 of 39 patients (89.7%) did not have VT recurrence, and 3 of 39 (7.5%) died. Antiarrhythmic drugs were continued in 53.8% (21/39). CONCLUSION: Functional substrate ablation resulted in high rates of noninducibility and freedom from VT. Mapping times were increased considerably. Our findings add to the encouraging trend reported by related techniques. Randomized multicenter trials are warranted to assess this next phase of VT ablation.

Algorithms to Identify Accessory Pathways' Location on the 12-Lead Electrocardiogram.

The ability to estimate accessory pathway (AP) position enables pre-procedural planning, reduces mapping times, and improves risk estimates as part of the patient consent process. In this article, the nomenclature and important concepts of AP localization algorithms are outlined. An overview of three prominent algorithms is then provided. Each represents an era of invasive treatment of APs: surgical therapy, endocardial ablation, and contemporary electroanatomic mapping. In this manner, the premises, pitfalls, and evolution of AP localization algorithms are illustrated. In addition, the pertinent features of their work are distilled in a simplified topographic algorithm with the interventional electrophysiologist in mind.

Inferolateral T wave inversion in athletes: phenotype-genotype correlation.

AIMS: Significant T wave inversion in young asymptomatic athletes is rare but poses a significant clinical challenge. Pre-participation sports screening programs identify such subjects. Clinical concern that such ECG changes represent an occult cardiomyopathy or forme fruste hypertrophic cardiomyopathy leads to diagnostic and therapeutic dilemma. We sought to genotype a cohort of such subjects with a normal cardiac phenotype identified in our unit over a 3-year period. METHODS: Ten athletes were referred from external screening. All exhibited deep T wave inversion inferolaterally. All had negative family history for sudden death and had a normal phenotype. A panel of 133 cardiac genes were screened. RESULTS: Ten male subjects with mean age of 39 years were screened. Seven had no evidence of mutations. Three subjects demonstrated variants of uncertain significance in 5 different genes: alpha-2-actinin (ACTN2), myopalladin (MYPN), the calcium channel genes CACNA1C and TRPM4 and potassium channel gene KCNQ1. The variants found have not been described in cardiomyopathies or channelopathies. At 3-year follow-up, one patient had undergone detraining, and his ECG showed complete resolution of all T wave changes. He did not have any demonstrated variants. CONCLUSIONS: The absence of mutations in target genes and heterogeneous sequence variations identified in this study suggest that inferolateral T wave inversion in athletes without a phenotype may potentially represent a benign repolarization syndrome related to athletic adaptation. This was the first study to assess a phenotype-genotype correlation in this population. Further genetic studies need to be undertaken in this area.

Ambulatory ECG predictors of atrial fibrillation are ineffective in severe sleep apnea.

BACKGROUND: Obstructive sleep apnea (OSA) is strongly associated with atrial fibrillation (AF). Long-term ECG monitoring with implantable loop recorders facilitates the identification of undiagnosed AF in 20% of severe OSA cases. However, ambulatory ECG (AECG) monitoring is less resource intensive, and various parameters have been shown to predict AF. The aim of this study was to assess the efficacy of such AECG-based AF predictors in identifying patients with severe OSA most at risk. METHODS: Prospective observational study including patients with severe OSA and no history of AF. Patients had two 24-h AECG recordings, and if no AF was detected, implanted with a loop recorder (maximum 3 years). RESULTS: Of 25 patients implanted, AF ≥ 10 s was detected in 5 patients. None of the parameters from the AECG recordings were significantly different between patients who did and did not develop AF. CONCLUSIONS: AECG-based parameters were not effective for the prediction of AF in this severe OSA cohort.