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Objectives: This study hypothesized that early coupled ventricular extrastimuli (V 2 ) stimulation might yield a more robust differentiation between atrioventricular nodal re-entrant tachycardia (AVNRT) and atrioventricular re-entrant tachycardia (AVRT)., Background: Programmed V 2 during supraventricular tachycardia are useful to differentiate AVNRT from AVRT by subtracting the ventriculoatrial (VA) interval from the stimulus to atrial depolarization (stimulus atrial [SA]) interval, but all such maneuvers have limitations., Methods: Patients with either AVNRT or AVRT were investigated. The entire tachycardia cycle length (TCL) was scanned with V 2 delivered from the right ventricular apex. The SA-VA difference was calculated with V 2 clearly resetting the tachycardia. The prematurity of V 2 was calculated by dividing the coupling interval (CI) by the TCL., Results: A total of 210 patients (102 with AVNRT) were included. The SA-VA difference was >70 ms in all AVNRT patients and was <70 ms in all AVRT patients with right and septal accessory pathways (APs), except for those with decremental APs, in whom there was an overlap between AVNRT and AVRT with left APs. However, a SA-VA difference >110 ms with a CI/TCL of <65% distinguished AVNRT from AVRT using the left AP, with sensitivity and specificity of 87% and 100%, respectively. Ventricular overdrive pacing resulted in tachycardia termination or AV dissociation in 28% of patients compared with 15% of patients using the V 2 technique (p = 0.008)., Conclusions: A SA-VA of >70 ms using the V 2 technique differentiated AVNRT from AVRT using septal and right APs. Use of the V 2 technique with a short CI differentiated AVNRT from AVRT using left APs. The V 2 technique less frequently resulted in tachycardia termination compared with ventricular entrainment., (Copyright © 2018 American College of Cardiology Foundation. Published by Elsevier Inc. All rights reserved.)

Background: Previous observations have reported that the number of pacing stimuli required to entrain a tachycardia varies on the basis of arrhythmia type and location, but a quantitative formulation of the number needed to entrain (NNE) that unifies these observations has not been characterized., Objective: We sought to investigate the relationship between the number of pacing stimulations, the tachycardia cycle length (TCL), the overdrive pacing cycle length (PCL), and the postpacing interval (PPI) to accurately estimate the timing of tachycardia entrainment., Methods: First, we detailed a mathematical derivation unifying electrophysiological parameters with empirical confirmation in 2 patients undergoing catheter ablation of typical atrial flutter. Second, we validated our formula in 44 patients who underwent various catheter ablation procedures. For accuracy, we corrected for rate-related changes in conduction velocity., Results: We derived the equations NNE = |(PPI - TCL)/(TCL - PCL)| + 1 and Tachycardia advancement = (NNE - 1) × (TCL - PCL) - (PPI - TCL), which state that the NNE and the amount of tachycardia advancement on the first resetting stimulation are determined using regularly measured intracardiac parameters. In the retrospective cohort, the observed PPI - TCL highly correlated with the predicted PPI - TCL (mean difference 5.8 ms; r = 0.97; P < .001), calculated as PPI - TCL = (NNE - 1) × (TCL - PCL) - tachycardia advancement., Conclusion: The number of pacing stimulations required to entrain a reentrant tachycardia is predictable at any PCL after correcting for cycle length-dependent changes in conduction velocity. This relationship unifies established empirically derived diagnostic and mapping criteria for supraventricular tachycardia and ventricular tachycardia. This relationship may help elucidate when antitachycardia pacing episodes are ineffective or proarrhythmic and could potentially serve as a theoretical basis to customize antitachycardia pacing settings for improved safety and effectiveness., (Copyright © 2016 Heart Rhythm Society. All rights reserved.)

Background: Catheter ablation of ventricular arrhythmias (VAs) with cryoenergy has not been widely reported., Objective: The purpose of this study was to assess the feasibility and safety of cryoablation for VA., Methods: Cases where cryoablation of VA was attempted as the initial strategy or was considered to prevent potential damage to other structures such as the coronary arteries, phrenic nerve, and His bundle were collected. Thirty-three patients with either normal heart or structural heart disease undergoing VA ablation using cryoenergy at six different institutions were enrolled in the study. Epicardial access was obtained when appropriate., Results: Fifteen patients (7 men) underwent endocardial ablation, 13 (9 men) epicardial ablation (from the coronary sinus in 7), and 5 (2 men) aortic cusp ablation. Mean age was 54 ± 8 years, and ejection fraction was 45% ± 5%. In 15 (45%) patients, VAs were successfully ablated, whereas cryoablation was unsuccessful in the remaining 18 (55%) patients. Cryoablation was successful in all parahisian cases (100%). In three patients, epicardial cryoablation was successful after several failed attempts with open irrigated catheter. An aortic dissection occurred during catheter placement in the aortic cusp. At follow-up of 24 ± 5 months, all patients with acute success were free from clinical VA., Conclusion: Use of cryoenergy for ablation of VA has excellent success for arrhythmias near the His bundle; however, success rates at other sites appear less favorable. Cryoablation may be considered as an alternative approach for reducing complications during ablation of VAs originating from sites close to other relevant cardiac structures (conduction system, coronary arteries, phrenic nerve) and, in rare cases, could be used epicardially when radiofrequency energy applications have failed., (Copyright © 2011 Heart Rhythm Society. Published by Elsevier Inc. All rights reserved.)

Purpose: Catheter ablation of ventricular tachycardia (VT) depends on the localization of VT circuit. Late potential (LP) recordings in sinus rhythm suggest slow conduction and may help to identify the reentry circuit., Methods: Detailed entrainment mapping was performed to identify VT circuits in 15 patients with structural heart disease. LPs were identified during baseline non-VT rhythm and were defined as electrogram signals occurring beyond the end of surface QRS. The QRS-LP interval was measured from onset of QRS to the latest LP component., Results: Entrainment was performed in 21 VTs, of which three entrance, 13 isthmus, 17 exit, and one outer loop sites were identified (n = 34). Bipolar electrograms (n = 133 sites) at and in proximity (<1.5 cm distance) to the VT circuit were analyzed. A higher incidence of LP was recorded near isthmus (89%) compared to entrance (57%) or exit (20%), p < 0.05. The QRS-LP intervals were markedly longer at entrance (218 +/- 27 ms) and isthmus (194 +/- 40 ms) compared to those recorded at exit (131 +/- 29 ms), p < 0.05., Conclusions: Electrograms near the VT circuit isthmus have a higher incidence of LP compared to that of entrance and exit; and the QRS-LP interval is significantly longer near entrance and isthmus compared to exit sites. These findings have important implications in substrate-based ablation strategies targeting LPs.

Background: Despite improvements in cardiac resynchronization therapy (CRT) implantation techniques, a significant minority of CRT attempts are unsuccessful. Inability to cannulate the coronary sinus (CS) because of difficult anatomy is a major reason for unsuccessful CRT implantation. Direct visualization of intracardiac structures during the implant may facilitate access into the CS. The present study describes CRT implantation with the aid of an endocardial visualization catheter (EVC)., Methods: Fifty-eight consecutive patients (mean age 72 +/- 12 years; ejection fraction 26.2% +/- 7.0%; New York Heart Association [NYHA] class 2.9) underwent CRT implantation using a steerable fiberoptic EVC (Acumen Medical, Inc., Sunnyvale, CA)., Results: The EVC was able to visualize the CS ostium in all cases. The CS was successfully cannulated in 57 (98.3%) of 58 patients. The time from vascular access to CS visualization was 6 +/- 5 minutes, and the total time to CS access was 8 +/- 6 minutes. Successful left ventricle (LV) lead implantation was accomplished in 55 (94.8%) of 58 patients. Three patients who had a previous history of failed LV lead implantation were successfully implanted using the EVC., Conclusion: Fiberoptic imaging of intracardiac structures during CRT implantation may be performed rapidly in a wide range of patients with an EVC. The ability to visualize right atrial anatomy may aid CS access and LV lead implantation.

Background: Detailed anatomic characterization of endocardial substrate of ventricular tachycardia (VT) is limited., Objectives: The purpose of this study was to determine the endocardial dimensions and local electrogram voltage characteristics of the reentrant circuit. VT-related conducting channels corresponding to zones of slow conduction may be identified., Methods: Electroanatomic mapping was performed in 26 patients with uniform VT. Entrainment mapping was performed in 53 VTs, of which 19 entrance, 37 isthmus, 48 exit, and 32 outer loop sites were identified. The color display of voltage maps was adjusted to identify conducting channels associated with VT circuits. A conducting channel was defined as a path of multiple orthodromically activated sites within the VT circuit that demonstrated an electrogram amplitude higher than that of surrounding areas as evidenced by voltage color differences., Results: Forty-seven (84%) of 56 entrance or isthmus sites were located within dense scar (<0.5 mV). Nearly all exits (92%) were located in abnormal endocardium (<1.5 mV), with more than half (54%) located in the border zone (0.5-1.5 mV). VT-related conducting channels was identified in 18 of 32 VTs with detailed mapping (average length 32 +/- 22 mm). The voltage threshold in the conducting channels ranges from 0.1 to 0.7 mV (mean 0.33 +/- 0.15 mV)., Conclusion: (1) Most entrance and isthmus sites of hemodynamically stable VT are located in dense scar, whereas exits are located in the border zone. (2) VT-related conducting channels may be identified by careful voltage threshold adjustment. These findings have important implications regarding strategies for substrate-based VT ablation.

Background: Although catheter mapping has been used to define the endocardial electrogram characteristics in patients with ventricular tachycardia (VT) and coronary disease, characterization of the electrophysiological substrate in patients with VT and nonischemic cardiomyopathy is limited., Methods and Results: Left ventricular endocardial electroanatomical mapping was performed in 19 patients with nonischemic cardiomyopathy and monomorphic VT with an average of 178+/-83 sites per chamber mapped. Abnormal bipolar electrogram was defined as endocardial voltage signal amplitude of <1.8 mV. The extent and location of abnormal endocardium was estimated by measuring areas of abnormal electrogram recordings from 3D voltage maps. The origin of VT was approximated by identifying sites of entrainment with concealed fusion or early presystolic activity and/or by pace mapping. Abnormal electrograms were recorded over a 41+/-28 cm2 area that represented 20+/-12% of total endocardial surface. The majority of patients (14/19 patients) had only a modest area (<25%) of endocardial abnormality. All patients had abnormal low-voltage endocardial areas located near the ventricular base in the perivalvular region. There were 3+/-1 VT morphologies per patient. The majority (88%) of the 57 mapped VTs originated from the ventricular base, corresponding to regions with abnormal endocardial electrograms., Conclusions: Electroanatomical mapping in patients with monomorphic VT and nonischemic cardiomyopathy typically demonstrates a modest-sized basal area of endocardial electrogram abnormalities. The VT site of origin corresponds to these basal electrogram abnormalities. These findings have important implications regarding strategies for VT ablation in this setting.

Introduction: Isoproterenol is used to assess and facilitate AV nodal conduction, and thus potentiate the induction of supraventricular arrhythmias. It is commonly administered in increasing doses until a predetermined decrease in sinus cycle length, usually 20% to 30%, occurs. This regimen may result in undesirable side effects. We have observed that effects of isoproterenol on the AV node may occur prior to achieving the target sinus cycle length. The purpose of this study was to determine whether the sinus and AV nodes have equal sensitivity to isoproterenol., Methods and Results: Thirty-eight consecutive patients, who underwent electrophysiologic evaluation for a variety of indications, were given incremental doses of isoproterenol at 0.007, 0.014, 0.021, and 0.028 microgram/kg per minute. Sinus cycle length and AV node function were assessed at baseline and after 5 minutes at each dose. The percent change from baseline in AV node function was compared with the change in sinus cycle length at each dose interval. Significantly greater decreases were observed in the anterograde and retrograde AV nodal Wenckebach cycle length (P < 0.0001) than in the sinus cycle length at the lowest isoproterenol dose (0.007 microgram/kg per min). These differences were not apparent at higher doses. A sustained supraventricular tachycardia was inducible in 15 of 38 patients in the presence of isoproterenol, of which 40% occurred at the lowest dose., Conclusions: The AV node is more sensitive than the sinus node to the effects of isoproterenol. Lower doses of isoproterenol than those commonly used may often facilitate the induction of a supraventricular tachyarrhythmia, thus reducing side effects.

Introduction: A male patient with an atriofascicular pathway underwent catheter ablation of the atriofascicular pathway during atrial fibrillation., Methods and Results: The patient had preexcited atrial fibrillation both clinically and repeatedly during electrophysiologic study. A preexcited tachycardia with a 1:1 AV relationship and regular RR intervals was also induced. Catheter ablation of the atriofascicular pathway could only be performed during persistent atrial fibrillation, based on mapping of the pathway's insertion into the right bundle branch. Following successful ablation and cardioversion to sinus rhythm, a regular QRS tachycardia (atrioventricular [AV] nodal reentry) having the same rate, atrial activation sequence, and His-atrial time as the regular preexcited tachycardia noted preablation was initiated. An AV nodal slow pathway modification eliminated this tachycardia. Neither atrial fibrillation nor AV nodal reentry has recurred on follow-up., Conclusion: This is the first report of atriofascicular mapping and ablation performed exclusively during atrial fibrillation and illustrates the utility of mapping the pathway's ventricular insertion. Other unusual features ("bystander" pathway activation during AV nodal reentry, possible role of the pathway in genesis of atrial fibrillation) are discussed.