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Background: Susceptibility to ventricular arrhythmias and sudden cardiac death can be reduced by modulation of autonomic tone. Spinal cord stimulation (SCS) presumably affects autonomic tone and reduces myocardial ischemia.Objective: The purpose of this study was to investigate whether SCS could reduce myocardial ischemia, infarct size, and ventricular arrhythmias as well as repolarization alterations in a porcine ischemia-reperfusion model.Methods: Anesthetized common Landrace pigs were randomized to SCS (n = 10) or sham treatment (n = 10) before, during, and after 45 minutes of coronary occlusion. Area at risk, infarct size, and spontaneous ventricular arrhythmias were analyzed. Continuous three-dimensional vectorcardiograms was recorded and analyzed with respect to ECG intervals, ST-segment, and T-vector and T-vector-loop morphology.Results: SCS was associated with significantly (P <.04) fewer episodes of nonsustained ventricular tachycardia (NSVT) and sustained ventricular tachycardia (SVT), particularly during mid-left anterior descending artery (LAD) occlusion (SCS vs non-SCS; NSVT, mid- and proximal LAD: 0 vs 22 and 45 vs 72; SVT, mid- and proximal LAD: 3 vs 15 and 5 vs 5). No difference in ventricular fibrillation episodes was observed. The SCS group had significantly less ST elevation (P <.03) but similar area at risk, infarct size, and ratio of infarct size/area at risk. Ischemia induced increases of T(amplitude) and T(area) suggesting increased repolarization gradients, which were significantly reduced by SCS (P <.01 for both).Conclusion: SCS appears to have an antiarrhythmic effect on spontaneous NSVT and SVT during ischemia-reperfusion in association with a reduction of repolarization alterations. Vectorcardiography signs of myocardial ischemia were reduced by SCS, but this intervention was not accompanied by any effect on infarct size. [ABSTRACT FROM AUTHOR]

Background: Data on long-term effects of catheter ablation vs antiarrhythmic drugs (AADs) on health-related quality of life (HRQoL) and atrial fibrillation (AF) burden are limited., Objective: The study aimed to assess long-term HRQoL and rhythm data in patients with symptomatic AF., Methods: The 75 patients who underwent ablation and 74 receiving AAD in the Catheter Ablation compared with Pharmacological Therapy for Atrial Fibrillation trial were followed for 48 months. The General Health subscale of the 36-Item Short-Form Health Survey, time to first AF episode ≥1 hour, and AF burden, recorded by implantable cardiac monitors, were compared., Results: One hundred forty-seven patients completed follow-up, with 7 crossovers in the ablation group and 34 crossovers in the AAD group. General Health improved by ablation from a median of 62 points at baseline to 79.2 points at follow-up (P < .001) and by AAD from a median of 67 to 77 points (P < .001), without treatment differences (P = .77). Time to first AF episode ≥1 hour was longer (median 257 days in the ablation group vs 180 days in the AAD group; P = .025). The cumulative AF burden during follow-up was lower in the ablation group (median 0.3%; interquartile range [IQR] 0%-1.4%) than in the AAD group (1.6%; IQR 0.1%-11.0%) (P = .01). The cumulative reduction in AF burden compared with baseline was greater in the ablation group (median -89.5%; IQR -98.4% to -51.3%) than in the AAD group (-52.7%; IQR -92.6% to 263.6%); P < .001)., Conclusion: HRQoL improvement at long-term did not differ between ablation and AAD groups despite a larger reduction in AF burden after ablation. The results should be interpreted in the light of a high crossover rate in the AAD group., Competing Interests: Disclosures All authors have declared no conflicts of interest., (Copyright © 2024 Heart Rhythm Society. Published by Elsevier Inc. All rights reserved.)

Background: Potassium channel dysfunction in congenital and acquired forms of long QT syndrome types 1 and 2 (LQT1 and LQT2) increases the beat-to-beat variability of the QT interval., Objective: To study about the little known variability (instability) of other aspects of ventricular repolarization (VR) in humans by using vectorcardiography., Methods: Beat-to-beat analysis was performed regarding vectorcardiography derived RR, QRS, and QT intervals, as well as T vector- and T vector loop-based parameters during 1-minute recordings of uninterrupted sinus rhythm at rest in 41 adult LQT1 (n = 31) and LQT2 (n = 10) mutation carriers and 41 age- and sex-matched control subjects. The short-term variability for each parameter, describing the mean orthogonal distance to the line of identity on the Poincaré plot, was calculated., Results: Mutation carriers showed significantly larger (by a factor 2) instability in most VR parameters compared to controls despite higher instantaneous heart rate variability (STVRR) in the control group. The longer the QT interval, the greater was its instability, and the instability of VR dispersion measures., Conclusions: A greater instability of most aspects of VR already at rest seems to be a salient feature in both LQT1 and LQT2, which might pave the way for early afterdepolarizations and torsades de pointes ventricular tachycardia. In contrast, no signs of increased VR dispersion per se were observed in mutation carriers., (Copyright © 2013 Heart Rhythm Society. Published by Elsevier Inc. All rights reserved.)

Background: Prolonged exercise can induce cardiac fatigue, which is characterized by biomarker release and impaired myocardial function. The impact on ventricular electrophysiology is largely unknown., Objective: The objective of this study was to examine changes in ventricular repolarization after a 30-km cross-country race in runners aged >or=55 years., Methods: Fifteen healthy participants (62 +/- 5 years) were assessed using biomarkers (N-terminal pro-brain natriuretic peptide [NT-proBNP], troponin T [TnT]), tissue Doppler echocardiography, and vectorcardiography at baseline, within 1 hour postrace and on days 1 and 6 postrace., Results: During the race, NT-proBNP increased from 42 ng/L (interquartile range 25-117) to 187 ng/L (113-464), and TnT increased from undetectable levels to 0.03 microg/L (0.015-0.05). Global strain (19.1% +/- 2.2%) decreased on day 1 (17.2% +/- 1.8%) and day 6 (17.9% +/- 1.5%; P <.01). QT(c) increased from 431 +/- 15 ms prerace to 445 +/- 22 ms postrace and 445 +/- 15 ms on day 1 (P <.05), mainly because of an increased T(peak-end) interval (prerace 108 +/- 13 ms, postrace 127 +/- 43 ms, day 1 127 +/- 43 ms; P <.05). Postrace, T(area) (baseline 75 +/- 26 microVs) peaked on day 1 (105 +/- 42 microVs) and remained high on day 6 (89 +/- 37 microVs; P <.05). Runners with higher baseline NT-proBNP developed greater impairment of myocardial velocities (rho = -0.68 to -0.54; P <.05) and a larger increase in T(area) (rho = 0.73; P <.01)., Conclusion: Cardiac fatigue induced by prolonged exertion is associated with sustained abnormalities in ventricular repolarization. Runners with higher baseline NT-proBNP are especially liable to such alterations of cardiac function.

Background: Patients with an accessory pathway (AP) have an increased propensity to develop atrial fibrillation (AF), but the mechanism is unknown., Objective: The purpose of this study was to identify crucial risk factors and to test the hypothesis that reflection and/or microreentry of atrial impulses propagating into the AP triggers AF., Methods: Five hundred thirty-four patients successfully treated with radiofrequency ablation of AP at two university hospitals were evaluated. Patients were separated into those with concealed vs those with manifest AP in terms of their propensity to develop AF. To investigate AF triggering mechanisms, linear and branched two-dimensional models of atrium-to-ventricle propagation across a heterogeneous 1 x 6 AP using human ionic kinetics were simulated., Results: A history of AF was twice as common in patients with manifest AP vs concealed AP irrespective of AP location. AF was more likely to occur in older males and in patients with larger atria. There was no correlation between AF history and AP refractory measures. However, the electrophysiologic properties of APs seemed to fulfill the prerequisites for reflection and/or microreentry of atrially initiated impulses. In the linear AP model, repetitive atrial stimulation resulted in progressively larger delay of atrium-to-ventricle propagation across the passive segment. Eventually, sufficient time for repolarization of the atrial segment allowed for reflection of an impulse that activated the entire atrium and by wavefront-wavetail interaction with a new atrial stimulus AF reentry was initiated. Simulations using the branched model showed that microreentry at the ventricular insertion of the AP could also initiate AF via retrograde atrial activation as a result of unidirectional block at the AP-ventricle junction., Conclusion: Propensity for AF in patients with an AP is strongly related to preexcitation, larger atria, male gender, and older age. Reflection and microreentry at the AP may be important for AF initiation in patients with manifest (preexcited) Wolff-Parkinson-White syndrome. Similar mechanisms also may trigger AF in patients without an AP.

Background: Right ventricular apical (RVA) pacing induces electrophysiological and structural remodeling. Cardiac memory (CM) evolves during the course of pacing and is readily apparent on electrocardiography (ECG) or vectorcardiography (VCG) when normal ventricular activation resumes., Objective: This study sought to assess ventricular repolarization (VR) changes during pacing and intermittent normal ventricular conduction by ECG and VCG and to determine the temporal and conformational evolution of CM., Methods: Twenty sick sinus patients received a dual-chamber rate-adaptive (DDD-R) pacemaker and were paced from the RVA endocardium. The pacemakers were programmed to a short AV delay to maximize ventricular preexcitation. The ECG and VCG were recorded before and 1 day after implantation, and then daily for the first week (n=6) or weekly for 5 to 8 weeks (n=14), with the pacemakers temporarily programmed to AAI (normal ventricular activation)., Results: The first parameters to change were T-vector amplitude, T(area), and T(peak)-T(end) (T(p-e)), which decreased within 1 day after initiating pacing. CM became apparent between day 1 and day 3, was fully established after 1 week, and then remained stable. Signs of increased VR heterogeneity were observed as the T loop became more circular (decreased T(egenv)) and distorted (increased T(avplan)), which have previously been observed in conditions with increased risk for arrhythmias. Over weeks, VR duration was prolonged (increased QTc). In contrast, during ventricular pacing, a gradual shortening of the repolarization time was observed, suggesting a stabilizing adaptive process., Conclusion: In sick sinus syndrome patients in whom ventricular pacing is indicated, switching between normal AV conduction and ventricular pacing should be minimized to avoid periods of repolarization instability.

Objectives: The purpose of this study was to assess the temporal characteristics of cardiac memory in a human pacing model., Background: Cardiac memory is induced by periods of altered ventricular activation and in the canine pacing model develops in 2 to 3 weeks., Methods: Cardiac memory development (phase 1) and resolution (phase 2) was followed qualitatively (ECG) and quantitatively (vectorcardiography [VCG]) in 20 patients with symptomatic sinus bradycardia receiving DDD-R pacing at physiologic rates. During phase 1, maximum ventricular pacing in the right ventricular apical endocardium was achieved by short AV delay. ECG and VCG were recorded during normal ventricular activation prior to implantation (sinus rhythm), 1 day after and then weekly for 5 to 8 weeks during AAI pacing (n = 14, "long-term"), and daily during 1 week (n = 6, "short-term"). In phase 2, the remaining cardiac memory was related to the amount of ventricular pacing. A long AV delay was chosen to reduce ventricular pacing, and 14 patients were seen once after 4 to 5 weeks., Results: ECG and VCG showed marked changes in all patients within 1 week's pacing and remained stable during phase 1. Of the 14 long-term patients, 13 showed significant change in T vector azimuth (mean -150 degrees ) and 11 in T vector elevation (mean 63 degrees ). At the end of phase 2, a linear relation existed between remaining cardiac memory (%) and amount (%) of delivered ventricular pacing., Conclusions: Cardiac memory developed and reached steady state within 1 week of right ventricular endocardial pacing at physiologic rates in man, was preserved in proportion to delivered ventricular pacing, and completely resolved within 1 month in its absence.

Objective: Three-dimensional characterization of the ventricular repolarization by the T vector and T vector loop morphology in coronary artery disease (CAD), and their response to short-term (no flow) ischemia induced by coronary occlusion during a percutaneous intervention (PCI)., Background: The risk for sudden cardiac death is increased in conditions of acute or permanently heterogeneous ventricular repolarization, for which ischemia is a risk factor., Methods: Fifty-six CAD patients without visible collateral circulation were studied during an elective single-vessel PCI, and 10 healthy controls twice at rest. T vector parameters (Televation, Tazimuth, and QRS-T angle), and T loop parameters (Tarea, Tavplan, and Teigenv) were measured by vectorcardiography. ST vector magnitude (ST-VM) and its change (STC-VM) were used for reference., Results: At rest, T vector loop morphology (Tarea, Teigenv) was significantly different in CAD patients and controls, while T vector angles did not separate the groups. Ischemia induced significant changes in T loop parameters in the entire CAD group, whereas in the LAD subgroup significant changes were seen also in T vector angle. The T loop morphology was significantly different at baseline and a more pronounced response to ischemia (Tarea) was seen in patients with, than in those without, a history of hypertension., Conclusion: T loop morphology, rather than the T vector angle, separated CAD patients from healthy controls. Coronary occlusion had significant impact on ventricular repolarization, as assessed by T vector and morphology analysis, and most prominently in the LAD group. Hypertensive patients appeared especially vulnerable to ischemia.