Alexander Yang

Strategy for Safe Performance of Extrathoracic Magnetic Resonance Imaging at 1.5 Tesla in the Presence of Cardiac Pacemakers in Non–Pacemaker-Dependent Patients A Prospective Study With 115 Examinations

Background— The purpose of the present study was to evaluate a strategy for safe performance of extrathoracic magnetic resonance imaging (MRI) in non–pacemaker-dependent patients with cardiac pacemakers. Methods and Results— Inclusion criteria were presence of a cardiac pacemaker and urgent clinical need for an MRI examination. Pacemaker-dependent patients and those requiring examinations of the thoracic region were excluded. The study group consisted of 82 pacemaker patients who underwent a total of 115 MRI examinations at 1.5T. To minimize radiofrequency-related lead heating, the specific absorption rate was limited to 1.5 W/kg. All pacemakers were reprogrammed before MRI: If heart rate was <60 bpm, the asynchronous mode was programmed to avoid magnetic resonance (MR)–induced inhibition; if heart rate was >60 bpm, sense-only mode was used to avoid MR-induced competitive pacing and potential proarrhythmia. Patients were monitored with ECG and pulse oximetry. All pacemakers were interrogated immediately before and after the MRI examination and after 3 months, including measurement of pacing capture threshold (PCT) and serum troponin I levels. All MR examinations were completed safely. Inhibition of pacemaker output or induction of arrhythmias was not observed. PCT increased significantly from pre- to post-MRI (P=0.017). In 2 of 195 leads, an increase in PCT was only detected at follow-up. In 4 of 114 examinations, troponin increased from a normal baseline value to above normal after MRI, and in 1 case (troponin pre-MRI 0.02 ng/mL, post-MRI 0.16 ng/mL), this increase was associated with a significant increase in PCT. Conclusions— Extrathoracic MRI of non–pacemaker-dependent patients can be performed with an acceptable risk-benefit ratio under controlled conditions and by taking both MR- and pacemaker-related precautions.

Comparison of Cryoballoon and Radiofrequency Ablation of Pulmonary Veins in 40 Patients with Paroxysmal Atrial Fibrillation: A Case‐Control Study

Introduction: Ablation of pulmonary veins (PV) is an established therapeutic option for patients with symptomatic drug‐refractory paroxysmal atrial fibrillation (AF). Radiofrequency (RF) is currently the most widespread energy source for PV ablation. Cryothermal energy applied with a cryoballoon technique as an alternative has recently evolved.

Individualized selection of pacing algorithms for the prevention of recurrent atrial fibrillation: Results from the VIP registry.

Objectives: The VIP registry investigated the efficacy of preventive pacing algorithm selection in reducing atrial fibrillation (AF) burden.

Induction of atrial fibrillation in mice by rapid transesophageal atrial pacing.

Abstract.Objective: Atrial fibrillation (AF) as an “indicator arrhythmia” for enhanced atrial vulnerability in mouse hearts has not yet been systematically examined. We therefore evaluated a transesophageal rapid atrial stimulation protocol for the induction of AF in C57Bl/6 mice. Methods: 40 C57Bl/6 mice (19 female and 21 male; 5.2 ± 2.1 months; 18 – 27 g) were examined by closed chest transesophageal atrial stimulation. Baseline ECG and electrophysiological parameters, AF-inducing stimulation cycle length (CL) and AF duration were analyzed. Results: The surface ECG demonstrated a significantly faster heart rate in female mice (R-R: 138.7 ± 19.9 ms versus 150.5 ± 15.7 ms, P < 0.05). AF was inducible in 90 % of the population and not inducible in 4 mice, all female (21 % in this subgroup). Mean induction CL was 27.4 ± 7.3 ms. Mean AF duration was 26.9 ± 42.6 s before spontaneous termination. In a subgroup of 4 female and 4 male mice (mean age 7.5 months), successive testing of AF induction showed a range of higher susceptibility to AF at stimulus amplitudes of 3.0 – 4.0 mA and stimulation CLs between 15 – 25 ms. AF induction was observed to be constantly reproducible in the individual animals. No correlation to pacing stimulus length and amplitude was found. Conclusions: This study demonstrates that it is possible to reproducibly induce self-terminating AF and supraventricular arrhythmias in mice by transesophageal atrial burst stimulation. The presented method allowing serial testings of the same animal can be a useful tool in further investigations with transgenic mice and might be helpful in the characterization of underlying genetic or molecular mechanisms of AF.

Gold-Tip Electrodes—A New “Deep Lesion” Technology for Catheter Ablation? In Vitro Comparison of a Gold Alloy Versus Platinum–Iridium Tip Electrode Ablation Catheter

Radiofrequency (RF) catheter ablation is widely used to induce focal myocardial necrosis using the effect of resistive heating through high‐frequency current delivery. It is current standard to limit the target tissue–electrode interface temperature to a maximum of 60–70°C to avoid char formation. Gold (Au) exhibits a thermal conductivity of nearly four times greater than platinum (Pt–Ir) (3.17 W/cm Kelvin vs 0.716 W/cm Kelvin), it was therefore hypothesized that RF ablation using a gold electrode would create broader and deeper lesions as a result of a better heat conduction from the tissue–electrode interface and additional cooling of the gold electrode by “heat loss” to the intracardiac blood. Both mechanisms would allow applying more RF power to the tissue before the electrode–tissue interface temperature limit is reached. To test this hypothesis, we performed in vitro isolated liver and pig heart investigations comparing lesion depths of a new Au‐alloy‐tip electrode to standard Pt–Ir electrode material.

Influence of obstructive sleep apnea on heart rate turbulence

AbstractBackgroundPatients with obstructive sleep apnea (OSA) are at increased risk for cardiovascular disease. Increased sympathetic drive is considered as one of the underlying mechanisms. Both heart rate turbulence (HRT) and heart rate variability (HRV) are parameters to describe autonomic regulation. We investigated the influence of sleep–disordered breathing (SDB) on HRT and HRV in patients with OSA.MethodsSixty–five patients underwent overnight polysomnography for clinically suspected SDB and simultaneous Holter monitoring (11 p.m.–6 a.m.). Patients with diabetes mellitus, a history of cardiac disease, left ventricular dysfunction, periodic breathing pattern, and those on beta–blockers or theophylline were excluded. According to the apnea–hypopnea index (AHI), the patients were assigned to group A (AHI <20, n = 31) or group B (AHI ≥20, n = 34). HRV (time domain, frequency domain) and HRT (onset, slope) were then related to the severity of SDB.ResultsNighttime turbulence slope (TS) correlated inversely with the AHI (r = –0.45, p = 0.01) and was significantly lower in group B (8.9 ± 1.6 ms/R–R interval) compared with that in group A (19.8 ± 4.0 ms/R–R interval, P = 0.01). This relationship remained stable after adjusting TS for the number of ventricular premature contractions. No significant differences in turbulence onset or parameters of nighttime HRV were observed.ConclusionsAlterations in nighttime HRT correlate with the severity of SDB, indicating abnormalities in cardiac autonomic activity in moderate–to–severe OSA even in the absence of overt cardiac disease. These changes may be associated with the subsequent development of cardiovascular disease.

Impact of age and basic heart rate on heart rate turbulence in healthy persons.

Postextrasystolic acceleration of heart rate (HR), known as HR turbulence (HRT) is attenuated in patients with coronary artery disease at increased risk of adverse events. The influence of age and basic HR on HRT have not been evaluated in a large cohort of persons. In 95 healthy individuals, HRT onset (TO) and slope (TS) were calculated from 24‐hour ambulatory electrocardiograms, as well as the turbulence timing (TT). Gender specific differences in TO and TS were compared in simple, linear, weighted regression model. The influence of age and the basic HR preceding ventricular premature contractions on HRT were examined. We found that, in men and women, TO decreases as basic HR increases (P < 0.01). In contrast, in men, TS decreased as basic HR increases, whereas in women, basic HR influenced TS only slightly (P < 0.01). A multiple, linear regression model revealed a decrease in HRT with increasing age in men. In conclusion, physiological acceleration of the HR within the first 11 beats after premature ventricular complex (VPC) was observed in >75% of healthy individuals. An accelerating HR preceding the VPC influenced HRT in men. An increasing age was associated with a decrease in HRT in men and a decrease in TO in women. These results illustrate the importance of physiological modulations of HRT when used for risk stratification, especially in older populations.

Influence of the point of origin on heart rate turbulence after stimulated ventricular and atrial premature beats

Abstract.Background:Heart rate turbulence (HRT) is a new and auspicious parameter for risk stratification in patients suffering from structural heart disease. The HRT parameters onset (TO) and slope (TS) are derived from Holter ECGs. Only a few studies have evaluated physiologic properties like age or prematurity of the ventricular beat on HRT. Until now, to our knowledge, little is known about the influence of the point of origin of the premature beat on HRT. Therefore, we conducted a study consisting of 25 patients (pts) with premature beats generating from 2 different sites in the atrium and ventricle.Methods:During an electrophysiologic study, premature extra beats were induced. The high right atrium (HRA) and the lateral part of the coronary sinus (CS) represented the atrial pacing sites, while the right ventricular apex (RVAP) and right ventricular outflow tract (RVOT) represented the ventricular pacing sites. Prematurity started at 450 ms and was decreased to the refractoriness of each site. TO and TS were computed and correlated to the site of origin and the coupling interval (CI).Results:Atrial TO was positive in 9 pts (HRA) and 7 (CS) as well as ventricular TO in 2 pts, respectively. TO induced in CS correlated with the CI (r = –0.50, p < 0.05). TS was negative, independent of the site of origin. Atrial TS showed no correlation with the CI. TO generated from both ventricular sites was positive in 2 pts. TO from RVAP correlated with the CI (r = –0.81, p < 0.005), but not with RVOT. TS from both ventricular sites exhibited no correlation with the pacing site, but correlated with themselves (r = –0.69, p < 0.03).Conclusion:The site of origin of the premature beat exhibits no influence on heart rate turbulence slope. The prematurity of the extra beat correlates with turbulence onset, but not with slope. Finally, the site of origin revealed no influence on HRT slope. Therefore, the calculation of heart rate turbulence derived from extra beats extracted from Holter ECG is reliable.

“Torsade de Pointes” in Patients with Structural Heart Disease and Atrial Fibrillation Treated with Amiodarone, β-Blockers, and Digitalis

Amiodarone is one of the most efficient and safe antiarrhythmic drugs in the treatment of atrial fibrillation (AF). Yet, though rare, proarrhythmic effects remain a clinical problem. We present three cases of amiodarone‐associated “Torsade de pointes” tachycardia (Tdp) in patients treated concomitantly with heart rate controlling medication for AF. Amiodarone loading therapy was started for the treatment of tachyarrhythmic AF in all the three patients. All presented with a history of coronary heart disease, resulting in a severely reduced left ventricular ejection fraction in two patients. One received oral amiodarone loading, in the others, amiodarone was administered intravenously because of hemodynamically relevant AF episodes. Amiodarone therapy was combined with a heart rate controlling medication including a β‐blocking agent and digitalis in all the cases. All the subjects suffered from clinically relevant Tdp in the early run after initiation of amiodarone loading (max. 48 hours). The mean QTc in all patients before induction of Tdp was prolonged. The present case reports imply that amiodarone in combination with β‐blocker/digitalis therapy may be associated with an elevated proarrhythmic risk in selected patients with structural heart disease and AF.

Advanced Pacemaker Diagnostic Features in the Characterization of Atrial Fibrillation: Impact on Preventive Pacing Algorithms

YANG, A., et al.: Advanced Pacemaker Diagnostic Features in the Characterization of Atrial Fibrillation: Impact on Preventive Pacing Algorithms. Pacing algorithms to prevent PAF are mainly based on the suppression of premature atrial complexes (PACs), which play an important role in its initiation. In contrast to 24‐hour ambulatory electrocardiograms, advanced pacemaker (PM) diagnostic features are capable of recording AF episodes during long follow‐up periods and of characterizing AF in a detailed fashion. For the specific use of these algorithms, a detailed characterization of AF was performed in 91 dual chamber PM recipients with histories of AF. Fifteen patients with episodes of oversensing due to far‐field signals or frequent episodes of “2:1‐undersensing” of atrial flutter were excluded. The remaining 76 patients had high recurrence rates of AF (median 0.8 episodes/day), however, the majority of episodes lasted <7 minutes. Despite frequent PACs (median 10.8/hour) during sinus rhythm, a median of 66.4% of the AF episodes were preceded by <2 PACs/min before onset. In conclusion, frequent, short‐lived AF episodes seem best suited for AF preventive pacing therapies. However, the small number of PACs preceding many AF episodes may limit the efficacy of PAC suppressing algorithms. (PACE 2003; 26[Pt. II]:310–313)