Munoz, Freddy Del‐Carpio

Abstract Pulsed electric fields (PEFs) have emerged as an ideal cardiac ablation modality. At present numerous clinical trials in humans are exploring PEF as an ablation strategy for both atrial and ventricular arrhythmias, with early data showing significant promise. As this is a relatively new technology there is limited understanding of its principles and biophysics. Importantly, PEF biophysics and principles are starkly different to current energy modalities (radiofrequency and cryoballoon). Given the relatively novel nature of PEFs, this review aims to provide an understanding of the principles and biophysics of PEF ablation. The goal is to enhance academic research and ultimately enable optimization of ablation parameters to maximize procedure success and minimize risk.

Background: Rigorous study of ventricular fibrillation (VF) is not feasible in humans. The spatiotemporal characteristics of prolonged VF remain undefined, limiting our understanding of this lethal rhythm. Methods: VF was mapped in 4 canines. The endocardial and epicardial left ventricle (LV) and right ventricle (RV) were sequentially mapped at 0 to 15, 15 to 30, 30 to 45, and 45 to 60 minutes post-induction. Ten consecutive beats were used to determine the average cycle length and regularity index of ventricular and His-Purkinje system signals in discrete regions during each time interval. Results: Average VF time was 58±12 minutes. The shortest ventricular cycle length was present in the RV apical region (70±10 msec) at 0 to 15 minutes and at 15 to 30 minutes (89±31 msec) and LV apical region at 45 to 60 minutes (242±163 msec). The His-Purkinje system cycle length was the shortest at the RV outflow tract (75±3 msec) at 0 to 15 minutes, RV inflow and free wall (89±12 msec) at 15 to 30 minutes, LV apical region (83±14 msec) at 30 to 45 minutes, and inferior and inferolateral LV (145±23 msec) at 45 to 60 minutes. Regularity index was the highest in the RV inflow and free wall (78%) at 0 to 15 minutes, RV apical region (86%) at 15 to 30 minutes, LV septum and epicardial anterior RV (80%) at 30 to 45 minutes, and anterior and anterolateral LV (75%) at 45 to 60 minutes. Conclusions: These data suggest significant regional changes in electrical activity throughout VF in canines. A transition of fastest electrical activity from RV to LV apical regions across VF was observed. These novel insights of the temporal and spatial changes of VF merit further evaluation in diseased hearts to assess for reproducibility of findings.

AbstractProviders should be aware of the possibility of cardiac resynchronization therapy‐related proarrhythmia which could be life‐threatening. His‐bundle pacing may serve as an alternative, more physiological, option in the management as it preserves the normal sequence of depolarization from the septum to the lateral wall, and from endocardium to epicardium.

AbstractBackgroundAtrial fibrillation (AF) among patients with heart failure with reduced ejection fraction (HFrEF) is associated with adverse clinical outcomes. Our primary aim was to evaluate patient‐centered outcomes and surrogate outcomes following catheter ablation (CA) of AF among patients with HFrEF compared to standard medical therapy with or without device therapy (atrioventricular node ablation and cardiac resynchronization therapy).MethodsA systematic literature review was performed limiting our searches to randomized control trials reporting outcomes of CA compared to standard medical therapy with or without device therapy were included. Patient‐centered outcomes were relative reduction in all‐cause mortality, heart failure readmissions, and recurrence of AF. Surrogate outcomes of interest were change in ejection fraction, change in peak oxygen consumption, reduction in brain natriuretic peptide levels, change in 6‐minute walk distance, and change in Minnesota living with heart failure score.ResultsSeven randomized control trials (Patient n = 721) met our inclusion criteria. All trials used radiofrequency energy for CA of AF. CA for AF was associated with significantly lower all‐cause mortality (Risk ratio [RR] = 0.52, 95% confidence interval [CI] = 0.35‐0.76, P = 0.001, I2 = 0%), lower rate of heart failure readmission (RR = 0.58, 95% CI = 0.46‐0.74, P < 0.001, I2 = 0%) and lower rate of AF recurrence (RR = 0.33, 95% CI = 0.22‐0.50, P < 0.001, I2 = 68%) as compared to standard medical therapy. Surrogate outcomes showed a similar benefit favoring CA.Conclusion and RelevanceCatheter ablation for AF in HFrEF is associated with improvement in patient‐centered outcomes and surrogate outcomes when compared to standard medical therapy with or without device therapy.

AbstractBackgroundCardiac resynchronization therapy (CRT) reverses left ventricular remodeling and improves left ventricular systolic function. However, little is known about whether CRT improves ventricular conduction.ObjectiveTo determine the relationship between CRT response and QRS narrowing.MethodsThe study included consecutive patients who underwent CRT with defibrillator (CRT‐D) implantation between January 2002 and December 2012 and had subsequent generator replacement (GR). At the time of GR, super‐responder was defined as those who had left ventricular ejection fraction (LVEF) of 50% or more; patients who had an LVEF of 36–49% with an increase of more than 5% were considered responders, and the others were nonresponders. All patients were assessed 6 months after CRT‐D implantation and at the time of GR.ResultsOf 114 study patients, 58 (50.9%) were nonresponders, 29 (25.4%) responders, and 27 (23.7%) super‐responders. QRS narrowing at 6 months was significant in super‐responders (175.4 ± 21.4 to 159.7 ± 20.7 ms, P = 0.001) and responders (169.0 ± 21.3 to 157.7 ± 17.6 ms, P = 0.008). At time of GR, only super‐responders had further QRS narrowing (159.7 ± 20.7 to 146.3 ± 19.2 ms, P < 0.001). QRS duration change after 6 months was independently associated with super‐response (hazard ratio: 1.20 for every 5 ms QRS duration narrowing; 95% confidence interval, 1.06–1.38; P = 0.005), and QRS narrowing of 10 ms or more was associated with lower risk of all‐cause mortality after GR.ConclusionContinuous QRS narrowing after CRT, as an electrical marker, is associated with a super‐response to CRT. Further QRS narrowing 6 months after CRT implantation was associated with lower risk of mortality after GR.

AbstractBackgroundQRS fragmentation (fQRS) during baseline ventricular conduction, a myocardial fibrosis marker, is associated with increased risk of ventricular tachyarrhythmias but may not manifest unless ventricular activation change is provoked. We examined the association of fQRS during right ventricular (RV) pacing with death and ventricular tachyarrhythmia in patients with left ventricular (LV) dysfunction undergoing electrophysiology study (EPS).Methods and resultsStudy participants had LV dysfunction (ejection fraction < 50%) undergoing EPS from January 2002 to May 2014 at Mayo Clinic in Rochester, Minnesota. fQRS during RV stimulation involved >2 notches on R/S waves identified in ≥2 contiguous standard electrocardiographic leads representing anterior, inferior, or lateral ventricular segments. Primary outcomes were ventricular tachyarrhythmias that were symptomatic or required intervention and total and cardiac deaths. In all, 528 patients participated (mean age, 65 years; male sex, 80%). Of them, 312 (59%) had ischemic cardiomyopathy and mean (SD) left ventricular ejection fraction (LVEF) of 33.2% (9.5%); 457 (87%) had implantable cardiac devices (implanted defibrillator, n = 380). Mean (SD) follow‐up was 3.2 (3.0) years. fQRS during RV pacing was observed in 292 patients (60%) in any ventricular segment. Patients with fQRS during RV pacing had 2.5 higher rate of ventricular tachyarrhythmia events than patients with no fQRS (hazard ratio [95% CI], 2.45 [1.5–4.2]; P < 0.01), after correcting for baseline ventricular conduction defect and QRS duration, LVEF, inducible sustained ventricular tachycardia, diabetes mellitus, chronic kidney disease, and ischemic cardiomyopathy.ConclusionsRV stimulation can unmask fQRS, and it is associated with increased risk of ventricular tachyarrhythmia in LV dysfunction.

The use of energy drinks, which often contain stimulants, is common among young persons, yet there have been few reports of adverse cardiac events. We report the case of a 27-year-old man who was admitted to our facility with an acute ST-segment elevation myocardial infarction in the setting of using energy drinks. Angiography revealed no obstructive coronary disease. The patient had elevation of cardiac troponin. Noninvasive testing with echocardiography and cardiac magnetic resonance imaging demonstrated both abnormalities in resting wall motion at the anterior apex along with late gadolinium enhancement of the anterior wall, respectively. The patient also underwent formal invasive evaluation with an intracoronary Doppler study demonstrating normal coronary flow reserve and acetylcholine provocation that excluded endothelial dysfunction and microvascular disease. The patient recovered and has abstained from consuming additional energy drinks with no reoccurrence of symptoms. A review of some of the potential cardiac risks associated with consuming energy drinks is presented.

ECG Lead I and Outflow Tract ArrhythmiaIntroductionOutflow tract ventricular arrhythmia (OTVA) can be complicated to target for ablation when originating from either the periaortic or pulmonary valve (PV) region. Both sites may present with a small R wave in lead V1. However, the utility of lead I in distinguishing these arrhythmia locations is unknown.Methods and ResultsThirty‐six consecutive patients (mean age 41 ± 14 years, 13 male) underwent catheter ablation for OTVA. OTVA origin was determined from intracardiac electrogram tracings and electroanatomic maps. Observers blinded to results measured QRS waveform amplitude and duration from standard 12‐lead ECG tracings. Measurements with highest diagnostic performance were modeled into an algorithm. Sites of successful ablation were anterior right ventricular outflow tract (RVOT; n = 6), posterior RVOT (n = 4), PV (n = 18), and right coronary cusp (RCC; n = 8). Highest performing surface ECG discriminators were from lead I to V1 vectors: RCC, lead I R wave ≥ 1.5 mV, and V1 R wave ≥2.0 mV (sensitivity 87%, specificity 93%); PV, V1 R wave > 0 mV, and lead I R/(R+S) ≤ 0.75 (sensitivity 78%, specificity 72%); anterior RVOT, V1 R wave = 0 mV, and lead I R/(R+S) <0.4 (sensitivity 67%, specificity 97%); posterior RVOT, V1 R wave > 0 mV, and lead I R/(R+S) > 0.75 (sensitivity 75%, specificity 84%). Sequential algorithmic application of these criteria resulted in an overall accuracy of 72% in predicting site of OTVA origin.ConclusionsA relatively large R wave in lead I is seen with RCC origin but not PV origin. A sequential algorithm has limited but potentially significant value beyond assessment of lead I in approaching OTVA.