Long QT Syndromes

Atrioventricular node ablation for atrial fibrillation in the era of conduction system pacing

Despite key advances in catheter-based treatments, the management of persistent atrial fibrillation (AF) remains a therapeutic challenge in a significant subset of patients. While success rates have improved with repeat AF ablation procedures and the concurrent use of antiarrhythmic drugs, the likelihood of maintaining sinus rhythm during long-term follow-up is still limited. Atrioventricular node ablation (AVNA) has returned as a valuable treatment option given the recent developments in cardiac pacing. With the advent of conduction system pacing, AVNA has seen a revival where pacing-induced cardiomyopathy after AVNA is felt to be overcome. This review will discuss the role of permanent pacemaker implantation and AVNA for AF management in this new era of conduction system pacing. Specifically, this review will discuss the haemodynamic consequences of AF and the mechanisms through which 'pace-and-ablate therapy' enhances outcomes, analyse historical and more recent literature across various pacing methods, and work to identify patient groups that may benefit from earlier implementation of this approach.

Acute and long-term outcomes of simultaneous atrioventricular node ablation and leadless pacemaker implantation

AIMS

Leadless pacemaker (LDP) allows implantation using a femoral approach. This access could be utilized for conventional atrioventricular nodal ablation (AVNA). It could facilitate unifying the two procedural components. Data regarding its feasibility and long-term outcomes remain lacking. We aim to evaluate the feasibility and long-term outcomes of sequential LDP and AVNA.

METHODS

Prospective, observational multicenter study including consecutive patients with indication for single-chamber pacemaker placement. In those with additional indication for AVNA, ablation was performed immediately after the LPD through the same sheath.

RESULTS

A total of 137 patients were included. Mean age was 77.9 ± 10.5 years; 74 (54%) were men. Immediately following LDP implantation, 27 patients (19.7%) underwent concurrent AVNA. There were six (5.5%) complications in patients referred for LDP procedures and three (11%) in those who underwent a combined approach. None of these complications were solely attributable to the added AVNA component. No mechanical dislodgement, electrical damage to any device, or electromagnetic interference ever took place. During a mean follow-up period of 123 ± 48 days, three patients (3.6%) died of noncardiovascular causes. The remaining population stayed alive without significant arrhythmias. There were no relevant differences with regard to sensing and pacing thresholds between patients in the two groups.

CONCLUSIONS

AVNA can safely be performed immediately following LDP. A combined approach obviates the need for additional vascular access and optimizes feasibility and comfort for patients and healthcare providers. It offers an acceptable safety and efficacy profile, both acutely and upon intermediate-term follow-up.

Two-Year Follow-up in Atrial Fibrillation Patients Referred for Catheter Ablation of the Atrioventricular Node

INTRODUCTION

At the present time there is still concern regarding the long-term deleterious effects of right ventricular apical pacing in patients referred for auriculoventricular node ablation (AVNA). Furthermore, scarce information is available regarding differences in the follow up according to the baseline cardiopathy and predictors associated with a worse outcome.

METHODS

104 consecutives patients referred for AVNA were retrospectively analyzed. Patients included were seen in the outpatient clinic at 6, 12 and 24 months post ablation (mean follow-up 24 ± 2 months). An echocardiogram two years after the procedure was obtained in 68 patients. Three categories were done according to the change in the left ventricular function (LVEF) (increase, decrease or absence of change, defined as less than 10% variation in either LVEF).

RESULTS

After two years of follow up there was a decrease in the rate of hospital admission (from 0.9 admission/year to 0.35, p<0.001), an increase in the functional status in at least one NYHA class in 58 patients, and an increase in the global LVEF (from 48.9% to 54,1%; p<0.001). Valvular replacement and LVEF less than 50% were independently associated with a decrease in the LVEF. Regarding safety issues, one patient who presented a polymorphic ventricular tachycardia (Torsade de pointes) 60 minutes after the ablation.

CONCLUSIONS

AVNA results in a decrease in hospital admission rates and an improvement in functional status. Baseline LVEF < 50% and mitral valvulopathy were multivariate predictor of LVEF decline, hence, it is our belief that, in this particular population, the "ablate and pace" strategy is not the most suitable option, and or maybe a biventricular pacemaker should be implanted or an AF ablation reconsidered." Finally, although it is a safe procedure and rate of complications were low, there is a potential risk of fatal complications.

Effect of pacing method on risk of sudden death after atrioventricular node ablation and pacemaker implantation in patients with atrial fibrillation

BACKGROUND

Sudden death may occur after radiofrequency catheter ablation of the atrioventricular node (AVN) and permanent pacemaker implantation. It is unclear whether a faster initial heart rate with gradual rate reduction decreases the risk of sudden death.

OBJECTIVE

To evaluate the effects of initial pacing at a faster rate after AVN ablation, with a gradual rate decrease over 3 months, on the rate of sudden death in patients with atrial fibrillation.

METHODS

We compared the rate of likely or possible procedure-related sudden death in 2 groups of patients who had AVN ablation and pacemaker implantation. The study cohort was treated between January 2005 and December 2009, and pacemakers were programmed to a lower rate of 90 beats/min after the procedure, with a monthly decrement of 10 beats/min until 60 beats/min was reached. The control group was treated between July 1990 and December 1998 when pacemakers were programmed to a lower rate of 60 beats/min immediately after ablation.

RESULTS

The study cohort included 520 patients (mean age 73.6 ± 10.3 years), and the control cohort comprised 334 patients (mean age 68.1 ± 1.1 years). Sudden death deemed likely or possibly related to ablation and pacemaker implantation occurred in 1 patient in the study cohort (0.2%) and in 7 patients (2.1%) in the control group (P = .007).

CONCLUSIONS

Sudden death was significantly decreased in the study cohort compared to controls. The faster lower pacing rate immediately after AVN ablation with a gradual decrease is a plausible mechanism for the improved clinical outcome.

Epinephrine-induced T-wave notching in congenital long QT syndrome

OBJECTIVES

The purpose of this study was to characterize the effect of epinephrine on T-wave morphology in patients with congenital long QT syndrome (LQTS).

BACKGROUND

QT prolongation is a paradoxical, LQT1-specific response to low-dose epinephrine infusion. At rest, notched T waves are more common in LQT2.

METHODS

Thirty subjects with LQT1, 28 with LQT2, and 32 controls were studied using epinephrine provocation. Twelve-lead ECG was recorded continuously, and QT, QTc, and heart rate were obtained during each stage. Blinded to phenotype and genotype, T-wave morphology was classified as normal, biphasic, G1 (notch at or below the apex), or G2 (distinct protuberance above the apex).

RESULTS

At baseline, 97% LQT1, 71% LQT2, and 94% control had normal T-wave profiles. During epinephrine infusion, G1- and G2-T waves were more common in LQT2 than in LQT1 (75% vs 26%, P = .009). However, epinephrine-induced G1-T waves were present in 34% of control. Epinephrine-precipitated biphasic T waves were observed similarly in all groups: LQT1 (6/30), LQT2 (3/28), and control (4/32). During low-dose epinephrine infusion (< or =0.05 microg/kg/min), G1-T waves occurred more frequently in LQT2 (LQT1: 25% vs 3%; control 9%, P = .02). Low-dose epinephrine-induced G2-T waves were detected exclusively in LQT2 (18%). Low-dose epinephrine elicited G1/G2-T waves in 8 of 15 LQT2 patients with a nondiagnostic baseline QTc.

CONCLUSIONS

Biphasic and G1-T waves are nonspecific responses to high-dose epinephrine. Changes in T-wave morphology during low-dose epinephrine (<0.05 microg/kg/min) may yield diagnostic information. G2-notched T waves elicited during low-dose epinephrine may unmask some patients with concealed LQT2.

Novel therapeutics for treatment of long-QT syndrome and torsade de pointes

Long-QT syndrome is a clinically and genetically heterogeneous syndrome characterized by lengthening of the QT interval and increased dispersion of the ventricular repolarization on surface electrocardiogram and a propensity to malignant ventricular arrhythmias, torsade de pointes and ventricular fibrillation, which may lead to sudden cardiac death. Long-QT syndrome mostly affects adolescents and young adults with structurally and functionally normal hearts and is caused by aberrations in potassium and sodium ion channels. Standard therapies for long-QT syndrome include correction of the underlying cause, alleviation of the precipitating factors, magnesium sulfate, isoproterenol, antiadrenergic therapy (beta-adrenergic receptor blockers, left cervicothoracic sympathectomy), cardiac pacing, and implantable cardioverter defibrillator. The potential therapies include sodium channel blockers (mexiletine, flecainide, lidocaine, pentisomide, phenytoin), potassium, potassium channel activators (nicorandil, pinacidil, cromakalim), alpha-adrenergic receptor blockers, calcium channel blockers, atropine, and protein kinase inhibitors. The purpose of this review is to outline the established therapies and update the recent advances and potential future strategies in the treatment of long-QT syndrome and torsade de pointes.

Sudden death after radiofrequency ablation of the atrioventricular node in patients with atrial fibrillation

OBJECTIVES

We evaluated the incidence and predictors of sudden death after atrioventricular (AV) node ablation and pacemaker implantation.

BACKGROUND

Sudden death may occur after radiofrequency catheter ablation of the AV node and pacemaker implantation in patients with atrial fibrillation (AF). Whether it is related to the procedure or to pre-existing heart disease remains unclear.

METHODS

All patients who had radiofrequency catheter ablation of the AV node and pacemaker implantation for rate control of medically refractory AF were identified retrospectively and observed prospectively. All patients with sudden death after ablation were identified. The relationship between the procedure and sudden death was defined on the basis of the time between the two as "likely," "possibly" or "unlikely."

RESULTS

Of 334 consecutive patients with AF who underwent AV node ablation, nine had sudden death after the ablation. Four patients (1.2%) had sudden death likely related to the procedure: in 3 patients, arrest occurred within 48 h after the procedure; in one patient, arrest occurred four days after the procedure. In three other patients (0.9%), sudden death was possibly related to the procedure because the event occurred within three months afterward. The remaining two deaths were unrelated to the procedure. Diabetes, New York Heart Association functional class (>or=II), preprocedure ventricular arrhythmia, mitral or aortic stenosis, aortic regurgitation and chronic obstructive pulmonary disease were independent predictors for sudden death.

CONCLUSIONS

Sudden death likely or possibly related to catheter ablation occurred in 7 of 334 patients (2.1%). Risk of sudden death is highest within two days after the procedure.