Mapping Atrial Fibrillation: 2015 Update

Atrial fibrillation requires a trigger that initiates the arrhythmia and substrate that favors perpetuation. Cardiac mapping is necessary to locate triggers and substrate so that an ablation strategy can be optimized. The most commonly used cardiac mapping approach is isochronal or activation mapping, which aims to create a spatial model of electrical wavefront propagation. Historically, activation mapping has been successful for mapping point source and single or double wave reentrant arrhythmias, while mapping multiple wavelets or driving sources that underlie most episodes of atrial fibrillation remains challenging. In the multiple wavelet model of AF there is no particular area critical to sustain atrial fibrillation, and a "critical mass" of atrium is required to maintain AF. Recent studies suggest endocardial and epicardial dissociation may play an important role. Investigation of driving sources that sustain AF has focused on the presence of rotors. Rotors in human AF have now been observed using multiple imaging modalities, however ablation strategies targeting rotors remain of unproven benefit. In addition, substrate mapping of AF is now feasible. Increasing degrees of atrial fibrosis on delayed enhancement magnetic resonance imaging (DE-MRI) has been shown to correlate with poor procedural outcomes for AF ablation, which suggests the increased burden of scar promotes more complex and extensive arrhythmia substrate. Atrial fibrosis is also identifiable using electrogram voltage tagging in an electro-anatomic mapping system. Patient-specific ablation strategies targeting areas of fibrosis are currently under investigation. Recent technological advances have facilitated greater understanding of the potential role for AF mapping and has allowed initiation of clinical studies to evaluate the effectiveness of mapping-based intervention. Multi-modality mapping is likely to play an increasingly important role in AF ablation, but is currently limited by the inability to simultaneously record and interpret electrical signals from both atria and from both the epicardium and endocardium.

Better Lesion Creation And Assessment During Catheter Ablation

Permanent destruction of abnormal cardiac tissue responsible for cardiac arrhythmogenesis whilst avoiding collateral tissue injury forms the cornerstone of catheter ablation therapy. As the acceptance and performance of catheter ablation increases worldwide, limitations in current technology are becoming increasingly apparent in the treatment of complex arrhythmias such as atrial fibrillation. This review will discuss the role of new technologies aimed to improve lesion formation with the ultimate goal of improving arrhythmia-free survival of patients undergoing catheter ablation of atrial arrhythmias.

Voltage-based device tracking in a 1.5 Tesla MRI during imaging: initial validation in swine models

PURPOSE

Voltage-based device-tracking (VDT) systems are commonly used for tracking invasive devices in electrophysiological cardiac-arrhythmia therapy. During electrophysiological procedures, electro-anatomic mapping workstations provide guidance by integrating VDT location and intracardiac electrocardiogram information with X-ray, computerized tomography, ultrasound, and MR images. MR assists navigation, mapping, and radiofrequency ablation. Multimodality interventions require multiple patient transfers between an MRI and the X-ray/ultrasound electrophysiological suite, increasing the likelihood of patient-motion and image misregistration. An MRI-compatible VDT system may increase efficiency, as there is currently no single method to track devices both inside and outside the MRI scanner.

METHODS

An MRI-compatible VDT system was constructed by modifying a commercial system. Hardware was added to reduce MRI gradient-ramp and radiofrequency unblanking pulse interference. VDT patches and cables were modified to reduce heating. Five swine cardiac VDT electro-anatomic mapping interventions were performed, navigating inside and thereafter outside the MRI.

RESULTS

Three-catheter VDT interventions were performed at >12 frames per second both inside and outside the MRI scanner with <3 mm error. Catheters were followed on VDT- and MRI-derived maps. Simultaneous VDT and imaging was possible in repetition time >32 ms sequences with <0.5 mm errors, and <5% MRI signal-to-noise ratio (SNR) loss. At shorter repetition times, only intracardiac electrocardiogram was reliable. Radiofrequency heating was <1.5°C.

CONCLUSION

An MRI-compatible VDT system is feasible.

Epicardial phrenic nerve displacement during catheter ablation of atrial and ventricular arrhythmias: procedural experience and outcomes

BACKGROUND

Arrhythmia origin in close proximity to the phrenic nerve (PN) can hinder successful catheter ablation. We describe our approach with epicardial PN displacement in such instances.

METHODS AND RESULTS

PN displacement via percutaneous pericardial access was attempted in 13 patients (age 49±16 years, 9 females) with either atrial tachycardia (6 patients) or atrial fibrillation triggered from a superior vena cava focus (1 patient) adjacent to the right PN or epicardial ventricular tachycardia origin adjacent to the left PN (6 patients). An epicardially placed steerable sheath/4 mm-catheter combination (5 patients) or a vascular or an esophageal balloon (8 patients) was ultimately successful. Balloon placement was often difficult requiring manipulation via a steerable sheath. In 2 ventricular tachycardia cases, absence of PN capture was achieved only once the balloon was directly over the ablation catheter. In 3 atrial tachycardia patients, PN displacement was not possible with a balloon; however, a steerable sheath/catheter combination was ultimately successful. PN displacement allowed acute abolishment of all targeted arrhythmias. No PN injury occurred acutely or in follow up. Two patients developed acute complications (pleuro-pericardial fistula 1 and pericardial bleeding 1). Survival free of target arrhythmia was achieved in all atrial tachycardia patients; however, a nontargeted ventricular tachycardia recurred in 1 patient at a median of 13 months' follow up.

CONCLUSIONS

Arrhythmias originating in close proximity to the PN can be targeted successfully with PN displacement with an epicardially placed steerable sheath/catheter combination, or balloon, but this strategy can be difficult to implement. Better tools for phrenic nerve protection are desirable.

Role of alternative interventional procedures when endo- and epicardial catheter ablation attempts for ventricular arrhythmias fail

BACKGROUND

Ventricular tachycardia (VT) refractory to antiarrhythmic drugs and standard percutaneous catheter ablation techniques portends a poor prognosis. We characterized the reasons for ablation failure and describe alternative interventional procedures in this high-risk group.

METHODS AND RESULTS

Sixty-seven patients with VT refractory to 4±2 antiarrhythmic drugs and 2±1 previous endocardial/epicardial catheter ablation attempts underwent transcoronary ethanol ablation, surgical epicardial window (Epi-window), or surgical cryoablation (OR-Cryo; age, 62±11 years; VT storm in 52%). Failure of endo/epicardial ablation attempts was because of VT of intramural origin (35 patients), nonendocardial origin with prohibitive epicardial access because of pericardial adhesions (16), and anatomic barriers to ablation (8). In 8 patients, VT was of nonendocardial origin with a coexisting condition also requiring cardiac surgery. Transcoronary ethanol ablation alone was attempted in 37 patients, OR-Cryo alone in 21 patients, and a combination of transcoronary ethanol ablation and OR-Cryo (5 patients), or transcoronary ethanol ablation and Epi-window (4 patients), in the remainder. Overall, alternative interventional procedures abolished ≥1 inducible VT and terminated storm in 69% and 74% of patients, respectively, although 25% of patients had at least 1 complication. By 6 months post procedures, there was a significant reduction in defibrillator shocks (from a median of 8 per month to 1; P<0.001) and antiarrhythmic drug requirement although 55% of patients had at least 1 VT recurrence, and mortality was 17%.

CONCLUSIONS

A collaborative strategy of alternative interventional procedures offers the possibility of achieving arrhythmia control in high-risk patients with VT that is otherwise uncontrollable with antiarrhythmic drugs and standard percutaneous catheter ablation techniques.

Feasibility, efficacy, and safety of radiofrequency ablation of atrial fibrillation guided by monitoring of the initial impedance decrease as a surrogate of catheter contact

BACKGROUND

The initial impedance decrease during radiofrequency (RF) ablation is an indirect marker of catheter contact and lesion formation. We aimed to assess feasibility, efficacy, and safety of an ablation approach guided by initial impedance decrease.

METHODS

A total of 25 patients with paroxysmal AF had point-by-point, wide antral pulmonary vein (PV) isolation. RF applications were aborted if a decrease of at least 5 Ω did not occur in the first 10 seconds; otherwise, ablation was continued for at least 20 seconds. Power was 30 Watts and reduced to 15-25 Watts on the posterior wall.

RESULTS

A total of 28% of RF applications were terminated because of inadequate impedance decrease. The remaining lesions showed a median decrease of 7.6 Ω (IQR 5.0-10.7) at 10 seconds and median duration of RF lesions was 38 seconds. Note that, 100 PVs were isolated with 49 rings. PVI occurred before anatomic completion of the ablation ring of adequate lesions in 39/49 (80%) and concurrent with ring completion in 7/49 (14%). Additional lesions were required in 3/49 (6%) rings. After PVI, additional lesions were required to eliminate dormant conduction in 2/47 (4%) and pace-capture on the ablation line in 24/49 vein pairs (49%). During short-term follow-up, 3 nonfatal esophageal injuries and 2 late pericardial effusions occurred. During a mean follow-up of 431 ± 87 days, 21/25 patients (84%) remained free of recurrent symptomatic atrial arrhythmias.

CONCLUSIONS

PVI guided by initial impedance decrease is feasible and results in PVI concurrent with or before completion of the ablation ring in 94% of patients. Single procedure efficacy after one year of follow-up was 84%. Near-term complications suggest that deeper lesions are created, indicating that further reduction of RF-power and duration is warranted.

Ventricular tachycardia in cardiac sarcoidosis: characterization of ventricular substrate and outcomes of catheter ablation

BACKGROUND

Cardiac sarcoid-related ventricular tachycardia (VT) is a rare disorder; the underlying substrate and response to ablation are poorly understood. We sought to examine the ventricular substrate and outcomes of catheter ablation in this population.

METHODS AND RESULTS

Of 435 patients with nonischemic cardiomyopathy referred for VT ablation, 21 patients (5%) had cardiac sarcoidosis. Multiple inducible VTs were observed with mechanism consistent with scar-mediated re-entry in all VTs. Voltage maps showed widespread and confluent right ventricular scarring. Left ventricular scarring was patchy with a predilection for the basal septum, anterior wall, and perivalvular regions. Epicardial right ventricular scar overlay and exceeded the region of corresponding endocardial scar. After ≥1 procedures, ablation abolished ≥1 inducible VT in 90% and eliminated VT storm in 78% of patients; however, multiple residual VTs remained inducible. Failure to abolish all inducible VTs was because of septal intramural circuits or extensive right ventricular scarring. Multiple procedure VT-free survival was 37% at 1 year, but VT control was achievable in the majority of patients with fewer antiarrhythmic drugs compared with preablation (2.1±0.8 versus 1.1±0.8; P<0.001).

CONCLUSIONS

Patients with cardiac sarcoidosis and VT exhibit ventricular substrate characterized by confluent right ventricular scarring and patchy left ventricular scarring capable of sustaining a large number of re-entrant circuits. Catheter ablation is effective in terminating VT storm and eliminating ≥1 inducible VT in the majority of patients, but recurrences are common. Ablation in conjunction with antiarrhythmic drugs can help palliate VT in this high-risk population.

Ventricular Arrhythmias Near the Distal Great Cardiac Vein

Background—

Catheter ablation for ventricular arrhythmia (VA) near the distal great cardiac vein (GCV) is often challenging, and data are limited.

Methods and Results—

Analysis was performed in 30 patients (19 men; age, 52.8±15.5 years) who underwent catheter ablation for focal VA (11 ventricular tachycardia and 19 premature contractions) with early activation in the GCV (36.7±8.0 ms pre-QRS). Angiography in 27 patients showed earliest GCV site within 5 mm of a coronary artery in 20 (74%). Ablation was performed in the GCV in 15 patients and abolished VA in 8. Ablation was attempted at adjacent non-GCV sites in 19 patients and abolished VA in 5 patients (4 from the left ventricular endocardium and 1 from the left coronary cusp); all success had VA with an initial r wave in lead I and activation ≤7 ms after the GCV (GCV–non-GCV interval). In 13 patients, percutaneous epicardial mapping was performed, but because of adjacent coronaries only 2 received radiofrequency application with VA elimination in 1. Surgical cryoablation was performed in 3 patients and abolished VA in 2. Overall acute success was achieved in 16 (53%) patients. After a median of 2.8 months, 13 patients remained free of VA. Major complications occurred in 4 patients, including coronary injury requiring stenting.

Conclusions—

Ablation for this arrhythmia is challenging and often limited by the adjacent coronary vessels. Success of anatomically guided endocardial ablation may be identified by a short GCV–non-GCV interval and r wave in lead I.

Correlates and Prognosis of Early Recurrence After Catheter Ablation for Ventricular Tachycardia due to Structural Heart Disease

Background—

Catheter ablation for ventricular tachycardia (VT) from structural heart disease has a significant risk of recurrence, but the optimal duration for in-hospital monitoring is not defined. This study assesses the timing, correlates, and prognostic significance of early VT recurrence after ablation.

Methods and Results—

Of 370 patients (313 men; aged 63.0±13.2 years) who underwent a first radiofrequency ablation for sustained monomorphic VT associated with structural heart disease from 2008 to 2012, sustained VT recurred in 81 patients (22%) within 7 days. In multivariable analysis, early recurrence was associated with New York Heart Association classification ≥III (odds ratio [OR] 1.90, 95% confidence interval [CI] 1.03–3.48; P =0.04), dilated cardiomyopathy (OR 1.93, 95% CI 1.03–3.57; P =0.04), prevalence of VT storm before the procedure (OR 2.62, 95% CI 1.48–4.65; P =0.001), a greater number of induced VTs (OR 1.24, 95% CI 1.07–1.45; P =0.006), and acute failure or no final induction test (OR 1.88, 95% CI 1.03–3.40; P =0.04). During a median of 2.5 (1.2, 4.0) years of follow-up, early VT recurrence was an independent correlates of mortality (hazard ratio 2.59, 95% CI 1.52–4.34; P =0.0005).

Conclusions—

Patients who have early recurrences of VT after ablation are a high risk group who may be identifiable from their clinical profile. Further study is warranted to define the optimal treatment strategies for this patient group.

Left atrial passive emptying function determined by cardiac magnetic resonance predicts atrial fibrillation recurrence after pulmonary vein isolation

BACKGROUND

Although pulmonary vein isolation has become a mainstream therapy for selected patients with atrial fibrillation (AF), late recurrent AF is common and its risk factors remain poorly defined. The purpose of our study was to test the hypothesis that reduced left atrial passive emptying function (LAPEF) as determined by cardiac magnetic resonance has a strong association with late recurrent AF after pulmonary vein isolation.

METHODS AND RESULTS

Three hundred forty-six patients with AF referred for cardiac magnetic resonance pulmonary vein mapping before pulmonary vein isolation were included. Maximum LA volumes (VOLmax) and volumes before atrial contraction (VOLbac) were measured; LAPEF was calculated as (VOLmax-VOLbac)/VOLmax×100. Kaplan-Meier curves were constructed to determine late recurrent AF stratified by LAPEF quintile. Cox proportional hazards regression was used to adjust for known markers of recurrence. During a median follow-up of 27 months, 124 patients (35.8%) experienced late recurrent AF. Patients with recurrence were more likely to have nonparoxysmal AF (75.8% versus 51.4%; P<0.01), higher mean VOLmax (60.2 versus 52.8 mL/m(2); P<0.01), and lower mean LAPEF (19.1% versus 26.0%; P<0.01). Patients in the lowest LAPEF quintile were at highest risk of developing recurrent AF (2-year recurrence for lowest versus highest: 60.5% versus 17.3%; P<0.01). After adjusting for known predictors of recurrence, patients with low LAPEF remained significantly more likely to recur (hazard ratio for lowest versus highest quintile, 3.92; 95% confidence interval, 2.01-7.65).

CONCLUSIONS

We found a strong association between LAPEF and recurrent AF after pulmonary vein isolation that persisted after multivariable adjustment.

Feasibility study of electrocardiographic and respiratory gated, gadolinium enhanced magnetic resonance angiography of pulmonary veins and the impact of heart rate and rhythm on study quality

BACKGROUND

We aimed to assess the feasibility of 3 dimensional (3D) respiratory and ECG gated, gadolinium enhanced magnetic resonance angiography (MRA) on a 3 Tesla (3 T) scanner for imaging pulmonary veins (PV) and left atrium (LA). The impact of heart rate (HR) and rhythm irregularity associated with atrial fibrillation (AF) on image and segmentation qualities were also assessed.

METHODS

101 consecutive patients underwent respiratory and ECG gated (ventricular end systolic window) MRA for pre AF ablation imaging. Image quality (assessed by PV delineation) was scored as 1 = not visualized, 2 = poor, 3 = good and 4 = excellent. Segmentation quality was scored on a similar 4 point scale. Signal to noise ratios (SNRs) were calculated for the LA, LA appendage (LAA), and PV. Contrast to noise ratios (CNRs) were calculated between myocardium and LA, LAA and PV, respectively. Associations between HR/rhythm and quality metrics were assessed.

RESULTS

35 of 101 (34.7%) patients were in AF at time of MRA. 100 (99%) patients had diagnostic studies, and 91 (90.1%) were of good or excellent quality. Overall, mean ± standard deviation (SD) image quality score was 3.40 ± 0.69. Inter observer agreement for image quality scores was substantial, (kappa = 0.68; 95% confidence interval (CI): 0.46, 0.90). Neither HR adjusting for rhythm [odds ratio (OR) = 1.03, 95% CI = 0.98,1.09; p = 0.22] nor rhythm adjusting for HR [OR = 1.25, 95% CI = 0.20, 7.69; p = 0.81] demonstrated association with image quality. Similarly, SNRs and CNRs were largely independent of HR after adjusting for rhythm. Segmentation quality scores were good or excellent for 77.3% of patients: mean ± SD score = 2.91 ± 0.63, and scores did not significantly differ by baseline rhythm (p = 0.78).

CONCLUSIONS

3D respiratory and ECG gated, gadolinium enhanced MRA of the PVs and LA on a 3 T system is feasible during ventricular end systole, achieving high image quality and high quality image segmentation when imported into electroanatomic mapping systems. Quality is independent of HR and heart rhythm for this free breathing, radiation free, alternative strategy to current MRA or CT based approaches, for pre AF ablation imaging of PVs and LA.

Reentrant Ventricular Tachycardia Originating From the Periaortic Region in the Absence of Overt Structural Heart Disease

Background—

In the absence of overt structural heart disease, most left ventricular outflow tract ventricular tachycardias (VTs) have a focal origin and are benign. We hypothesized that multiple morphologies (MMs) of inducible left ventricular outflow tract VT may indicate a scar-related VT that can mimic idiopathic VT.

Methods and Results—

Of 54 consecutive patients referred for ablation of sustained outflow tract VT without overt structural heart disease, 24 had left ventricular outflow tract VT, 10 had MM VT, and 14 had a single VT (SM). The MM group were older (70.3±4.3 versus 53.9±15.9 years; P =0.004), had more hypertension (100% versus 29%; P =0.0006), and had longer PR intervals and QRS durations compared with the SM group. In contrast to the SM group, the MM group VTs had features consistent with reentry, including induction by programmed stimulation without isoproterenol, entrainment in some, and abnormal electrograms in the periaortic area. Periaortic region voltages suggested scar in the MM group, but not in the SM group. MRI in 2 MM patients was consistent with scar, but not in 10 SM patients. Longer radiofrequency applications were required in the MM group than in the SM group. At a median follow-up of 9.7 (3.0–32.0) months, recurrences tended to be more frequent in the MM group than in the SM group (70% versus 22%; P =0.07).

Conclusions—

VTs from small regions of periaortic scar can mimic idiopathic VT but are suggested by multiple VT morphologies and are more difficult to ablate. Whether these patients are at greater risk, as feared for other scar-related VTs, warrants further study.

Myocardial extracellular volume expansion and the risk of recurrent atrial fibrillation after pulmonary vein isolation

OBJECTIVES

This study tested whether myocardial extracellular volume (ECV) is increased in patients with hypertension and atrial fibrillation (AF) undergoing pulmonary vein isolation and whether there is an association between ECV and post-procedural recurrence of AF.

BACKGROUND

Hypertension is associated with myocardial fibrosis, an increase in ECV, and AF. Data linking these findings are limited. T1 measurements pre-contrast and post-contrast in a cardiac magnetic resonance (CMR) study provide a method for quantification of ECV.

METHODS

Consecutive patients with hypertension and recurrent AF referred for pulmonary vein isolation underwent a contrast CMR study with measurement of ECV and were followed up prospectively for a median of 18 months. The endpoint of interest was late recurrence of AF.

RESULTS

Patients had elevated left ventricular (LV) volumes, LV mass, left atrial volumes, and increased ECV (patients with AF, 0.34 ± 0.03; healthy control patients, 0.29 ± 0.03; p < 0.001). There were positive associations between ECV and left atrial volume (r = 0.46, p < 0.01) and LV mass and a negative association between ECV and diastolic function (early mitral annular relaxation [E'], r = -0.55, p < 0.001). In the best overall multivariable model, ECV was the strongest predictor of the primary outcome of recurrent AF (hazard ratio: 1.29; 95% confidence interval: 1.15 to 1.44; p < 0.0001) and the secondary composite outcome of recurrent AF, heart failure admission, and death (hazard ratio: 1.35; 95% confidence interval: 1.21 to 1.51; p < 0.0001). Each 10% increase in ECV was associated with a 29% increased risk of recurrent AF.

CONCLUSIONS

In patients with AF and hypertension, expansion of ECV is associated with diastolic function and left atrial remodeling and is a strong independent predictor of recurrent AF post-pulmonary vein isolation.