Faculty Bibliography

OBJECTIVES/OBJECTIVE:This study sought to assess loss of pulmonary vein (PV) excitability to pacing relative to the development of entrance block and the anatomic completion of the circumferential radiofrequency ablation (RFA) line. BACKGROUND:During encircling RFA for PV isolation (PVI), entrance block develops before anatomic completion of encirclement (early) in some patients. We hypothesized that early entrance block may be associated with loss of PV excitability to pacing. METHODS:In 30 patients undergoing PV isolation (age 61 ± 10 years, 21 men), excitability to pacing was assessed at predefined PV sites when entrance block developed and after completion of the RFA line. RESULTS:Of 60 PV pairs, 37 developed entrance block early, with a gap ≥10 mm in the RFA line. In only 35% of PV pairs in this subgroup, both PV sleeves captured, and all of the capturing PV pairs showed exit block (no conduction from PV to atrium) despite the presence of an excitable gap. In the remaining 23 PV pairs, entrance block did not occur until encircling RFA was anatomically complete. In 83% of these PV pairs, both sleeves captured with exit block (p < 0.001 compared with early block PVs). CONCLUSIONS:The majority of PV pairs develops entrance and exit block before complete anatomic encircling by RFA lesions. Early entrance block is frequently associated with loss of PV sleeve excitability, consistent with a spreading wave of injury or edema rather than a permanent conduction barrier. This may help to explain the significant rate of PV conduction recovery associated with the acute endpoints of entrance and exit block.

BACKGROUND: Radiofrequency ablation (RFA) from the epicardial space for ventricular arrhythmias is limited or impossible in some cases. Reasons for epicardial ablation failure and the effect on outcome have not been systematically analyzed. METHODS AND RESULTS: We assessed reasons for epicardial RFA failure relative to the anatomic target area and the type of heart disease and assessed the effect of failed epicardial RFA on outcome after ablation procedures for ventricular arrhythmias in a large single-center cohort. Epicardial access was attempted during 309 ablation procedures in 277 patients and was achieved in 291 procedures (94%). Unlimited ablation in an identified target region could be performed in 181 cases (59%), limited ablation was possible in 22 cases (7%), and epicardial ablation was deemed not feasible in 88 cases (28%). Reasons for failed or limited ablation were unsuccessful epicardial access (6%), failure to identify an epicardial target (15%), proximity to a coronary artery (13%), proximity to the phrenic nerve (6%), and complications (<1%). Epicardial RFA was impeded in the majority of cases targeting the left ventricular summit region. Acute complications occurred in 9%. The risk for acute ablation failure was 8.3x higher (4.5-15.0; P<0.001) after no or limited epicardial RFA compared with unlimited RFA, and patients with unlimited epicardial RFA had better recurrence-free survival rates (P<0.001). CONCLUSIONS: Epicardial RFA for ventricular arrhythmias is often limited even when pericardial access is successful. Variability of success is dependent on the target area, and the presence of factors limiting ablation is associated with worse outcomes.

AIMS: In patients presenting with spontaneous sustained ventricular tachycardia (VT) from the outflow-tract region without overt structural heart disease ablation may target premature ventricular contractions (PVCs) when VT is not inducible. We aimed to determine whether inducibility of VT affects ablation outcome. METHODS AND RESULTS: Data from 54 patients (31 men; age, 52 +/- 13 years) without overt structural heart disease who underwent catheter ablation for symptomatic sustained VT originating from the right- or left-ventricular outflow region, including the great vessels. A single morphology of sustained VT was inducible in 18 (33%, SM group) patients, and 11 (20%) had multiple VT morphologies (MM group). VT was not inducible in 25 (46%) patients (VTni group). After ablation, VT was inducible in none of the SM group and in two (17%) patients in the MM group. In the VTni group, ablation targeted PVCs and 12 (48%) patients had some remaining PVCs after ablation. During follow-up (21 +/- 19 months), VT recurred in 46% of VTni group, 40% of MM inducible group, and 6% of the SM inducible group (P = 0.004). Analysis of PVC morphology in the VTi group further supported the limitations of targeting PVCs in this population. CONCLUSION: Absence of inducible VT and multiple VT morphologies are not uncommon in patients with documented sustained outflow-tract VT without overt structural heart disease. Inducible VT is associated with better outcomes, suggesting that attempts to induce VT to guide ablation are important in this population.

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.

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+/-16y, 9 females) with either atrial tachycardia (AT; 6 patients) or atrial fibrillation triggered from a superior vena cava focus (1 patient) adjacent to the right PN or epicardial ventricular tachycardia (VT) origin adjacent to the left PN (6 patients). An epicardially placed steerable sheath/4mm-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 VT cases, absence of PN capture was achieved only once the balloon was directly over the ablation catheter. In 3 AT 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, pericardial bleeding 1). Survival free of target arrhythmia was achieved in all AT patients, however a non-targeted VT 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.

BACKGROUND: -Mapping to identify scar-related ventricular tachycardia (VT) reentry circuits during sinus rhythm focuses on sites with abnormal electrograms, or pace-mapping findings of QRS morphology and long stimulus to QRS (S-QRS) intervals. We hypothesized that 1. these methods do not necessarily identify the same sites and 2. some electrograms are "far-field" potentials that can be recognized by pacing. METHODS AND RESULTS: -From 12 patients with coronary disease and recurrent VT undergoing catheter ablation we retrospectively analyzed electrograms and pacing at 546 separate low bipolar voltage (<1.5mV) sites. Electrograms were characterized as showing evidence of slow conduction if late potentials (56%) or fractionated potentials (76%) were present. Neither was present at (13%) sites. Pacing from the ablation catheter captured 70% of all electrograms. Higher bipolar voltage and fractionation were independent predictors for pace capture. There was a linear correlation between the S-QRS duration during pacing and the lateness of a capturing electrogram (p<0.001), but electrogram and pacing markers of slow conduction were discordant at 40% of sites. Sites with far-field potentials, defined as those that remained visible and not captured by pacing stimuli, were identified at 48% of all pacing sites, especially in areas of low bipolar voltage and late potentials. Initial RF energy application rendered 74% of targeted sites electrically unexcitable. CONCLUSIONS: -Far-field potentials are common in scar areas. Combining analysis of electrogram characteristics and assessment of pace capture may refine identification of substrate targets for RF ablation.

One of the currently accepted paradigms for catheter ablation of persistent atrial fibrillation (AF) is wide antral pulmonary vein isolation, followed by some combination of adjunctive ablation that may include, but is not limited to, linear left atrial ablation, complex fractionated atrial electrogram ablation, rotor ablation, and box isolation of fibrosis until sinus rhythm is restored1-3 . These lesion sets often include establishment of perimitral conduction block, either as an empiric linear ablation, or to terminate and prevent perimitral flutter