Faculty Bibliography

BACKGROUND:Micra is a leadless pacemaker that is implanted in the right ventricle and provides rate response via a 3-axis accelerometer (ACC). Custom software was developed to detect atrial contraction using the ACC enabling AV synchronous pacing. OBJECTIVE:To sense atrial contractions from the Micra ACC signal and provide AV synchronous pacing. METHODS:The MASS/MASS2 early feasibility studies showed intracardiac accelerations related to atrial contraction can be measured via ACC in the Micra leadless pacemaker. MARVEL was a prospective multicenter study designed to characterize the closed-loop performance of an AV synchronous algorithm downloaded into previously implanted Micra devices. AV synchrony (AVS) was measured during 30-minutes of rest and during VVI pacing. AVS was defined as a P-wave visible on a surface ECG followed by a ventricular event <300ms. RESULTS:A total of 64 patients completed the MARVEL study procedure at 12 centers in 9 countries. Patients were implanted with a Micra for a median of 6.0 months (range: 0-41.4). High-degree AV block was present in 33 patients while 31 had predominantly intrinsic conduction during the study. Average AVS during AV algorithm pacing was 87.0% (CI: 81.8%-90.9%); 80.0% in high-degree block patients and 94.4% in patients with intrinsic conduction. AVS was significantly greater (P<0.001) during AV algorithm pacing compared to VVI in high-degree block patients while AVS was maintained in patients with intrinsic conduction. CONCLUSION/CONCLUSIONS:Accelerometer-based atrial sensing is feasible and significantly improves AV synchrony in patients with AV block and a single-chamber leadless pacemaker implanted in the right ventricle.

Background: Unfavorable outcomes for stepwise linear ablation of non-paroxysmal atrial fbrillation (NPAF) in clinical trials may be attributable to pro-arrhythmic effects of incomplete ablation lines. It is unknown if recurrent arrhythmia following stepwise linear ablation is more likely to be successfully ablated compared to recurrent arrhythmia following a more limited initial procedure The optimal ablation strategy for catheter ablation of NPAF using a contact-force sensing (CFS) radiofrequency ablation (RFA) catheter remains unclear. Objective: To compare 2-procedure outcomes of stepwise linear RFA to left atrial posterior wall isolation in patients undergoing NPAF ablation using a CFS RFA catheter. Methods: We compared clinical outcomes of two cohorts of 100 consecutive NPAF patients undergoing frst-time RFA using a CFS RFA catheter. Group 1: stepwise linear ablation (July 2014-July 2015); Group 2: left atrial posterior wall isolation (October 2015-June 2016). Arrhythmia recurrence was assessed using 2-week event monitors at 3-month intervals following ablation procedures. Results: Baseline characteristics of the two groups were similar. Mean follow-up time was 656 +/- 361 days for Group 1 and 436 +/- 228 days for Group 2. At 24-month follow up, Kaplan-Meier estimated single procedure arrhythmia free survival was signifcantly greater in Group 2 compared to Group 1 (76% vs 59%, respectively; p = 0.01), primarily driven by a higher rate of recurrence of atrial tachycardia (12% vs 35%, respectively; p < 0.001). Among patients with recurrent arrhythmia after a single procedure, Group 2 patients were less likely to require repeat ablation compared to Group 1 (6/24 vs 34/41, respectively; p < 0.001) and less likely to recur after repeat ablation (1/6 vs 13/34, respectively; p = 0.001). Conclusion: Compared to stepwise linear ablation, LA posterior wall isolation for catheter ablation of NPAF resulted in a lower incidence of recurrent arrhythmia at 2 years, a lower likelihood of requiring repeat ablation amongst patients with recurrence, and a lower likelihood of recurrence following a second ablation

Background: Catheter ablation has become an increasingly common elective therapy for symptomatic atrial fbrillation (AF). Few data are available regarding outcomes of urgent AF ablation performed during AF related hospital admission, and the impact of these procedures on healthcare utilization. Objective: To evaluate patient characteristics, procedural outcomes, and impact on healthcare utilization in patients undergoing urgent AF ablation. Methods: Procedural outcomes of patients undergoing urgent frst-time AF ablation during an AF related hospital admission between 1/2014 and 8/2017 at a single tertiary care medical center were compared to those of 2:1 matched control patients undergoing frst-time elective AF ablation. An inverse probability weighted marginal structural model was constructed and the weighted means of the average hospital days and number of hospital visits in the six-months post ablation were compared. Results: 25 patients (1% of frst-time AF ablations) underwent an urgent procedure. There were no major procedural complications in either group. Incidence of arrhythmia recurrence within one year was similar in urgent and elective patients (20% vs. 18%, respectively, p=0.85). Urgent ablation patients had a greater number of hospital utilization days in the 6-months pre-ablation (mean 8.9+/-4.5 vs 2.6+/-1.1, p<.001) and a similar number of hospital utilization days in the 6-months post-ablation (1.8+/-4.5 vs 0.59+/- 1.07, p=.05) The marginal structural model of the change in number of hospital visits due to being in the urgent ablation group was-0.924 (-1.43 to-0.41; P <0.001). Conclusion: Urgent ablation for treatment resistant, symptomatic AF is feasible and safe with procedural outcomes were similar to those of elective AF ablation. There is and increased rate of healthcare utilization in prior to ablation in the urgent group, and a statistically signifcant reduction in healthcare utilization following urgent AF ablation. Defning the cost-effectiveness of and optimal patient selection for urgent ablation requires further investigation

Background: Optimal contact-force during atrial fbrillation (AF) radiofrequency (RF) ablation is associated with improved procedural outcomes The extent to which ablation catheter spatial stability varies between patients and predicts procedural success is unknown. Objective: To examine the prognostic signifcance of intra-procedure ablation catheter spatial stability on one year arrhythmia recurrence following ablation of paroxysmal atrial fbrillation. Methods: 100 consecutive patients undergoing frst time RF ablation for paroxysmal AF under general anesthesia were analyzed. Spatial localization of the ablation catheter sampled at 60 Hz during RF application was extracted from the CARTO3 system (Biosense Webster, Inc.) and analyzed using custom software (MATLAB, Mathworks, USA) to determine mean and maximum catheter excursion relative to mean catheter location during point-by-point RF ablation. All lesions for a given patient were then averaged to form composite measures of catheter stability The primary end point was freedom from documented recurrence of atrial arrhythmia lasting longer than 30 seconds after a single ablation procedure. Results: At one year, 86% of patients were free from recurrent AF. There was no signifcant difference in clinical and echocardiographic baseline characteristics between patients with and without recurrent arrhythmia There was no signifcant difference in lesion number, average contact-force, average impedance decrease, or RF time between patients who did recur and those who did not. For all patients, maximum catheter excursion was 2.84 +/- 0.40mm and mean catheter excursion was 0.99 +/- 0.16mm. Patients with arrhythmia recurrence had signifcantly greater maximum (3.07 +/- 0.38mm vs 2.80 +/- 0.40mm, p = 0.03) and mean (1.08 +/- 0.13mm vs 0.98 +/- 0.17mm, p = 0.01) catheter excursion compared to those without recurrence. Univariate regression demonstrated that maximal catheter excursion was a signifcant predictor of arrhythmia recurrence (OR 5.1 per 1mm excursion increase, 95% CI 1.2-21.9, p=0.03). Conclusion: Quantitative measures of ablation catheter spatial stability may be novel and potentially modifable predictors of procedural success during RF ablation of AF

Background: Recent studies suggest RF ablation at high power for short durations may be safer and more effcient than using conventional power levels. Comparative data exploring the kinetics and safety of lesion formation at high power/short duration vs. conventional methods is lacking. Objective: The goal of this study is to compare lesion formation and safety across study conditions in an intracardiac model. Methods: Canines (n=24) were anesthetized and intracardiac RF energy was applied in both ventricles over a wide range of conditions (20-50 W, 5-60 s, 5-40 g) in a quasi-random fashion using a contact force, irrigated RF ablation catheter. Hearts were then stained with 1% TTC and formalin fxed Hearts were sectioned and lesions measured A common regression model for lesion width, depth and steam pop likelihood was created, and subsequently realized for three RF powers (see fgure). With these models, the time to achieve target lesion sizes and the relative steam pop risk were compared. Results: Of the 228 lesions created, 227 were found (99%). At 50 W, the maximum lesion width growth rate was 1.4 mm/s, vs. 0.9 mm/s (40 W) and 0.7 mm/s (30 W). Steam pop risk grew by 0.25%/s when ablating at 30 W vs. 1.1%/s at 50 W. Comparable lesions could be created at 30 W and 50 W power with similar steam pop risk (e.g., 30 W took 42 s to create a 10 mm wide lesion vs. 10 s at 50 W with similar risk). Conclusion: In this study, RF ablation lesions can be created about two times faster when using 50 W vs. 30 W; however the steam pop risk increased 4.4 fold. Though lesions are created more effciently, there is a much lower margin for error when ablating at 40-50 W. [Figure Presented]