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Aims Evaluate whether Bachmann’s bundle pacing (BBp) defined by electrocardiographic (ECG) criteria is associated with less atrial fibrillation/tachycardia (AF/AT) compared with anatomically defined right atrial septal pacing (RASp) and right atrial appendage pacing (RAAp). Methods and results This is a retrospective study comparing BBp with non-specific RASp and RAAp on new incidence, burden, and recurrence of AF/AT. We included patients who underwent atrial lead placement between 2006 and 2019 and received > 20% atrial pacing. BBp was defined by paced P-wave morphology and fluoroscopic lead position. Compared with RASp (n = 107) and RAAp (n = 108), AF/AT burden was lower in the BBp (n = 134) group by repeated measures ANOVA (P < 0.001). Over 2-year follow-up, AF/AT burden increased in the RASp (P < 0.01) and RAAp (P < 0.01) groups but did not significantly change in the BBp group (P = 0.91). Atrial arrhythmia burden was lower in the BBp group than the RASp and RAAp groups at 12–15, 18–21, and 24–27 months (P < 0.05) after pacemaker placement. Risk of AF/AT recurrence was lower in BBp than RASp (HR 0.43; P < 0.01) and RAAp patients (HR 0.29, P < 0.01). Risk of de novo AF/AT was also lower in BBp than in RASp (OR 0.12; P < 0.01) and RAAp patients (OR 0.20, P < 0.01). Conclusion Bachmann’s bundle pacing defined using P-wave criteria was associated with decreased atrial arrhythmia burden, recurrence, and de novo incidence compared with right atrial septal pacing and right atrial appendage pacing.

Background Lower heart rates (HRs) prolong diastole, thereby raising filling pressures and wall stress (1,2), slowing myocardial relaxation (3), and increasing central blood pressure via superposition of reflected peripheral pressure waves onto systole (2,4). As a result, lower HRs may be associated with higher brain natriuretic peptide (BNP) levels and incident atrial fibrillation (AF). Beta-blockers (BBs) may thereby increase the risk for AF. Purpose Examine the relationships of HR, BNP, BB use and new-onset AF in the REVEAL-AF and SPRINT cohort of subjects at risk for developing AF. Methods In REVEAL-AF, 383 subjects (52% male, mean age 71.5±9.8 years) without a history of AF and a mean CHA2DS2VASC score of 4.4±1.3 received an insertable cardiac monitor and were followed up to 30 months. Baseline HRs were averaged between 8AM and 8PM for the first week post-implantation. Adjudicated AF lasting ≥6 minutes was defined as new-onset AF. In SPRINT, 7595 patients (64% male, mean age 67.5±9.2 years) without prior history of AF and a mean CHA2DS2VASC score of 2.3±1.2 were followed for up to 60 months. Baseline average HR was derived from three seated measurements taken at the initial clinical visit. 12-lead ECG at baseline, 2 years, 4 years and close-out visit were used to determine presence of AF. Based on longitudinal medication inventories BB use was categorized into “on BB” vs “never on BB” for the duration of the trial. Results The median daytime HR in the REVEAL-AF cohort was 75bpm [interquartile range, IQR 68–83]. Subjects with below median HRs had 2.4-fold higher BNP levels when compared to subjects with above median HRs (median BNP [IQR]: 62pg/dl [37–112] vs. 26pg/dl [13–53], p Conclusion Lower HRs and BB use are associated with higher BNP levels and incident AF, supporting the hypothesis that lower HRs mimic and/or exacerbate the hemodynamic effects of diastolic dysfunction and promote atrial myopathy. The effects of BBs on clinical outcomes in patient populations outside the context of heart failure with reduced ejection fraction will need to be reassessed. Funding Acknowledgement Type of funding sources: Public grant(s) – National budget only. Main funding source(s): National Institute of Health

Author(s): Infeld, Margaret; Avram, Robert; Wahlberg, Kramer; Silverman, Daniel N; Habel, Nicole; Lustgarten, Daniel L; Pletcher, Mark J; Olgin, Jeffrey E; Marcus, Gregory M; Meyer, Markus

Dynamic left ventricular outflow tract obstruction (LVOTO) due to systolic anterior motion (SAM) of the mitral valve (MV) has been described in a small subset of patients with stress cardiomyopathy (SCM). However, encountering LVOTO, severe MV regurgitation and cardiogenic shock in SCM is

Aims A key mechanism responsible for atrial fibrillation is multi-wavelet reentry (MWR). We have previously demonstrated that ablation in regions of increased circuit density reduces the duration of, and decreases the inducibility of MWR. In this study, we demonstrate a method for identifying local circuit density using electrogram frequency and validated its effectiveness for map-guided ablation in a computer model of MWR. Methods and results We simulated MWR in tissues with variation of action potential duration and intercellular resistance. Electrograms were calculated using various electrode sizes and configurations. We measured and compared the number of circuits to the tissue activation frequency and electrogram frequency using three recording configurations [unipolar, contact bipolar, orthogonal closed unipolar (OCU)] and two frequency measurements (dominant frequency, centroid frequency). We then used the highest resolution electrogram frequency map (OCU centroid frequency) to guide the placement of lesions to high frequency regions. Map-guided ablation was compared with no ablation and random/blind ablation lesions of equal length. Electrogram frequency correlated with tissue frequency and circuit density as a function of electrode spatial resolution. Map-guided ablation resulted in a significant reduction in MWR duration (142 ± 174 vs. 41 ± 63 s). Conclusion Electrogram frequency correlates with circuit density in MWR provided electrodes have high spatial resolution. Map-guided ablation is superior to no ablation and to blind/random ablation.

Aims Catheter ablation strategies for treatment of cardiac arrhythmias are quite successful when targeting spatially constrained substrates. Complex, dynamic, and spatially varying substrates, however, pose a significant challenge for ablation, which delivers spatially fixed lesions. We describe tissue excitation using concepts of surface topology which provides a framework for addressing this challenge. The aim of this study was to test the efficacy of mechanism-based ablation strategies in the setting of complex dynamic substrates. Methods and results We used a computational model of propagation through electrically excitable tissue to test the effects of ablation on excitation patterns of progressively greater complexity, from fixed rotors to multi-wavelet re-entry. Our results indicate that (i) focal ablation at a spiral-wave core does not result in termination; (ii) termination requires linear lesions from the tissue edge to the spiral-wave core; (iii) meandering spiral-waves terminate upon collision with a boundary (linear lesion or tissue edge); (iv) the probability of terminating multi-wavelet re-entry is proportional to the ratio of total boundary length to tissue area; (v) the efficacy of linear lesions varies directly with the regional density of spiral-waves. Conclusion We establish a theoretical framework for re-entrant arrhythmias that explains the requirements for their successful treatment. We demonstrate the inadequacy of focal ablation for spatially fixed spiral-waves. Mechanistically guided principles for ablating multi-wavelet re-entry are provided. The potential to capitalize upon regional heterogeneity of spiral-wave density for improved ablation efficacy is described.

The goal of this study was to determine quantitative relationships between electrophysiologic parameters and the propensity of cardiac tissue to undergo atrial fibrillation. We used a computational model to simulate episodes of fibrillation, which we then characterized in terms of both their duration and the population dynamics of the electrical waves which drove them. Monte Carlo sampling revealed that episode durations followed an exponential decay distribution and wave population sizes followed a normal distribution. Half-lives of reentrant episodes increased exponentially with either increasing tissue area to boundary length ratio (A/BL) or decreasing action potential duration (APD), resistance (R) or capacitance (C). We found that the qualitative form of fibrillatory activity (e.g., multi-wavelet reentry (MWR) vs. rotors) was dependent on the ratio of resistance and capacitance to APD; MWR was reliably produced below a ratio of 0.18. We found that a composite of these electrophysiologic parameters, which we term the fibrillogenicity index (Fb = A/(BL*APD*R*C)), reliably predicted the duration of MWR episodes (r2 = 0.93). Given that some of the quantities comprising Fb are amenable to manipulation (via either pharmacologic treatment or catheter ablation), these findings provide a theoretical basis for the development of titrated therapies of atrial fibrillation.

Background— A key mechanism responsible for atrial fibrillation is multiwavelet re-entry (MWR). We have previously demonstrated improved efficiency of ablation when lesions were placed in regions of high circuit-density. In this study, we undertook a quantitative assessment of the relative effect of ablation on the probability of MWR termination and the inducibility of MWR, as a function of lesion length and circuit-density overlap. Methods and Results— We used a computational model to simulate MWR in tissues with (and without) localized regions of decreased action potential duration and increased intercellular resistance. We measured baseline circuit-density and distribution. We then assessed the effect of various ablation lesion sets on the inducibility and duration of MWR as a function of ablation lesion length and overlap with circuit-density. Higher circuit-density reproducibly localized to regions of shorter wavelength. Ablation lines with high circuit-density overlap showed maximum decreases in duration of MWR at lengths equal to the distance from the tissue boundary to the far side of the high circuit-density region (high-overlap, −43.5% [confidence interval, −22.0% to −65.1%] versus low-overlap, −4.4% [confidence interval, 7.3% to −16.0%]). Further ablation (beyond the length required to cross the high circuit-density region) provided minimal further reductions in duration and increased inducibility. Conclusions— Ablation at sites of high circuit-density most efficiently decreased re-entrant duration while minimally increasing inducibility. Ablation lines delivered at sites of low circuit-density minimally decreased duration yet increased inducibility of MWR.

We will lookat 4 specific insights—new, emerging, and largely unpub-lished—from4teamsoftheAorticInstituteatYale:clinical,surgical pathology, engineering, and molecular genetics.CLINICAL: CAN THE AORTIC WALLCOMMUNICATE WITH US?It is well known that most patients with thoracic aorticaneurysms (as many as 95%

We have developed a straightforward, physiologically based mathematical in silico model of cardiac electric activity to facilitate understanding of the fundamental principles that determine how excitation propagates through the heart. Despite its simplicity, the model provides a very powerful teaching tool. In fact, its simplicity is integral to the model's utility. The contrast between the minimal set of rules that govern the model's function and the widely varied complex behaviors it can manifest offers insight into the nature of emergent behavior in wave propagation. Emergence in this context refers to the richness of the tissue activation patterns that arise from the aggregate behavior of the simple cells that comprise the tissue. Each cell can be active, inactive, or refractory and interacts only with its immediate neighbors. From these simple building blocks, very elaborate global behaviors emerge. From the perspective of the electrophysiology student, the notion of emergent properties can act as a Rosetta stone for deciphering electrophysiological behavior. The spread of electric excitation through the intricate 3D structure of the heart can take widely varied forms, ranging from the orderly propagation seen during sinus rhythm to the marked disorganization seen during ventricular fibrillation. Observation of the diverse and sometimes complex patterns of conduction (eg, unidirectional block, reentry, spiral waves) as well as the responses to pacing maneuvers (eg, entrainment) suggests to the electrophysiology student a nearly infinite array of possibilities, the mastery of which can be daunting. However, with study, it becomes apparent that one need not memorize every possible cardiac behavior. Instead, there are overarching principles of cardiac excitation and propagation1 from which these varied phenomena emerge and through which one can understand and predict rather than memorize electrophysiological behavior. Understanding these fundamental principles is integral to mastering electrophysiology. A framework for interpreting clinical observations predicated on these …