Impact of outflow tract obstruction in the management of atrial fibrillation in hypertrophic cardiomyopathy: insights from the national readmission database
Authors: Narasimhan B , Wu L , Ho K , Amreia M , Shah A , Kantharia B 
Published: November 2020

Abstract

Background
Atrial fibrillation (AF) is commonly encountered in patients with Hypertrophic Cardiomyopathy (HCM). Presence of AF in this high risk population is detrimental due to its effect on hemodynamics, diastolic function and potential induction of ventricular tachyarrhythmias. For these reasons a rhythm control strategy is highly desirable, and yet catheter ablation of AF is consistently inefficacious with poorer overall outcomes. We hypothesize that in HCM presence of outflow tract obstruction by virtue of its effect on left atrial hemodynamics, altered circulatory flow patterns in the pulmonary veins, and stretch related triggered activities would create an arrhythmogenic substrate, and have significant impact on the outcomes of catheter ablation of AF. In this study, we aimed to evaluate AF ablation outcomes based on the presence or absence of outflow tract obstructions in patients with HCM.

Methods
We conducted a retrospective study using the AHRQ-HCUP National Readmission Database for the years 2016–17. All adults (≥18 years) with HCM undergoing AF ablation procedures were identified using ICD-9 codes. The cohort was divided into two groups; Obstructive HCM (Group A) and Non-Obstructive HCM (Group B)
Multivariate regression analysis was utilized to adjust for confounders. Independent risk factors for in-hospital mortality were identified using a proportional hazards model. Complications were defined as per the Agency for Health Care Research and Quality guideline.

Results
From a total of 71,451,419 patients in the NRD registry, 97 patients with HCM were identified and formed the study cohort. When divided based on the presence or absence of outflow tract obstruction, there were 25 patients with Obstructive HCM and 72 patients with Non-obstructive HCM.
Both groups were similar in clinical characteristics including CHADVASc scores and Charlson Comobidity indices as outlined in Table 1. Procedural outcome analysis revealed higher 30-day cardiac readmissions in the Obstructive HCM group compared to Non-obstructive HCM (25.2% vs 7.97%, p=0.049). The Obstructive HCM group had higher rates of atrial arrhythmias, 57.97%, compared to 32.44% in the non-obstructive HCM group, and heart failure exacerbations, 41.27% vs 25.82%. However, both indices did not reach statistical significance. The procedural complications rates tended to be higher in the non-obstructive HCM group, 10.8% vs. 5.6% in the Obstructive HCM group (p=0.54).

Conclusions
Presence of an obstructive component to HCM is associated with significantly increased short term cardiac readmissions predominantly driven by recurrent atrial arrhythmias and heart failure. These findings suggest negative influence of altered cardiac hemodynamics related to outflow tract obstruction on atrial arrhythmias. The arrhythmogenic substrate of HCM may therefore be different and less amenable to catheter ablation.
HCM ablation outcomes

Funding Acknowledgement
Type of funding source: None