Abstract Body (Do not enter title and authors here): INTRODUCTION
High-volume endurance exercise has been linked to increased atrial fibrillation (AF) risk. High blood pressure response (HBPR) to exercise in these athletes may correlate with adaptive remodeling conducive to AF risk. To investigate this potential mechanism of arrhythmia risk in the general population, we identified highly fit individuals with HBPR on stress testing and characterized structural and functional parameters on transthoracic echocardiography (TTE).

HYPOTHESIS
We hypothesized that individuals with HBPR would demonstrate abnormal structural and functional parameters and left atrial strain (LAS) more frequently than expected in the general population.

METHODS
We conducted a retrospective analysis of treadmill stress tests performed at our institution from 1/1/2012 to 12/31/24. Individuals achieving >10 METs and >150% of age/sex-predicted MET threshold, with HBPR to exercise (>220/85 in men, >200/80 in women) and available TTE within 2 years of stress test were included. Structural and functional parameters were characterized and compared against expected % abnormal in the general population per American Society of Echocardiography guidelines. LAS was quantified via TomTec software and compared against normal values in the general population determined by the World Alliance Societies of Echocardiography.

RESULTS
Of 5114 highly fit individuals undergoing stress testing, 1580 demonstrated HBPR (30.9%). 310 (mean age 65, 55% female) were included in the final analysis, including 175 (mean age 63, 55% female) with quantifiable LAS. Individuals with HBPR exhibited increased LV wall thickness, atrial enlargement and abnormal diastolic parameters more frequently than expected in to the general population. Though not statistically significant, LA reservoir and conduit strain were low normal and declined significantly in older age groups (Figure 1). Contractile strain was preserved regardless of age.

CONCLUSION
HBPR during exercise in highly fit individuals is common. Individuals with HBPR showed higher than expected prevalence of structural and functional changes which have been shown to correlate with higher rates of AF. In fit individuals, there is an age-related correlation with lower LAS in both men and women, despite sex comparable performance levels during stress testing. The structural and strain changes associated with exercise-related HBPR provide mechanistic understanding of age-dependent arrhythmia risk in fit patients.