Impact of heart rate related left bundle branch block on instantaneous fractional flow reserve in aged patients

I nterpretation of coronary physiology with fractional flow reserve (FFR) assumes stable relationships between flow, demand, and resistance, but conduction abnormalities such as left bundle branch block (LBBB) can disrupt myocardial activation, perfusion, and pressure-derived ischemic indices especially in aged patients.[1] Heart rate related LBBB is a transient, rate-dependent conduction delay that induces ventricular dyssynchrony and impairs regional perfusion, potentially altering instantaneous FFR (iFFR) accuracy, particularly in the left anterior descending artery or the left circumflex artery disease.[2] Because the physiological impact of heart rate related LBBB is unknown, we investigated its influence on iFFR in aged patients with intermediate stenoses in the left coronary artery.We conducted an observational study of consecutive patients evaluated for unstable angina at Padova South Hospitals, Monselice, Italy from October 2023 to August 2025.Eligible patients had symptom onset within three months, underwent elective coronary angiography, had mild-intermediate (40%-70%) left anterior descending artery or left circumflex artery stenosis by quantitative coronary angiography (QCA), preserved left ventricular ejection fraction (≥ 55%), and no significant valvular disease.The experimental group consisted of patients with documented heart rate related LBBB, defined as a typical LBBB pattern appearing only at higher heart rates and resolving at lower rates; controls had no history of heart rate related LBBB.Exclusion criteria included permanent LBBB, prior percutaneous coronary intervention or coronary artery bypass grafting, acute coronary syndromes, and significant valvular disease.