Exercise intolerance due to chronotropic incompetence uncovered by cardiopulmonary exercise test: an often overlooked manifestation of ischaemic heart disease.

A 60-year-old delivery man was referred for evaluation of unexplained exertional dyspnoea despite initial non-diagnostic investigations, including pulmonary function tests and dobutamine stress echocardiography. A symptom-limited cardiopulmonary exercise test (CPET) revealed chronotropic incompetence (CI), reduced oxygen uptake (VO2)/work slope at moderate-high workload, and ST-segment depression on recovery electrocardiogram. Coronary angiogram confirmed severe stenosis in right coronary artery and left anterior descending artery, for which he underwent percutaneous coronary stenting and cardiac rehabilitation. An interval CPET showed improvement in heart rate (HR) response and aerobic capacity. CI is characterized by an attenuated HR response to incremental exercise or an increased HR reserve despite maximal effort. Clinically, it is an independent predictor of adverse cardiovascular events and mortality. CI is frequently overlooked, highlighting the importance of CPET in the diagnostic workup of unexplained dyspnoea.