Invasive exercise hemodynamics in obstructive and non-obstructive hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is a heterogeneous disease, that may lead to exertional dyspnea through dynamic left ventricular outflow tract obstruction (LVOTO), left ventricular (LV) diastolic dysfunction and/or left atrial myopathy. Deciphering the relative contribution of these alterations to exercise pathophysiology may be clinically relevant. We sought to characterize the hemodynamic adaptation to exercise of HCM patients, using supine left and right heart catheterization. Twenty-five HCM patients underwent rest and exercise cardiac catheterization. Patients were subdivided into non-obstructive HCM (no-HOCM) and obstructive HCM (HOCM), these latter defined by LVOTO > 30 mmHg at rest (overt HOCM, irrespective of exercise LVOTO), or ≥ 50 mmHg during or after exercise despite LVOTO <30 mmHg at rest (latent HOCM). Ten patients (40%) were classified as no-HOCM while 15 (60%) were classified as HOCM (8 with overt HOCM and 7 with latent or post-exercise HOCM). LV end-diastolic pressure, mean pulmonary artery wedge pressure (PAWP) and PAWP V waves (the latter a marker of left atrial stiffness), did not differ between HOCM and no-HOCM at rest. However, during exercise both PAWP and PAWP V waves increased to a larger extent in no-HOCM (23±3 vs 14±3 mmHg and +28±4 vs +14±3 mmHg, respectively, p<0.05). In overt HOCM, LVOTO reduced by 22±8 mmHg (p<0.01) during exercise. Our findings suggest that during exercise no-HOCM patients may display steeper increase in left atrial pressure than HOCM, suggesting more advanced left atrial myopathy / low left atrial compliance. LVOTO may paradoxically reduce during supine exercise in overt HOCM.