Patterns of cardiac dysfunction coinciding with exertional breathlessness in hypertrophic cardiomyopathy

The commonest cause of breathlessness in hypertrophic cardiomyopathy (HCM) is left ventricular outflow tract (LVOT) obstruction which improves with its removal. However, in the absence of outflow tract obstruction, as in dilated cardiomyopathy, patients may be limited by similar symptoms, thus suggesting a potential common mechanism for the two conditions. We aimed to assess cardiac function at the time of symptoms in a group of unselected patients with HCM to identify other patterns of cardiac dysfunction which coincide with their breathlessness.

We studied 37 HCM patients (aged 55 ± 15 years, 13 female) with septal thickness >15 mm and 17 controls (aged 58 ± 12 years, 12 female) using Doppler echocardiography, at rest and at peak dobutamine stress. Stress end points were symptoms, >20 mmHg drop in systolic blood pressure, arrhythmia, or maximum dobutamine dosage of 40 μg/kg/min.

At rest: LV systolic function was maintained (EF 68 ± 7 v 76 ± 12%, respectively), LVOT velocity raised (p<0.005), lateral and septal long axis amplitude reduced (p<0.05 and p<0.005, respectively) and dyssynchronous and QRS duration was also broader (p<0.005) in patients compared to controls. At peak stress: Overall LVOT velocities were higher in patients than controls (4.3 ± 1.7 v 1.7 ± 1.0m/s, p<0.005, respectively) due to systolic anterior movement of the mitral valve and mitral regurgitation developing. In the 15 patients who did not develop significant LVOT obstruction (velocity <4m/s), LV ejection time increased and peak systolic amplitude did not increase. In the 10 patients with neither LVOT obstruction nor restrictive filling, QRS duration prolonged by 12 ms (p <0.05), post-ejection shortening worsened and peak systolic amplitude fell (p<0.005). Also, LV ejection time prolonged by 5s/min (p<0.05), filling time failed to increase as it did in controls (p<0.005) and Tei index was higher than controls (p<0.01).

Exertional breathlessness in HCM is associated with LV outflow tract obstruction and functional mitral regurgitation in almost two thirds of patients. The remaining one third have either resistant restrictive physiology or dyssynchronous cavity at fast heart rate. Despite similar exercise limiting breathlessness in the three groups, means of management should be quite different.