Computed tomography imaging to quantify the area of the endocardial subvalvular apparatus in hypertrophic cardiomyopathy - Relationship to outflow tract obstruction and symptoms.

BACKGROUND

Abnormalities of the endocardial subvalvular apparatus (SVA), which includes the papillary muscles directly attached to the mitral leaflet and left ventricular apical-basal muscle bundles, are occasionally identified in hypertrophic cardiomyopathy (HCM). Their associations with left ventricular outflow tract (LVOT) obstruction are unknown.

METHODS

We retrospectively reviewed cardiac computed tomography image data sets of 107 consecutive patients with HCM [56 obstructive (HOCM) and 51 non-obstructive (HNOCM)] as well as 53 controls. We evaluated anomalies of the SVA, measured the cross-sectional area of the SVA at the level of the LVOT, and subsequently assessed its correlation with the LVOT pressure gradient with and without medication.

RESULTS

The area of the SVA was greater in HOCM than in HNOCM patients and in the control group (2.5 ± 1.3 cm(2), 1.4 ± 0.8 cm(2), and 0.9 ± 0.6 cm(2), respectively; p < 0.0001). Anomalies in the SVA were more often observed in the HOCM group than in the HNOCM patients and controls (abnormal papillary muscles, 14%, 8%, and 0%, respectively; P = 0.010; LV apical-basal muscle bundles, 73%, 65%, and 45%, respectively; P = 0.0094). Among HOCM patients, logistic regression analysis demonstrated that an SVA area of 2.2 cm(2) was an independent risk factor of residual severe LVOT obstruction (≥50 mmHg) after medication (odds ratio, 10.1; 95% confidence interval, 2.05-49.80).

CONCLUSION

An increased area of the endocardial subvalvular apparatus could be an independent risk factor for clinically relevant LVOT obstruction refractory to medication.