Is there referral bias in outcomes of septal myectomy for hypertrophic cardiomyopathy?

Purpose: To determine the potential impact of referral bias on short- and long-term outcomes following septal myectomy for hypertrophic cardiomyopathy.

Methods: We reviewed 2303 adult patients who underwent transaortic septal myectomy for obstructive hypertrophic cardiomyopathy from January 1993 to April 2016. Patients were divided into 3 groups according to their permanent address: local (state) residents (n = 324), regional (surrounding 5 states) patients (n = 515), and national (outside 5 states) patients (n = 1464).

Results: Patient groups were similar for age, sex, preoperative New York Heart Association class, and left ventricular ejection fraction. Local patients had increased prevalence of diabetes mellitus (13%, 11%, 8%; P = .006), coronary artery disease (25%, 21%, 19%; P = .031), severe chronic lung disease (2.3%, 1.9%, 0.4%; P < .001), and atrial fibrillation (24%, 18%, 19%; P = .045) when compared with regional and national patients. Echocardiographic features did not differ between the 3 groups, including prevalence of moderate or greater mitral regurgitation (59%, 61%, 56%; P = .161). Local and regional patients were more likely to undergo concomitant procedures than national patients (P < .001). Mitral valve surgery was performed in 9.6% of the patients, more commonly in local and regional patients (12%, 12%, 8%; P = .018). There were 11 operative deaths (0.5%), and early mortality was similar among the groups. Geographic origin did not impact overall late survival.

Conclusions: Compared with distant referrals, local patients who undergo septal myectomy at our institution have more comorbid conditions, and require more concomitant surgical procedures. Despite these differences, referral patterns did not impact early or late outcomes following transaortic septal myectomy.