Sinus Tachycardia and Unrelieved Wall Stress Precede Left Ventricular Systolic Dysfunction During Preclinical...

The onset of cardiomyopathy in Duchenne muscular dystrophy (DMD) is insidious and poorly defined. We proposed integrated wall stress (iWS) as a marker of total left ventricular (LV) workload and tested whether the increased iWS represents early DMD cardiomyopathy.

Peak systolic wall stress (PS-WS) was calculated in M-mode echocardiography with simultaneous blood pressure measurement. iWS was defined as a product of PS-WS and heart rate (HR) divided by 60 (=PS-WS/RR interval). We measured iWS in normal controls (CTRL), DMD with normal LV shortening fraction (%LVSF ≥ 30%) (DMD-A), and DMD with decreased %LVSF (<30%) (DMD-B).

40 CTRL and 79 DMD patients were studied. Despite comparable %LVSF, both HR and iWS were significantly higher in DMD-A (n = 50) than in CTRL (p < 0.0001). iWS was significantly higher in DMD-B (n = 29) than in DMD-A (p < 0.0001) despite comparable HR. PS-WS was significantly higher in DMD-A than in CTRL and higher in DMD-B than in DMD-A, suggesting high HR is not a sole determinant of increased iWS in DMD-A compared with CTRL. In a longitudinal study in 35 DMD patients over 4.0 ± 2.0 years, iWS showed significant increase (p = 0.0062) alongside a significant decline in %LVSF (p < 0.0001).

iWS significantly increased in DMD before %LVSF declined. The progressive increase of iWS in DMD is initially associated with increased HR and then with increased PS-WS. iWS may serve as a useful echocardiographic marker in identifying preclinical DMD cardiomyopathy.