Systolic Time Interval Characteristics in Children with Duchenne's Progressive Muscular Dystrophy

Systolic time interval (STI) characteristics of 17 boys with Duchenne's muscular dystrophy (DMD) were compared with those of 80 normal boys who served as control subjects. The heart rate decreased linearly with age in normal control subjects (r = -.47, P < .01). By contrast, heart rate was significantly higher in patients with DMD (P <.001) and tended to increase further with age. Each STI variable for normal control subjects increased significantly with age (P ≤ .01); QII, left ventricular ejection time (LVET), and pre-ejection period (PEP), in addition, decreased with increasing heart rate (P ≤ .05). In dystrophic patients QII and LVET decreased with increasing heart rate (P < .001) but were not influenced by age. None of the other STI values in dystrophic patients was significantly influenced by either age or heart rate. Mean QII, LVET, and QI were shorter and PEP, isometric contraction time (ICT), and PEP/LVET ratio were longer (P < .001) for DMD patients than for normal control subjects. In 13/17 patients, QII and LVET were below the 95% confidence interval of the normal mean, whereas PEP, ICT, and PEP/LVET exceeded the upper limits of normal in 8, 9, and 11 patients, respectively. For dystrophic patients, the difference (Δ) between the observed values and those predicted from regression equations for normal control subjects was lower for QII, LVET, and QI (P < .01) but higher for PEP (P < .04), ICT, and PEP/LVET ratio (P < .001). Δ QII and Δ LVET increased with age (P = .001 and .032, respectively). Duchenne's muscular dystrophy is thus documented to be associated with substantial alterations in STI characteristics that suggest a compromise of global left ventricular performance. Some of these abnormalities increase with age, probably reflecting the progressive cardiomyopathy characteristic of this disease.