Mechanical Dyssynchrony and Abnormal Regional Strain Promote Erroneous Measurement of Systolic Function in Pediatric Heart Transplantation

Background Clinical experience suggests that measurement of left ventricular (LV) ejection fraction (EF) using two-dimensional echocardiography (2DE) is often at variance with results of three-dimensional echocardiography (3DE) in patients who have undergone heart transplantation (HT). The aim of this study was to test the hypothesis that LV mechanical dyssynchrony and abnormal regional strain are present in asymptomatic pediatric HT patients and that they promote errors in the measurement of LV function when 2DE is used. Methods HT subjects and normal volunteer children were prospectively enrolled. All had normal estimated right ventricular systolic pressure and function. LV EF, global and regional strain, and systolic dyssynchrony index (SDI) were quantified using real time 3DE. SDI was determined from volume-time curves of the 16 LV segments and expressed as the standard deviation of the heart rate-corrected time to reach minimal segmental systolic volume. Septal strain was defined as the average of five segments in the interventricular septum. In addition to 3DE, the Teichholz, biplane Simpson, and bullet (5/6 area-length) methods were used to measure EF using 2DE in each subject. Ninety-three examinations were done: 40 in the 40 normal control subjects (mean age, 14.6 ± 10.6 years; 10 male) and 53 in 36 HT subjects (mean age, 10.3 ± 6.2 years; 21 male). Results SDI was greater in HT patients (mean, 6.2 ± 4.3%) than in normal controls (mean, 2.2 ± 1.1%) (P <.0001). Global and septal strain was lower in HT patients than in normal controls. EF divergence (absolute difference between two- and three-dimensional EFs) was greater in HT patients (mean, 3.8 ± 2.2%) than in normal controls (mean, 0.7 ± 0.5%) (P <.0001). EF divergence had a strong positive correlation with SDI (adjusted r² = 0.46, P <.001) and negative correlations with all measures of strain (range of adjusted r² values, 0.13-0.32). SDI had no particular relation to LV mass or to QRS duration. Conclusions Children after HT have abnormal LV mechanics characterized by greater dyssynchrony and lower strain. These features correlate with, and possibly contribute to differences between measurements by 2DE and 3DE. EF should be calculated using 3DE in this population and others with dyssynchrony and regional strain abnormalities.