OBJECTIVES

Tissue Doppler imaging (TDI) represents a recent evolution of the Doppler technique. TDI allows quantitative measurement of myocardial velocities, providing new information in the analysis of myocardial function both in diastole and systole. Golden Retriever Muscular Dystrophy (GRMD) is a X-linked inherited neuromuscular disorder related to a spontaneous mutation of dystrophin gene, which also affects myocardium. Cardiac involvement may occur at an early stage of the disease, and is characterized by myocardial necrosis, mineralization and fibrosis, leading to progressive left ventricular dysfunction. The aim of the study was to evaluate the accuracy of TDI to detect early myocardial dysfunction in GRMD puppies by comparison with healthy Golden Retriever dogs.

MATERIALS

20 animals (25±11 weeks old), including 12 GRMD dogs and 8 dogs with a normal genotype (controls), were examined both by conventional echocardiography and TDI using a Sequoia system (Siemens Acuson) equipped with a 7 MHz phased-array transducer. Left ventricular end-diastolic diameter (LVDD), left ventricular end-systolic diameter (LVSD) and left ventricular ejection fraction (EF) were determined by conventional echocardiography using 2D-guided M-mode. M-mode TDI parameters were recorded from a short-axis view for measurement of endocardial and epicardial systolic velocities and subsequent myocardial velocity gradient (MVG) within the posterior wall. Conventional echo and TDI data were analyzed using a t-student test. A p value < 0.05 was considered as statistically significant.

RESULTS

No significant difference between GRMD and control groups was observed on conventional echographic parameters: LVDD (33±4 vs 35±4 mm, p=ns), LVSD (19±3 vs 20±4 mm, p=ns), EF (72±3 vs 76±4 %, p=ns). Conversely, systolic MVG was significantly decreased in GRMD dogs (0.9±0.1 vs 2.5±0.4 s-1, p<0.01), despite normal left ventricular dimension and function. This alteration of systolic MVG in GRMD dogs was related to a significant decrease in systolic endocardial velocities (4.6±0.1 vs 6.5±0.7 cm.s-1, p<0.01), whereas epicardial velocities were comparable in the 2 groups (3.9±0.1 vs 4.4±0.9 cm.s-1, p=ns).

CONCLUSION

These results show that TDI accurately detects the dystrophin mutant dogs despite normal conventional indices of systolic function. So, TDI is more sensitive than conventional echocardiography in assessing asymptomatic regional myocardial dysfunction. In the next future, TDI might allow an early diagnosis of dilated cardiomyopathy and could also represent a useful tool for evaluating the efficacy of early cardiac therapeutic interventions.