Usefulness of Tissue doppler imaging in the evaluation of pulmonary hypertension in dogs with heartworm

Abstract

Canine heartworm infection can cause a serious and highly fatal disease developed by the nematode Dirofilaria immitis. Severe cardiorespiratory clinical symptoms are related to the appearance and persistence of pulmonary hypertension (PH) of precapillary origin. The evaluation of the measurements obtained by transthoracic echocardiographic (TTE) exam offers the most comfortable and useful analysis indexes in canine heartworm disease. However, the hemodynamic functionality through the Tissue Doppler imaging (TDI) study in this disease is unknown. Therefore, the aim was to evaluate the potential use of TDI measurements in the diagnosis of animals suffering from HP caused by D. immitis. To this aim, 75 owned-dogs infected by D. immitis were evaluated. Of them 37 were male and 38 female, aged between 2-14 years and with a body weight range from 4 to 32 kg. A total of 16 different dog breeds were included. Parasite burden was echocardiographically estimated, and the presence and severity of PH was based on the determination of the right pulmonary artery distensibility index (RPADi) as previously described and validated for canine heartworm. An RPADi <29,5% correlated with presence of PH (>50mmHg). The global TDI index of myocardial function (G-TDI) was obtained by the determination of the peak myocardial velocities in systole (Stdi), early diastole (Etdi), and late diastole (Atdi), following previously established protocols. The following standard TDI indicators were also determined: isovolumic relaxation time (IVRT), isovolumic contraction time (IVCT), the TDI ratio of right E/A picks, and the right-ventricle TEI index (Figure 1). Based on the results obtained in the RPADi, 48% of the dogs were normotensive and 52% presented PH. High parasite burden was present in 62,8 % of the dogs. No statistically significant differences were observed in the TDI measurements regarding sex, age, breed and parasite burden. G-TDI was 6,1 ± 3,0 cm/s in dogs with PH and 17,9 ± 7,9 cm/s in normotensive dogs and significant differences were reported (P< 0.05). Similarly, significant differences (Table 1) were shown between presence or absence of PH in the study of IVRT (69,4 vs 35,9), IVCT (40,5 vs 16,6), TDI ratio of right E/A picks (0,61 vs 1,11), and the right-ventricle TEI index (0,63 vs 0,30) (P< 0.05). The study carried out shows that the measured TDI parameters can be a useful tool to assess PH in canine heartworm. Further studies are indicated with a larger sample size, aimed to determine standardize protocols and obtain reliable reference values for a correct diagnosis.