Assessment of pulmonary hypertension in dogs with heartworm by using the ratio between the right and left ventricle

Abstract

Adults of D. immitis taken out of an infected dog in a necropsy (veterinary cardiology service; University of las Palmas de Gran Canaria). Assessment of pulmonary hypertension in dogs with heartworm by using the ratio between the right and left ventricle 1º Introduction 3º Results 2º Methodology 4º Conclusion The infection caused by Dirofilaria immitis causes an increase in resistance to blood flow, which causes an increase in pressure in the pulmonary arteries and, consequently, the right ventricular cavity undergoes morphological changes that ultimately lead to the appearance of signs of congestive heart failure (Figure1). Currently, thoracic computed tomography (CT) is an alternative modality to the use of transthoracic echocardiography (TTE) to evaluate lesions caused by D. immitis. The measurement of ventricular diameters expressed in the ratio between the right ventricle and left ventricle (RV:LV) has been used in human medicine and recently in veterinary medicine to estimate pulmonary hypertension (PH) of different origins. The purpose of this study was to quantify the RV:RL ratio in dogs suffering from D. immtis, in order to assess the potential use of this measure in the diagnosis of PH in dogs with heartworm. Thoracic CT scans with contrast were performed in 31 owned-dogs with heartworm, diagnosed by presence of circulating D. immitis antigens. There were 16 male and 15 female, aged mean of 8,77 years and body weight ranged from 4.5-37.2 kg. A total of 15 different dog breeds were included. The presence or absence of PH was determined using TTE, based on the determination of the right pulmonary artery distensibility index (RPADi) as previously described and validated in heartworm disease (Figure 2). An RPADi <29.5% correlated with presence of PH (>50mmHg). The RV:LV ratio was determined following previously established protocols. The diameters of the right and left ventricles were obtained from acquired CT transverse images. The right ventricle and the left ventricle were measured at their largest diameter on the same axis. PH was echocardiographically present in 64.5% of the dogs, showing a mean RV:LV ratio of 0.94 ± 0.61 (99% CI: 0.83-1.22). Normotensive dogs (35.5%) had a mean RV:LV ratio of 0.62 ± 0.46 (99% CI: 0.33-0.81). Additionally, a high correlation was observed between RPADi and RV:LV in the dogs studied (R 2 >0.75) (P<0.05). The results showed significant differences in the RV:LV ratio between the presence or absence of PH in dogs with D. immitis and demonstrate that the measurement can be a useful tool to assess PH in patients with heartworm disease in images obtained by CT. New studies are indicated with a larger sample size, being able to standardize protocols and obtain reliable reference values to establish the presence and severity of PH in these dogs.