Right ventricular dyssynchrony measured with echocardiography in dogs during Dirofilaria immitis infection

Background: Dirofilaria immitis infection can lead to pulmonary hypertension (PH) and in advanced stages to vena cava syndrome. Assessment of right ventricular (RV) function by echocardiography is important in dogs with Heartworm Disease (HWD). The aim of this study was to evaluate RV myocardial dyssynchrony as a potential cause of parasite relocation within the pulmonary artery (PA) right atrium (RA) and RV in dogs with D. immitis infection. Methods: The study included 22 client-owned dogs over 15 kg: 11 with PH and filariae in PA, RA and RV (Group PHF), 7 D. immitis -positive dogs without echocardiography changes (Group WEC); and 4 healthy controls. Dogs were retrospectively enrolled between January and December 2024. All dogs underwent echocardiographic examination, and Speckle Tracking Echocardiography (STE) including global right ventricular longitudinal strain (GRVLS) and Right Ventricle Dyssynchrony (RVD). RVD was assessed by calculating the standard deviation of times to peak systolic strain for four mid-basal RV segments (RV-SD4) and six mid-basal-apical RV segments (RV-SD6). Results: RV-SD4 and RV-SD6 were higher in the PHF group compared to the WEC group: RV-SD4 40±22 vs 29±12 msec (Mann-Whitney U-test, U ₍₁₈₎ = 53.00, Z = 1.31, P = 0.189), and RV-SD6 52±26 vs 31±11 msec (t ₍₁₆₎ = -2.34, P = 0.034). RV-SD6 showed moderate positive correlation with GRVLS (Pearson's r ₍₇₎ = 0.580, P = 0.062), free wall RVLS (Pearson's r ₍₇₎ = 0.545, P = 0.083), right atrial area index (Pearson' s r ₍₇₎ = 0.532, P = 0.092) and moderate inverse correlation with the peak systolic velocity of the lateral tricuspid annulus (Pearson's r ₍₇₎ = -0.587, P = 0.057). RV-SD4 showed moderate positive correlation with Right Pulmonary Artery Distensibility Index (RPADI) (Pearson's r ₍₇₎ = 0.53. P = 0.09). Conclusions: Our study showed that dogs with PH and filarial in PA, RV and RA had myocardial dysfunction and RVD, which could potentially contribute to parasite relocation. Strain and dyssynchrony indices should be considered when evaluating D. immitis -positive patients with echocardiographic abnormalities.