Evaluation of Right Ventricular Function and Dyssynchrony in a Dog Model of Acute Pulmonary Embolism: Diagnostic Utility and Reversibility

Abstract

Background: The diagnosis of acute pulmonary thromboembolism is challenging in dogs. Little has been reported on changes in echocardiographic indices in dogs with acute pulmonary thromboembolism. The objective of this study was to validate the relationship between echocardiographic indices and right heart catheterization variables in dogs with acute pulmonary embolism and to identify a useful echocardiographic index for diagnosing acute pulmonary embolism.

Materials and methods: Six healthy laboratory beagles were included in the study. Echocardiography and right heart catheterization were performed in a dog model of acute pulmonary embolism produced by microsphere injection. Echocardiographic indices, including the right ventricular (RV) Tei index, RV longitudinal strain, and the dyssynchrony index using speckle tracking echocardiography, transmitral flow, and eccentricity index, were measured.

Results: The mean pulmonary arterial pressure increased (22.2 ± 1.2 mmHg) and the blood pressure decreased after microsphere injection. Although the mean pulmonary arterial pressure remained elevated, the blood pressure recovered 2 days after the microsphere injection. Most echocardiographic indices of RV function were significantly impaired following microsphere injection and recovered after 2 days. In contrast, the RV Tei index was significantly impaired after microsphere injection and the impairment persisted after 2 days. Multivariable analysis revealed that the RV Tei index was an independent echocardiographic predictor of pulmonary vascular resistance (β = 0.88, P < 0.001), and transmitral early diastolic wave was an independent predictor of the cardiac index (β = -0.86, P = 0.001).

Conclusions: The RV Tei index is a useful echocardiographic index for diagnosing acute pulmonary embolism. Ventricular interdependence may be an important factor causing low cardiac output in dogs with acute pulmonary embolism.

Keywords: Tei index; cardiac catheterization; microsphere injection; pulmonary hypertension; speckle tracking echocardiography.

Figure 1

Representative measurement of right ventricular Tei index and speckle tracking echocardiography. (A) Right ventricular Tei index was measured using dual pulsed-wave Doppler with a left parasternal short-axis view as follows: (a-b)/b. (B) Right ventricular Tei index was measured using tissue Doppler with an apical 4-chamber view as follows: (a-b)/b. (C) Right ventricular longitudinal strain and RV-SD6 were measured by speckle tracking echocardiography with a RV-focused apical 4-chamber view. Right ventricular free wall and septum were automatically divided into three segments (apical, middle, and basal). Global RVLS was calculated by averaging the peak longitudinal strain values in all six segments of the RV, and free wall and septal RVLS were calculated by averaging each value of three segments. This image shows the global RVLS. RV-SD6 was calculated as the standard deviation of the systolic shortening time of six right ventricular segments. The colored arrows indicate segmental systolic shortening time. AL, apical lateral free wall; AS, apical septum; BL, basal lateral free wall; BS, basal septum, ML, middle lateral free wall; MS, middle lateral septum; RV-SD6, standard deviation of the systolic shortening time of right ventricular six segments.

Figure 2

Changes in the hemodynamic variables and echocardiographic indices in a dog model of acute pulmonary embolism. Data are shown as the mean ± standard deviation. (A) Mean pulmonary arterial pressure and pulmonary vascular resistance. (B) Cardiac index. (C) Right ventricular Tei index by dual pulsed-wave Doppler and tissue Doppler. (D) Free wall and septal right ventricular longitudinal strain. (E) Systolic shortening time of free wall and septum. (F) Mitral early diastolic wave. *P < 0.05 compared with the baseline.

Figure 3

Representative images of right ventricular Tei index by dual pulsed-wave Doppler at baseline (A) acute period (B) and compensation period (C). (A) Right ventricular Tei index was 0.27 at baseline. (B) In acute period, right ventricular Tei index was increased (0.77). (C) In compensation period, right ventricular Tei index was still higher than baseline (0.63).

Figure 4

Representative images of speckle tracking echocardiography at baseline (A) acute period (B) and compensation period (C). (A) Global RVLS was −9.6% and RV-SD6 was 16.8 msec at baseline. (B) In acute period, global RVLS was significantly impaired compared with baseline (– 6.4%). Systolic shortening times of free wall were delayed (white arrows), and RV-SD6 was increased (81.5 msec). (C) In compensation period, global RVLS and RV-SD6 were returned to the baseline level (−8.6% and 10.1 msec). White color curve indicates global RVLS. RVLS, right ventricular longitudinal strain; RV-SD6, standard deviation of systolic shortening time of right ventricular six segments.

Figure 5

Changes in segmental RVLS and SST in a dog model of acute pulmonary embolism. Data are shown as the mean ± standard deviation. (A) Basal and middle free wall RVLS were significantly lower than baseline in acute period, and were return to the baseline level in compensation period. (B) All segmental free wall SST were significant long compared with baseline in acute period. White bar, baseline; black bar, acute period; gray bar, compensation period. A-RV, apical free wall; A-S, apical septum; B-RV, basal free wall; B-S, basal septum; M-RV, middle free wall; M-S, middle septum. RVLS, right ventricular longitudinal strain; SST, systolic shortening time. *P < 0.05 compared with the baseline.