Influence of heart rate on right ventricular function assessed by right heart catheterization and echocardiography in healthy anesthetized dogs

Background

Right ventricular (RV) functional assessment has received considerable attention in veterinary medicine since various diseases, such as cardiovascular, respiratory, endocrine, and neoplastic disease, may affect RV function. Heart rate (HR) is an important factor that can influence RV function through changes in loading condition and contractility. However, no study has yet evaluated the association between HR and RV function in the same individuals. This study aimed to evaluate the influence of elevated HR on RV function using right heart catheterization and echocardiography, and investigate the association between right heart catheterization and echocardiographic indices.

Results

Right atrial pacing was performed in eight dogs at 120, 140, 160, and 180 bpm. With an increase in HR, the RV systolic volume, RV diastolic volume, and stroke volume significantly decreased; however, the cardiac output, end-systolic elastance (Ees), and effective arterial elastance (Ea) significantly increased. Significant changes were not observed in RV pressure and Ees/Ea. The RV area normalized by body weight, RV fractional area change normalized by body weight (RV FACn), and tricuspid annular plane systolic excursion normalized by body weight (TAPSEn) significantly decreased with increased HR. Peak systolic myocardial velocity of the lateral tricuspid annulus (RV s’), RV strain, and RV strain rate of only the RV free wall analysis (RV-SrL_3seg) showed no significant changes with the increase in HR; however, there was an increase in the RV strain rate of the RV global analysis (RV-SrL_6seg). Multiple regression analysis revealed that HR, RV FACn, and RV- SrL_6seg had significant associations with the Ees, and the TAPSEn and RV-SrL_3seg with Ees/Ea.

Conclusions

Decreased venous return and shortened relaxation time decreased the RV FAC, TAPSE, RV s’, and RV strain, and might underestimate the RV function. Ees increased with the increase in HR, reflecting the myocardial force-frequency relation; as a result, RV-SrL_6seg could be a useful tool for Ees estimation. Additionally, the RV-SrL_3seg could detect RV performance, reflecting the balance between RV contractility and RV afterload.

Investigation of the influence of manual ventilation-controlled respiration on right ventricular pressure-volume loops and echocardiographic variables in healthy anesthetized dogs

OBJECTIVE

To evaluate the influence of manual ventilation-controlled respiration on right ventricular (RV) pressure-volume loop-derived and echocardiographic variables in dogs.

ANIMALS

8 healthy, anesthetized Beagles.

PROCEDURES

In a prospective experimental study, pressure-volume catheters were percutaneously inserted into the right ventricle of each dog, and manual ventilation was performed; RV pressure-volume loop (hemodynamic) data and conventional echocardiographic variables were assessed. Two-dimensional speckle tracking echocardiography-derived RV strain (RVS) and RV systolic strain rate (RVSR) were obtained with RV free wall-only analysis (free wall) and RV global analysis (RVGA; interventricular septum). Variables were compared between end-inspiratory and end-expiratory phases of respiration by statistical methods. Multiple regression analysis was used to assess associations between selected hemodynamic and echocardiographic variables.

RESULTS

The RV pressure significantly increased, and RV volume, stroke volume, tricuspid annular plane systolic excursion, RV fractional area change, peak myocardial systolic velocity of the lateral tricuspid annulus, and RV free wall only-assessed RVS and RVSR significantly decreased in the inspiratory phase, compared with the expiratory phase. There were no significant differences in end-systolic elastance or RVGA-assessed RVS or RVSR between respiratory phases. The RVGA-assessed RVSR was significantly associated with stroke volume and end-systolic elastance.

CONCLUSIONS AND CLINICAL RELEVANCE

Specific RV echocardiographic variables were significantly affected by respiration. In contrast, RVS and RVSR determined with RVGA were not affected by respiration and were associated with hemodynamic indicators of RV contractility.

Right Ventricular Myocardial Adaptation Assessed by Two-Dimensional Speckle Tracking Echocardiography in Canine Models of Chronic Pulmonary Hypertension

Background: Pulmonary hypertension (PH) is a life-threatening disease in dogs characterized by an increase in pulmonary arterial pressure (PAP) and/or pulmonary vascular resistance. Right ventricle adapts to its pressure overload through various right ventricular (RV) compensative mechanisms: adaptive and maladaptive remodeling. The former is characterized by concentric hypertrophy and increased compensatory myocardial contractility, whereas the latter is distinguished by eccentric hypertrophy associated with impaired myocardial function. Objectives: To evaluate the RV adaptation associated with the increase of PAP using two-dimensional speckle tracking echocardiography. Animals: Seven experimentally induced PH models. Methods: Dogs were anesthetized and then a pulmonary artery catheter was placed via the right jugular vein. Canine models of PH were induced by the repeated injection of microspheres through the catheter and monitored pulmonary artery pressure. Dogs were performed echocardiography and hemodynamic measurements in a conscious state when baseline and systolic PAP (sPAP) rose to 30, 40, 50 mmHg, and chronic phase. The chronic phase was defined that the sPAP was maintained at 50 mmHg or more for 4 weeks without injection of microspheres. Results: Pulmonary artery to aortic diameter ratio, RV area, end-diastolic RV wall thickness, and RV myocardial performance index were significantly increased in the chronic phase compared with that in the baseline. Tricuspid annular plane systolic excursion was significantly decreased in the chronic phase compared with that in the baseline. The RV longitudinal strain was significantly decreased in the sPAP30 phase, increased in the sPAP40 and sPAP50 phases, and decreased in the chronic phase. Conclusions: Changes in two-dimensional speckle tracking echocardiography-derived RV longitudinal strain might reflect the intrinsic RV myocardial contractility during the PH progression, which could not be detected by conventional echocardiographic parameters.

The influence of increased venous return on right ventricular dyssynchrony during acute and sustained hypoxaemia

NEW FINDINGS

What is the central question of this study? Right ventricular dyssynchrony is a marker of function that is elevated in healthy individuals exposed to acute hypoxia, but does it remain elevated during sustained exposure to high altitude hypoxia, and can it be normalised by augmenting venous return? What is the main finding and its importance? For the first time it is demonstrated that (i) increasing venous return in acute hypoxia restores the synchrony of right ventricular contraction and (ii) dyssynchrony is evident after acclimatisation to high altitude, and remains sensitive to changes in venous return. Therefore, the interpretation of right ventricular dyssynchrony requires consideration the prevailing haemodynamic state.

ABSTRACT

Regional heterogeneity in timing of right ventricular (RV) contraction (RV dyssynchrony; RVD) occurs when pulmonary artery systolic pressure (PASP) is increased during acute hypoxia. Interestingly, RVD is not observed during exercise, a stimulus that increases both PASP and venous return. Therefore, we hypothesised that RVD in healthy humans is sensitive to changes in venous return, and examined whether (i) increasing venous return in acute hypoxia lowers RVD and (ii) if RVD is further exaggerated in sustained hypoxia, given increased PASP is accompanied by decreased ventricular filling at high altitude. RVD, PASP and right ventricular end-diastolic area (RVEDA) were assessed using transthoracic two-dimensional and speckle-tracking echocardiography during acute normobaric hypoxia ( F i O 2  = 0.12) and sustained exposure (5-10 days) to hypobaric hypoxia (3800 m). Venous return was augmented with lower body positive pressure at sea level (LBPP; +10 mmHg) and saline infusion at high altitude. PASP was increased in acute hypoxia (20 ± 6 vs. 28 ± 7, P < 0.001) concomitant to an increase in RVD (18 ± 7 vs. 38 ± 10, P < 0.001); however, the addition of LBPP during hypoxia decreased RVD (38 ± 0 vs. 26 ± 10, P < 0.001). Sustained hypoxia increased PASP (20 ± 4 vs. 26 ± 5, P = 0.008) and decreased RVEDA (24 ± 4 vs. 21 ± 2, P = 0.042), with RVD augmented (14 ± 5 vs. 31 ± 12, P = 0.001). Saline infusion increased RVEDA (21 ± 2 vs. 23 ± 3, P = 0.008) and reduced RVD (31 ± 12 vs. 20 ± 9, P = 0.001). In summary, an increase in PASP secondary to acute and sustained exposure to hypoxia augments RVD, which can be at least partly reduced via increased venous return.

Utility of tricuspid annular plane systolic excursion normalized by right ventricular size indices in dogs with postcapillary pulmonary hypertension

Background

Tricuspid annular plane systolic excursion (TAPSE) is a common right ventricular (RV) function indicator. However, TAPSE was not decreased in dogs with myxomatous mitral valve disease (MMVD) and postcapillary pulmonary hypertension (PH) because of its load, angle, and body weight dependency, and TAPSE was considered a preload‐dependent index.

Objectives

To evaluate the utility of TAPSE normalized by RV size in dogs with postcapillary PH.

Animals

Twenty healthy dogs and 71 MMVD dogs with or without PH.

Methods

In this prospective observational study, end‐diastolic RV internal dimension (RVIDd), end‐diastolic and end‐systolic RV area, and end‐diastolic RV wall thickness were measured as RV size indices. The TAPSE was measured using B‐mode and M‐mode methods. Normalized TAPSE was calculated by dividing TAPSE by each RV size index. The RV strain was obtained as the detailed RV function using 2‐dimensional speckle tracking echocardiography. All indices were compared among the PH severity groups and in the presence of right‐sided congestive heart failure (R‐CHF).

Results

Although nonnormalized TAPSE was higher with PH severity progression, each normalized TAPSE showed a significant decrease in the severe PH group (P < .05). The TAPSE_B‐mode/RVIDd ratio had high area under the curve to predict R‐CHF and had moderate correlation with RV strain (P < .05). The TAPSE_B‐mode/RVIDd and left atrial‐to‐aortic diameter ratios were independent predictors for R‐CHF.

Conclusions and Clinical Importance

Normalized TAPSE could reflect RV systolic dysfunction in dogs with severe PH, which could not be detected by nonnormalized TAPSE. The TAPSE_B‐mode/RVIDd ratio might predict R‐CHF with high sensitivity and reproducibility.

Right ventricular function and dyssynchrony measured by echocardiography in dogs with precapillary pulmonary hypertension

INTRODUCTION

Assessment of the right ventricular (RV) function by echocardiography is important in dogs with pulmonary hypertension (PH). Few reports are available on RV function and dyssynchrony in dogs, especially in the context of precapillary PH.

ANIMALS

The study included 79 client-owned dogs: 25 dogs with precapillary PH and 54 control dogs.

METHODS

Dogs with precapillary PH were prospectively enrolled between December 2013 and February 2017. The echocardiographic indices of RV function, including RV strain and the dyssynchrony index by speckle-tracking echocardiography, were measured. Multivariate analysis was used to determine independent predictors of the RV dyssynchrony index.

RESULTS

Dogs with precapillary PH showed RV dilation, hypertrophy and right atrial dilation. Impaired echocardiographic indices of RV function, including RV strain, were observed. In addition, RV dyssynchrony occurred in dogs with precapillary PH. Multivariate analysis revealed that tricuspid regurgitation velocity and RV dilation were independent predictors of the RV dyssynchrony index.

CONCLUSIONS

Echocardiographic RV function indices are impaired in dogs with precapillary PH. In addition, RV dilation and elevated systolic pulmonary arterial pressure estimated by echocardiography are associated with RV dyssynchrony.