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

Pressure overload is associated with right ventricular dyssynchrony in heart failure with reduced ejection fraction

AIMS

The determinants and relevance of right ventricular (RV) mechanical dyssynchrony in heart failure with reduced ejection fraction (HFrEF) are poorly understood. We hypothesized that increased afterload may adversely affect the synchrony of RV contraction.

METHODS AND RESULTS

A total of 148 patients with HFrEF and 36 controls underwent echocardiography, right heart catheterization, and gated single-photon emission computed tomography to measure RV chamber volumes and mechanical dyssynchrony (phase standard deviation of systolic displacement timing). Exams were repeated after preload (N = 135) and afterload (N = 15) modulation. Patients with HFrEF showed higher RV dyssynchrony compared with controls (40.6 ± 17.5° vs. 27.8 ± 9.1°, P < 0.001). The magnitude of RV dyssynchrony in HFrEF correlated with larger RV and left ventricular (LV) volumes, lower RV ejection fraction (RVEF) and LV ejection fraction, reduced intrinsic contractility, increased heart rate, higher pulmonary artery (PA) load, and impaired RV-PA coupling (all P ≤ 0.01). Low RVEF was the strongest predictor of RV dyssynchrony. Left bundle branch block (BBB) was associated with greater RV dyssynchrony than right BBB, regardless of QRS duration. RV afterload reduction by sildenafil improved RV dyssynchrony (P = 0.004), whereas preload change with passive leg raise had modest effect. Patients in the highest tertiles of RV dyssynchrony had an increased risk of adverse clinical events compared with those in the lower tertile [T2/T3 vs. T1: hazard ratio 1.98 (95% confidence interval 1.20-3.24), P = 0.007].

CONCLUSIONS

RV dyssynchrony is associated with RV remodelling, dysfunction, adverse haemodynamics, and greater risk for adverse clinical events. RV dyssynchrony is mitigated by acute RV afterload reduction and could be a potential therapeutic target to improve RV performance in HFrEF.

Right Ventricular Response to Acute Hypoxia Exposure: A Systematic Review

Background: Acute hypoxia exposure is associated with an elevation of pulmonary artery pressure (PAP), resulting in an increased hemodynamic load on the right ventricle (RV). In addition, hypoxia may exert direct effects on the RV. However, the RV responses to such challenges are not fully characterized. The aim of this systematic review was to describe the effects of acute hypoxia on the RV in healthy lowland adults.

Methods: We systematically reviewed PubMed and Web of Science and article references from 2005 until May 2021 for prospective studies evaluating echocardiographic RV function and morphology in healthy lowland adults at sea level and upon exposure to simulated altitude or high-altitude.

Results: We included 37 studies in this systematic review, 12 of which used simulated altitude and 25 were conducted in high-altitude field conditions. Eligible studies reported at least one of the RV variables, which were all based on transthoracic echocardiography assessing RV systolic and diastolic function and RV morphology. The design of these studies significantly differed in terms of mode of ascent to high-altitude, altitude level, duration of high-altitude stay, and timing of measurements. In the majority of the studies, echocardiographic examinations were performed within the first 10 days of high-altitude induction. Studies also differed widely by selectively reporting only a part of multiple RV parameters. Despite consistent increase in PAP documented in all studies, reports on the changes of RV function and morphology greatly differed between studies.

Conclusion: This systematic review revealed that the study reports on the effects of acute hypoxia on the RV are controversial and inconclusive. This may be the result of significantly different study designs, non-compliance with international guidelines on RV function assessment and limited statistical power due to small sample sizes. Moreover, the potential impact of other factors such as gender, age, ethnicity, physical activity, mode of ascent and environmental factors such as temperature and humidity on RV responses to hypoxia remained unexplored. Thus, this comprehensive overview will promote reproducible research with improved study designs and methods for the future large-scale prospective studies, which eventually may provide important insights into the RV response to acute hypoxia exposure.