Right ventricular dyssynchrony during hypoxic breathing but not during exercise in healthy subjects: a speckle tracking echocardiography study.

Pulmonary hypertension (PH) has been shown to be associated with regional inhomogeneity (or dyssynchrony) of right ventricular (RV) contraction. Right ventricular dyssynchrony is an independent predictor of decreased survival in advanced PH, but has also been reported in patients with only mildly elevated pulmonary artery pressure (PAP). The mechanisms of RV dyssynchrony in PH remain uncertain. Our aim was to evaluate RV regional function in healthy subjects during acute hypoxia and during exercise. Seventeen healthy subjects (24 ± 6 years) underwent a speckle tracking echocardiography of the RV at rest in normoxia and every 15 min during a 60 min exposure to hypoxic breathing ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>F</mml:mi> <mml:mrow><mml:mi>I</mml:mi> <mml:msub><mml:mi>O</mml:mi> <mml:mn>2</mml:mn></mml:msub> </mml:mrow> </mml:msub> </mml:math> 12%). Ten of the subjects also underwent an incremental cycle ergometry in normoxia to 100 W, with the same echocardiographic measurements. Dyssynchrony was measured as the SD of the times to peak systolic strain of the four basal and mid RV segments corrected for the heart rate (RV-SD4). RV-SD4 increased during hypoxia from 12 ± 7 to 22 ± 11 ms in spite of mild increases in mean PAP (mPAP) from 15 ± 2 to 20 ± 2 mmHg and pulmonary vascular resistance (PVR) from 1.18 ± 0.15 to 1.4 ± 0.15 Wood units (WU). During exercise RV-SD4 did not significantly change (from 12 ± 6 ms to 14 ± 6 ms), while mPAP increased to 25 ± 2 mmHg and PVR was unchanged. These data show that in healthy subjects, RV contraction is inhomogeneous in hypoxia but not during exercise. Since PAP increases more during exercise, RV dyssynchrony in hypoxia may be explained by a combination of mechanical (RV afterload) and systemic (hypoxia) factors.