Association of Fitness and Obesity with Right Ventricular Function




Metzinger, Mark Philip

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BACKGROUND: Low Cardiorespiratory Fitness (CRF) and obesity are well-established risk factors for heart failure (HF). However, the mechanisms through which CRF and BMI influence HF risk remain uncertain especially with regards to the right ventricle. OBJECTIVES: We hypothesized that lower levels of CRF and higher measures of obesity in young adulthood along with greater decline in CRF and greater increase in BMI from young adulthood to middle-age would be associated with greater abnormalities in RV function in middle-age. METHODS: The CARDIA study is a multi-center longitudinal cohort study of young adults. For the present study, 3,433 participants with baseline CRF test and BMI data and echocardiographic examination at year 25 were selected. 2,544 participants with repeat CRF test and BMI data at year 20 were included in secondary analyses. CRF was measured as the maximal treadmill test duration (in seconds) using a graded, symptom-limited maximal treadmill test using a modified Balke protocol. Study participants were stratified into fit/fat groups using median CRF and median BMI as cutoffs. TAPSE (Tricuspid Annular Plane Systolic Excursion) and RVS' (velocity of tricuspid annular systolic motion) were used as measures of RV systolic function with larger values representing better function. PASP (Pulmonary Artery Systolic Pressure) (N = 1,292 with adequate tricuspid regurgitation jet) was used as a measure of pulmonary artery filling pressures. Multivariable adjusted linear regression analyses were performed to evaluate the independent associations of baseline CRF, baseline BMI, % change in CRF ((CRF at year 20 - CRF at year 0)/CRF at year 0 *100), and % change in BMI ((BMI at year 20 - BMI at year 0)/BMI at year 0 *100) with each echocardiographic measure of RV function at year 25. RESULTS: In unadjusted analysis, both TAPSE and RVS' were highest in the high fitness/high BMI group; PASP was highest with higher BMI. In multivariable adjusted linear regression analyses we observed a significant, direct association between baseline BMI and PASP such that higher BMI in young adulthood was associated with higher PA pressures in middle-age (β 0.12, P-value .0002); this remained significant after adjusting for % change in CRF and % change in BMI. A similar result was seen with % change in BMI and PASP. On the other hand, baseline CRF levels were not significantly associated with PASP (β -.0004, P-value 0.99). While there was a significant negative association between % change in CRF and PASP (β -0.08, P-value 0.02), this association became nonsignificant after adjusting for % change in BMI (β -0.05, P-value 0.22). There was a significant, direct association observed between both baseline CRF levels and baseline BMI and measures of RV systolic function (TAPSE and RVS') such that both higher CRF and BMI at baseline were associated with better RV systolic function in middle-age. Similar results were seen in groups stratified by CRF and BMI where greater RVS' and TAPSE were seen in the high fitness/high BMI group while the lowest PASP was seen in the high fitness/low BMI group. CONCLUSIONS: Given that obesity rather than fitness was associated with higher PASP suggests that the risk of HF seen with obesity could move through the pathway of elevated PA filling pressures while the risk seen with decreased fitness moves through an independent pathway. Given that both fitness and BMI moved in the same direction with regards to TAPSE and RVS', measures of RV systolic dysfunction appear to be less helpful in assessing HF risk. This may have important implications in better understanding the contributions of weight loss towards prevention of diseases characterized by RV dysfunction and pulmonary hypertension.

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