Excess weight, not sleep apnea, may be the underlying cause of right ventricular (RV) dysfunction, a new study suggests Writing in the February 7, 2006 issue of the Journal of the American College of Cardiology, Dr Chiew Y Wong (University of Queensland, Brisbane, Australia) and colleagues say their findings challenge the hypothesis that sleep apnea is to blame, at least in obese but otherwise healthy adults.
Wong et al used tissue Doppler echocardiography to measure RV systolic and diastolic velocities in 112 overweight subjects and 35 normal-weight subjects, among whom 22 also had sleep apnea. They found that with or without sleep apnea, subjects with BMIs higher than 35 had reduced RV function, while moderately overweight subjects had reduced RV function but to a lesser degree. After adjustment for age, log insulin, and mean arterial pressures, BMI remained a significant predictor of RV changes.The authors speculate that the causes of RV dysfunction in obese subjects are likely multifactorial but point out that obesity has also been linked to left ventricular dysfunction, suggesting a systemic problem. “The study demonstrates the presence of subclinical RV dysfunction in patients with overweight and obesity that was not explained by obstructive sleep apnea, diabetes, hypertension, or other comorbidities,” Wong et al conclude. “Such early RV changes are related to the degree of obesity and functional capacity and independent of presence of sleep-disordered breathing.”Obesity and the heart: A complex relationship In an accompanying editorial, Dr Sheldon E Litwin (University of Utah School of Medicine, Salt Lake City) writes that Wong et al’s study “convincingly” shows that obesity is associated with mild but significant reductions in systolic and diastolic RV function, a finding that has also been demonstrated for the left ventricle . That said, Litwin cautions that the study findings do not necessarily prove that obesity leads directly to heart failure, nor do they help predict the future risk of heart failure in individual obese patients.Particularly interesting to Litwin is the “obesity paradox.” As he explained in an interview with heartwire, “No one would argue with the notion that over the lifetime of a patient, obesity is detrimental. However, a relatively large number of studies have shown that overweight and obese patients have better outcomes – survival in most cases – than normal-weight patients in the setting of acute coronary syndromes or established heart failure.”Litwin hypothesizes that the long-term risks of obesity on the heart do, in fact, stem from related comorbidities such as diabetes, hypertension, and high cholesterol, which lead in time to CAD, but through a process that takes 20 to 30 years. In the short-term, however, Litwin proposes that obesity may in fact have beneficial effects on the heart. “I believe that the work of lifting and transporting an increased body mass during day-to-day activities might actually produce a training effect on the heart, similar to what would be achieved by lifting weights or wearing a heavy backpack during the day,” he commented. “Since obese subjects rest at night, the heart sees the increased work load only intermittently, potentially giving it a chance to rest or recover from the extra stress. Thus, the heart may be trained or ‘preconditioned’ by the presence of obesity. This could provide the short-term protection that has been reported in other studies.”Eventually, he acknowledged to heartwire, the risks of developing CAD and other complications of obesity would outweigh the possible benefits of excess weight, but the hypothesis is still worth investigating, particularly as the theory could apply to healthy-weight people achieving the same “preconditioning” through exercise and weightlifting.”Normal-weight people would see the benefit but not accrue the long-term risks associated with obesity,” Litwin proposed. “Certainly being lean and fit seems to be the optimal situation and should be highly encouraged in all people.” (Source:(1) Wong CY, O’Moore-Sullivan T, Leano R, et al. Association of subclinical right ventricular dysfunction with obesity. J Am Coll Cardiol 2006; 47:611-616. (2) Litwin SE. The growing problem of obesity and the heart. The plot “thickens.” J Am Coll Cardiol 2006; 47:617-619. The Heart: Shelley Wood: February 2006.)