Impaired cardiac function due to small heart and orthostatic intolerance in patients with myalgic encephalomyelitis

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Purpose: The etiology of chronic fatigue syndrome (CFS) remains unclarified. Recently, dysfunction of central nervous system by myalgic encephalomyelitis (ME) has been postulated as the cause of CFS. International Consensus Criteria identify patients with ME who are more physically debilitated and have greater physical and cognitive impairments. Orthostatic intolerance (OI) with symptoms of disabling fatigue, dizziness, diminished concentration, tremulousness and nausea while standing, appears to be a core symptom of ME, impairing the most basic activities of daily living. Cardiovascular dysfunction in association with a small heart or a small left ventricle (LV) and low cardiac output may be related to the pathophysiology of ME. Methods: Consecutive 40 patients who fullfilled the International Consensus Criteria for ME (14 males and 26 females, 31±10 years of age) and 40 age- and sex- matched sedentary control subjects (Controls) were studied. OI was determined either by subjective symptoms or by 10-min standing test. LV dimensions and function were determined echocardiographically. Results: OI was prevalent (95%) in ME. The mean heart rate was not significantly different between ME and Controls (68±11 vs. 70±11 beats/min, NS). The mean values of cardiothoracic ratio (39±5 vs. 43±4%, p<0.01), systolic (109±9 vs. 120±10 mmHg, p<0.05) and diastolic pressures (68±9 vs. 78±8 mmHg, p<0.05), LV end-diastolic (41±6 vs. 44±3 mm, p<0.01) and end-systolic (25±5 vs. 27±3 mm, p<0.05) dimensions, stroke volume index (32±8 vs. 38±6 ml/m2, p<0.01), cardiac index (2.1±0.4 vs. 2.7±0.5 ml/min/m2, p<0.01) and LV mass index (57±16 vs. 70±17 g/m2, p<0.01) were all significantly smaller in ME than in Controls. A smaller LV end-diastolic dimension (<40 mm) was significantly more prevalently noted in ME than in Controls (45% vs. 3%, p<0.01). A lower cardiac index (< 2 l/min/m2) was more prevalent in ME than in Controls (53% vs. 8%, p<0.01). The mean values of both LV fractional shortening (39±6 vs. 39±4%, NS) and LV ejection fraction (69±7 vs. 69±4%, NS) were quite comparable between the groups. Conclusions: OI was prevalent in ME. Both systolic and diastolic blood pressures were low in ME. A small size of LV associated with low cardiac output due to diminished stroke volume was frequently observed in ME. A small heart appears to be related to the genesis of ME via both cerebral and systemic hypoperfusion, which could make it difficult for patients to meet the demands of everyday activity. A small heart with impaired cardiac performance due to decreased preload appears to be an important target for the treatment of ME.