The effects of hemodynamic, vascular, and muscular parameters on maximal and submaximal exercise capacity in patients with fontan procedure

The exercise capacity of patients with Fontan procedure is related to the increased risk of morbidity and mortality. Therefore, investigating the exercise capacity and cardiovascular and peripheral factors that it may affect in these patients has become important. The study was conducted to investigate the effects of hemodynamic, vascular and muscular parameters on maximal and submaximal exercise capacity in patients with Fontan procedure. Thirty-one Fontan patients with a median age of 18 years (7-31 years) and 30 controls with a median age of 18 years (7-32 years) were included. All participants' demographic and clinical characteristics were recorded. Maximal exercise capacity was assessed by a modified Bruce protocolled cardiopulmonary exercise test (CPET) on a treadmill ergometer using the "breathe-by-breathe" method; submaximal exercise capacity was assessed by a 6-minute walk test (6MWT). For atrial strain measurements, transthoracic echocardiography measurements were performed and the reservoir phase (LASr), conduit phase (LAScd) and contractile phase (LASct) for atrial strain were recorded using the speckle tracing method. Hand grip strength and knee extensor muscle strength were assessed using a hand dynamometer. Muscle oxygenation (SmO2) was recorded during CPET and 6MWT with a device (Moxy, Fortiori Design LLC, Minnesota, USA) that measures local SmO2 and total hemoglobin (THb) in muscle using near infrared spectroscopy. Aortic stiffness was assessed by echocardiographic measurements using the aortic pulse wave velocity (aPWV) technique. There was no significant difference between Fontan patients and control subjects in terms of age and gender distribution (p>0.05). Body composition parameters, dominant hand grip strength (kg) and dominant knee extensor strength (kg) were similar in patients and controls (p>0.05). 6MWT resting SmO2, minimum SmO2 and recovery SmO2 were lower in Fontan patients compared to controls (p<0.05). CPET resting SmO2, minimum SmO2 and recovery SmO2 were lower in Fontan patients (p<0.05). In addition, LASr, LAScd, LASct and LASct/LASr values were lower in Fontan patients compared to controls (p<0.05). aPWV was higher in patients compared to control subjects (p<0.05). peakVO2 and 6MWT distance were also lower in Fontan patients compared to controls (p<0.05). According to multiple regression models, dominant knee extensor strength, age, LASct and aPWV were independent predictors of peakVO2, while dominant knee extensor strength and aPWV were independent predictors of 6MWT distance. In conclusion, knee extensor muscle strength, age, atrial contractile strain and aortic stiffness are independent determinants of maximal exercise capacity in Fontan patients. In addition, knee extensor strength and aortic stiffness are independent determinants of submaximal exercise capacity in Fontan patients. In addition to the routine laboratory and clinical tests, evaluation of exercise capacity and related paramaters is important for optimal clinical management of patients with Fontan procedure.