Novel echocardiographic measures of myocardial work predicts physical performance during prolonged strenuous exercise

Funding Acknowledgements

Type of funding sources: Private company. Main funding source(s): The North Sea Race, Laerdal Foundation

Background

Cardiac function is a major determinant of physical performance. Cardiac function at rest can be assessed by novel echocardiographic parameters of myocardial work. Physical performance can be accurately measured using sensors recording the power output during exercise. There is limited data on the relationship between resting echocardiographic parameters and power measurements during strenuous endurance exercise. The aim of this work was to study the relationship between power output during exercise and echocardiographic parameters of cardiac structure and function at rest, including echocardiographic parameters of myocardial work.

Method

Resting echocardiographic parameters of 40 healthy, middle aged, recreational athletes, were compared with power output recordings during two episodes of endurance exercise of different duration and intensity. The first exercise was a cardiopulmonary exercise (CPX) test, which included both a lactate threshold- and a maximal oxygen uptake test. The second exercise was a 91-km mountain bike leisure sport cycling race. Power output was measured on the bikes using power meters. All study subjects were assessed by echocardiography prior to the CPX test. Coronary Computed Tomography Angiography was performed 1-2 weeks after the race to exclude obstructive coronary artery disease.

Results

Study participants were 51.1 ±9.7 years old (73 % men), median 10.0 (7.0-21.3) years of endurance training, and a median of 10.0 (5.0-20.0) endurance exercise competitions during the past five years. Both left ventricular mass and left atrial volume were in the upper reference range: 84.0 (77.0-96.0) gram/m2, 32.0 ±8.5 mL/m2, and the left ventricles were mildly dilated; 81.6 (69.1-96.5) mL/m2 (end-diastole). Median exercise duration: CPX: 43 (IQR 40-45) minutes, race: 236 (214-268) minutes. Mean heart rate; CPX: 145 ±11 bpm, race: 154 ± 10 bpm. Maximal oxygen uptake (Vo2 max): 41.6 ±9 ml/min/kg. Mean power output: CPX: 2.9 ±0.5 watt/kg, race: 2.1 ±0.5 watt/kg. There were strong bivariate correlations between left atrial and ventricular volumes and performance parameters (Table 1). Left ventricular global longitudinal strain (LV GLS) was correlated with Vo2 max. The myocardial work parameters global wasted work (GWW) and global work efficiency (GWE) were correlated with all performance parameters except Vo2 max. In multivariable linear regression models, except for VO2 max, GWW was the most consistent and strongest predictor of physical performance in all models (Table 2).

Conclusion

The novel echocardiographic parameter of global wasted work (GWW), assessed at rest, was the strongest and most consistent predictor of physical work measured by power meters during prolonged strenuous exercise.

Echocardiographic parameters of myocardial work in relation to prolonged strenuous physical exercise

Background

Myocardial work (MW) assessed by echocardiography is a novel measure of left ventricular (LV) function. This measure is load-independent, and therefore a more accurate method for assessing LV function when there are changes in loading conditions. The purpose of this study was to examine alterations in MW parameters, blood pressure (BP) and LV global longitudinal strain (LV GLS) in relation to strenuous exercise, and to compare the response between two different physical stress situations.

Methods

59 healthy recreational athletes were assessed by echocardiography before-, immediately- and 24 hours after two episodes of high-intensity endurance exercise. The first exercise was a cardiopulmonary exercise (CPX) test, which included both a stepwise lactate threshold- and a maximal oxygen uptake test. The second exercise was a 91-km mountain bike leisure sport cycling competition. Global work index (GWI), global constructive work (GCW), global wasted work (GWW) and global work efficiency (GWE) were estimated from LV pressure-strain loops, constructed from a combination of LV GLS and non-invasive BP, using commercially available software package (Echopac V.202, GE).

Results

Subjects were 52 (43–59) years old (73% men). The duration of the CPX-test was 43 (40–45) minutes, and the race was 230 (210–245) minutes. The average heart rate during the CPX-test and the race was 144 (140–153) and 154 (148–161) beats per minute (bpm), respectively. The relative changes (percent) in systolic blood pressure (SBP) and LV GLS compared with pre-exercise values are demonstrated in Figure 1a, and GWI and GCW compared with pre-exercise values in Figure 1b. GWI at baseline was 2156 (1899–2400) mmHg% and GCW 2383 (2152–2668) mmHg%. There was a significant reduction in LV GLS (p=0.015), SBP, GWI and GCW following the CPX-test and the race (p<0.001), while there was an increase in heart rate and cardiac output (p<0.001). After the race, there was a significant (p=0.001) increase in GWW, and a reduction (p=0.006) in GWE.

Conclusion

There was a significant reduction in GWI and GCW after both the CPX-test and the race, suggesting that these markers reflect increased myocardial exhaustion following strenuous physical exercise.

Funding Acknowledgement

Type of funding sources: Private grant(s) and/or Sponsorship. Main funding source(s): This work was supported by ConocoPhillips and the Simon Fougner Hartmann Trust Figure 1aFigure 1b

P4425The exercise-induced troponin I elevation is highly correlated with power output during exercise in recreational cyclists with coronary atherosclerosis

Background

Following strenuous exercise there is an increase cardiac Troponins (cTn) elevation considered being a physiological response. During prolonged strenuous physical activity, high work-loads may induce demand myocardial ischemia due to an oxygen demand/supply mismatch in susceptible subjects, causing an excessive cTn elevation.

Purpose

This study aimed to assess the relationship between exercise-induced cTnI elevation and direct measurement of work performed during prolonged strenuous exercise in subjects with and without atherosclerotic CAD.

Methods

Work during a 91 km mountain bike race was quantified by Stages™ power meters. Power (Watt) and heart rate data were stored in Garmin™ Forerunner 935 monitors. Coronary computed tomography angiography was performed after the race. Blood pressure was measured 4 times during the race. Blood samples (hs-cTnI from Abbot Diagnostics) were obtained one day prior to the race and at 3 and 24 h after the race. Data are presented as mean±SD or median (25th and 75th percentile).

Results

40 subjects (10 women) were included in the final analysis. 15 Participants (4 women) had atherosclerosis, none had obstructive CAD. These participants were significantly older (55±8 years vs. 46±8 years p=0.007) and had higher training volumes (METS: 69 (64–102) hrs/week) compared with normal subjects (METS: 51 (33–88) hrs/week) (p=0.03). Baseline cTnI was higher (p=0.04) in the atherosclerotic group (4.5 (3.4–8.8) ng/L) compared with normals (2.6 (1.6–4.8) ng/L). There were no differences in baseline blood pressure, peak VO2 max, heart rate or BMI. There was no significant difference in race duration between normals (3.9 (3.5–4.5) hrs) and subjects with atherosclerosis (4.1 (3.6–4.5) hrs). During the race there were no differences in peak power or peak Watt/kg. cTnI increased after the race in all participants, but there were no differences between groups: 3h: atherosclerosis: 89 (27–131) ng/L vs. normal 77 (36–104) ng/L, 24h: atherosclerosis: 13 (6.3–23.7) ng/L vs. normal: 17 (12–37) ng/L. There were no significant difference between the groups in average power during the race: atherosclerosis: 167±50 Watt vs. 174 (±50) Watt or ratio: 2.0±0.49 Watt/kg vs 2.2±0.58 Watt/kg during the race. Maximal systolic and diastolic blood pressures during the race were higher (p=0.002) in the atherosclerotic group: SBP: 241±14 mmHg vs. 219±26 mmHg, DBP: 107±8 vs 95±8 mmHg. In atherosclerotic subjects cTnI both at 3h and 24 h were highly correlated (p<0.001) with Watt/kg ratio during the race in contrast to no correlations in the normal group (Figure).

Conclusions

Our findings suggest that the presence of coronary atherosclerosis, even in the absences of significant stenosis, alters the relationship between workload and the troponin response. This indicates different release kinetics in exercise-induced cTn in participants with and without CAD, with prolonged elevation in cTnI in CAD subjects exceeding the highest work-intensities.

Acknowledgement/Funding

Grant Western Norway Health service, Grant ConocoPhillips, Grant Simon Fougner Hartmanns Familyfund