The Impact of Prolonged Strenuous Exercise on Right Ventricular Structure and Function: Insights from Novel Echocardiography and Electrocardiography
The body of evidence investigating post-exercise changes in left (LV) and right ventricular (RV) structure and function, commonly referred to as exercise induced cardiac fatigue (EICF), demonstrates a reduction in both systolic and diastolic function. RV dilatation and reduced LV filling are also evident. The mechanism responsible for this phenomenon is not fully understood, however a recent theory suggests that an elevated afterload on the RV and subsequent interaction between the ventricles may be implicated. Based on this, the aims of this thesis were: 1) to assess the RV structural and functional response to a 100 mile ultra-marathon applying novel techniques to determine the transient or persistent nature of RV post-exercise changes, 2) to provide a holistic assessment of all cardiac chambers, including the simultaneous derivation of structure and function for both the LV and RV in the same cardiac cycle following a 100 mile ultra-marathon, 3) to establish the acute response to a 100 mile ultra-marathon in both the 12-lead ECG and right-sided ECG and 4) to assess RV structure and function during a 6 hour upright cycling exercise bout, including the simultaneous estimation of PAP. The key finding from the Chapter 3 was a 10% reduction (P = 0.007) in RV strain and early diastolic strain rate immediately post-race that remained depressed following 6 hours of recovery. The application of area-deformation loops in Chapter 4 highlighted a leftward shift of the LV loop and rightwards shift of the RV loop immediately post-race with concomitant reduction in both LV and RV strain (-29 to -26% and -23 to -19% respectively, P = 0.01). The LV loop reflected a change in cardiac mechanics immediately post-race, supported by the increase in the systolic-diastolic strain gradient (P < 0.05). Following 6 hours of recovery, the strain gradient returned to baseline values but both RV and LV loops were still displaced from baseline values. There was a 22% elevation in the ST segment in leads V2R and V3R following the 100 mile ultra-marathon in Chapter 5. A heterogeneous response was observed with respect to T wave changes with 50% of right-sided ECGs demonstrating a significant change pre to post-race. The laboratory based study in Chapter 6 established the most appropriate technique with respect to reliability, feasibility and appropriate absolute values to quantify RV function during exercise. MST and TVI provide disparate RV strain values at 50 (25 and 30%), 70 (20 and 35%) and 90% (15 and 32%) maximum heart rate. CoV for global RV strain during exercise ranged from 7 to 11% for TVI and 14 to 73% for MST. In Chapter 7, the RV in-exercise response was assessed throughout prolonged cycling exercise with concomitant estimation of RV afterload. In contrast to the field-based studies, an initial increase in RV strain (-26 to -28%) was maintained as exercise progressed with no elevation in RV afterload or subsequent structural adaptation.
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