Left ventricular mechanical response to isometric exercise assessed by longitudinal strain and myocardial work in healthy adults
M E B Otto, M M Pereira, J L P PortelaAbstract
Background
Left ventricular (LV) ejection fraction is limited by load dependency and may fail to identify subtle mechanical adaptations. Global longitudinal strain (GLS) and myocardial work (MW) integrate deformation and afterload, providing a more comprehensive assessment of LV mechanics. Isometric handgrip exercise represents a simple and reproducible model of acute pressure overload.
Purpose
To characterise LV mechanical responses to isometric handgrip exercise using GLS and myocardial work indices in healthy adults.
Methods
Thirty healthy individuals (mean age 29.3 ± 6.1 years; 50% male) underwent transthoracic echocardiography at rest and during sustained handgrip at 30–40% of maximal voluntary contraction. Blood pressure and heart rate were recorded. GLS, global myocardial work index (GWI), global constructive work (GCW), global wasted work (GWW) and global work efficiency (GWE) were derived from non-invasive pressure–strain loops. Paired comparisons and effect sizes were calculated.
Results
Handgrip elicited a significant haemodynamic response, with systolic blood pressure increasing from 115 ± 16 to 133 ± 18 mmHg and heart rate from 72 ± 12 to 82 ± 10 bpm (both p<0.0001). LV ejection fraction remained unchanged (64.8% vs 64.4%; p=0.62). GLS showed a mild reduction (20.4 ± 2.6% vs 19.6 ± 2.5%; p=0.028; Cohen’s d = 0.42), mainly in basal segments. In contrast, MW indices increased substantially: GWI rose from 1810 ± 322 to 2054 ± 403 mmHg% (p=0.0002; d = 0.77), GCW from 2172 ± 371 to 2486 ± 453 mmHg% (p<0.0001; d = 1.05), and GWW from 108 ± 44 to 160 ± 76 mmHg% (p=0.0008; d = 0.68). GWE showed a small reduction (94.8 ± 1.8% vs 93.6 ± 2.5%; p=0.022; d = 0.44), remaining within physiological limits. Segmental analysis demonstrated greater MW increases in basal and mid-ventricular segments, with no significant apical changes.
Conclusion(s)
In healthy adults, isometric handgrip induces preserved ejection fraction, mild load-related GLS reduction and marked increases in myocardial work. MW indices, particularly GWI and GCW, are more sensitive than GLS or ejection fraction for detecting acute LV contractile adaptation to pressure overload. Handgrip combined with myocardial work analysis is a robust approach for assessing LV mechanical reserve.