TY - JOUR
T1 - End-diastolic myofiber stress and ejection strain increase with ventricular volume overload
AU - Donker, D.W.
AU - Volders, PGA
AU - Arts, T.
AU - Bekkers, BBACM
AU - Hofstra, L
AU - Spätjens, Roel L. H.
AU - Beekman, Jet D. M.
AU - Borgers, M
AU - Crijns, HJGM
AU - Vos, MA
PY - 2005/7
Y1 - 2005/7
N2 - Background Myocardial stress and strain are considered primary mechanical stimuli for hypertrophic remodeling. Their values and significance in the intact beating heart during chronic overload remain poorly characterized. Methods and results Left-ventricular (LV) dimensions (echocardiography) and pressure ( invasive) were simultaneously recorded in anesthetized dogs at sinus rhythm (SR), acute and 1, 2, 6, 12 weeks of atrioventricular block (AVB), leading to structural, electrical and contractile remodeling. Mechanical load of the myocardium was quantified as myofiber stress (sigma(f)), being force along myofiber orientation per cross-sectional area, and natural myofiber strain (e(f)), being change in natural logarithm of myofiber length ( l) divided by its reference length: e(f) = ln( l/l(ref)). Time courses of sigma(f) and e(f) were calculated from LV pressure and dimensions, using a validated mathematical model of cardiac mechanics. End-diastolic sigma(f) increased from 2.0 +/- 0.1 kPa at SR to 3.4 +/- 0.3 kPa at acute AVB, remaining elevated for > 6 weeks. Systolic sigma(f) was not affected by AVB. Ejection strain rose instantly upon AVB, reaching a maximum at 2 weeks: 0.24 +/- 0.02 vs. 0.10 +/- 0.01 at SR. The increase of myofiber stroke work ( sigma(f)-e(f) loop area) from 3.1 +/- 0.3 at SR to 6.0 +/- 0.5 kJ/m(3)/ beat at 1 week AVB was attributed mainly to an increase of strain during ejection. Stroke work and ejection strain remained elevated up to 12 weeks. The rate of LV-mass increase was maximal (2.2 +/- 0.4 g/day) at 1 week AVB. Conclusions Serial mechanical phenotyping is feasible in the intact anesthetized dog with chronic ventricular overload. Our new approach yields values of mechanical load that are comparable to those found in isolated myocardium by others. In chronic AVB, both end-diastolic myofiber stress and ejection strain are increased. Early increases of both parameters coincide with peak hypertrophic growth, suggesting their important role for mechanotransduction. Peak systolic sigma f is likely not important for hypertrophy in this model, since it does not change throughout the experiment.
AB - Background Myocardial stress and strain are considered primary mechanical stimuli for hypertrophic remodeling. Their values and significance in the intact beating heart during chronic overload remain poorly characterized. Methods and results Left-ventricular (LV) dimensions (echocardiography) and pressure ( invasive) were simultaneously recorded in anesthetized dogs at sinus rhythm (SR), acute and 1, 2, 6, 12 weeks of atrioventricular block (AVB), leading to structural, electrical and contractile remodeling. Mechanical load of the myocardium was quantified as myofiber stress (sigma(f)), being force along myofiber orientation per cross-sectional area, and natural myofiber strain (e(f)), being change in natural logarithm of myofiber length ( l) divided by its reference length: e(f) = ln( l/l(ref)). Time courses of sigma(f) and e(f) were calculated from LV pressure and dimensions, using a validated mathematical model of cardiac mechanics. End-diastolic sigma(f) increased from 2.0 +/- 0.1 kPa at SR to 3.4 +/- 0.3 kPa at acute AVB, remaining elevated for > 6 weeks. Systolic sigma(f) was not affected by AVB. Ejection strain rose instantly upon AVB, reaching a maximum at 2 weeks: 0.24 +/- 0.02 vs. 0.10 +/- 0.01 at SR. The increase of myofiber stroke work ( sigma(f)-e(f) loop area) from 3.1 +/- 0.3 at SR to 6.0 +/- 0.5 kJ/m(3)/ beat at 1 week AVB was attributed mainly to an increase of strain during ejection. Stroke work and ejection strain remained elevated up to 12 weeks. The rate of LV-mass increase was maximal (2.2 +/- 0.4 g/day) at 1 week AVB. Conclusions Serial mechanical phenotyping is feasible in the intact anesthetized dog with chronic ventricular overload. Our new approach yields values of mechanical load that are comparable to those found in isolated myocardium by others. In chronic AVB, both end-diastolic myofiber stress and ejection strain are increased. Early increases of both parameters coincide with peak hypertrophic growth, suggesting their important role for mechanotransduction. Peak systolic sigma f is likely not important for hypertrophy in this model, since it does not change throughout the experiment.
KW - hypertrophy
KW - stress
KW - strain
KW - mechanotransduction
KW - echocardiography
KW - remodeling
U2 - 10.1007/s00395-005-0525-8
DO - 10.1007/s00395-005-0525-8
M3 - Article
C2 - 15795796
SN - 0300-8428
VL - 100
SP - 372
EP - 382
JO - Basic Research in Cardiology
JF - Basic Research in Cardiology
IS - 4
ER -