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Myocardial contractility and contraction duration are unrelated in the left ventricle with moderate pressure-overload
T Aoyagi1, S Momomura, H Matsui
1Department of Medicine, Brigham and Women's Hospital, Boston, MA 02115.
Insights
In hypertrophic rat hearts, contraction duration was prolonged, but myocardial contractility remained normal. This study introduces a novel method for load-independent assessment of ventricular function in hypertrophy.
Area of Science:
- Cardiology
- Physiology
- Biomedical Engineering
Background:
- Left ventricular hypertrophy (LVH) is a common cardiac condition.
- Assessing myocardial contractility and contraction duration independently of loading conditions is crucial for understanding cardiac function in LVH.
- Previous methods often struggle to accurately differentiate between intrinsic myocardial properties and loading effects.
Purpose of the Study:
- To introduce and validate a novel approach for the load-independent assessment of both myocardial contractility and contraction duration in isolated rat hearts.
- To investigate whether myocardial contractility and contraction duration are altered in a model of pressure-overload-induced left ventricular hypertrophy (LVH).
Main Methods:
- Isolated isovolumic rat hearts from Wistar rats with DOCA-salt induced LVH (n=7) and control rats (n=7) were used.
- Load-independent assessment of myocardial contractility using shortening-afterload (Sm-sigma aft) and ejection fraction-afterload (EF-sigma aft) relations.
- Evaluation of contraction duration using indices such as time to maximum stiffness and pressure time integral divided by peak pressure.
Main Results:
- Indices of contraction duration were significantly prolonged in the LVH group compared to controls.
- Myocardial contractility, assessed via Sm-sigma aft and EF-sigma aft relations, was preserved in the LVH group.
- The degree of hypertrophy was identified as an independent determinant of prolonged contraction duration.
Conclusions:
- A novel, load-independent method for assessing myocardial contractility and contraction duration in whole ventricles was successfully introduced.
- Moderate pressure-overload hypertrophy leads to a prolonged contraction duration with preserved myocardial contractility.
- This finding has implications for understanding diastolic dysfunction and therapeutic strategies in hypertrophic cardiomyopathy.
Abstract:
Both myocardial contractility and contraction duration were assessed load-independently in isolated hypertrophic and control rat hearts. Hemodynamic parameters for isolated isovolumically contracting hearts were compared for 7 Wistar rats with DOCA-salt induced hypertrophy (LVH) and 7 controls. Loads were altered by changing the volume of an intraventricular balloon. Myocardial contractility was assessed in terms of the shortening-afterload (Sm-sigma aft), and the ejection fraction-afterload (EF-sigma aft) relations at common preloads, based upon the systolic myocardial stiffness concept. Indices of contraction duration (time to maximum stiffness, pressure time integral divided by peak pressure and the time required for left ventricular (LV) peak pressure to be reduced by a half) were prolonged in LVH. Multiple regression analyses indicated that the degree of hypertrophy was an independent determinant of the contraction duration. The Sm-sigma aft and EF-sigma aft relations at common preloads demonstrated normal contractility in the LVH group. The time constant of the fall in LV pressure and the diastolic myocardial stiffness remained normal in the LVH group. Thus, we introduced the new approach to load-independently assess both the myocardial contractility and the contraction duration in a whole ventricle. A prolonged contraction duration in the presence of normal myocardial contractility was observed in a ventricle with moderate pressure-overload hypertrophy.