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Inotropic changes in the left ventricle: the effect of changes in heart rate, aortic pressure and end-diastolic
Insights
Left ventricular dP/dt max effectively quantifies inotropic changes, outperforming other cardiac variables. This index is crucial for understanding heart contractility under various physiological conditions.
Area of Science:
- Cardiology
- Physiology
Background:
- Assessing left ventricular contractility is vital in cardiovascular research.
- Previous methods for evaluating inotropic state have shown limitations.
Purpose of the Study:
- To determine the reliability of left ventricular dP/dt max as an index of inotropic changes.
- To compare dP/dt max with other commonly used indices of contractility.
Main Methods:
- Intravenous isoprenaline infusion in controlled conditions (constant heart rate, mean aortic pressure, and end-diastolic pressure).
- Measurement of left ventricular dP/dt max, peak left ventricular pressure, systole duration, and stroke work.
- Stepwise increments in isoprenaline infusion rate and heart rate alterations.
Main Results:
- Left ventricular dP/dt max changed significantly with isoprenaline infusion and was proportional to intrinsic heart rate changes.
- dP/dt max proved to be a reliable quantitative index of inotropic state.
- Peak left ventricular pressure, systole duration, and stroke work were unreliable indicators of inotropic changes.
- Altering heart rate or mean aortic pressure resulted in minor inotropic changes when assessed by dP/dt max.
Conclusions:
- Left ventricular dP/dt max is a superior and quantitative index for assessing inotropic changes.
- Other commonly used variables are unreliable for indicating the heart's inotropic state.
- Understanding inotropic changes is critical for cardiovascular diagnostics and therapeutics.
Abstract:
1. Under conditions where heart rate, mean aortic pressure and enddiastolic pressure in the left ventricle are held constant, the intravenous infusion of isoprenaline is accompanied by large changes in dP/dt max in the left ventricle.2. Under similar conditions, during stepwise increments in the rate of infusion of isoprenaline the changes in dP/dt max (measured at a constant paced heart rate) were proportional to changes in the free (intrinsic) heart rate. It is concluded that dP/dt max is a quantitative index of inotropic changes in the left ventricle.3. In comparison to dP/dt max, three other variables which have been used to indicate inotropic changes in the heart (peak pressure in the left ventricle, duration of systole and stroke work at constant end-diastolic pressure), were shown to be unreliable indices of inotropic changes.4. Using dP/dt max to indicate inotropic changes, alteration in the heart rate while mean aortic pressure and end-diastolic pressure in the left ventricle were held constant, and in mean aortic pressure while heart rate ane end-diastolic pressure in the left ventricle were held constant, were each shown to be accompanied by small inotropic changes in the heart.5. Under similar conditions, changes in end-diastolic pressure in the left ventricle alone were not accompanied by inotropic changes as indicated by dP/dt max.