End-systolic pressure-length relations during changes in regional contractile state

Area of Science:

• Cardiovascular Physiology
• Cardiac Mechanics
• Myocardial Contractility

Background:

• The end-systolic pressure-length relationship (ESPLR) is a key indicator of left ventricular contractility.
• Heterogeneous myocardial contraction, common in various cardiac conditions, complicates the assessment of global cardiac function.

Purpose of the Study:

• To investigate the impact of altered regional contractility on the end-systolic pressure-length relationship (ESPLR) in a canine model.
• To determine how pharmacologically induced changes in myocardial contractile state affect ESPLR parameters.

Main Methods:

• Open-chest dogs were used to measure regional myocardial length sonomicrometrically in areas supplied by the left circumflex (LCX) and left anterior descending (LAD) coronary arteries.
• The ESPLR was assessed during transient reductions in arterial pressure induced by occluding the inferior caval vein.
• Regional contractility was modulated using infusions of isoproterenol (to enhance) and lidocaine (to impair) into the LCX artery.

Main Results:

• Isoproterenol infusion into the LCX significantly increased percent shortening and the slope (Ees) of the ESPLR in the LCX region, while the intercept (Lo) remained unchanged.
• In the LAD region, which was not directly infused, Ees and Lo were unaffected by isoproterenol.
• Lidocaine infusion into the LCX dose-dependently reduced regional percent shortening, with Ees showing a non-significant trend to decrease with mild hypokinesis and increase with severe hypokinesis.

Conclusions:

• Regional enhancement of contractility, as with isoproterenol, increases the slope of the ESPLR in the affected region without altering the intercept.
• Regional impairment of contractility by lidocaine has complex effects on ESPLR, with the slope potentially increasing at severe levels of dysfunction.
• These findings highlight the influence of regional myocardial function on the overall pressure-length relationship and cardiac performance.