Increasing cardiac contractility after myocardial infarction exacerbates cardiac injury and pump dysfunction

Area of Science:

• Cardiovascular Biology
• Cardiac Electrophysiology
• Heart Failure Pathophysiology

Background:

• Myocardial infarction (MI) is a major cause of heart failure (HF) and mortality.
• The distinct contributions of myocyte death versus impaired contractility to post-MI HF remain unclear.

Purpose of the Study:

• To investigate the role of myocyte contractility and calcium handling in post-MI cardiac dysfunction.
• To test if preventing depressed myocyte contractility can avert heart failure after MI.

Main Methods:

• Developed a mouse model with inducible, cardiac-specific L-type calcium channel β2a subunit expression.
• Compared myocyte and cardiac function in control and β2a mice before and after experimentally induced MI.
• Assessed calcium (Ca2+) current, sarcoplasmic reticulum Ca2+ load, contractility, and Ca2+ transients.

Main Results:

• Mice with increased Ca2+ current (β2a) showed enhanced function pre-MI but greater ventricular dilation, myocyte hypertrophy, and death post-MI.
• Cardiac pump function was more depressed, and survival was poorer in β2a mice after MI.
• Post-MI myocytes in β2a mice failed to develop depressed Ca2+ handling, maintaining elevated Ca2+ current and contractility.

Conclusions:

• Maintaining myocyte contractility post-MI by enhancing Ca2+ influx is detrimental to cardiac pump function.
• This strategy paradoxically reduces myocyte number, exacerbating heart failure and mortality.
• Targeting Ca2+ handling to maintain contractility is not a viable strategy to improve outcomes after myocardial infarction.