Contractile function is preserved in unloaded hearts despite atrophic remodeling

Area of Science:

• Cardiovascular Biology
• Cardiac Remodeling
• Heart Transplantation Models

Background:

• Mechanical unloading of a failing heart can promote reverse remodeling and improve function.
• However, unloading may also induce detrimental remodeling, such as myocardial atrophy, potentially impairing cardiac function.

Purpose of the Study:

• To investigate the myocardial changes resulting from long-term unloading using a heterotopic heart transplantation model.
• To characterize both macroscopic and cellular alterations, as well as functional consequences of sustained cardiac unloading.

Main Methods:

• Utilized a heterotopic heart transplantation model to achieve long-term mechanical unloading of a normal heart for 3 months.
• Assessed macroscopic, cellular (stereology), and functional (Langendorff perfusion) parameters to evaluate myocardial changes.

Main Results:

• Observed significant myocardial atrophy, with a 67% reduction in myocyte volume and a 43% reduction in interstitial tissue volume.
• The number of cardiomyocyte nuclei decreased significantly, but nucleic density and cardiomyocyte volume per nucleus remained constant.
• Despite increased ventricular stiffness, contractile function was preserved, evidenced by unaltered maximal developed pressure and enhanced contractility and relaxation rates.

Conclusions:

• Long-term unloading induces atrophic remodeling affecting both myocyte and interstitial compartments.
• The unloaded heart exhibits reduced myocardial volume and increased stiffness.
• Contractile capacity is maintained in the long-term unloaded heart despite structural changes.