Cardiomyopathy translates to “heart muscle disease,” so cardiomyopathy is a broad term used to describe a variety of issues that result from disease of the myocardium, or heart muscle.
When cardiomyopathy develops as a way to compensate for some other underlying disease like hypertension or valve diseases, it’s called secondary cardiomyopathy, but when it develops all by itself it’s called a primary cardiomyopathy.
Restrictive cardiomyopathy is where the heart muscle is restricted, meaning it becomes stiffer and less compliant. The muscles and size of the ventricles, though, stay about the same or maybe they only get slightly enlarged.
Normally, when blood fills the ventricles, they’re compliant so they stretch out and allow more blood to fill in. When blood fills into restricted ventricles, though, they aren’t allowed to expand. So stiffer, less compliant ventricles means that the ventricles can’t stretch, and less blood fills into the ventricle, which means the heart’s starts to fail to pump out enough blood to the body. So restrictive cardiomyopathy causes heart failure, and since filling happens during diastole, we say this is a type of diastolic heart failure.
Now several mechanisms can lead to stiffer heart muscles and restrictive cardiomyopathies. One of these is amyloidosis. Amyloids are proteins that have been misfolded, and once misfolded they become insoluble and can deposit in various tissues and organs, making them less compliant.
Familial amyloid cardiomyopathy is a genetic disorder where mutant transthyretin protein, or TTR, is misfolded and prone to depositing in the heart tissue. TTR’s a protein that usually circulates in the blood and helps transport thryoxine and retinol. And mutations in TTR are more common in African Americans. Similarly, senile cardiac amyloidosis is where, over time, wild-type, or normal TTR deposits in the heart, and this is typically seen in the elderly.
