What Is Hibernating Myocardium?

Hibernating myocardium is the term used to describe a portion of the muscle that makes up the middle layer of heart tissue, the myocardium, that has gone into a state of dormancy due to an inadequate supply of blood. This often occurs as a result of coronary artery disease (CAD). The muscle has not "died," but it ceases to function.

For some people with hibernating myocardium, portions of the heart muscle that appear to be severely damaged and non-functional are still viable and can be “revived” if the blood supply is reestablished.

Hibernating myocardium typically causes no discernible symptoms, although some people experience chest pain or shortness of breath. A doctor can diagnose the condition with specialized imaging tests. Treatment often involves surgery.

Symptoms

If you have hibernating myocardium, it's unlikely you'll know it based on how you feel or your ability to function. Some people with the condition experience generalized symptoms that could indicate any number of diseases or conditions that affect the heart or lungs, such as chest pain or dyspnea (shortness of breath).

However, because only a portion of the heart is dormant and blood flow and oxygenation is not severely interrupted, most people with hibernating myocardium do not have symptoms.

Causes

The myocardium layer of the heart is made up of thick muscle that rhythmically contracts and relaxes in order to pump blood. The pathophysiological mechanism that underlies hibernating myocardium is not well understood.

This is what is known. Like a bear hibernating through the winter, despite all appearances, the hibernating heart muscle is not dead, but instead has become dormant. In this state of self-protective inactivity, the portion of affected heart shuts down all functions that are not immediately critical.

Because only a portion of the heart tissue goes dormant, the organ as a whole can continue to pump, which is why hibernation myocardium is largely asymptomatic.

The heart muscle may go into hibernating myocardium when CAD is severe enough to produce myocardial ischemia, meaning the heart muscle isn't getting enough oxygenated-blood.

Plaque and cholesterol buildup can cause ischemia by partially or fully blocking coronary arteries and compromising blood flow to the heart, starving it of oxygen-rich blood.  In fact, ischemia is likely the reason for chest pain that occurs with hibernating myocardium.

Diagnosis

Often hibernating myocardium as adjacent to muscle that is completely dead. Therefore, an essential aspect of diagnosing hibernating myocardium is determining how much affected heart muscle is non-viable (dead) and how much is potentially revivable. Scarring that is visible on imaging tests distinguishes the two.

Cardiac MRI Studies

Cardiac magnetic resonance imaging (MRI) allows a cardiologist to see how much blood flow is reaching the muscle and as well as how much scar tissue is present compared with healthy tissue.

Dobutamine Stress Echocardiogram (Echo)

For this test, a stimulant called dobutamine is injected into a vein in order to "wake up" hibernating tissue by causing the heart to beat faster.

Performing an echocardiogram on a person while they are exercising can diagnose ischemia by visualizing segments of the heart muscle that fail to contract normally when deprived of sufficient oxygen.

Nuclear Imaging Studies

Positron emission tomography (PET) scans and single-photon emission computerized tomography (SPECT) scans can evaluate heart muscle viability by assessing blood flow to the heart as well as how the the organ utilizes glucose: Scarred, dead tissue does not use glucose but hibernating muscle does.

Treatment

The goal of treatment for hibernating myocardium is to reestablish adequate blood flow with early surgical intervention. There are a number of surgical procedures that can achieve this:

• Angioplasty: For this procedure, a catheter with a small balloon on the end is inserted near the blocked or narrowed area of a coronary artery. Once in position, the balloon is inflated, thereby compressing the blockage against the walls of the artery, increasing its diameter and allowing for the free flow of blood. 
• Stent placement: A stent is a tiny wire mesh tube that is surgically implanted to hold open an artery and allow blood flow. Stents are permanent; placement often is often combined with angioplasty.
• Coronary Artery Bypass Grafting (CABG): Bypass surgery is the most invasive option. In this procedure, a heart surgeon removes arteries or veins from other parts of the body and uses them to reroute the blood around the clogged artery to supply blood flow to your heart muscle. Some people require more than one bypass grafts, depending on how many coronary arteries are damaged. Bypass surgery is an in-patient procedure and requires several days in the hospital.

A Word From Verywell

If surgery successfully restores the blood flow to hibernating myocardium, there’s a good chance the tissue can “wake up” and begin working again, ultimately making a significant difference in quality of life. It is important to note that the improvement, once blood flow returns to dormant sections, depends on how severely the heart was impacted. It can take weeks some times for the affected parts of the heart muscle to function again. But if you're evaluated and treated properly for hibernating myocardium, chances are high you will ultimately have full function of your heart.