Definition and Overview
Myocardial ischemia is a heart condition that can cause permanent damage to the heart muscle. It occurs when blood flow to the coronary arteries is partially or completely blocked (atherosclerotic coronary artery disease or CAD) leaving the heart with an insufficient amount of oxygen, preventing it from efficiently pumping blood throughout the body.
The condition affects approximately 1.5 million people in the United States and is responsible for approximately 14% of deaths worldwide. Although it is highly treatable when diagnosed and treated early, most cases are not found until the patient suffers from a heart attack. This is because myocardial ischemia does not normally produce symptoms (silent myocardial ischemia).
As a preventive measure, patients may undergo regular screening tests and certain diagnostic procedures to determine their CAD risk level. This is the best way to catch the disease early on when it is highly responsive to treatment. If there is a blockage in the coronary arteries, patients can undergo treatment before the disease progresses. Normal blood flow to the coronary arteries can be restored by making heart-healthy choices, taking certain medications, or undergoing surgery.
Causes of Condition
Myocardial ischemia occurs due to blocked coronary arteries, resulting in decreased blood flow to the heart. It can develop slowly or occur spontaneously. The blockage can be caused by:
Atherosclerosis - Characterised by the build-up of plaque inside the artery. Plaque is made up of substances found in the blood including but not limited to calcium, cholesterol, and fat.
Coronary artery vasospasm - The temporary constriction of the smooth muscle that causes coronary arteries to narrow. This can occur spontaneously but is usually brief and temporary. It is normally caused by high blood pressure and high cholesterol level.
Thrombosis - Atherosclerosis can cause the coronary arteries to rupture, which can lead to the formation of blood clots (thrombosis). Blood clots, depending on their size, can either partially or completely block the flow of oxygen-rich blood to the heart, causing mild to severe symptoms, including a sudden heart attack.
Uncommon or rare myocardial ischemia causes include:
Arterial embolism – When a blood clot forms in other parts of the body and travels to the coronary arteries through the bloodstream.
Certain heart disease or conditions
Heart surgery complications
Penetrating wound to the heart
Use of cocaine, which can increase the risk of coronary artery vasospasm
Extreme cold temperatures
Up to one-third of patients do not experience myocardial ischemia symptoms. Those who do complain of the following:
Chest pressure or pain
Dizziness, fainting, or lightheadedness
Neck, jaw, shoulder or arm pain
Oedema of the legs and feet
Meanwhile, several factors have been confirmed to increase the risk of myocardial ischemia. These include:
High blood cholesterol/triglyceride levels
High blood pressure
Tobacco smoking and long-term exposure to secondhand smoke
Who to See and Types of Treatments Available
Ideally, patients should seek treatment for coronary artery disease before it leads to a heart attack or heart failure. However, the lack of symptoms makes this impossible in many cases. Hence, regular screening, particularly for those who have risk factors, is highly recommended.
Patients showing severe symptoms of myocardial ischemia or those with a history of chronic myocardial ischemia are mostly examined and treated in the emergency room where they immediately undergo myocardial ischemia ECG or electrocardiogram. This is a simple, painless, and non-invasive test that records the heart’s electrical activity. Any irregularities found in this test may indicate the presence of myocardial ischemia. The goal of myocardial ischemia treatment at this point is to prevent a heart attack by restoring normal blood flow to the heart.
Other diagnostic tests that are commonly performed before any treatment is initiated include:
Coronary angiography - An X-ray test that determines if the coronary arteries are blocked or narrowed. It is also used to assess the severity of the narrowing of the affected artery.
Coronary calcium scan - Using computed tomography (CT), this test is done to see if there is calcium buildup in the coronary arteries.
Echocardiogram - A non-invasive ultrasound test that detects problems of the heart valves or chambers, which can also be indicative of myocardial ischemia.
Nuclear myocardial scan - Provides a wealth of information that helps clinicians in assessing blood flow to the affected coronary artery. It also helps determine the left ventricular ejection fraction and whether the arterial walls have already thickened. The test uses imaging technology, such as positron emission tomography (PET), and a radioactive substance (tracer) to create detailed pictures of the heart.
Stress test - Aims to measure the patient’s cardiovascular capacity by monitoring the heart rate while doing certain exercises.
Treatment of myocardial ischemia depends on the severity of the condition. Mild cases are treated with medications. Depending on the causes of myocardial ischemia, patients are prescribed with drugs that can open the blocked arteries, reduce the risk of blood clots, relax the heart muscle, decrease blood pressure, or reduce the heart’s workload.
In more severe cases, patients undergo surgical procedures that aim to improve blood flow to the heart, which immediately corrects and reverses the condition. These procedures include:
Angioplasty - A minimally invasive procedure that uses a balloon catheter to clear plaque buildup in the coronary artery. The treated vein is then supported with a mesh to prevent it from collapsing.
Coronary artery bypass surgery or CABG is reserved for severe cases. It involves the use of healthy artery from other parts of the body to bypass the blocked portion of the artery.
If medications fail to provide symptoms relief and if the patient does not qualify for more invasive procedures, enhanced external counter pulsation or EECP is recommended. It is performed by inflating and deflating cuffs that are wrapped in the lower limbs to compress certain blood vessels in order to increase blood flow to the heart.
Following successful treatment, patients are advised to quit smoking and adopt a healthier lifestyle. They are also advised to seek treatment for underlying conditions, learn how to effectively manage their stress, and maintain a healthy weight.
Mann DL, et al. Approach to the patient with chest pain. In: Braunwald's Heart Disease: A Textbook of Cardiovascular Medicine. 10th ed. Philadelphia, Pa.: Saunders Elsevier; 2014.
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