Heart Attack

(Also called: myocardial infarction)

Heart attack is the condition whereby the heart muscle’s supply of oxygen-rich blood cannot meet its demand for oxygen-rich blood. If severe and prolonged, this supply-demand imbalance can lead to the death of heart muscle cells, called myocardial infarction. Most commonly, heart attack is related to constriction of the coronary arteries, the blood vessels that feed the heart with its own blood supply. This constriction is typically caused by the buildup of cholesterol plaque in the walls of these arteries (coronary artery disease).

For reasons that are not entirely clear, these plaques are prone to cracking. When this occurs, the blood flowing by these disrupted plaques is exposed to underlying tissues, causing the blood to clot inside the artery. This phenomenon is often referred to as an acute coronary syndrome. The resulting sudden reduction of blood supply to the heart muscle cells causes them to die.

There are two types of heart attack. If the coronary artery in question gets completely blocked by clot, blood flow stops entirely and the full thickness of heart muscle fed by that artery is damaged. This causes a characteristic change on the electrocardiogram (ECG) called ST-segment elevation. This type of heart attack is thus called an ST-elevation myocardial infarction (STEMI).

If the coronary artery is partially blocked by clot, blood flow decreases but does not stop. Only part of the heart muscle is damaged and ST-segment elevation is not seen on the ECG. This is called a non-ST-elevation myocardial infarction or non-STEMI heart attack. In general, STEMIs are larger heart attacks than non-STEMIs, and the larger the size of the heart attack, the greater the chance of complications down the road, for example congestive heart failure.

Symptoms

A heart attack is just as likely to occur at rest as it is during exertion. Symptoms can include any of the following:

• Chest pain, often described as a tightness or heaviness
• Pain in the upper abdomen
• Pain in the back, neck, jaw, or arm
• Shortness of breath
• Sweating
• Nausea
• Loss of consciousness

Anyone who thinks he or she is having a heart attack should call 911.

Diagnosis: STEMI Protocol

A STEMI heart attack is diagnosed based on symptoms and the characteristic ECG pattern. The University of Ottawa Heart Institute’s STEMI Regional Program has established a protocol to ensure that all STEMI patients in the region receive the best care as quickly as possible. If a patient calls 911 with symptoms of a heart attack, trained paramedics perform and interpret an ECG in the field. If the diagnosis of STEMI is made, the patient will be transported directly to the Heart Institute for treatment.

If the patient arrives on his or her own to a local emergency department and the diagnosis of STEMI is made, the patient will be taken immediately by ambulance to the Heart Institute. Patients diagnosed with STEMI in more distant parts of the region are given clot-busting drugs (thrombolytics) and transported to the Heart Institute by helicopter.

The STEMI program has reduced STEMI deaths in the Ottawa region by 50 per cent.

Diagnosis: Non-STEMI

A non-STEMI heart attack does not present the same ECG pattern as a STEMI. This is because the artery is not completely blocked and the full thickness of the heart muscle is not being starved of oxygen-rich blood. This can make the diagnosis more challenging.

Patients suspected of having a non-STEMI heart attack should be evaluated at the nearest emergency department. There, they are interviewed about their symptoms and given a physical examination. They also get an ECG, a chest X-ray, and have a series of blood tests. If heart cells have died, a protein (cardiac troponin) is released into the blood. Often, it is a positive test for this protein that confirms the heart attack diagnosis.

Treatment/Management: STEMI

The initial treatment of heart attack relates specifically to the underlying cause of the problem. In STEMI cases, the cause is a completely blocked artery. The treatment is to open the artery as quickly as possible in order to restore normal blood flow.

There are two ways to open the artery. One option is clot-busting medication. The advantage of this approach is that it can be administered in any emergency department. The disadvantages are that it is effective only 60 to 80 per cent of the time, and there is a risk of serious bleeding.

The alternative treatment is emergency angioplasty in which a small balloon is inserted via the wrist or the groin and inflated in the blocked artery to open it mechanically. This treatment is successful in more than 90 per cent of cases, but it can be performed only in specialized centres, such as the Heart Institute. For most patients in the Ottawa region, emergency angioplasty is the preferred treatment for STEMI.

Treatment/Management: Non-STEMI

For non-STEMI heart attacks, initial treatment focuses on preventing the constricted artery from becoming completely blocked. Blood thinners (but not clot busters) are given to keep the clot from growing and to allow the patient’s own clot-busting proteins to take effect. Once the patient has stabilized, testing is performed to assess the risk of further complications, such as another heart attack. Non-invasive tests can include:

• Treadmill Testing: This test measures how well the heart functions when challenged to work harder than normal (for example, during exercise).
• Nuclear Perfusion Imaging: This imaging tool is used to identify areas of the heart that are receiving less blood than they should.

More commonly, an angiogram is the first test performed. This allows doctors to directly view the arteries and determine the amount and location of plaque buildup. If significant blockages are found in important parts of the coronary artery tree, one of two mechanical treatments is usually used:

• Angioplasty and Stenting: The narrowed portions of the heart arteries are ballooned and propped open by small metal mesh tubes called stents.
• Coronary Artery Bypass Grafting (CABG): Arteries from the chest or arm, or veins from the leg, are used to bypass the narrowed portions of the heart arteries.

Treatment/Management: All Heart Attacks

All heart attack patients usually undergo further tests to assess how much heart muscle damage has occurred. These tests might include:

• Echocardiogram: The echo is an ultrasound test to assess the motion of the heart walls as well as the function of the heart valves.
• MUGA Scan (left ventricular function study): This scan is a nuclear medical test considered the gold standard to measure the heart’s pumping capacity.

All heart attack patients require medical and lifestyle intervention in order to prolong their lives and decrease the chances of a recurrent heart attack.

Drug Therapies

Typically, five oral medications are given to patients during hospitalization and following discharge. These include:

• Aspirin to lower the risk of another heart attack
• Additional blood thinners (such as clopidogrel) to lower the risk of another heart attack and to prevent clots from building up on stents
• Beta-blockers to lower the risk of abnormal heart rhythms and to promote healing of heart muscle damage
• ACE inhibitors or angiotensin receptor blockers to promote healing of the heart and to lower the risk of another heart attack
• Statins to lower cholesterol and the risk of another heart attack

Many of these medications have been shown to decrease mortality after a heart attack. Patients should not stop taking any heart medication without the express instructions or consent of their physician.

Other medications may be needed to control risk factors associated with heart disease, including elevated blood pressure and cholesterol, diabetes, and nicotine addiction. Nitroglycerine is usually prescribed to patients at discharge in case a recurrence of chest pain occurs. Further medications may be required to treat some complications of heart attack, such as abnormal heart rhythms or heart failure.

Lifestyle

Upon discharge from the Heart Institute, patients are offered enrolment in a cardiac rehabilitation program. The aim is to encourage and support patients to adopt the necessary lifestyle changes to improve their long-term prognosis. Issues that are specifically addressed and promoted include:

• Exercise
• Heart healthy diet
• Weight management
• Smoking cessation
• Stress management