How a Heart Attack Is Diagnosed

A heart attack, referred to medically as myocardial infarction, occurs when the blood flow to a part of the heart suddenly slows or stops, causing damage to the heart muscle. Roughly 735,000 heart attacks occur in the United States each year. Of these, around 26% of women and 19% of men will die as a result of the event within a year, according to the American Heart Association (AHA). 

Knowing the signs and obtaining a timely diagnosis can increase your chances of survival and recovery.

Self-Check

The signs and symptoms of a heart attack can vary from one person to the next. For some, there may be overt signs with tell-tale symptoms. Others may experience only minor pain similar to indigestion, while others still will have no symptoms until cardiac arrest (the catastrophic loss of heart function) strikes.

The earliest sign may be recurrent chest pressure that comes and goes in waves or a sudden, sharp chest pain (called angina) that occurs with activity.

It's important to know the signs of a heart attack in order to receive prompt treatment. Here are 11 common and not-so-common signs of a heart attack that you should never ignore:

• Chest pain, tightness, or pressure lasting for several minutes
• Nausea, indigestion, heartburn, stomach pain, or vomiting
• Breaking out in a cold sweat for no obvious reason
• Sudden dizziness or lightheadedness
• Pain that radiates down the left side of your body (generally starts from the chest and moves outward)
• Jaw or throat pain, often radiating up from the chest
• Sudden fatigue and shortness of breath from activities you can usually tolerate
• The sudden development of loud snoring, choking, or gasping while asleep (signs of obstructive sleep apnea)
• A persistent cough with white or pinkish mucus
• Swollen ankles, lower legs, and feet (peripheral edema)
• Heart palpitations or irregular heartbeats (arrhythmia)

Even if your symptoms are nonspecific, it is best to have them checked.

According to a 2012 study in the European Heart Journal, as many as 30% of people experiencing a heart attack will have nonspecific symptoms easily confused for other conditions.

Labs and Tests

Upon arrival at the emergency room, you would be given a physical examination and a battery of test to not only diagnose acute myocardial infarction (AMI) but also to characterize its severity.

According to international consensus, AMI is defined as an elevation in key cardiac biomarkers (substances in blood consistent with a cardiac event) accompanied by at least one of the following: symptoms of ischemia (the restriction of blood flow), characteristic changes in the electrical activity of the heart (as measured by the electrocardiogram), evidence of arterial blockage as seen on an angiogram, and/or changes in the motion of the heart as seen on imaging studies.

Cardiac Biomarkers

Cardiac biomarkers are substances released into the blood when the heart is damaged or stressed. The markers are measurable indicators of heart function that can confirm a heart attack based on the level and timing of the elevation.

The types of blood tests used to diagnose a heart attack include:

• Troponin Test: The most sensitive blood test for detecting heart muscle damage, generally speaking, 12 hours after the cardiac event
• Creatinine Kinase (CK-MB) Test: Measures an enzyme specific to the heart muscle, typically peaking within 10 to 24 hours of the event
• Glycogen Phosphorylase Isoenzyme BB (GPBB) Test: Measures an enzyme that will rise sharply within seven hours of the event and remain elevated for one to three hours
• Lactate Dehydrogenase (LDH) Test: Peaks at 72 hours and may indicate AMI or other conditions involving tissue damage (like cancer, bone fractures, and liver disease)
• Albumin Cobalt Binding (ACB) Test: Measures the amount of cobalt bound to the protein albumin, the binding of which decreases after a heart attack
• Myoglobin Test: A protein detection test that has low specificity but peaks early (around two hours), allowing for early diagnosis
• Soluble Urokinase-Type Plasminogen Activator Receptor (suPAR) Test: A novel cardiac marker that measures immune activation after a heart attack

Electrocardiogram

An electrocardiogram (ECG) is a device that measures the electrical activity of the heart and produces a graph of the voltages generated for heartbeats.

The procedure involves the connection of a series of electrodes to your chest and limbs. Commonly, 10 electrodes are attached to form 12 ECG leads. Each of the 12 leads reads a specific electrical impulse.

The impulses are broadly classified at the P wave (associated with the contraction of the heart atrium), the QSR complex (associated with contraction of the heart ventricles), and the T wave (associated with the resting of the ventricles).

When diagnosing a heart attack, the doctor will specifically look at the ST segment (the portion of the ECG reading that connects the QSR complex to the T wave). The segment can not only help confirm the diagnosis but tell the doctor which kind of heart attack you are having, namely ST-elevation myocardial infarction (STEMI) in which the blockage of a coronary artery is complete or Non-ST-elevation myocardial infarction (NSTEMI), in which there is only a partial obstruction or narrowing of a coronary artery.

Anywhere from 25% to 40% of heart attacks can be classified as STEMI, according to a 2013 report from the AHA and the American College of Cardiology Foundation (ACCF).

Imaging

Imaging plays an important role in the diagnosis and characterization of a heart attack. The different techniques can describe the nature of the arterial blockage and the extent of the heart muscle damage.

Among the studies commonly used include a chest X-ray, which utilizes electromagnet radiation to create two-dimensional images of the heart and blood vessels. In addition, your doctor may perform an echocardiogram, which uses sound waves to create live video images of the heart, allowing doctors to see how it is pumping and how blood moves from one chamber to the next.

A cardiac computed tomography (CT) captures a continual series of X-ray images as you lie in a tube-like chamber. The images are then composited by a computer to create a three-dimensional image of the heart structure. A cardiac magnetic resonance imagining (MRI) works similarly to a CT scan but involves powerful magnetic and radio waves to create highly detailed images, especially of soft tissues.

A coronary catheterization (angiogram) involves the injection of a dye into your heart via a narrow tube (catheter) that has been fed through an artery in your groin or leg. The dye provides better contrast and definition to an X-ray study.

In the days or weeks after your heart attack, you might also have a cardiac stress test to measure how your heart responds to exertion. You may be asked to walk on a treadmill or pedal a stationary bike while attached to an ECG machine. If you are unable to engage in physical activity, you may be given an intravenous injection to stimulate the heart in the same way that exercise does.

Your doctor might also recommend a nuclear stress test, an imaging technique that uses a radioactive tracer to evaluate how well blood flows through the heart during activity and rest.

Differential Diagnoses

In the same way that a heart attack can be mistaken for other ailments, there are common and uncommon conditions that can be mistaken for a heart attack. In fact, some conditions are so strikingly similar in their symptoms that a battery of tests will be needed to differentiate them.

This process of elimination, known as the differential diagnosis, would involve a review of the other possible causes of the cardiac event. Examples include:

• Anxiety or panic attacks, differentiated by the absence of abnormal cardiac markers and by symptoms such as hyperventilation
• Aortic dissection, a serious condition involving tears in the inner lining of the aorta, differentiated by evidence of the tears on imaging studies
• Costochondritis, inflammation of the joints in the upper ribs, differentiated by chest discomfort while breathing and by normal cardiac biomarkers, ECG, and imaging studies
• Gastroesophageal reflux disease (GERD), usually differentiated by a physical exam and normal cardiac biomarkers
• Myocarditis, inflammation of the heart muscle differentiated by a cardiac MRI and by blood markers for inflammation (using ESR and C-reactive protein tests)
• Pericarditis, inflammation of the lining of the heart (pericardium) differentiated by a distinctive dip in the ST segment as well as evidence of pericardial fluid on an echocardiogram
• Pneumonia, differentiated by infiltration of fluids in the lungs on a chest X-ray and an increased white blood cell (WBC) count indicative of an infection
• Pneumothorax, a collapsed lung differentiated by a chest X-ray
• Pulmonary embolism, a blood clot in the lungs differentiated by abnormal arterial blood gases and a positive D-dimer test (used to diagnose blood clots)
• Unstable angina, a random pattern of angina differentiated by normal cardiac biomarkers