Chapter 6: Diagnosis of a Heart Attack

A heart attack is a medical emergency in which every minute counts. Prompt and accurate diagnosis allows doctors to restore blood flow before irreversible damage occurs. Modern cardiology has transformed the diagnosis of myocardial infarction through advanced laboratory tests, imaging technologies, and rapid emergency protocols. Today, many hospitals can diagnose a heart attack within minutes of a patient’s arrival and begin life-saving treatment immediately.

The diagnosis of a heart attack is based on three key elements: the patient’s symptoms, evidence of heart muscle damage, and findings from diagnostic tests. No single test is sufficient in every case. Instead, physicians combine information from medical history, physical examination, electrocardiography (ECG), blood tests, and imaging studies to confirm the diagnosis and determine the best treatment.

The Importance of Early Diagnosis

The heart muscle depends on a constant supply of oxygen-rich blood. When a coronary artery becomes blocked, heart muscle cells begin to die within minutes. The longer the blockage persists, the greater the damage. Early diagnosis allows doctors to perform emergency treatments such as angioplasty or thrombolytic therapy before too much heart muscle is lost.

Cardiologists often use the phrase “Door-to-Balloon Time” for patients with ST-elevation myocardial infarction (STEMI). This refers to the time between the patient’s arrival at the hospital and the inflation of a balloon during primary percutaneous coronary intervention (PCI). Current guidelines aim for a door-to-balloon time of less than 90 minutes because rapid restoration of blood flow significantly improves survival.

Medical History

The diagnostic process begins with a detailed medical history. Physicians ask about the nature of the symptoms, when they began, how long they have lasted, and whether they are associated with physical activity or emotional stress.

Important questions include:

• When did the chest pain begin?
• Where is the pain located?
• Does the pain spread to the arm, jaw, neck, or back?
• How would you describe the pain—pressure, squeezing, burning, or sharp?
• Does rest relieve the symptoms?
• Have you experienced similar episodes before?
• Do you have diabetes, high blood pressure, or high cholesterol?
• Do you smoke?
• Have you had a previous heart attack or coronary stent?
• Is there a family history of early heart disease?

The answers help determine the likelihood that the symptoms are caused by a heart attack rather than another condition.

Physical Examination

A physical examination provides important clues about the patient’s condition and identifies complications.

During the examination, healthcare providers assess:

• Blood pressure
• Heart rate
• Respiratory rate
• Oxygen saturation
• Body temperature
• Level of consciousness

The physician listens to the heart with a stethoscope to detect abnormal heart sounds, murmurs, or irregular rhythms. The lungs are examined for crackles, which may indicate fluid accumulation caused by heart failure. The legs may be checked for swelling, and the skin is observed for signs such as cold sweating, pale complexion, or bluish discoloration due to poor circulation.

Although the physical examination alone cannot confirm a heart attack, it provides valuable information about the severity of the condition.

Electrocardiogram (ECG)

The electrocardiogram, commonly known as the ECG or EKG, is one of the most important diagnostic tools for heart attacks. It records the electrical activity of the heart through electrodes placed on the patient’s chest, arms, and legs.

An ECG is painless, non-invasive, and usually takes only a few minutes to perform. Because it provides immediate information, it is typically the first test performed when a heart attack is suspected.

The ECG can identify:

• ST-segment elevation
• ST-segment depression
• T-wave inversion
• New left bundle branch block
• Abnormal heart rhythms
• Evidence of previous heart attacks

ST-Elevation Myocardial Infarction (STEMI)

In STEMI, the ECG shows a characteristic elevation of the ST segment. This finding indicates complete blockage of a coronary artery and severe injury to the heart muscle.

Patients with STEMI require immediate restoration of blood flow, usually by emergency angioplasty and stent placement.

Non-ST-Elevation Myocardial Infarction (NSTEMI)

Patients with NSTEMI usually do not show ST-segment elevation. Instead, the ECG may reveal ST depression, T-wave inversion, or even appear normal during the early stages.

Because ECG findings may change over time, repeat ECGs are often performed if symptoms continue.

Cardiac Biomarkers

When heart muscle cells die, they release specific proteins into the bloodstream. Measuring these proteins is one of the most reliable methods for confirming myocardial infarction.

Cardiac Troponin

Cardiac troponin is the most sensitive and specific biomarker for heart muscle injury.

There are two major forms:

• Troponin I
• Troponin T

Troponin levels usually begin to rise within three to six hours after the onset of a heart attack, peak within 24 hours, and may remain elevated for one to two weeks.

High-sensitivity troponin tests can detect very small amounts of heart muscle damage, allowing earlier diagnosis than older laboratory methods.

A rising and falling pattern of troponin strongly supports the diagnosis of acute myocardial infarction.

Creatine Kinase-MB (CK-MB)

Before troponin testing became widely available, CK-MB was the primary blood test used for diagnosing heart attacks.

Although less sensitive than troponin, CK-MB remains useful in certain situations, particularly when evaluating possible reinfarction because its levels return to normal more quickly.

Other Blood Tests

Several additional laboratory tests help evaluate the patient’s overall condition and identify contributing factors.

These include:

• Complete blood count (CBC)
• Blood glucose
• Kidney function tests
• Electrolytes
• Lipid profile
• Liver function tests
• Coagulation profile

These tests guide treatment decisions and help detect conditions that may influence recovery.

Echocardiography

An echocardiogram uses ultrasound waves to create moving images of the heart.

It provides valuable information about:

• Heart chamber size
• Heart muscle movement
• Pumping function
• Valve function
• Blood flow
• Presence of fluid around the heart

Areas of heart muscle damaged by a heart attack often contract poorly or not at all. These abnormalities help confirm the diagnosis and estimate the extent of injury.

The echocardiogram also measures the left ventricular ejection fraction (LVEF), which represents the percentage of blood pumped from the left ventricle with each heartbeat.

A normal LVEF is generally between 55% and 70%. Lower values indicate impaired pumping ability and may influence treatment decisions.

Coronary Angiography

Coronary angiography is considered the gold standard for identifying blocked coronary arteries.

During this procedure, a thin catheter is inserted into an artery in the wrist or groin and guided to the coronary arteries. A contrast dye is injected while X-ray images are obtained.

Coronary angiography allows doctors to determine:

• Which artery is blocked
• The exact location of the blockage
• The severity of narrowing
• The number of affected arteries
• Whether angioplasty or bypass surgery is needed

If a significant blockage is found, treatment can often be performed immediately during the same procedure.

Percutaneous Coronary Intervention (PCI)

Although PCI is primarily a treatment, it begins during coronary angiography.

A small balloon is advanced to the blocked area and inflated to open the artery. In most cases, a metal mesh tube called a stent is then placed to keep the artery open.

Drug-eluting stents gradually release medication that reduces the risk of the artery becoming blocked again.

CT Coronary Angiography

Computed tomography (CT) coronary angiography is a non-invasive imaging technique that provides detailed images of the coronary arteries.

It is particularly useful for:

• Patients with low to intermediate risk
• Evaluation of chest pain
• Detecting coronary artery narrowing
• Assessing calcium buildup

Unlike conventional angiography, CT coronary angiography does not require catheter insertion into the coronary arteries.

Coronary Calcium Score

A specialized CT scan can measure calcium deposits within the coronary arteries.

The calcium score estimates the amount of atherosclerotic plaque present and helps predict future cardiovascular risk.

Higher calcium scores indicate greater plaque burden and higher risk of heart attack.

This test is most useful for preventive risk assessment rather than diagnosing an acute heart attack.

Cardiac Magnetic Resonance Imaging (MRI)

Cardiac MRI provides highly detailed images of the heart muscle.

It can identify:

• Areas of dead heart muscle
• Scar tissue
• Inflammation
• Heart muscle viability
• Congenital abnormalities

Cardiac MRI is particularly valuable for distinguishing heart attacks from conditions such as myocarditis or stress-induced cardiomyopathy.

Nuclear Cardiology

Nuclear imaging evaluates blood flow to the heart muscle using small amounts of radioactive tracers.

Common tests include:

• Myocardial perfusion imaging
• Stress nuclear scan
• PET scan

These studies identify areas receiving inadequate blood flow and assess the amount of living heart muscle that may benefit from revascularization.

Stress Testing

Stress tests evaluate how the heart performs during physical activity or medication-induced stress.

Common forms include:

• Exercise treadmill ECG
• Stress echocardiography
• Nuclear stress testing

Stress testing is generally not performed during an active heart attack but is often used after recovery to evaluate residual coronary artery disease and guide future treatment.

Differential Diagnosis

Several medical conditions can resemble a heart attack.

These include:

• Gastroesophageal reflux disease (GERD)
• Gastritis
• Peptic ulcer disease
• Pulmonary embolism
• Pneumonia
• Aortic dissection
• Pericarditis
• Myocarditis
• Panic attacks
• Costochondritis
• Muscle strain

Because some of these conditions are also life-threatening, careful evaluation is essential.

Modern Diagnostic Protocols

Most hospitals follow standardized chest pain pathways.

Patients with suspected heart attacks usually receive:

• Immediate ECG
• Blood samples for troponin
• Continuous heart rhythm monitoring
• Oxygen if needed
• Aspirin unless contraindicated
• Intravenous access
• Rapid consultation with a cardiologist

If STEMI is diagnosed, emergency PCI is activated immediately.

If NSTEMI is suspected, serial ECGs, repeated troponin measurements, and risk assessment determine whether early coronary angiography is required.

Artificial Intelligence in Diagnosis

Artificial intelligence is becoming increasingly important in cardiovascular medicine.

AI systems can:

• Interpret ECGs rapidly
• Detect subtle abnormalities
• Predict heart attack risk
• Analyze cardiac imaging
• Assist emergency physicians

Although AI improves efficiency, final clinical decisions remain the responsibility of experienced healthcare professionals.

Chapter Summary

Accurate diagnosis of a heart attack requires the integration of symptoms, physical examination, ECG findings, blood tests, and imaging studies. The ECG rapidly identifies STEMI, while cardiac troponin confirms heart muscle damage. Echocardiography evaluates heart function, and coronary angiography identifies the blocked artery and often allows immediate treatment. Modern diagnostic techniques have greatly improved survival by enabling earlier recognition and faster restoration of blood flow.

The next chapter will discuss emergency treatment of a heart attack, including first aid, emergency medical services, aspirin, nitroglycerin, oxygen therapy, clot-dissolving medications, primary angioplasty, coronary stenting, coronary artery bypass surgery, and the critical steps that save lives during the first hours of a myocardial infarction.