Understanding STEMI vs NSTEM ECG

Recognizing the differences between STEMI and NSTEMI is important. STEMI and NSTEMI indicate varying levels of myocardial infarction. They manifest distinctly on an ECG. This blog aims to explain the differences between STEMI (ST Elevation Myocardial Infarction) and NSTEMI (non-ST Elevation Myocardial Infarction) ECG Findings.

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ECG patterns associated with STEMI and NSTEMI can be detected with advancements in technology, such as wearable devices and fitness trackers, which improve outcomes in cardiac events.

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Patients benefit from the knowledge of these types of changes in ECG with timely medical intervention and quick recovery. Gauze is committed to raising awareness of heart health and helping people to take early action.

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Acute Coronary Syndrome (ACS)

Acute coronary syndrome is an umbrella term that indicates reduced blood flow to the heart. The conditions include a heart attack and unstable angina. 

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• Heart attack or Myocardial infarction occurs when cells die or heart tissue is damaged. 

• Unstable angina is when the blood flow through the heart decreases, but it is not severe enough to cause cell death or a heart attack. The reduced blood flow increases the risk of a heart attack.

Acute coronary syndrome is a medical emergency that causes severe chest pain and discomfort. It needs immediate medical attention.

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The goal of treatment is to:

• Improve blood flow.

• Treat complications.

• Prevent future problems.

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Anatomy of a coronary artery

• The arteries supplying blood to the heart lie on the surface.

• These arteries deliver blood and oxygen to their myocardial tissue and keep the heart beating.

• The three main coronary arteries are :

                       Left anterior descending artery (LAD)

                       Circumflex artery

                       Right coronary artery (RCA).

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The right coronary artery

It travels down the right side of the heart, between the right atrium and right ventricle, supplying blood to:

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• Right atria.

• Right ventricle.

• Inferior and posterior surface of the left ventricle (85% of people).

• SA node (60% of people).

• AV bundle (85 to 90% of people).

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Left coronary artery

The left coronary artery is thicker at the start and is called the left main coronary artery. It branches into   

• Left Anterior Descending.

• Circumflex artery.

Left anterior descending artery

LAD lies on the surface of the heart, between the right and left ventricles, extending to the inferior surface of the left ventricle in most patients, and supplies blood to:

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• Interior surface and part of the lateral surface of the left ventricle.

• The anterior 2/3rd of the interventricular septum.

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The circumflex artery

• The circumflex artery wraps itself around the left side of the heart, between the left atrium and left ventricle in the back. And supplies to.

• Left Atrium.

• Other parts of the lateral surface of the left ventricle.

• SA node 40%.

• AV bundle 10 to 15%.

• Rarely the inferior and posterior portions of the left ventricle.

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The posterior descending artery

• The posterior descending artery branches off RCA and rarely from the circumflex artery.

•  Whichever one does from the posterior descending artery is the dominant coronary artery.

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Events leading to Acute coronary syndrome

• Prolonged ischemia (reduced blood supply) can lead to infarction, which is cell death of the heart tissue.

• Cell death causes the release of troponin, an enzyme that is usually not found in systemic circulation.

• Cardiac ischemia is secondary to atherosclerosis, which is plaque build-up within coronary arteries.

• Unhealthy eating habits, obesity, sedentary lifestyle, hyperlipidemia, smoking, and genetics usually cause atherosclerosis.

• The plaque dislodges, releasing contents into the bloodstream and causing local inflammation to begin the coagulation of blood.

• The blood clot completely occludes an artery, causing infarction.

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Symptoms of MI

The most common symptoms of heart attack include

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• Chest pain.

• Shortness of breath.

• Nausea, stomach pain or discomfort, which may feel like indigestion.

• Palpitations.

• Anxiety.

• Sweating.

• Feeling dizzy, light-headed or fainting.

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Types of Myocardial Infarction

Different types of heart attacks are.

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ST Elevation Myocardial Infarction (STEMI)

STEMI is a condition marked by a complete blockage of a coronary artery.

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• It causes full injury to the heart muscle.

• Patients experience chest pain. Often crushing or pressure-like.

• An ECG confirms STEMI by showing ST-segment elevation.

• According to the American Heart Association, 20% of all heart attacks are STEMI in the USA.

• Angioplasty of thrombolysis is required for restoring blood flow and minimizing damage.

Non-ST-segment Elevation Myocardial Infarction (NSTEMI)

It refers to complete occlusion of the coronary artery that does not cause ST segment elevation on the ECG.

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• Some heart tissue dies, but it is less extensive than STEMI.

• Infarction is limited to the inner layer of the myocardium.

• It shows T wave inversion or ST segment depression with or without T wave.

• NSTEMI ECG presents with a normal ECG.

• Troponin levels are elevated due to myocardial cell death.

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Unstable in angina

• Unstable angina refers to chest pain and signals an imminent heart attack.

• Stable angina is triggered by physical exertion and resolves with rest. Unstable angina conversely occurs at rest and lasts longer.

Coronary artery spasm

• It occurs due to the temporary construction of coronary arteries, which reduces blood flow to the heart.

• The spasm causes chest pain and is triggered by stress, smoking or drug use.

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Broken heart syndrome (Takotsubo Cardiomyopathy)

• It is a rare temporary heart condition triggered by extreme emotional stress.

• It mimics the symptoms of a heart attack but does not have blocked coronary arteries.

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STEMI  

Recognizing STEMI patterns requires careful attention to ECG. 

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Key changes in STEMI ECG

Specific changes in the ECG waveform provide critical information about the presence of myocardial infarction. They include.

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• ST-segment elevation.

• T wave inversion.

• Development of pathological Q waves.

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Healthcare providers can assess the severity of the blockage through these changes.

ST Elevation patterns

For recognizing STEMI cases, ST elevation thresholds occur in true STEMI presentation.

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• V2. V3 Leads: > 2.5 mm for men < 40 years, > 2M for men > 40 years, > 1.5mm for women.

• All other leads: > 1mm 2 or more contiguous leads.

• They appear as ST depression in electrically opposite leads.

• These changes help to confirm a diagnosis.

• Concave ST elevations or less ominous and are indicative of benign variants called early repolarization.

• Convex upwards ST elevation indicates large MI. It is called tombstoning.
  
  

Reciprocal ST Depression, T wave inversion and pathological Q waves in STEMI

Reciprocal ST depressions accompany ST elevations. ST depressions are mirror images of ST elevations Thus, they occur in leads at opposite angles compared with leads displaying ST elevations. In patients with STEMI, the ST segments normalize within 15 hours and are followed by T wave inversions. These inversions last longer than a month.

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Pathological Q waves 

• Appear if the infarct is large. 

• Q waves are abnormally wide and deep. They convey that the infraction was extensive.

• Infarctions causing pathological Q waves are called Q wave infarctions

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T waves

T wave inversions are considered evidence of myocardial ischemia if:

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• At least one millimeter deep.

• Present in > 2 Continuous leads with dominant R waves (R/S ratio > 1).

• Not present on old ECG.

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T wave inversion is significant, as seen in leads with upright QRS complexes. It is a normal variant in lead III, aVR, and V1.

Pathologic Q Waves

• Q waves are a sign of previous MI.

• They are a result of an absence of electrical activity.

• They take several hours or days to develop. Once they develop, they rarely go away. But if the MI is reperfused early, pathologic Q waves disappear. But in most cases, they persist indefinitely.

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Types of STEMI

Three coronary arteries provide blood flow to the heart muscles. Depending on the artery that gets blocked, damage occurs in areas of the heart muscles.

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Anterior STEMI

When the blockage occurs in the left anterior descending (LAD) artery, the largest artery supplying blood to the anterior or front of the heart, a heart attack affecting this area has a great negative effect.

Inferior or lateral STEMI

It involves the right coronary artery, RCA supplying the inferior (bottom) of the heart or the left circumflex artery (LCX), which supplies the side wall of the heart. RCA and LCX are smaller than the LAD artery and supply fewer heart muscles, so STEMI is less severe than anterior STEMI.

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Significance of ST segment elevation in STEMI

ST-segment elevation indicates MI. It is the period between the contraction and relaxation of the ventricles. An ST elevation suggests a disturbance in the heart's electrical activity due to ischemia. It occurs when there is a complete obstruction of the coronary artery, which supplies blood to the heart muscles. It is a medical emergency. It helps in

Immediate diagnosis

It signifies prevention is experiencing horror direct that requires urgent intervention. Quick diagnosis enables timely treatment decisions.

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Location of infarction

Signifies which coronary artery is blocked. ST elevation in inferior leads II, III, and aVF indicates right coronary artery involvement. ST elevation in anterior leads (V1- V4) suggests left anterior descending artery is blocked.

Assessment of severity

The higher the elevation, the more extensive the damage and the higher the risk of complications.

Prognosis indicator

The persistence of elevation in the ST segment after treatment signifies ongoing ischemia or incomplete reperfusion. It reveals treatment effectiveness and necessary adjustments that may be required.

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NSTEMI 

It is caused by a sudden decrease in blood flow to the heart muscle without a complete blockage, leading to tissue damage. A partial blockage results in less severe damage to the heart. It is associated with the presence of unstable plaques in the coronary arteries, which rupture and lead to thrombosis, reducing blood flow.

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Causes

Conditions reducing the heart's blood supply are:

Plaque

A wax-like substance derived from cholesterol in blood. A plaque buildup slows the blood flow to the heart. These plaques cause blood clots to form rapidly and narrow the lumen of the blood vessels.

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Vasospasm

The lining of smooth muscles on the blood vessels controls the size of the blood vessels. The muscle lining of arteries in the heart can also undergo a spasm and this is known as vasospasm. It can also cause a heart attack by limiting the blood flow, though it is rare.

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Coronary embolism

A blood clot gets stuck in one of the heart's arteries. And partially or completely stops the blood flow.

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Myocarditis

Inflammation of the muscles of the heart, which may occur usually due to a viral infection.

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Poisons and toxins

They can cause damage to the heart muscles. A common example is carbon monoxide poisoning.

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Cardiac Contusion

A contusion is a bruise, a bruise occurring in the heart muscle, majorly in car crashes.

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ECG interpretation in NSTEMI

NSTEMI Common ECG changes include:

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• ST segment depression.

• T wave Inversion.

• Transient ST-segment elevation.

• Q Waves.

These changes are subtle and evolve. It is why serial ECGs are important in the diagnosis of NSTEMI. Comparing ECG at different points helps clinicians detect the dynamic changes that may otherwise be overlooked on a single ECG.

ST depression

• It is a key indicator of NSTEMI and the most significant ECG finding.

• A downward displacement of the ST segment occurs.

• Horizontal or down-sloping ST depression > 0.5 m in 2 or more contiguous leads.

• A new ST depression.

T wave Inversion

They are deep and symmetrical and are seen in leads with ST depression. ST depression and T wave inversion together strongly indicate myocardial ischemia.

Q waves

They are sometimes seen in NTEMI and are more evident if there has been previous myocardial damage.

Transient ST segment elevations

Often ST segment elevations are observed, which do not last more than 20 minutes. These transient changes show the dynamic nature of coronary artery blockage in NSTEMI.

Distinguishing Features Between STEMI and NSTEMI

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Occurrence

NTEMI and STEMI are both types of heart attacks that occur due to blockage in the coronary arteries. NSTEMI occurs when a partial blockage occurs in one or more coronary arteries. STEMI is when a complete blockage occurs in one of the coronary arteries. It results in a severe heart attack.

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Symptoms

The symptoms include chest pain, discomfort, shortness of breath, nausea, and lightheadedness. The severity of the symptoms varies in 2 types of heart attacks. Patients experiencing STEMI experience intense and prolonged chest pain compared to those having NSTEMI. Besides, STEMI is likely to cause complications such as cardiogenic shock or sudden cardiac arrest.

Diagnosis

Diagnosis requires: 

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• medical history.

• physical examination.

• diagnostic tests.

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In NSTEMI, ECG shows changes indicative of ischemia, while in STEMI, ST-segment elevation is clear-cut.

Treatment

Treatment for NSTEMI and STEMI aims to restore blood flow in heart muscles and prevent further damage. Patients with NSTEMI undergo percutaneous coronary intervention (PCI) to open blocked arteries. STEMI, on the other hand, requires emergency coronary angioplasty or thrombolytic therapy to restore blood flow.

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Prognosis

The prognosis of both NSTEMI and STEMI depends on:

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• The extent of damage to heart muscles.

• Presence of underlying conditions.

• How quickly was the treatment started?

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STEMI is considered severe compared to NSTEMI. It has a high risk of complications and mortality. Patients having STEMI require more intensive treatments, but with prompt and appropriate treatment, both can be managed effectively.

Prevention

NSTEMI And STEMI Can be prevented by adopting heart-healthy lifestyles.

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• Managing risk factors such as blood pressure, high cholesterol, diabetes and smoking.

• Regular exercise.

• Balanced diet.

• Stress Management.

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Taking medications as prescribed and having regular checkups helps to monitor and control risk factors for heart disease.

Key Differences Between STEMI and NSTEMI on ECG

STEMI and NSTEMI are two different forms of heart attack with unique characteristics on an ECG. The nature and extent of heart muscle damage differs, leading to distinct ECG changes. STEMI presents as an elevated ST segment, indicating complete myocardial damage. NSTEMI ECG has ST segment depression or T wave inversion, which indicates partial damage.

ST segment changes, elevation versus depression

ST segment changes help to distinguish between STEMI from NSTEMI. In STEMI, the ST segment is elevated, and there is complete arterial blockage and extensive heart muscle damage. The ECG in NSTEMI shows ST segment depression and T wave inversion, which shows reduced blood flow or ischemia.

T wave patterns and U wave considerations

T waves in STEMI are elevated with full-thickness myocardial injury. NSTEMI has an inverted T wave, suggesting ischemia but no full-thickness damage. U waves appeared in NSTEMI, indicating electrolyte imbalance or additional strain on the heart.

Location and extent of heart damage

STEMI causes full-thickness myocardial damage to the entire wall of the heart muscle. NSTEMI damages only a part of the heart muscle wall.

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Modern Diagnostic Approach

Recent advances in diagnostic cardiology have enhanced our ability to differentiate between STEMI and NSTEMI cases.

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Integration of emerging modalities

Besides ECG, we use advanced imaging techniques such as Cardiac magnetic resonance imaging. It is the most sensitive cardiac imaging technique.

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It helps in

• Cardiac MRI for detailed tissue characterization.

• CT angiography for coronary vessel assessment.

• Echocardiography for real-time wall motion evaluation.

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Role of cardiac biomarkers

High-sensitivity cardiac proponent testing has improved the ability to detect even minor cardiac muscle damage.

Conclusion

Timely intervention is essential in STEMI and NSTEMI. The earlier these conditions are diagnosed the less damage. Regular checkups monitor the heart and indicate an impending complication. Using AI in ECG analysis helps to make us aware of possible complications and make informed decisions. Gauze, with its AI-powered tools, helps to manage STEMI and NSTEMI heart conditions.