Which type of myocardial infarction (MI) is the most deadly?

Types of Myocardial Infarction and Their Mortality Risk

ST-segment elevation myocardial infarction (STEMI) is the most deadly type of myocardial infarction due to its association with complete coronary artery occlusion, extensive myocardial damage, and high early mortality rates. 1, 2, 3

Classification of Myocardial Infarction Types

• Type 1 MI (Spontaneous MI): Caused by atherosclerotic plaque rupture, ulceration, fissuring, erosion, or dissection with resulting intraluminal thrombus in coronary arteries, leading to decreased myocardial blood flow and myocyte necrosis 1, 4

• Type 2 MI (Secondary to Ischemic Imbalance): Occurs when conditions other than CAD contribute to an imbalance between myocardial oxygen supply and demand, such as coronary spasm, endothelial dysfunction, tachyarrhythmias, respiratory failure, or severe anemia 1, 4

• Type 3 MI (Cardiac Death): Patients who suffer cardiac death with symptoms suggestive of myocardial ischemia and presumed new ischemic ECG changes but without available biomarker values 1

• Type 4 MI (Associated with Revascularization): Periprocedural myocardial injury during PCI with elevated cardiac troponin values 1

• Type 5 MI (Associated with CABG): Periprocedural myocardial injury during CABG with elevated cardiac biomarker values 1, 4

Mortality Risk by MI Type

STEMI (Most Deadly)

• STEMI represents the most acute manifestation of coronary artery disease and is associated with the highest early mortality rates 1, 2, 3

• Early mortality is highest among patients with ST-segment elevation, intermediate among patients with ST-segment depression, and lowest among patients with T-wave inversion on admission ECG 2

• Patients with STEMI who do not receive reperfusion therapy have a significantly higher 30-day mortality rate (12%) compared to those who receive it (4.4%) 2

• Complete thrombotic occlusion of an epicardial coronary vessel leads to transmural infarction, extensive myocardial damage, and higher risk of fatal complications 1, 3

Factors Increasing Mortality Risk in STEMI

• Advanced age (>75 years) significantly increases mortality risk in STEMI patients 1, 5

• Left ventricular ejection fraction <40% is independently associated with increased 1-year mortality (HR: 3.70) 5

• Hemodynamic instability (Killip class ≥III, systolic blood pressure <100 mmHg) significantly worsens prognosis 5

• Failure to achieve successful reperfusion (TIMI flow <3) independently predicts higher mortality 5, 6

• Reperfusion injury paradoxically can exacerbate cardiac damage even after successful restoration of blood flow 6

Clinical Presentation and Diagnosis

• The ECG is an integral part of the diagnostic work-up and should be acquired and interpreted promptly (within 10 minutes) after clinical presentation 1

• ST-segment elevation on ECG is the most sensitive and specific marker for acute myocardial infarction, typically appearing within minutes after symptom onset 2

• Dynamic changes in ECG waveforms during acute myocardial ischemic episodes often require multiple ECG recordings, especially if the initial ECG is non-diagnostic 1

• The sensitivity of out-of-hospital ECG for STEMI detection immediately after resuscitation from cardiac arrest is approximately 88%, with a specificity of 69% 7

Treatment Implications

• Early diagnosis and immediate reperfusion are the most effective ways to limit myocardial ischemia, reduce infarct size, and decrease the risk of post-STEMI complications and heart failure 3

• Primary PCI has become the preferred reperfusion strategy; if PCI cannot be performed within 120 minutes of STEMI diagnosis, fibrinolysis therapy should be administered 3

• For patients who do not receive any form of reperfusion, anticoagulation therapy with low molecular weight heparin provides a clear additional mortality benefit versus placebo 1

• In the treatment of late-presenting patients with STEMI (beyond 12 hours after symptom onset), clinical evaluation and risk stratification are crucial for decision-making between therapeutic interventions 1

Common Pitfalls and Caveats

• A completely normal ECG in a patient with chest pain does not exclude the possibility of acute coronary syndrome, as 1-6% of these patients will eventually have myocardial infarction 2

• Posterior ST-segment elevation (hidden on standard 12-lead ECG) occurs in approximately 4% of patients with acute myocardial infarction and can be missed if not specifically looked for 2

• MI may present with atypical symptoms or even without symptoms, especially in women, elderly, diabetics, and post-operative or critically ill patients 4

• Prompt recognition of STEMI equivalents is essential, including hyperacute T-wave changes, true posterior MI, and multilead ST depression with ST elevation in lead aVR 4