What is the cause of shortness of breath, particularly when lying down, in a patient with a history of ischemic heart disease (IHD), diabetes, and hypertension, with electrocardiogram (ECG) findings of ST-elevation and chest x-ray showing pulmonary edema?

Acute Myocardial Infarction with Acute Heart Failure

This patient is experiencing acute myocardial infarction (AMI) with acute heart failure as a complication—the ST-elevations on ECG represent active myocardial injury causing left ventricular dysfunction, which has resulted in pulmonary edema. The correct answer is A. Acute coronary disease, as this is the primary pathophysiologic process driving all other findings.

Why This is Acute Coronary Disease

The ST-elevation pattern in leads II, III, aVF, V5, and V6 indicates acute myocardial infarction affecting both inferior and lateral territories, which is the underlying cause of her symptoms. 1

• ST-elevation myocardial infarction (STEMI) is defined by ST-segment elevation on ECG and represents transmural myocardial ischemia requiring immediate reperfusion therapy 1
• The distribution across inferior (II, III, aVF) and lateral (V5, V6) leads suggests extensive myocardial involvement, which explains the rapid development of heart failure 1
• Her history of ischemic heart disease, diabetes, and hypertension places her at high risk for acute coronary events 2, 3

Understanding the Clinical Presentation

Left ventricular failure during acute myocardial infarction manifests as breathlessness, sinus tachycardia, third heart sound, and pulmonary rales—exactly matching this patient's presentation. 1

• Orthopnea (dyspnea when lying down) is a cardinal feature of left heart backward failure due to increased venous return in the supine position 1
• Pulmonary edema on chest X-ray confirms elevated left ventricular filling pressures from acute myocardial dysfunction 1
• The absence of chest pain does not exclude AMI—approximately 30% of patients with acute heart failure present without chest pain/discomfort, particularly elderly patients and those with diabetes 4

Why the Other Options Are Incorrect

Option B (Pulmonary edema) and D (Decompensated heart failure) describe the consequence rather than the cause. 1

• Pulmonary edema is the radiographic and clinical manifestation of left ventricular failure, not the underlying etiology 1
• Decompensated heart failure is the hemodynamic state resulting from acute myocardial injury 1
• The ESC guidelines explicitly state that acute coronary syndrome with ST-elevation is the primary diagnosis when these ECG changes are present, with heart failure classified as a complication (Killip class 2-3 based on extent of pulmonary rales) 1

Option C (Pulmonary embolism) is excluded by the ECG pattern. 1

• Pulmonary embolism does not cause ST-elevation in this distribution 1
• The inferior and lateral ST-elevations are pathognomonic for coronary territory ischemia 1

Immediate Management Implications

This patient requires emergent reperfusion therapy—either primary percutaneous coronary intervention (PCI) within 90 minutes or fibrinolytic therapy if PCI is unavailable. 1

• Aspirin 150-325 mg should be administered immediately (chewable, non-enteric coated) 1
• Oxygen, loop diuretics, and intravenous nitroglycerin (starting at 0.25 μg/kg/min unless hypotensive) should be given for pulmonary congestion 1
• The presence of heart failure (Killip class 2-3) indicates large infarct size and warrants consideration for invasive hemodynamic monitoring and possible mechanical support 1

Critical Pitfall to Avoid

Do not be misled by the absence of chest pain or the presence of pulmonary edema into delaying recognition of STEMI. 4, 5

• Acute pulmonary edema due to ischemic heart disease without chest pain carries a 70% two-year mortality rate in patients over 70 years 5
• Patients with fewer typical cardiac symptoms are paradoxically at higher risk for delayed treatment and worse outcomes 4
• The ST-elevations mandate immediate activation of the cardiac catheterization laboratory regardless of symptom presentation 1