The Chest Pain Patient
Week 4: Cardiovascular System | Difficulty: Intermediate | Time: 40 minutes
Learning Objectives
- Interpret cardiac anatomy and blood flow in the context of coronary artery disease
- Explain the pathophysiology of myocardial infarction
- Connect ECG findings to specific areas of cardiac damage
- Understand cardiac output and its determinants in acute cardiac events
- Apply knowledge of cardiac conduction to rhythm interpretation
Case Presentation
Patient: David Patterson, 58-year-old male
History: Hypertension, hyperlipidemia, smoker (20 pack-years)
Chief Complaint: "Crushing chest pain for the past 45 minutes"
History: Hypertension, hyperlipidemia, smoker (20 pack-years)
Chief Complaint: "Crushing chest pain for the past 45 minutes"
David presents to the Emergency Department with severe substernal chest pain described as "crushing" and "like an elephant sitting on my chest." Pain radiates to his left jaw and arm. He is diaphoretic and nauseated. Symptoms began at rest while watching television. He took aspirin 300mg at home. No relief with rest.
Vital Signs
Blood Pressure
168/98
mmHg
Heart Rate
102
bpm
Respiratory Rate
22
/min
Temperature
36.9
°C
SpO2
93%
room air
ECG Findings
12-lead ECG shows:
- Sinus tachycardia at 102 bpm
- ST-segment elevation in leads II, III, aVF (1-2mm)
- ST-segment depression in leads V1-V3
- Reciprocal changes present
Interpretation: Inferior wall STEMI (ST-Elevation Myocardial Infarction)
Laboratory Results
| Test | Result | Normal Range |
|---|---|---|
| Troponin I | 2.8 ng/mL | < 0.04 ng/mL |
| CK-MB | 45 U/L | < 25 U/L |
| Total Cholesterol | 6.8 mmol/L | < 5.0 mmol/L |
| LDL Cholesterol | 4.2 mmol/L | < 3.0 mmol/L |
Clinical Reasoning Questions
1. Which coronary artery is most likely occluded based on the ECG findings?
Correct! Right Coronary Artery (RCA)
ST elevation in leads II, III, and aVF indicates inferior wall MI. The inferior wall of the heart is supplied by the RCA in 80% of people (right-dominant circulation). Reciprocal ST depression in anterior leads (V1-V3) confirms the inferior location. RCA occlusion also commonly affects the SA and AV nodes, explaining the sinus tachycardia.
ST elevation in leads II, III, and aVF indicates inferior wall MI. The inferior wall of the heart is supplied by the RCA in 80% of people (right-dominant circulation). Reciprocal ST depression in anterior leads (V1-V3) confirms the inferior location. RCA occlusion also commonly affects the SA and AV nodes, explaining the sinus tachycardia.
2. What is the pathophysiological mechanism causing the elevated troponin?
Correct! Myocardial cell necrosis releases troponin
Troponin is a regulatory protein found in cardiac muscle cells (cTnI and cTnT). When coronary occlusion causes ischemia, cardiac cells become necrotic and die. This releases intracellular contents including troponin into the bloodstream. Elevated troponin indicates myocardial damage. CK-MB also rises but is less specific to cardiac tissue than troponin.
Troponin is a regulatory protein found in cardiac muscle cells (cTnI and cTnT). When coronary occlusion causes ischemia, cardiac cells become necrotic and die. This releases intracellular contents including troponin into the bloodstream. Elevated troponin indicates myocardial damage. CK-MB also rises but is less specific to cardiac tissue than troponin.
3. Which factor would NOT contribute to reduced cardiac output in this patient?
Correct! Increased preload from fluid overload
Reduced cardiac output (CO = HR × SV) occurs through multiple mechanisms in MI:
• Loss of contractile tissue → reduced stroke volume
• Conduction abnormalities → arrhythmias affecting HR
• Hypertension → increased afterload makes pumping harder
• However, this patient does NOT have fluid overload (no JVD, no pulmonary edema, normal weight)
In fact, MI patients often have reduced preload from sweating, vomiting, and decreased venous return due to poor cardiac function.
Reduced cardiac output (CO = HR × SV) occurs through multiple mechanisms in MI:
• Loss of contractile tissue → reduced stroke volume
• Conduction abnormalities → arrhythmias affecting HR
• Hypertension → increased afterload makes pumping harder
• However, this patient does NOT have fluid overload (no JVD, no pulmonary edema, normal weight)
In fact, MI patients often have reduced preload from sweating, vomiting, and decreased venous return due to poor cardiac function.
Bioscience Integration
Coronary Anatomy and Blood Supply
- Right Coronary Artery (RCA): Supplies inferior wall, right ventricle, SA node (60%), AV node (90%)
- Left Anterior Descending (LAD): Supplies anterior wall, anterior septum, bundle branches
- Left Circumflex (LCx): Supplies lateral wall, left atrium, SA node (40%)
Inferior MI suggests RCA occlusion, explaining potential bradyarrhythmias if conduction system affected.
Nursing Implications
- Time-critical: "Time is muscle" - goal is reperfusion within 90 minutes
- Monitoring: Continuous ECG, vital signs, oxygen saturation
- Complications: Monitor for arrhythmias, cardiogenic shock, heart failure
- Medications: Antiplatelet, anticoagulation, beta-blockers, nitrates