What are the ECG findings and management for cardiac conditions like atrial fibrillation, ventricular tachycardia, and ST-elevation myocardial infarction?

ECG Findings and Management for Key Cardiac Conditions

The 12-lead ECG is the most critical diagnostic tool for identifying cardiac conditions like atrial fibrillation, ventricular tachycardia, and ST-elevation myocardial infarction, providing essential information for immediate management decisions that directly impact mortality and morbidity outcomes. 1, 2

Atrial Fibrillation (AF)

ECG Findings:

• Absence of P waves
• Irregular ventricular rhythm (irregularly irregular)
• Replacement of P waves with rapid oscillatory or fibrillatory waves
• Variable R-R intervals
• QRS complexes typically normal unless aberrant conduction present

Management:

1. Rate Control Strategy:

   • Beta-blockers (metoprolol, esmolol)
   • Non-dihydropyridine calcium channel blockers (diltiazem, verapamil)
   • Digoxin (particularly in heart failure patients)

2. Rhythm Control Strategy:

   • Electrical cardioversion for hemodynamically unstable patients
   • Pharmacological cardioversion:
     • Class IC agents (flecainide, propafenone) for patients without structural heart disease
     • Class III agents (amiodarone, sotalol) for patients with structural heart disease

3. Anticoagulation:

   • Based on CHA₂DS₂-VASc score
   • Direct oral anticoagulants (DOACs) preferred over warfarin in non-valvular AF
   • Consider bridging with heparin if cardioversion planned

Ventricular Tachycardia (VT)

ECG Findings:

• Wide QRS complexes (>120 ms)
• Rate typically 100-250 bpm
• AV dissociation (P waves unrelated to QRS complexes)
• Fusion beats or capture beats may be present
• Monomorphic: uniform QRS morphology
• Polymorphic: changing QRS morphology (includes Torsades de Pointes)

Management:

1. Unstable VT (with hemodynamic compromise):

   • Immediate synchronized electrical cardioversion
   • Defibrillation if pulseless VT

2. Stable Monomorphic VT:

   • IV amiodarone (150 mg over 10 minutes, then infusion)
   • IV procainamide (alternative)
   • IV lidocaine (particularly in ischemic settings)

3. Polymorphic VT/Torsades de Pointes:

   • IV magnesium sulfate (2g)
   • Correct electrolyte abnormalities (especially potassium, magnesium)
   • Temporary overdrive pacing if drug-induced or congenital long QT
   • Isoproterenol for bradycardia-dependent Torsades

4. Long-term Management:

   • ICD placement for most patients with sustained VT
   • Catheter ablation for recurrent episodes
   • Antiarrhythmic drugs as adjunctive therapy

ST-Elevation Myocardial Infarction (STEMI)

ECG Findings:

• ST-segment elevation at the J-point in at least two contiguous leads:
  • ≥2 mm (0.2 mV) in men or ≥1.5 mm (0.15 mV) in women in leads V2-V3
  • ≥1 mm (0.1 mV) in other contiguous chest leads or limb leads 1
• Reciprocal ST depression in opposite leads
• Q waves may develop (indicating necrosis)
• T-wave inversion following ST elevation
• Location-specific patterns:
  • Anterior: ST elevation in V1-V4
  • Inferior: ST elevation in II, III, aVF
  • Lateral: ST elevation in I, aVL, V5-V6
  • Posterior: ST depression in V1-V3 (consider posterior leads V7-V9)
  • Right ventricular: ST elevation in right-sided leads (V3R-V6R)

Management:

1. Immediate Actions:

   • Oxygen therapy if hypoxic (SaO₂ <95%) 3
   • IV access and cardiac monitoring
   • Pain relief with titrated IV opioids 3
   • Aspirin 162-325 mg chewed
   • Nitroglycerin (sublingual/IV) if no contraindications

2. Reperfusion Strategy:

   • Primary PCI within 90 minutes of first medical contact (preferred)
   • Fibrinolytic therapy if PCI not available within 120 minutes
   • Door-to-needle time ≤30 minutes for fibrinolytics 3
   • Door-to-balloon time ≤90 minutes for PCI

3. Adjunctive Therapies:

   • P2Y₁₂ inhibitor (clopidogrel, ticagrelor, prasugrel)
   • Anticoagulation (unfractionated heparin, enoxaparin, bivalirudin)
   • Beta-blockers (if no contraindications)
   • ACE inhibitors/ARBs (within 24 hours if no contraindications)
   • High-intensity statin therapy

4. Cardiac Arrest Management:

   • Immediate defibrillation for VF/pulseless VT
   • Therapeutic hypothermia for post-arrest comatose patients 3
   • Immediate angiography with view to primary PCI for resuscitated cardiac arrest with STEMI on ECG 3

Common Pitfalls in ECG Interpretation

STEMI Mimics:

• Left ventricular hypertrophy with strain pattern
• Left bundle branch block (no longer considered a standalone STEMI equivalent) 1
• Benign early repolarization
• Pericarditis/myocarditis
• Brugada syndrome
• Takotsubo cardiomyopathy 3

Diagnostic Challenges:

• Normal ECG does not exclude ACS (approximately 5% of patients with normal ECGs ultimately found to have AMI) 1
• ST depression in V1-V3 may represent posterior wall MI 1, 2
• Comparison with previous ECGs is essential when available 1
• Serial ECGs at 10-minute intervals during the first hour if clinical suspicion is high but initial ECG is non-diagnostic 1

Risk Stratification:

• The degree of ST depression shows a strong relationship to outcome 3
• ST depression on presenting ECG portends the highest risk of death at 6 months 3
• Dynamic ECG changes provide additional prognostic information 3

Key Monitoring Recommendations

• Initiate ECG monitoring at the point of first medical contact in all patients with suspected myocardial infarction 3
• Continue ECG monitoring for at least 24 hours or until alternative diagnosis established 3
• Consider telemetry monitoring after CCU discharge for high-risk patients 3
• Monitor ST-segment resolution during treatment as it provides important prognostic information 3

By understanding these characteristic ECG findings and implementing appropriate management strategies, clinicians can significantly improve outcomes for patients with these critical cardiac conditions.