Cardiovascular · Year 1 · from Cardiovascular

Case 2: Ventricular Tachycardia in Ischemic Cardiomyopathy

Patient Presentation

Demographics: 58-year-old male

Chief Complaint: Palpitations and near-syncope

History of Present Illness: A 58-year-old male with history of prior inferior STEMI (5 years ago, treated with PCI to RCA) and ischemic cardiomyopathy (EF 30%, has ICD) presents with sudden onset of rapid palpitations while sitting at his desk. He felt lightheaded and "almost passed out" but remained conscious. His ICD delivered a shock and his symptoms resolved. He reports no chest pain, dyspnea, or preceding symptoms. He has been compliant with his medications including metoprolol, lisinopril, and atorvastatin.

Physical Examination:

• Post-shock: BP 118/72 mmHg, HR 68 bpm (regular), RR 16/min, SpO2 98% on room air
• General: Alert, appears fatigued but comfortable
• Cardiovascular: Regular rhythm, no murmurs, ICD pocket visible in left pectoral region
• Lungs: Clear

Workup

• ICD Interrogation:
• Sustained monomorphic VT at 210 bpm detected
• Duration: 45 seconds before therapy
• Anti-tachycardia pacing (ATP) unsuccessful
• Shock delivered at 35J - successful termination
• Stored electrogram shows wide complex tachycardia with RBBB morphology
• ECG (post-event):
• Sinus rhythm, 68 bpm
• Q waves in II, III, aVF (inferior MI)
• LBBB at baseline
• Labs:
• K 4.2, Mg 2.0
• Troponin mildly elevated (likely demand ischemia)
• BNP 380 pg/mL
• Echocardiogram: EF 28%, inferior and posterior akinesis, no new abnormalities

Diagnosis

Sustained monomorphic ventricular tachycardia - appropriate ICD therapy delivered Substrate: Scar-related reentry from prior inferior MI

Cardiac Arrhythmias Correlation:

Mechanism of Monomorphic VT:

1. Reentry Around Scar Tissue:

• Prior MI created heterogeneous scar tissue
• Surviving myocyte bundles within scar form slow conduction channels
• Creates substrate for reentrant circuit
• Fixed circuit = uniform (monomorphic) QRS morphology

1. Components of Scar-Related Reentry:

• Central isthmus: Slow conducting channel through scar
• Entrance site: Where impulse enters isthmus
• Exit site: Where impulse emerges to activate ventricle
• QRS morphology determined by exit site location

1. Why Monomorphic?

• Fixed anatomic circuit
• Each beat follows same path
• Consistent QRS appearance beat-to-beat
• Contrast with polymorphic VT (multiple foci or shifting circuit)

ECG Features of VT:

• Wide QRS (>120 ms) - ventricular origin
• AV dissociation (P waves independent of QRS)
• Capture/fusion beats if present (pathognomonic)
• Monomorphic: Uniform QRS morphology

Distinguishing VT from SVT with Aberrancy:

Rule: When in doubt, treat wide complex tachycardia as VT

ICD Function:

1. Detection: Sensed rapid ventricular rate >180 bpm
2. Discrimination: Determined ventricular origin (not SVT)
3. Anti-tachycardia pacing (ATP): Burst pacing to interrupt reentry - unsuccessful
4. Defibrillation: High-energy shock terminated arrhythmia

Treatment

Acute Management:

1. Hemodynamically stable post-shock - observation
2. Electrolyte repletion (maintain K >4.0, Mg >2.0)
3. Continue beta-blocker

VT Prevention:

1. Antiarrhythmic drug therapy:

• Amiodarone or sotalol to suppress VT episodes
• Amiodarone preferred with low EF
• Reduces ICD shocks but does not eliminate VT risk

1. Catheter Ablation:

• Consider for recurrent VT despite drug therapy
• Maps and ablates critical isthmus of reentry circuit
• Can eliminate or reduce VT burden

ICD Management:

• Appropriate shock - device functioning properly
• Program to maximize ATP before shock (reduces painful shocks)
• Adjust detection parameters if needed

Optimize Heart Failure Therapy:

• Ensure on guideline-directed medical therapy
• Consider cardiac resynchronization if criteria met

Clinical Pearl

Arrhythmia Mechanisms Summary:

Clinical Significance of This Case: This patient's ICD functioned as intended - detecting and terminating a potentially fatal arrhythmia. Without the ICD, sustained VT at 210 bpm could have degenerated to ventricular fibrillation and sudden cardiac death. This case illustrates:

1. The importance of primary prevention ICD in patients with EF <35%
2. Scar-related reentry as the most common mechanism of VT in ischemic cardiomyopathy
3. The role of antiarrhythmic drugs and ablation in reducing VT burden

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