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What Are Malignant Arrhythmias?
Malignant arrhythmias are life-threatening cardiac rhythm disturbances that can rapidly lead to hemodynamic collapse, cardiac arrest, and death if not treated immediately.
They typically arise from ventricular myocardium and are characterized by instability and high mortality risk.
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Key Types of Malignant Arrhythmias
1. Ventricular Tachycardia (VT)
Sustained VT (>30 seconds) or causing instability
Monomorphic or polymorphic
May present with palpitations, syncope, or shock
2. Ventricular Fibrillation (VF)
Chaotic, disorganized ventricular activity
No effective cardiac output
Most common rhythm in sudden cardiac death
3. Torsades de Pointes
Polymorphic VT associated with prolonged QT interval
Characteristic “twisting of points” ECG pattern
Often drug-induced or electrolyte-related
4. High-grade AV Block with Escape Failure
Complete heart block with inadequate escape rhythm
Can lead to asystole or sudden collapse
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Etiology and Triggers
Structural Heart Disease
Ischemic heart disease (most common)
Prior myocardial infarction (scar-related reentry)
Cardiomyopathies (HCM, DCM, ARVC)
Electrical Disorders (Channelopathies)
Long QT syndrome
Brugada syndrome
Catecholaminergic polymorphic VT (CPVT)
Metabolic & Drug Causes
Hypokalemia / Hyperkalemia
Hypomagnesemia
QT-prolonging drugs (e.g., antiarrhythmics, macrolides)
Acute Triggers
Acute MI
Hypoxia
Acidosis
Sympathetic surge
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Pathophysiology
Reentry circuits (most common in post-MI VT)
Triggered activity (early/late afterdepolarizations)
Abnormal automaticity
These mechanisms disrupt coordinated ventricular contraction → ↓ cardiac output → circulatory collapse
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Clinical Presentation
Palpitations
Dizziness / presyncope
Syncope
Sudden cardiac arrest
Hypotension / shock
⚠️ Some patients present with sudden death as the first manifestation
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ECG Clues
Wide complex tachycardia → suspect VT
AV dissociation
Fusion and capture beats
Polymorphic QRS (torsades/VF precursor)
Prolonged QT interval
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Emergency Management (ACLS-Based)
Unstable Patient
Immediate synchronized cardioversion (VT with pulse)
Immediate defibrillation (pulseless VT/VF)
Stable VT
IV antiarrhythmics:
Amiodarone
Lidocaine
Procainamide
Torsades de Pointes
IV magnesium sulfate
Overdrive pacing if recurrent
Correct Reversible Causes (Hs & Ts)
Hypoxia, Hypokalemia, Hydrogen ion (acidosis)
Toxins, Tamponade, Thrombosis
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Long-Term Management
Implantable Cardioverter Defibrillator (ICD)
Gold standard for secondary prevention
Indicated in survivors of VT/VF
Medications
Beta-blockers
Amiodarone / Sotalol
Catheter Ablation
Effective in scar-related VT
Reduces ICD shocks
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Risk Stratification
High-risk features:
LVEF ≤35%
Prior MI
Syncope of suspected arrhythmic origin
Inducible VT on EP study
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Prevention
Optimize heart failure therapy
Correct electrolytes
Avoid QT-prolonging drugs
Genetic screening in inherited syndromes
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Key Takeaways
Malignant arrhythmias = immediate threat to life
VT and VF are the most critical rhythms
Early recognition + rapid defibrillation saves lives
ICD is cornerstone of long-term prevention
Always search for and treat underlying cause
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