Ventricular arrhythmias (ventricular tachycardia, ventricular fibrillation, and ventricular flutter) – etiology, pathogenesis, and clinical manifestations.
Ventricular arrhythmias are abnormal heart rhythms originating below the His bundle, in the ventricles. They are often serious and potentially life-threatening because they compromise effective cardiac output.
1 Ventricular tachycardia (VT)
Etiology
- Ischemic heart disease (most common), especially post-myocardial infarction (scar-related reentry circuits).
- Cardiomyopathies (dilated, hypertrophic).
- Myocarditis.
- Electrolyte imbalances ( hypokalemia, hypomagnesemia).
- Drug toxicity (e.g., digoxin, antiarrhythmics).
- Channelopathies (e.g., long QT syndrome → torsades de pointes variant).
Pathogenesis
- Reentrant circuits within diseased ventricular myocardium (especially scar tissue).
- Less commonly, enhanced automaticity of ventricular foci or triggered activity.
- Sustained monomorphic VT: uniform QRS morphology (single reentry loop).
- Polymorphic VT: varying QRS shapes (e.g., torsades de pointes).
Clinical manifestations
- Palpitations, "fluttering" in chest.
- Dizziness, lightheadedness.
- Dyspnea.
- Hypotension, syncope (if decreased cardiac output).
- May degenerate into ventricular fibrillation → sudden cardiac death.
2 Ventricular fibrillation (VF)
Etiology
- Acute myocardial infarction (most common cause of sudden cardiac death).
- Severe heart failure.
- Electrolyte disturbances (severe hypokalemia, hyperkalemia ).
- Electrical accidents (electric shock).
- Drug toxicity (e.g., proarrhythmic effect of antiarrhythmics).
Pathogenesis
- Multiple small reentrant circuits throughout the ventricles → chaotic, rapid electrical activity.
- No organized ventricular contraction → no effective cardiac output.
- Rapidly leads to circulatory collapse and death if not immediately reversed (e.g., defibrillation).
Clinical manifestations
- Sudden loss of consciousness.
- Absence of pulse and blood pressure.
- Agonal breathing or apnea.
- Cardiac arrest → death within minutes without intervention.