Conceptual Overview

Ventricular rhythms originate below the bundle of His - from the bundle branches, Purkinje fibers, or ventricular myocardium itself. Because these impulses bypass the normal conduction system, the QRS is characteristically wide (≥120 ms) and often bizarre in morphology.

Ventricular rhythms span a clinical spectrum from completely benign (isolated PVCs in a structurally normal heart) to immediately lethal (ventricular fibrillation). Understanding these rhythms is essential because management differs dramatically:

  • PVCs: Usually benign; treat only if symptomatic or causing cardiomyopathy
  • Ventricular tachycardia: Can be stable or unstable; management depends on hemodynamics
  • Torsades de Pointes: Unique treatment (magnesium, overdrive pacing) - standard antiarrhythmics can worsen it
  • Ventricular fibrillation: Cardiac arrest rhythm requiring immediate defibrillation
  • Idioventricular rhythm: Escape rhythm - never suppress it
The wide complex question: Not all wide-complex tachycardias are ventricular in origin. SVT with aberrant conduction, pre-excitation (WPW), and hyperkalemia can all produce wide QRS complexes. However, the golden rule in emergency medicine is: treat all wide-complex tachycardia as VT until proven otherwise. Misdiagnosing VT as SVT and giving AV nodal blockers (e.g., verapamil) can be fatal.
Premature Ventricular Complexes (PVCs)

PVCs are premature depolarizations originating from an ectopic ventricular focus. They are the most common ventricular arrhythmia and are found in the majority of adults on 24-hour Holter monitoring.

ECG Characteristics

  • Wide QRS (≥120 ms): Bizarre morphology, different from normal sinus beats
  • No preceding P wave: (or P wave buried within QRS / unrelated)
  • Full compensatory pause: The interval from the beat before the PVC to the beat after equals exactly two normal R-R intervals
  • Discordant T wave: T wave deflects opposite to the major QRS deflection

PVC Patterns & Terminology

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Term Definition Clinical Significance
Unifocal All PVCs identical morphology (same focus) Generally more benign
Multifocal PVCs with ≥2 different morphologies More concerning; suggests irritable myocardium
Bigeminy Every other beat is a PVC May compromise cardiac output
Trigeminy Every third beat is a PVC Less hemodynamic impact
Couplet Two consecutive PVCs More significant than isolated PVC
Triplet / NSVT Three consecutive PVCs Non-sustained VT if rate >100 bpm
R-on-T phenomenon PVC falls on T wave of preceding beat Can trigger VT/VF (vulnerable period)

When PVCs Become Problematic

  • PVC burden >10-15%: Can cause PVC-induced cardiomyopathy (reversible with ablation)
  • Structural heart disease: Post-MI PVCs increase VT/VF risk
  • R-on-T: Can trigger polymorphic VT or VF during the vulnerable repolarization period
  • Symptoms: Palpitations, presyncope, or exercise intolerance warrant evaluation
Interpolated PVCs: Occasionally a PVC occurs between two normal sinus beats without a compensatory pause - the PVC is "sandwiched" between normal beats. This happens when the sinus rate is slow enough to allow the next sinus beat to conduct normally. These are benign but can confuse rhythm interpretation.
Ventricular Tachycardia (VT)

Ventricular tachycardia is defined as ≥3 consecutive ventricular beats at a rate >100 bpm. It is a potentially lethal rhythm that can deteriorate to ventricular fibrillation at any moment.

Classification

  • Non-sustained VT (NSVT): ≥3 beats, lasts <30 seconds, terminates spontaneously
  • Sustained VT: Lasts ≥30 seconds OR causes hemodynamic compromise requiring intervention
  • Monomorphic VT: All QRS complexes have identical morphology (single re-entry circuit)
  • Polymorphic VT: QRS morphology continuously changes (multiple foci or shifting circuit)

Monomorphic VT

  • Most common cause: Re-entry around myocardial scar (prior MI)
  • ECG: Regular, wide-complex tachycardia with uniform QRS morphology
  • Rate: Typically 150-250 bpm
  • AV dissociation: P waves march independently of QRS (pathognomonic for VT)
  • Capture beats: Occasional narrow QRS (sinus impulse "captures" the ventricle through normal conduction)
  • Fusion beats: QRS morphology intermediate between sinus and VT (simultaneous activation)

Polymorphic VT

  • With normal QT: Usually ischemic in origin - treat as acute coronary syndrome
  • With prolonged QT: Torsades de Pointes (see dedicated section below)
  • Clinical significance: More unstable than monomorphic VT; frequently degenerates to VF

Wide Complex Tachycardia: VT vs. SVT with Aberrancy

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Feature Favors VT Favors SVT with Aberrancy
AV dissociation Present (P waves independent of QRS) Absent (1:1 P:QRS relationship)
Capture/fusion beats Present (diagnostic for VT) Absent
QRS width >160 ms (RBBB) or >140 ms (LBBB) Narrower, typical BBB morphology
Concordance All precordial leads point same direction Normal R wave progression
Axis Northwest axis (negative I, negative aVF) Normal or typical BBB axis
History Prior MI, structural heart disease Young, prior SVT, known BBB

Management of Stable Monomorphic VT

  1. Amiodarone 150 mg IV over 10 minutes (first-line)
  2. Procainamide 20 mg/min (alternative; avoid if QT prolonged)
  3. Lidocaine 1-1.5 mg/kg IV (second-line; preferred in ischemic VT)
  4. Synchronized cardioversion if medications fail or patient deteriorates
The verapamil trap: NEVER give calcium channel blockers (verapamil, diltiazem) to wide-complex tachycardia of uncertain origin. If the rhythm is VT (80% of wide-complex tachycardias), verapamil can cause hemodynamic collapse and death. If in doubt, treat as VT.
Torsades de Pointes

Torsades de Pointes (TdP) - "twisting of the points" - is a specific form of polymorphic VT that occurs in the setting of a prolonged QT interval. The QRS complexes appear to rotate around the isoelectric baseline, with a characteristic "spindle-shaped" waxing and waning of amplitude.

ECG Characteristics

  • Polymorphic QRS: Continuously changing amplitude and axis
  • Sinusoidal oscillation: QRS complexes appear to twist around the baseline
  • Preceded by long QT: QTc >500 ms is highest risk
  • "Short-long-short" initiation: A PVC (short coupling) → compensatory pause (long) → another PVC triggers TdP
  • Rate: Usually 150-300 bpm
  • Self-terminating: Often occurs in paroxysms, but can degenerate to VF

Common Causes of QT Prolongation

  • Medications (most common acquired cause):
    • Antiarrhythmics: sotalol, procainamide, amiodarone, dofetilide
    • Antibiotics: azithromycin, fluoroquinolones, erythromycin
    • Antipsychotics: haloperidol, droperidol, ziprasidone
    • Antiemetics: ondansetron (high dose IV), metoclopramide
    • Methadone
  • Electrolyte abnormalities: Hypokalemia, hypomagnesemia, hypocalcemia
  • Congenital long QT syndromes: LQTS types 1-3 (ion channelopathies)
  • Bradycardia: Slow heart rates prolong QT, increasing TdP risk
  • CNS events: Subarachnoid hemorrhage, stroke

Treatment (Differs from Standard VT!)

  1. Magnesium sulfate 2g IV over 2-5 minutes (FIRST LINE even with normal Mg levels)
  2. Overdrive pacing: Temporary transvenous pacing at 90-110 bpm shortens QT and suppresses TdP
  3. Isoproterenol: Increases heart rate as bridge to pacing
  4. Correct electrolytes: Potassium to 4.0-4.5 mEq/L; replish magnesium
  5. Discontinue offending drugs
  6. Defibrillation if pulseless (unsynchronized shock)
Do NOT give amiodarone for Torsades! Amiodarone itself prolongs the QT interval and can worsen Torsades de Pointes. Similarly, avoid procainamide, sotalol, and most class IA/III antiarrhythmics. The treatment is magnesium and overdrive pacing - the opposite approach from monomorphic VT.
The "short-long-short" sequence: TdP classically initiates with a PVC → long pause → another PVC that falls on the T wave. This "short-long-short" pattern is a hallmark. In patients with prolonged QT who develop frequent PVCs with this pattern, anticipate Torsades and have magnesium and pacing ready before it occurs.
Ventricular Fibrillation

Ventricular fibrillation (VF) is a chaotic, disorganized electrical activity in the ventricles with no coordinated contraction and no cardiac output. It is the most common initial rhythm in out-of-hospital cardiac arrest from cardiac causes.

ECG Characteristics

  • Chaotic, irregular undulations: No discernible P waves, QRS complexes, or T waves
  • Variable amplitude and frequency: No organized pattern
  • Coarse VF: Higher amplitude oscillations; more recently initiated; higher chance of successful defibrillation
  • Fine VF: Low-amplitude oscillations; prolonged arrest; may be difficult to distinguish from asystole

Common Causes

  • Acute MI: Most common cause; VF occurs in 5-10% of STEMI patients
  • Degeneration from VT: Monomorphic or polymorphic VT can deteriorate to VF
  • Electrolyte abnormalities: Severe hyperkalemia, hypokalemia, hypomagnesemia
  • Electrocution / lightning strike
  • Commotio cordis: Impact to chest during T wave vulnerable period
  • Channelopathies: Brugada syndrome, long QT syndrome, catecholaminergic polymorphic VT
  • Drug toxicity: Digoxin, cocaine, sympathomimetics

Management

  1. Immediate defibrillation: Unsynchronized shock (120-200J biphasic)
  2. CPR: Minimize interruptions; 2-minute cycles
  3. Epinephrine 1 mg IV/IO: Every 3-5 minutes
  4. Amiodarone: 300 mg IV/IO first dose, then 150 mg second dose (for refractory VF/pVT)
  5. Lidocaine: Alternative to amiodarone (1-1.5 mg/kg first dose)
  6. Identify and treat reversible causes: H's and T's
Coarse vs. fine VF: Coarse VF suggests a more recently initiated arrest and is more likely to respond to defibrillation. Fine VF indicates the myocardium is increasingly depleted of energy. If you encounter fine VF, prioritize high-quality CPR to improve myocardial oxygen delivery before shockling. Some protocols advocate epinephrine before the first shock in fine VF to "coarsen" the rhythm.
Fine VF vs. asystole: Distinguishing fine VF from asystole can be difficult. Check the rhythm in multiple leads - fine VF may appear as a flat line in one lead but show fibrillatory waves in another. If in doubt, do NOT shock asystole (it won't help). Prioritize CPR and epinephrine.
Idioventricular & Escape Rhythms

When all higher pacemakers (SA node, AV node) fail, ventricular myocytes can generate their own intrinsic rhythm. These escape rhythms are a safety net - they maintain some cardiac output when the conduction system above has failed.

Ventricular Escape Rhythm

  • Rate: 20-40 bpm (intrinsic ventricular automaticity rate)
  • QRS: Wide (>120 ms), bizarre morphology
  • Clinical context: Complete heart block, sinus arrest, or late-stage bradycardia
  • Hemodynamics: Rate is often too slow for adequate cardiac output
  • Treatment: Never suppress! Treat the underlying cause. Pace if symptomatic

Accelerated Idioventricular Rhythm (AIVR)

  • Rate: 40-100 bpm (faster than escape, slower than VT)
  • QRS: Wide, regular, monomorphic
  • Classic association: Reperfusion after thrombolytic therapy or PCI - a sign that the artery has reopened
  • Also seen in: Digoxin toxicity, myocarditis, post-cardiac surgery
  • Hemodynamics: Usually well-tolerated; self-limited
  • Treatment: Observation only. Do NOT give antiarrhythmics - suppressing AIVR can unmask severe bradycardia or asystole
"AIVR = reperfusion sign": In the setting of acute MI treatment, the appearance of AIVR is one of the clinical indicators of successful reperfusion. While it should not be used in isolation to confirm reperfusion, combined with chest pain resolution and ST segment normalization, AIVR is a reassuring sign. Do not treat it - it will resolve on its own as the heart stabilizes.
Never suppress an escape rhythm: Ventricular escape beats and rhythms exist because higher pacemakers have failed. Giving antiarrhythmics or lidocaine to suppress ventricular escape beats can result in asystole and death. The treatment is to fix the reason the higher pacemakers aren't working (e.g., correct hyperkalemia, place a pacemaker for complete heart block).
Quick Reference
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Rhythm Rate (bpm) QRS Key Feature Treatment
Isolated PVCs Premature beats Wide, bizarre Full compensatory pause Reassurance; beta-blocker if symptomatic
NSVT >100 Wide, ≥3 beats <30 sec, self-terminates Risk stratify; may need ICD if structural disease
Monomorphic VT 150-250 Wide, uniform AV dissociation, capture/fusion beats Amiodarone; cardioversion if unstable
Polymorphic VT (normal QT) 150-300 Wide, varying Ischemic etiology likely Treat ischemia; defibrillation if pulseless
Torsades de Pointes 150-300 Twisting axis Prolonged QT; short-long-short Magnesium; overdrive pacing; AVOID amiodarone
Ventricular fibrillation N/A Chaotic No organized complexes; no pulse Defibrillation; CPR; epinephrine; amiodarone
Ventricular escape 20-40 Wide Safety net rhythm; never suppress Treat cause; pacing if symptomatic
AIVR 40-100 Wide, regular Reperfusion sign; self-limited Observe only; DO NOT suppress
Clinical Pearls
"When in doubt, it's VT": In adults with wide-complex tachycardia, approximately 80% are ventricular tachycardia. Statistical probability alone favors VT. Add any history of structural heart disease, prior MI, or heart failure, and the probability exceeds 95%. Procainamide and amiodarone are safe for both VT and SVT with aberrancy - verapamil is only safe for SVT.
The Brugada criteria for VCT differentiation: A stepwise approach: (1) Absence of RS complex in any precordial lead → VT. (2) R to S interval >100 ms in any precordial lead → VT. (3) AV dissociation → VT. (4) Morphology criteria in V1-V2 and V6 → VT vs. SVT. This algorithm has a sensitivity of ~99% and specificity of ~97% for distinguishing VT from SVT.
Commotio cordis: A blunt, non-penetrating impact to the chest (baseball, hockey puck, steering wheel) that arrives during the vulnerable repolarization period (upslope of T wave) can trigger VF in a structurally normal heart. Peak age: 10-18 years. Survival depends entirely on immediate CPR and early defibrillation. AEDs at youth sporting events save lives.
PVC cardiomyopathy: Frequent PVCs (burden >10-15% on Holter) can cause a reversible dilated cardiomyopathy. The mechanism involves ventricular dyssynchrony from the ectopic activation. Key point: ejection fraction often normalizes after successful PVC ablation. A 24-hour Holter is essential in any patient with new cardiomyopathy and frequent PVCs.
Don't forget the H's and T's: In cardiac arrest with VF/pVT, always consider reversible causes: H's - Hypovolemia, Hypoxia, Hydrogen ion (acidosis), Hypo/Hyperkalemia, Hypothermia. T's - Tension pneumothorax, Tamponade, Toxins, Thrombosis (coronary/pulmonary). Treating refractory VF without addressing a reversible cause is a losing battle.
References
  1. Al-Khatib SM, Stevenson WG, Ackerman MJ, et al. 2017 AHA/ACC/HRS Guideline for Management of Patients With Ventricular Arrhythmias. Circulation. 2018;138(13):e272-e391.
  2. Brugada P, Brugada J, Mont L, et al. A new approach to the differential diagnosis of a regular tachycardia with a wide QRS complex. Circulation. 1991;83(5):1649-1659.
  3. Panchal AR, Bartos JA, Cabañas JG, et al. Part 3: Adult Basic and Advanced Life Support: 2020 AHA Guidelines for CPR and ECC. Circulation. 2020;142(16_suppl_2):S366-S468.
  4. Drew BJ, Ackerman MJ, Funk M, et al. Prevention of Torsade de Pointes in Hospital Settings. Circulation. 2010;121(8):1047-1060.
  5. ECG Library - LITFL - Life in the Fast Lane. https://litfl.com/ecg-library/
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