Ventricular Rhythms and PVCs

Introduction to Ventricular Rhythms

• Originate below the AV node from the His-Purkinje system or the ventricles.
• Indicate severe cardiac distress.
• Require immediate intervention.

Key Characteristics of Ventricular Rhythms

• Absence of P waves or presence of dissociated P waves.
• QRS complexes that are wide and bizarre with a duration greater than 0.12 seconds.
• Can have regular or irregular rhythms.
• Possible hemodynamic instability may be present.

Premature Ventricular Complex (PVC)

• A premature beat originates from an ectopic focus in the ventricles, occurring earlier than expected.

ECG Characteristics of PVCs

• Rate depends on the underlying rhythm.
• Rhythm is irregular due to premature beats.
• P waves are absent before the PVC.
• PR interval is not measurable.
• QRS duration is wide, bizarre, and not preceded by a P wave, with a duration greater than 0.12 seconds.
• T wave has opposite polarity of the QRS complex.

Causes of PVCs

• Stimulants like caffeine, nicotine, and alcohol.
• Electrolyte imbalances such as hypokalemia and hypomagnesemia.
• Hypoxia.
• Myocardial infarction (MI).
• Heart failure.

Clinical Significance of PVCs

• Occasional PVCs are generally benign.
• Frequent PVCs may indicate ventricular irritability.
• Monitor for progression to ventricular tachycardia or fibrillation.

Unifocal PVCs

• Originate from a single ectopic focus.
• All PVCs appear identical in morphology.

Multifocal PVCs

• Originate from multiple ectopic foci.
• PVCs have different morphologies.
• Are more concerning and indicate widespread ventricular irritability.

R-on-T Phenomenon

• A PVC occurs on the downslope of the T wave of the preceding beat.
• Can potentially trigger ventricular tachycardia or fibrillation.
• Is dangerous because it increases the risk of lethal arrhythmias.
• Often seen in hypokalemia, hypoxia, or myocardial infarction.

Runs and Couplets

• Couplet: consists of two consecutive PVCs.
• Run (Salvo): consists of three or more consecutive PVCs and is considered nonsustained ventricular tachycardia if lasting less than 30 seconds.

Ventricular Tachycardia (VT)

• A fast, life-threatening ventricular rhythm with three or more consecutive PVCs at a rate greater than 100 bpm.

ECG Characteristics of VT

• Rate is between 100-250 bpm.
• Rhythm can be regular (monomorphic) or irregular (polymorphic).
• P waves are absent or dissociated.
• PR interval is not measurable.
• QRS duration is wide with a duration greater than 0.12 seconds and bizarre.

Types of VT

• Monomorphic VT: All QRS complexes have the same shape.
• Polymorphic VT (Torsades de Pointes): QRS complexes vary in shape and amplitude.

Causes of VT

• Acute myocardial infarction (MI).
• Electrolyte imbalances (hypokalemia, hypomagnesemia).
• Cardiomyopathy.
• Prolonged QT interval, specifically in Torsades de Pointes.

Clinical Significance & Treatment of VT

• Stable VT (with a pulse): Treat with antiarrhythmics like amiodarone or lidocaine.
• Unstable VT (with a pulse): Perform synchronized cardioversion.
• Pulseless VT: Requires immediate defibrillation and CPR.

Ventricular Fibrillation (VFib)

• A chaotic, disorganized rhythm with no effective cardiac output.

ECG Characteristics of VFib

• Rate is indeterminate.
• Rhythm is irregular and chaotic.
• P waves are absent.
• PR interval is not measurable.
• QRS complexes are absent, with fibrillatory waves instead.

Causes of VFib

• Acute MI or ischemia.
• Severe electrolyte imbalances.
• Electrocution.
• Drowning or hypoxia.

Clinical Significance & Treatment of VFib

• A medical emergency requiring immediate CPR and defibrillation.
• Advanced cardiac life support (ACLS) protocols include the administration of epinephrine and amiodarone.

Idioventricular Rhythm (IVR)

• A slow ventricular escape rhythm that occurs due to the failure of higher pacemakers (SA node and AV node).

ECG Characteristics of IVR

• Rate is typically 20-40 bpm; in accelerated IVR, the rate is 40-100 bpm.
• Rhythm is regular.
• P waves are absent or dissociated.
• PR interval is not measurable.
• QRS duration is wide, with a duration greater than 0.12 sec, and bizarre.

Causes of IVR

• End-stage heart failure.
• Severe conduction disturbances.
• Post-cardiac arrest.

Clinical Significance & Treatment of IVR

• If symptomatic, treatment includes atropine, pacing, or epinephrine infusion.

Asystole (Flatline)

• A complete cessation of electrical activity in the heart.

ECG Characteristics of Asystole

• Absence of P waves, QRS complexes, and T waves.

Causes of Asystole

• Severe hypoxia.
• Massive MI.
• Electrolyte disturbances.
• End-stage cardiac disease.

Clinical Significance & Treatment of Asystole

• Confirm in multiple leads to rule out fine VFib.
• Requires immediate CPR, epinephrine, and treatment of reversible causes ("H's and T's").
• Asystole is a non-shockable rhythm, so defibrillation is not indicated.