Ventricular Arrhythmias

Ventricular arrhythmias are a group of rhythm disorders which arise distal to the bundle of His.¹

As ventricular stimuli are not conducted by the intraventricular conduction system, its QRS complex is wide due to a mechanism similar to bundle branch blocks.

The most common cause of ventricular arrhythmias is the onset of ectopic stimuli (ventricular extrasystoles, ventricular tachycardia), but they also might be originated as an escape phenomenon in the absence of atrial stimuli.

The electrocardiogram is a key test in ventricular arrhythmias, especially in the most serious cases such as ventricular tachycardia.

Whenever the stability of the patient allows it, we must have a 12-lead EKG and a rhythm strip performed in order to diagnose the type of arrhythmia and whether it is ventricular or supraventricular tachycardia.

Premature Ventricular Complexes

Related article: Premature ventricular complexes.

Isolated premature ventricular complex:
PVC marked by the arrow on an EKG in sinus rhythm. The compensatory pause is marked in blue.

Premature ventricular complexes (PVCs) are ectopic stimuli originated in the ventricles which cause a premature ventricular depolarization.²

PVCs occur in patients with or without structural heart disease and tend to become more prevalent with increasing age. They can increase in number in clinical situations such as infections, ischemia, stress or consumption of toxic substances.

Premature Ventricular Complexes Classification

According Number of Foci:

• Unifocal: every premature ventricular complex presents the same morphology.
• Multifocal: presence of PVCs with different morphologies.

According to Frequency

• Frequent: 10 or more PVCs per hour, or 6 PVCs or more per minute.
• Occasional: fewer than 10 PVCs per hour, or fewer than 5 per minute.

According to Pattern of Presentation:

• Isolated PVC: there is no regular repeating pattern.
• Ventricular bigeminy: every sinus beat is followed by a premature ventricular complex.
• Ventricular trigeminy: every second sinus beat is followed by a PVC.
• Ventricular quadrigeminy: every third sinus beat is followed by a PVC.
• Couplet: two consecutive PVCs.
• Nonsustained ventricular tachycardia: three or more consecutive PVCs.

Ventricular bigeminy: premature ventricular complexes alternating with a normal beat.

Three or more consecutive PVCs are by definition a ventricular tachycardia.

Patients with atrial fibrillation may have isolated beats with wide QRS due to aberrant ventricular conduction (Ashman phenomenon), which may cause diagnostic confusion with premature ventricular complexes.

The diagnosis of these phenomenon is mainly based on the presence of the long-short sequence that ended in a wide QRS complex without compensatory pause (read Ashman phenomenon).

More information: Premature ventricular complexes.

Ventricular Escape Rhythm or Idioventricular Rhythm

Ventricular escape rhythm or idioventricular rhythm occurs in the absence of supraventricular stimuli or with bradycardias with heart rate below 40 bpm (sick sinus syndrome or complete AV block distal to the bundle of His).³

Ventricular escape rhythm is observed on the electrocardiogram as a slow, regular rhythm (between 20 and 50 bpm) with broad QRS complexes.

Sometimes it is impossible to tell a ventricular escape rhythm apart from a junctional escape rhythm with associated bundle branch block.

Normally no P waves are seen, but disassociated P waves or retrograde P waves could be seen less often.

Accelerated Idioventricular Rhythm

Accelerated idioventricular rhythm (AIVR) is mainly observed after the reperfusion of an occluded artery in an acute coronary syndrome and is caused by an abnormal automatism of the ventricles.

The electrocardiogram shows a rhythm with QRS complexes that have ventricular morphology (similar to ventricular tachycardia) but with low rates (between 60 and 110 bpm) and gradual onset and termination that set it apart from ventricular tachycardia, which usually starts with a premature ventricular complex.

It is a sign of coronary reperfusion, so its appearance in a ST-segment elevation myocardial infarction indicates a good prognosis.

Ventricular Tachycardia

Related articles: Ventricular tachycardias, ventricular tachycardia criteria.

We define ventricular tachycardia (VT) as the occurrence of three or more consecutive ventricular beats originating from the ventricles at a rate exceeding 100 bpm.^2 3

If the duration of the episode is less than 30 seconds, it is classified as non-sustained ventricular tachycardia (NSVT); if it persists for 30 seconds or longer, or requires electrical cardioversion, it is termed sustained ventricular tachycardia (SVT).

Non-sustained monomorphic ventricular tachycardia, 17 beats.

Ventricular tachycardias can be classified as monomorphic if the QRS complexes exhibit an identical morphology, or polymorphic if the QRS complexes display a changing or multiform morphology from beat to beat.^2 3

The primary cause of ventricular tachycardia is ischemic heart disease, driven by reentrant mechanisms within myocardial regions damaged by an infarction.

Other underlying causes of ventricular tachycardia include dilated or hypertrophic cardiomyopathies, arrhythmogenic right ventricular cardiomyopathy

Ventricular tachycardia is typically a regular tachycardia with a heart rate between 100 and 250 bpm, although an irregular rhythm may be observed in certain clinical cases.

During ventricular tachycardia, atrial activity is independent of the ventricles, unless ventriculoatrial conduction is present (see electrocardiographic criteria for ventricular tachycardia).

Remember: Every wide-QRS tachycardia is ventricular tachycardia until proven otherwise.

Its clinical presentation varies widely, ranging from minimal symptoms or palpitations to syncope, heart failure, cardiogenic shock, and cardiac arrest.

Torsades de Pointes

Related article: Torsades de pointes.

Electrocardiogram of torsades de pointes.

Torsades de pointes is a specific variant of polymorphic ventricular tachycardia associated with the prolongation of the QT interval.

On the EKG, it is characterized by cyclic variations in the amplitude of the QRS complexes, which appear to twist around the isoelectric baseline.^2 3

More information: Ventricular tachycardias, ventricular tachycardia criteria, torsades de pointes.

Ventricular Fibrillation

Electrocardiogram with ventricular fibrillation.

Ventricular fibrillation is a rapid (greater than 250 bpm), irregular ventricular rhythm characterized by chaotic morphology that results in the total loss of cardiac contraction, making it fatal without treatment.^2 3

Its primary etiology is ischemic heart disease, although it can occur in most cardiac disorders, including hypertrophic and dilated cardiomyopathies. Its only effective treatment is electrical defibrillation.

On the EKG, ventricular fibrillation is characterized by irregular undulations in shape and morphology, with no distinguishable QRS complexes or T waves.

Key Point: Ventricular fibrillation constitutes cardiac arrest, and its only effective treatment is electrical defibrillation.