Ventricular Rhythms
While exploring information about ECGs, you may see "Ventricular" and "Idioventricular" being used interchangeably for the ventricular rhythms less than 100. While both are technically correct, the "idio-" prefix highlights that it's the ventricles alone that's responsible for the heart's electrical activity (i.e. without the effects of the SA or AV node).
Idioventricular Escape Rhythm
| Parameter | Definitions |
|---|---|
| HR | Less than 40 |
| Regularity | Regular |
| P | Not available |
| QRS | Wide QRS complexes |
| P:QRS Ratio | Not available |
Idioventricular Escape Rhythm occurs when the ventricles fail to receive an impulse from either the SA node or AV node and so generates an impulse itself. The ventricles naturally pace between 20 and 40 and ofter results in significantly decreased cardiac output. This rhythm usually arises following an MI.
Since an Idioventricular Escape Rhythm occurs below the level of the AV node, medications like atropine are generally not effective.
Accelerated Idioventricular Rhythm
| Parameter | Definitions |
|---|---|
| HR | Between 40 and 100 |
| Regularity | Regular |
| P | Not available |
| QRS | Wide QRS complexes |
| P:QRS Ratio | Not available |
Accelerated Idioventricular Rhythm (AIVR) is a rhythm that often appears post-MI, with electrolyte imbalances and drug toxicities, and with other cardiomyopathies. With a heart rate between 40 and 100, it occurs as a result of a focus within the ventricle becoming the dominant pacemaker of the heart. Despite it's bizarre appearance, patients can otherwise tolerate this particular arrhythmia. Most symptoms that arise in these patients are due to the underlying cause, rather than the rhythm itself.
The mainstay "treatment" is to treat the underlying cause. When either the underlying cause is resolved or the SA firing rate is higher than the ventricular rate, the AIVR typically resolves.
Caution with Antiarrhythmics
Administration of antiarrhythmics may cause severe hemodynamic compromise. In the worst case scenario if both the SA node and AV nodes have failed, "resolving" the AIVR may accidentally cause asystole if no backup pacemaker cells are available.
(Monomorphic) Ventricular Tachycardia
| Parameter | Definitions |
|---|---|
| HR | Greater than 100 |
| Regularity | Regular |
| P | Not available |
| QRS | Wide QRS complexes |
| P:QRS Ratio | Not available |
Monomorphic Ventricular Tachycardia arises from a simple focus in the ventricles and presents with a "regularly" generated wide-complex QRS. Most cases of ventricular tachycardia is a result of some sort of structural or metabolic heart issue. The treatments to convert out of a ventricular tachycardia can be effective, but without treating the underlying cause the ventricular tachycardia may return.
Did you check a pulse?
Ventricular tachycardia may not provide enough cardiac output to provide a pulse - start immediate CPR!
Polymorphic Ventricular Tacyhcardia: Torsades de Pointes
While there are many forms of polymorphic ventricular tachycardia (a v. tach. rhythm with varying shapes), the most common and concerning one in the emergency setting is Torsades de Pointes.
| Parameter | Definitions |
|---|---|
| HR | Greater than 100 |
| Regularity | Irregular |
| P | Not available |
| QRS | Wide QRS complexes, heights progressively increasing and decreasing |
| P:QRS Ratio | Not available |
Torsades de Pointes (Tdp) is a specific type of polymorphic ventricular tachycardia (where the QRS shape changes from beat-to-beat) with a characteristicly wavy and "twisting" appearance. It's often a complication of a patient with a lengthy prolonged QT interval.
While converting the ventricular tachycardia may resume a normal rhythm, the Torsades de Pointes will likely recur if the underlying prolonged QT inverval remains.
In addition to treating the ventricular tachycardia, magnesium is the preferred treatment to stabilize the cardiac membranes. In addition, refrain from using other QT-prolonging medications, and treat any other electrolyte abnormalities.
Did you check a pulse?
Ventricular tachycardia may not provide enough cardiac output to provide a pulse - start immediate CPR!
Treating Pulsing Ventricular Tachycardia
In the emergency department, ventricular tachycardia with a pulse is treated as per ACLS guidelines.
Ventricular Fibrillation
| Parameter | Definitions |
|---|---|
| HR | None |
| Regularity | Irregular |
| P | Not available |
| QRS | Chaotically polymorphic |
| P:QRS Ratio | Not available |
Ventricular Fibrillation is complete disorganization of the ventricles. As such, there's no coordinated effort in the heart to pump the blood and cardiac essentially drops to zero. In the emergency setting, it's often related directly to some sort of disease, trauma, or ischemia in the heart.
Treating Pulseless Ventricular Tachycardia and Ventricular Fibrillation
In the emergency department, ventricular tachycardia without a pulse and ventricular fibrillation are treated as per ACLS guidelines.
Perform immediate CPR and defibrillate as soon as possible! In Canada and the United States, treatment is based on the AHA/HSF Advanced Cardiac Life Support Cardiac Arrest algorithm:
Knowing the Hs and Ts can help try to navigate what caused the ventricular fibrillation. For more information, check out the following resources:
For more information, check out the AHA ACLS Cardiac Arrest pathway here: