American Medical Resource Institute | ACLSONLINE.US
Monomorphic and Polymorphic Ventricular Tachycardias (Wide QRS Tachycardias)

Monomorphic and Polymorphic Ventricular Tachycardias (Wide QRS Tachycardias)

Some types of tachycardia can be difficult to identify and properly treat. A broad QRS (or wide QRS) complex (width greater than .12 seconds) is known as a broad QRS tachycardia.
Wide-complex tachycardias can be seen in two general forms: monomorphic and polymorphic. These
can often be distinguished from other tachycardic mechanisms by the width, shape, and consistency of the QRS complex (it may be either wide QRS supraventricular or ventricular tachycardia). Treatment will be determined by the specific electrophysiology and condition of the patient.

Identifying Symptoms

A variety of symptoms may be present with any form of tachycardia which a patient may suffer. These symptoms can include shortness of breath, chest pain, dizziness, fatigue, altered mental state, and other signs of shock.  

You first need to determine whether the tachycardia is caused by the underlying physiological changes. (i.e. pain, hypovolemia, etc.). When the heart rate exceeds 150 per minute, patients are increasingly likely to exhibit more serious symptoms (ranging from syncope to cardiac arrest). Immediate treatment is mandatory in the event of hemodynamic instability. 
If treating more immediate causes (i.e. analgesia, fluid repletion, etc.) is unsuccessful, the etiology could be due to more serious causes that may include myocardial ischemia, congenital cardiac conditions, serious electrolyte imbalances, pharmacologic intoxication (often stimulants), or side effects of other therapeutic drugs.

Identifying Patterns

Examining the morphology and behavior of the QRS pattern may assist you in determining what type of wide QRS tachyarrhythmia the patient is experiencing.

Monomorphic VT

Monomorphic ventricular tachycardia will have QRS complexes greater than or equal to .12 second (120 milliseconds). These QRS complexes appear uniform and symmetrical. This suggests that the impulses and/or circuitry of the heart is causing complexes to originate in the same area of the ventricle.

Polymorphic Ventricular Tachycardia

Polymorphic VT has QRS complexes greater than or equal to .12 second (120 milliseconds). QRS complexes may appear wider or higher than monomorphic (or other types of) VT. Because the electrical impulses and circuitry for this type of VT originate in various locations within the ventricles, the QRS morphology will also be asymmetrical.

Determining Treatment

Treatment for these forms of broad QRS tachycardia will require assessment of the patient’s condition and the appearance of the QRS. Once that assessment has been completed, treatment options can then be determined by a series of decisions covered in the ACLS Tachycardia Algorithm.

Stable or Unstable?

First, determine if the patient is stable or unstable. “Unstable” ranges from signs of inadequate perfusion to no cardiac output whatsoever. Patients made unstable by the onset of the arrhythmia should receive immediate counter-shock (DC cardioversion). No time should be wasted terminating a life-threatening arrhythmia.

Assess Symptoms

If the patient is stable, you will then want to determine whether the symptoms are caused by the tachycardia or an underlying condition that caused the tachycardia. In the second situation, treating the underlying cause will constitute the proper intervention. Carefully monitor the patient’s airway and oxygenation status. Proper equipment should be present in case the patient develops a need to support their respiratory and/or oxygenation level.

Stable Broad QRS Tachycardias

Should a patient present as stable, oxygen should be administered if indicated, IV access established, and a 12-lead ECG obtained. Should the patient’s condition become unstable, (i.e. altered mental status, signs of shock, signs of inadequate perfusion, ischemic chest discomfort and severe heart failure), emergency cardioversion is suggested.

Treatment Methods

Electrical Cardioversion

When treating broad QRS tachycardias, It is beneficial to use the “synchronized” mode of cardioversion. In this mode, therapeutic energy is released when the device senses a QRS complex. The theory behind this action is to avoid the “relative refractory period” of the cycle and hopefully reduce the induction of ventricular fibrillation (VF). This seems to be more effective when the heart rate is in the lower ranges (<150 beats per minute),
If use of the synchronized mode causes any delay in electrically converting a patient with an unstable, life-threatening arrhythmia, the therapeutic shock should be delivered immediately using the unsynchronized mode.
Refer to the recommendations provided with the defibrillator to determine the recommended energy settings. Generally, broad QRS regular arrhythmias require lower therapeutic energy, whereas those with irregular rhythms (atrial fibrillation with a broad QRS) commonly require higher energy for successful conversion. If the attempted cardioversion causes ventricular fibrillation (VF), immediate defibrillation is mandatory. If the synchronizer circuit is activated, turn it off and deliver an immediate countershock using the appropriate therapeutic energy.


In the case of stable patients, adenosine can be considered to rule out VT versus broad QRS supraventricular tachycardia (SVT). If the adenosine converts the arrhythmia, it is not VT.
Referring to stable patients, other pharmacologic agents are commonly used. The following doses have been recommended:

Final Thoughts 

Monomorphic and polymorphic broad QRS tachycardias occur frequently. Differentiating between broad QRS VT and SVT is often difficult. However, both share a commonality in patients with an unstable response to the arrhythmia: immediate electrical termination of the arrhythmia is needed. The actual diagnosis of SVT versus VT is definitively made by the cardiologist-electrophysiologist in the EP lab.

Want More Study Resources?

When you register for your exam, you get access to exclusive practice tests and case studies.

Get Access Now

Ready To Register For Your Exam?

Included FREE:
  • Instant Card and CE Certificate
  • Case Study Library
  • Online Review with Practice Questions
  • Review and Retake of Exam
Included FREE:
  • Instant Card and CE Certificate
  • Case Study Library
  • Online Review with Practice Questions
  • Review and Retake of Exam
Get BLS Free When You Register for Both ACLS & PALS
  • Instant Card and CE Certificate
  • Case Study Library
  • Online Review with Practice Questions
  • Review and Retake of Exam