Ventricular tachycardia refers to a wide QRS complex heart rhythm — that is, a QRS duration beyond 120 milliseconds — originating in the ventricles at a rate of greater than 100 beats per minute. This can be hemodynamically unstable, causing severe hypotension, and can thus be life-threatening. Ventricular fibrillation, asystole and sudden cardiac death can occur soon after ventricular tachycardia if action is not taken immediately.
Ventricular tachycardia can occur with many variations of the QRS morphology, depending on where the arrhythmia originates, which sometimes makes diagnosis on ECG challenging. Below are two examples of ventricular tachycardia with different QRS morphologies — one with a right bundle branch block morphology and one with a left bundle branch block morphology. VT can also occur with QRS morphologies anywhere in between. You can find links to many more examples of VT at the bottom of this review.
Ventricular tachycardia can be classified as sustained or non-sustained VT, or NSVT. Sustained VT is any ventricular tachycardia that lasts for more than 30 seconds or is symptomatic. Non-sustained VT lasts for less than 30 seconds and is asymptomatic.
Ventricular tachycardia should be described by type (monomorphic or polymorphic), duration (sustained or non-sustained) and heart rate — i.e. monomorphic VT non-sustained at a heart rate of 220 bpm or sustained polymorphic VT at a heart rate of 250 bpm.
Electrophysiologists may also describe the location within the ventricles from where the VT is originating. This can be determined by the morphology of the QRS complex. For example, VT that has a LBBB morphology must come somewhere from the right ventricle; this is because the electrical potential takes a long time to reach the left ventricle, similar to what occurs with a simple LBBB.
Polymorphic VT (Torsades de Pointes) is a form of VT with multiple QRS morphologies. Polymorphic VT is best treated with intravenous magnesium. Patients with a prolonged QT interval have a higher risk for developing polymorphic VT. Removing offending drugs that prolong the QT interval and correcting potassium or calcium imbalances is crucial. Here is an example of polymorphic VT:
Ventricular tachycardia can be difficult to distinguish from supraventricular tachycardia, or SVT, with aberrancy. The Brugada Criteria are most commonly used to differentiate between these two entities — a clinically important distinction. Similar rules are provided in the American College of Cardiology/American Heart Association Guidelines. If present, “fusion beats” and “capture beats” can also be helpful to diagnose VT.
A fusion beat — also known as Dressler’s beat — occurs when sinus node activity (P wave) begins to conduct through the normal conduction pathway during an episode of VT. The abnormal ventricular impulse then conducts retrograde (backward) across the atrioventricular node, colliding with the sinus impulse. The resulting QRS is a fusion of the normal QRS morphology and the ventricular morphology from the VT.
A capture beat is similar to a fusion beat, except the QRS morphology looks completely like the normal QRS complex, as the sinus node impulse conducts to the ventricles before the retrograde ventricular activation occurs.
A few general rules apply to diagnosing ventricular tachycardia:
- If there is any question regarding diagnosis, treat the patient as if the rhythm is VT.
- The rhythm is much more likely to be VT in patients with ischemic heart disease or systolic congestive heart failure.
- VT is more likely with advancing age. Some references state that in patients aged older than 40 years, assume the rhythm is VT — though this is not 100% accurate.
The Brugada criteria/algorithm is outlined below.
1. Do you see concordance present in the precordial leads (V1-V6)?
Sometimes explained as the absence of a “RS complex,” concordance simply means “all up” or “all down.” A simple way to think of this would be to ask the question: Are all QRS complexes completely upright (positive) or completely downward (negative) in the precordial leads? If the answer is yes, then VT is the diagnosis. The images below show positive and negative concordance during VT.
2. Is the R to S interval greater than 100 ms in any one precordial lead?
If the R to S interval exceeds 100 ms in any one precordial lead, then VT is the diagnosis. Simply use calipers to measure the distance between the R wave and S wave in each precordial lead. An example is below.
3. Do you see atrioventricular dissociation?
If AV dissociation is present, the diagnosis is VT. AV dissociation occurs when P waves, representing atrial depolarization, are seen at different rates than the QRS complexes. This is present in only a small percentage of VT ECG tracings, but it is diagnostic of VT. Frequently, this is difficult to see due to the fast rate of the QRS complex. Below is an ECG strip of a patient with VT. See the PP interval when in sinus rhythm then march out the P waves within the wide QRS complex to find the AV dissociation that is present, confirming the diagnosis of VT.
4. Examine the morphology of the QRS complex to see if it meets the specific criteria for VT.
VT is frequently either in a right bundle branch block (upright in V1) or a left bundle branch block pattern (downward in V1).
If upward in lead V1 (RBBB pattern), then VT is present in the following situations:
- A monophasic R or biphasic qR complex in V1
- A rS complex in lead V6 favors VT
- A RSR’ or “bunny-ear” pattern present in V1, with the R peak being higher in amplitude than the R’ peak (see image below)
If downward in lead V1 (LBBB pattern), then VT is present in the following situations:
- The presence of any Q or QS wave in lead V6 favors VT
- A wide R wave (≥ 40 ms) in lead V1 or V2 favors VT; see image below
- Slurred or notched downstroke of the S wave in V1 or V2 favors VT
- Duration of onset of QRS complex to peak of QS or S wave greater than 60 ms favors VT
Note that rhythms can, at times, originate in the ventricles but have a heart rate less than 100 bpm. These rhythms — called “idioventricular rhythms” — are sometimes referred to as “slow ventricular tachycardia” or “slow VT” because they meet the diagnostic criteria for VT, but the heart rate is below 100 bpm. When the heart rate is less than 60 bpm, and the rhythm originates in the ventricle, it is simply called an “idioventricular rhythm.” When the heart rate is between 60 and 100 bpm, it is referred to as an “accelerated idioventricular rhythm,” or AIVR; this is a common hemodynamically stable rhythm that occurs after myocardial infarction and requires no treatment. Some examples of both VT and idioventricular rhythms are below.
1. Surawicz B et al. ACC/AHA recommendations for the standardization and interpretation of the electrocardiogram. Circulation. 2009;119:e235-240.
2. Chou's Electrocardiography in Clinical Practice: Adult and Pediatric, 6e