Ventricular Tachycardia – Monomorphic VT

Ventricular Tachycardia (VT) is a broad complex tachycardia originating from the ventricles. There are several different forms of VT — the most common is monomorphic VT, which originates from a single focus within the ventricles.

ECG features of monomorphic VT
  • Regular, broad complex tachycardia
  • Uniform QRS complexes within each lead — each QRS is identical (except for fusion/capture beats)
Monomorphic ventricular tachycardia VT
Monomorphic VT: Regular, broad complex tachycardia

Monomorphic VT can be difficult to differentiate from other causes of broad complex tachycardia.

Other ECG features suggestive of VT include:

  • Very broad complexes (>160ms)
  • Absence of typical RBBB or LBBB morphology
  • Extreme axis deviation (“northwest axis”)
  • AV dissociation (P and QRS complexes at different rates)
  • Capture beats — occur when the sinoatrial node transiently ‘captures’ the ventricles, in the midst of AV dissociation, to produce a QRS complex of normal duration
  • Fusion beats — occur when a sinus and ventricular beat coincide to produce a hybrid complex of intermediate morphology
  • Positive or negative concordance throughout the chest leads, i.e. leads V1-6 show entirely positive (R) or entirely negative (QS) complexes, with no RS complexes seen
  • Josephson’s sign – Notching near the nadir of the S-wave
  • Brugada’s sign – The distance from the onset of the QRS complex to the nadir of the S-wave is > 100ms
  • RSR’ complexes with a taller “left rabbit ear”. This is the most specific finding in favour of VT. This is in contrast to RBBB, where the right rabbit ear is taller

Below are some examples of positive and negative concordance, and Brugada’s and Josephson’s sign. For more examples of the other suggestive features, see VT versus SVT.

ECG Positive concordance in VT
Positive concordance: Predominantly positive QRS complexes throughout precordial leads
ECG VT Negative precordial concordance 2
Negative concordance: Predominantly negative QRS complexes throughout precordial leads
ECG VT V2 RS interval RBBB morphology 700
Josephson’s sing (left): Notching near nadir of S wave
Brugada’s sign (right): R-S interval > 100 ms

Causes of Monomorphic VT

Clinical Significance
  • VT may impair cardiac output with consequent hypotension, collapse, and acute cardiac failure. This is due to extreme heart rates and loss of coordinated atrial contraction (“atrial kick”)
  • The presence of pre-existing poor ventricular function is strongly associated with cardiovascular compromise
  • Decreased cardiac output may result in decreased myocardial perfusion with degeneration into VF
  • Prompt recognition and initiation of treatment (e.g. electrical cardioversion) is required in all cases of VT

Ventricular Tachycardia Classification is based on:
1. Clinical Presentation
  • Haemodynamically stable
  • Haemodynamically unstable — e.g hypotension, chest pain, cardiac failure, decreased conscious level

This is the most important classification clinically and influences immediate management.

2. Duration
  • Sustained = Duration > 30 seconds, or requiring intervention due to haemodynamic compromise
  • Non-sustained = Three or more consecutive ventricular complexes, terminating spontaneously in < 30 seconds
3. Morphology

Mechanisms of Ventricular Tachycardia

Three mechanisms exist for initiation and propagation of ventricular tachycardia:

1. Reentry (commonest mechanism)
  • Requires two distinct conduction pathways
  • Under normal circumstances, impulses cancel each other out (0)
  • Conduction block in one pathway develops due to myocardial scarring, usually as a result of prior ischaemia/infarction (1)
  • Strong ventricular impulses from the normal/slowed pathway can re-enter the blocked region (2), creating a re-entry circuit (3)
2. Triggered Activity
3. Abnormal Automaticity
  • Accelerated abnormal impulse generation by a region of ventricular cells

ECG Examples – Monomorphic VT
Example 1
Monomorphic ventricular tachycardia VT 8

Monomorphic VT:

  • Classic monomorphic VT with uniform QRS complexes
  • Indeterminate axis
  • Very broad QRS (~200 ms)
  • Notching near the nadir of the S wave in lead III = Josephson’s sign

Example 2
Monomorphic ventricular tachycardia VT 2

Monomorphic VT:

  • Very broad QRS complexes (~ 200 ms) with uniform morphology
  • Fusion and capture beats are seen in the rhythm strip
  • Brugada’s sign is present: the time from the onset of the QRS complex to nadir of S wave is > 100 ms (best seen in V6)

NB: The rhythm strip is recorded after the other 12 leads rather than simultaneously


Example 3
Monomorphic ventricular tachycardia VT 3

Monomorphic VT:

  • Very broad complexes (~ 200 ms in V5-6)
  • Northwest axis (-120 degrees)
  • Brugada’s sign — the distance from the onset of the QRS complex to the nadir of the S-wave is > 100ms
  • Josephson’s sign — notching near the nadir of the S wave is seen in leads II, III, aVF
  • Possibly some superimposed P waves in aVF

Example 4
Monomorphic ventricular tachycardia VT 4 and bigeminy

Monomorphic VT alternating with ventricular bigeminy.

The ventricular complexes have the following features:

  • Very broad QRS duration (> 160 bpm)
  • Positive concordance in the precordial leads (dominant R waves in V1-6)
  • Brugada’s sign – time from onset of QRS to nadir of S wave > 100 ms; best seen in leads aVR and aVL

Example 5
Monomorphic ventricular tachycardia VT 5

Monomorphic VT:

  • Extreme axis deviation / northwest axis is present
    • -150 degree; QRS positive in aVR, negative in I + aVF
  • There is a RBBB-like pattern in V1 with a taller left rabbit ear – this is very specific for VT

Example 6 

Monomorphic VT:

  • Northwest axis
  • Tall monophasic R wave in V1 with an rS complex in V6 (small R wave, big S wave)  — this pattern is also very specific for VT

This ECG fulfils the Brugada Morphology Criteria for VT.

NOTE: in the presence of a dominant R wave in V1 (“RBBB morphology”), VT is diagnosed if:

  • There is an RSR’ complex with a taller left rabbit ear
  • There is a tall monophasic R wave
  • There is an rS complex in V6 (R/S ratio < 1)

See “VT versus SVT with aberrancy” for more details.


Example 7
Monomorphic-ventricular-tachycardia-VT-71

Monomorphic VT:

  • This ECG is a difficult one!
  • Although there is a broad complex tachycardia (HR > 100, QRS > 120), the appearance in V1 is more suggestive of SVT with aberrancy, given that the the complexes are not that broad (< 160 ms) and the right rabbit ear is taller than the left
  • However, on closer inspection there are signs of AV dissociation, with superimposed P waves visible in V1
  • Also, the presence of a northwest axis and an rS complex in V6 (tiny R wave, deep S wave) indicate that this is VT
ECG VT AV dissociation
AV dissociation: superimposed P waves at a different rate to the QRS complexes

Differential Diagnosis of Wide-Complex Tachycardia

Several arrhythmias can present as a wide-complex tachycardia (QRS > 120 ms), including:

Differentiating between the various causes of wide-complex tachycardia is challenging and not always possible.


Clinical Features Suggestive of VT
  • Age > 35 (positive predictive value of 85%)
  • Structural heart disease
  • Ischaemic heart disease
  • Previous MI
  • Congestive heart failure
  • Cardiomyopathy
  • Family history of sudden cardiac death (suggesting conditions such as HOCM, congenital long QT syndrome, Brugada syndrome or arrhythmogenic right ventricular dysplasia that are associated with episodes of VT)

Diagnostic Algorithms
  • A number of diagnostic algorithms exist to help aid in the diagnosis of VT.
  • No algorithm is 100% accurate in predicating VT
  • Algorithms can be complex and require specific and unfamiliar measurements to be calculated
  • Flow charts for the four commonly used algorithms (ACC, Brugada, Ultra-simple Brugada, Vereckei ) can be found over at ECGpedia.org.

Remember

  • If in doubt, treat as VT!

Read more about the different types of VT by following these links: 


Advanced Reading

Online

Textbooks


LITFL Further Reading

ECG LIBRARY

Electrocardiogram

MBBS (UWA) CCPU (RCE, Biliary, DVT, E-FAST, AAA) Adult/Paediatric Emergency Medicine Advanced Trainee in Melbourne, Australia. Special interests in diagnostic and procedural ultrasound, medical education, and ECG interpretation. Editor-in-chief of the LITFL ECG Library. Twitter: @rob_buttner

Emergency Physician in Prehospital and Retrieval Medicine in Sydney, Australia. He has a passion for ECG interpretation and medical education | ECG Library |

2 Comments

  1. Hi Ed,

    There was interesting discussion points by Amal on ecgweekly re; rabbit ears this week in diffrentiating SVT and VT

    Important to know about, but important to remember “suggestive” doesn’t mean that any or many of these features are a good thing to hang our hats on in terms of ruling “out” VT was my take home?

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