January 30, 2024

Wide Complex Tachycardia in Cardiac Telemetry

 Pragmatic Approach How to Diagnose Ventricular Tachycardia in Cardiac Telemetry 


By: @ecgrhythms

What is a wide complex tachycardia?


A wide complex tachycardia (WCT) is defined as a cardiac rhythm with a rate of > 100 bpm and QRS width/duration ≥120 ms or 0.12 sec. Other acronym used is WQRST.

WCT are described as right bundle branch block (RBBB) - like configuration or left bundle branch block (LBBB)-like configuration.

A RBBB is recognized by a QRS duration ≥ 120 ms with a predominantly positive portion in V1 (Figure 1A). LBBB has QRS duration of ≥120 ms with a predominantly negative terminal portion in V1 (Figure 1B).


Figure 1 – A. RBBB configuration in V1. B. LBBB configuration in V1.


What are the probabilities of a Wide Complex Tachycardia (WCT)?


A WCT can be any of the following:

  • Ventricular Tachycardia (VT) ~ 80%
  • Supraventricular tachycardia (SVT):
    • with aberrancy in the His-Purkinje system
    • with anterograde accessory pathway conduction
    • with bizarre baseline QRS
    • in presence of drug effect or electrolyte imbalance
  • Ventricular pacing
  • Electrocardiogram artifact


A Short Review of Aberrancy

 A narrow QRS complex is the considered normal and it requires highly synchronous activation of the ventricles (Figure 2) which is made possible though the rapidly conducting His-Purkinje system (HPS).

 The term aberrancy (aberration or aberrant intraventricular conduction) is used to describe transient bundle branch block (BBB) and does not include QRS abnormalities caused by preexisting BBB, preexcitation, or the effects of drugs/electrolyte.  The mechanism of aberration can occur anywhere in the His-Purkinje system (red box in Figure 2). The transient BBB is due to impulse transmission of a supraventricular beat during period of physiologic refractoriness and/or depressed conductivity. The supraventricular electrical impulse is conducted abnormally through the ventricular conducting system. This results in a wide QRS complex that may be confused with a ventricular ectopic beat or PVC or VT.

Technicians often used other terms instead of aberrancy like bundle-switch, intermittent bundle, conduction change and intermittent ventricular conduction delay. However, the appropriate term should be aberrancy or aberrant intraventricular conduction.



Figure 2 - Cardiac Conduction System

 Why not call all WCT VT?

 The (pretest) probability that a WCT is VT is 80% (4 out 5). If patients are known to have prior myocardial infarction and the symptom of tachycardia occurred after the probability increases to > 90%. However, those data are often not known.

 The purpose of arriving at the correct diagnosis is to avoid harm to the patient. If SVT is treated as VT and given amiodarone or electrical cardioversion (which may not be harmful) it is not the optimal therapy. If it was atrial flutter, cardioversion will entail a risk of stroke.  If VT is treated as SVT (using diltiazem/verapamil), hemodynamic deterioration may occur. If SVT are managed as VT, they might be placed on long-term amiodarone which carries a number of long-term problems or an implantable defibrillator with repeated generator change. However, hunting the diagnosis is second only to stability of the patient. If the patient is unstable then immediate cardioversion and then once stable the various morphological characteristics and algorithms are used.

 How to diagnose VT in Cardiac Telemetry?

 Algorithms were created and studied differentiating VT from SVT with aberrancy with a focus on characteristics unique to VT. If those characteristics are not present, then it is presumed SVT until proven. Algorithms are not perfect and it should also be noted that algorithms find it hard to distinguish VT from pre-excited SVT.

 The popular algorithms developed utilize the 12 lead ECG. However, in this age of ECG telemetry, most wide QRS tachycardia are captured and saved in central telemetry which can view all the limb leads and a V1 +/- V6.


Figure 3 – Typical Central Telemetry Set-up

What are the ECG Criteria or Algorithms for the Diagnosis of VT?


The following are the criteria and algorithms to differentiate VT from SVT with aberrancy:


·         Sandler and Marriot Criteria (1965)

·         Wellens Criteria of RBBB (1978)

·         Kindwall criteria of LBBB (1988)

·         Brugada algorithm (1991)

·         Griffith algorithm (1994)

·         Bayesian analysis (2000)

·         Vereckie algorithm I (2007)

·         Vereckie algorithm II (2008)

·         Pava Criteria of lead II (2010)

·         VT score (2014)

·         Limb Lead Algorithm (2019)


What are ECG Criteria/Features that are practical or useful in cardiac telemetry?


The following are useful to diagnose VT:


·         The Initiation "Logic" ("K. Wang Logic")

·         AV Dissociation

·         Fusion Beat

·         Capture Beat

·         R wave Peak Time in Lead II (Pava Criteria)

·         V1 and V6 Morphology

·         aVR algorithm (Vereckie algorithm)

·         Limb lead algorithm


The Initiation (“K. Wang Logic”)


According to Dr. K Wang (and as mentioned in  Chou's Electrocardiography in Clinical Practice), it is easy to identify VT and SVT with aberrancy if the initial or baseline is sinus rhythm. There are 3 things to remember.


1.       When the run of WCT is preceded by a premature P wave (often the P wave has a different morphology), then it is SVT with aberrant conduction.


 Figure 4 – A WCT preceded by a PAC


The ECG case above (Figure 4)  is from a 75 yr old patient with pontine infarct with several episodes of wide and narrow complex tachycardia. After 3 narrow QRS complexes, a PAC can be seen right after R3 (orange arrow) conducted with a long PRI. The WCT (~150 bpm) then starts. The initiation by a PAC is typical of AV nodal reentry tachycardia which is one of the SVT's. (Please refer to separate discussion on SVT's).


2.       If the WCT is preceded by a regularly (not prematurely) occurring sinus P wave (the PR interval is shorter than that of normally conducted sinus beats), it is ventricular tachycardia. (Figure 5)




Figure 5 – A WCT preceded by  a regular sinus P wave with short PRI


3.       If the WCT is not preceded by a P wave, it is ventricular tachycardia. (Figure 6)


Figure 6 – A WCT not preceded by a P wave


Figure7 - An Flow Diagram on Initiation Logic


Figure 7 shows the diagram to simplify the 3 events.

AV dissociation


During VT, there is independent beating of the atria and ventricles (AV Dissociation). In patients with underlying sinus rhythm, the atria are depolarized by an impulse coming from the sinoatrial (SA) node while the ventricles are controlled by an ectopic ventricular beat (Figure 8) . The atrial rate is slower compared to the ventricular rate. AV dissociation is difficult to spot but not impossible. AV dissociation is easier to see in slower VT but difficult to appreciate during fast rates. Multiple simultaneous leads are needed to compare distortions and determine if those distortions are indeed P waves.

Look for AV dissociation in the case below. Map the P waves and the QRS.



Figure 8 – WCT case for AV dissociation


Distinct P waves are marked in red arrows and not so obvious P waves are marked with blue arrows (Figure 9). To check if those are indeed real P waves, you can do simultaneous lead comparison. Take for example the identified P wave before R5. The P wave is upright in II and aVF and inverted in aVR. Other P waves in this case are hidden from view or are buried in the QRS. From 2 sequential P waves, we can then use a caliper to march the P waves.


Figure 9 – P waves marked with arrows


The P to P interval is 18 small boxes (cycle length 720 ms) or an atrial rate of about 83 bpm.  The R to R interval is 14 small boxes (cycle length 540 ms) or a ventricular are of about 107 bpm. At that rate difference, we can see dissociation. Another way of visual recognition is using a ladder diagram (Figure 10). However, this might be time consuming in the acute setting. For educational purposes the ladder diagram is presented below. The diagram will show independent beating of the atria and ventricles or AV dissociation.



Figure 10 – Ladder diagram showing AV dissociation


Fusion Beat


The ventricles may be also be depolarized both by the ectopic ventricular impulse and a supraventricular impulse resulting in a QRS complex that is intermediate in morphology between the sinus beat and the ectopic ventricular beat. This complex is a fusion beat.


The previous ECG case featuring AV dissociation will be used. In the strip below (Figure 11), the morphology of R4, R10 and R16 is different compared to the rest of the R waves. The duration of these 3 R waves is about 0.12 seconds (vs. 0.16 sec).



Figure 11 – Fusion beats highlighted with arrows


The reason for the difference in QRS morphology is because R4, R10 and R16 are fusion beats. This is best illustrated in the ladder diagram (Figure 12).



Figure 12– Ladder diagram showing fusion beats


Below (Figure 13) is another example of a fusion beat (red arrows) which supports that the WCT is VT and not SVT with aberrancy. The first 4 complexes are sinus beats. After the 5th complex is the full duration of the WCT. If you only use leads II and V1, it will be difficult for you to appreciate the difference in the shape of complex #5 which is a fusion beat. However, if you use full disclosure to see all limb leads, you will appreciate that complex #5 is different in shape from the first 4 complexes and the WCT.



Figure 13 – Fusion beat highlighted by arrows


Capture beat


During slower VT, occasional supraventricular impulse may be transmitted through the AV node and depolarize the ventricles resulting in a normal looking QRS (capture beat) in the middle of wide QRS beats.


The interval of a capture beat is shorter than during the tachycardia or its rate is faster compared to the WCT.


The complexes below (red box) are captured beat (Figure 14). It has the same morphology or shape with that of a sinus beat (latter part of the strip). The presence of the capture beats means that the WCT is VT.



Figure 14 – Capture beats highlighted in red box


 R Wave Peak Time in Lead II  (Pava Criteria)

 In lead II, the R Wave Peak Time (RWPT) is the QRS duration from the initiation of depolarization until the first change of polarity. On the surface ECG, it is measured from the beginning of the QRS until the first change in QRS direction regardless it changed to negative to positive. Figure 15 is an example on how to measure RWPT.

VT is the likely diagnosis if the RWPT in lead II is ≥ 50 ms.


The sensitivity, specificity and positive predictive value of RWPT in lead II are 93.2%, 99.3% and 98.2%, respectively.

The other name of RWPT in lead II is the Pava Criteria based on the first author of the paper.



Figure 15 - How to measure the RWPT


Figure 16 are examples of different QRS morphologies in lead II with RWPT 50 ms .


Figure 16 - Representative samples of different RWPT 50 ms  (Figures from Jastrzebski M, et al. 2016. The ventricular tachycardia score: a novel approach to electrocardiographic diagnosis of ventricular tachycardia. Europace 18, 578–584)

V1 and V6 morphology


The typical secondary lead in cardiac telemetry is lead V. It is usually placed in the V1 position. Some of the telemetry systems have 6 wires. The 4 wires are for the limbs and the other 2 wires are chest leads. These 2 wires can be positioned in the V1 and V6 position.


The following morphology in V1 and V6 supports VT:


       RBBB-VT or Wellen's RBBB-VT criteria (Figure 17)


v  V1 -  Monophasic R, QR, or RsR’ (rabbit ear with right greater than left)

v  V6 – R/S ratio < 1, QR or QS, monophasic R


       LBBB-VT or Kindwall LBBB-VT Criteria (Figure 18)


v  V1- Initial r > 30 ms, nadir of S > 60 ms, notched downstroke

v  V6 – any q, QS or QR


Figure 17 – V1 and V6 morphology criteria for VT (top) and SVT with RBBB morphology (bottom)

 (From Garner J and Miller J. 2013. Wide Complex Tachycardia – Ventricular Tachycardia or Not Ventricular Tachycardia, That Remains the Question. Arrhythmia & Electrophysiology Review 2013;2(1):2329)

Figure 18 – V1 and V6 morphology for VT (top) and SVT with LBBB morphology (bottom)

(From Garner J and Miller J. 2013. Wide Complex Tachycardia – Ventricular Tachycardia or Not Ventricular Tachycardia, That Remains the Question. Arrhythmia & Electrophysiology Review 2013;2(1):2329)


 aVR Algorithm (Vereckie Algorithm)


In VT diagnosis, morphologic stepwise approach was developed. The most popular algorithm developed was the Brugada algorithm. However, the Brugada algorithm cannot be used in cardiac telemetry because it needs a 12L ECG. The new aVR algorithm (Vereckie II) is useful in cardiac telemetry because it only utilizes lead aVR.

The new Vereckie algorithm is shown below (Figure 19 and 20). The algorithm in a stepwise fashion looks at aVR for (1) an initial R wave, (2) initial r or q wave > 40 ms, (3) a notch in the descending limb of a predominantly negative QRS and (4) vi/vt 1. Vi stands for voltage change in the initial or first 40 ms and vt stands for voltage change in the terminal or last 40 ms. If any of the features mentioned is present then the WCT is VT.



Figure 19 – The New Vereckie Algorithm




Figure 20 – Morphologic features supporting VT in the New Vereckie Algorithm (From Garner J and Miller J. 2013. Wide Complex Tachycardia – Ventricular Tachycardia or Not Ventricular Tachycardia, That Remains the Question. Arrhythmia & Electrophysiology Review 2013;2(1):2329)


Limb Lead Algorithm


The limb lead algorithm is another stepwise approach utilizing the limb leads (I, II, III, aVR, aVL and aVF).

In a stepwise fashion is looks at (1) the aVR if monophasic, (2) predominantly negative QRS in I, II and III and (3) the opposing QRS complexes in the limb leads (Figure 21).


Opposing QRS complexes in the limb leads is described as:


·         monophasic QRS complexes (QS/R) in all 3 inferior leads sharing the same polarity (all positive or all negative, but including a notched R or QS complex),

·         monophasic QRS complexes (R/QS) in 2 or 3 of the remaining limb leads, with a polarity opposite to that of the inferior leads.


If any of the features mentioned is present then the WCT is VT.



Figure 21 - Limb Lead Algorithm




Figure 22 - The Limb Lead Algorithm



The diagnosis of VT has undergone evolution.  There is still “no one criterion to end all criteria”. If uncertain about the diagnosis of a WCT, it is wise to treat it as VT. You will be correct 80% of the time. However, all pragmatic/practical criteria and algorithms must be used to differentiate VT from SVT with aberrancy:


·         The Initiation

·         AV Dissociation

·         Fusion Beat

·         Capture Beat

·         R wave Peak Time in Lead II (Pava Criteria)

·         V1 and V6 Morphology

·         aVR algorithm (Vereckie algorithm)

·         Limb lead algorithm



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