Friday, September 14, 2018

Idiopathic Ventricular Tachycardias for the EM Physician

Written by Pendell Meyers, reviewed by Steve Smith and Scott Weingart
“Idiopathic ventricular tachycardias” refer to a group of tachydysrhythmias originating below the AV node and bundle of His but differing in etiology, prognosis, and treatment compared to classic ventricular tachycardia (VT). The name “idiopathic” is becoming more and more inappropriate, as various specific subgroups and specific etiologies are being discovered, including right ventricular outflow tract VT, fascicular VT, and bundle branch reentrant VT. To understand these entities one must first understand the differences between classic VT and idiopathic VTs.
Classic VT is by far the most common cause of wide complex regular tachycardia. It originates in (usually pathologic) myocardium, which is associated with advanced age, cardiovascular disease, structural heart disease and/or ischemia. Classic VT is associated with the prognosis of its underlying etiology, and is generally considered to have a significant rate of deterioration and hemodynamic compromise, largely due to the poor underlying myocardial function. On EKG, Classic VT tends to have longer QRS duration and a wider, less organized conduction morphology as compared with idiopathic VT, reflecting the key concept that classic VT does not usually originate in or near the intrinsic conduction system whereas many of the “idiopathic” VTs do. Unlike “idiopathic” VT, classic VT is more likely to show moderately specific signs such as AV dissociation, fusion beats, precordial QRS concordance, precordial R to S-wave nadir greater than 100 msec, R greater than R’ in V1, large upright R-wave in aVR, etc., however none of these are reliable in isolation.
Idiopathic VTs as a group are more commonly seen in younger, healthier patients than the typical classic VT patient, and are generally considered to have excellent prognosis with low rates of hemodynamic compromise and rhythm deterioration. These arrhythmias can be either automatic or reentrant in mechanism, and they often respond to antiarrhythmic medications that would ordinarily be ineffective or even contraindicated in classic VT. Idiopathic VTs can be better understood in their known subtypes, of which there are at least 3-4 at this time:
1) Right Ventricular Outflow Tract VT (RVOT VT)
Mechanism: triggered activity originating in the RVOT, which then accesses part of the nearby conduction system (thought to access the RBB within the septum).
Basic ECG Characteristics: precordial LBBB pattern with inferior frontal plane axis
Treatment: usually responsive to adenosine

Associations: Arrhythmogenic Right Ventricular Dysplasia
Variants: a similar arrhythmia has been described as originating from the LV outflow tract, with RBBB morphology with inferior frontal plane axis (RBBB + LPFB morphology). Response to treatment is unknown.

2) Fascicular Left Ventricular Tachycardia

Mechanism: Reentrant arrhythmia originating in or near specific parts of the intrinsic conduction system of the LV. There are at least three subtypes based on location, with the two most important being Posterior Fascicle VT (most common by far) and Anterior Fascicle VT.
Basic ECG Characteristics:
Posterior Fascicle VT: Precordial RBBB morphology with left axis deviation (or LAFB morphology) in the frontal plane
Anterior Fascicle VT: Precordial RBBB morphology with right axis deviation (or LPFB morphology) in the frontal plane
Treatment: Posterior fascicle VT is usually thought to be sensitive to verapamil. Anterior fascicle VT does not seem to have a consistently reported pharmacologic treatment.

3) Bundle Branch Reentrant Tachycardia (BBRVT)

Mechanism: Reentrant loop including at least one portion of the intrinsic conduction system. Unlike other idiopathic VTs, BBRVT is more often associated with underlying structural heart disease.

Image obtained from:

Basic ECG Characteristics: Depending on the bundles/fascicles involved and the direction of conduction, any combination of bundle branch and/or fascicular block morphology can be produced. The most common type reported seems to access the RBB anterogradely and the LBB retrogradely, causing the ECG to show LBBB morphology.
Treatment: This group of arrhythmias does not seem to have an effectively pharmacologic treatment. Neither adenosine nor verapamil have been reported to be consistently effective for these rhythms, however they are so rare that research is severely limited.

Classic vs. Idiopathic VTs
Classic VTIdiopathic VTs
Risk of Hemodynamic compromise / rhythm deteriorationHigherLower
QRS durationWiderNarrower
LV function on POCUSWorseBetter

General ECG Features of VTs, Idiopathic VTs, and SVTs with aberrancy:

Because the idiopathic VTs (unlike classic VT) frequently utilize the intrinsic conduction system, they are often indistinguishable from SVT with aberrancy due to morphology including bundle branch blocks and/or fascicular blocks. Differentiating classic VT from SVT with aberrancy and/or idiopathic VT is not the focus of this post (see posts like this onethis one, and this one), however there are some helpful rules of thumb worth mentioning here:
  • QRS duration of 140-200 msec or greater is more likely to be classic VT and/or hyperkalemia, but can also certainly be SVT with aberrancy.  Most idiopathic/fascicular VTs have QRS duration 140 ms or less.
  • If the first portion of the QRS is conducted in a wide, disorganized, irregular way, then classic VT is by far more likely. If the first portion of the QRS is conducted in a rapid, steep, organized way, then this implies usage of the intrinsic conduction system, which takes place in SVT with aberrancy and many idiopathic VTs.
  • The ventricular rate of a regular wide complex monomorphic tachycardia cannot be reliably used to differentiate idiopathic from classic VT because the typical ranges are mostly overlapping and there are not really any reliable upper limits for either entity.
  • Most importantly: VT is by far the most common cause of wide complex regular tachycardia, and there is no perfectly reliable way to distinguish classic VT from idiopathic VT from SVT with aberrancy on the surface 12-lead ECG.

Prospective Differential Diagnosis and Treatment Plan based on ECG Features:

As EM physicians we rarely know the exact rhythm prospectively when we are standing in front of a patient with wide complex regular tachycardia. What we can do prospectively is identify QRS morphology that matches one of the following stereotypical patterns:

RBBB + LAFB (leftward frontal axis) Morphology

Rhythm differential includes classic VT, SVT with RBBB+LAFB, posterior fascicle VT, BBRVT, and probably other rare and obscure rhythms. If you believe it is one of the idiopathic VTs rather than classic VT or SVT with RBBB+LAFB, then posterior fascicle VT may be the most likely etiology. Posterior fascicle VT is usually sensitive to verapamil. However, one must consider the chance of giving verapamil inadvertently to to classic VT, which is formally contraindicated. Synchronized cardioversion (assuming you avoid shocking on the T-wave) is the only therapy which is both safe and effective among all etiologies in this category. Experts such as Dr. Smith might consider giving verapamil if electricity does not work AND the patient has very good LV function on POCUS, no history of cardiomyopathy, MI, heart failure, etc.

RBBB + LPFB (rightward frontal axis) Morphology:

Rhythm differential includes classic VT, SVT with RBBB+LPFB, anterior fascicle VT, BBRVT, LVOT VT, and probably other rare and obscure rhythms. If you believe it is one of the idiopathic VTs rather than classic VT or SVT with RBBB+LPFB, then anterior fascicle VT may be the most likely etiology. Anterior fascicle VT is thought to be somewhat less sensitive to verapamil than posterior fascicle VT, but there are some cases with reported efficacy. However, one must again consider the chance of giving verapamil inadvertently to to classic VT, which is classically contraindicated. Synchronized cardioversion (assuming you avoid shocking on the T-wave) is the only therapy which is both safe and effective among all etiologies in this category.

LBBB + Inferior frontal plane axis Morphology:

Rhythm differential includes classic VT, SVT with LBBB, RVOT VT, BBRVT, and probably other rare and obscure rhythms. If you believe it is one of the idiopathic VTs rather than classic VT or SVT with LBBB, then RVOT VT would be the most likely consideration in this category, which would typically be adenosine sensitive. This is convenient because adenosine is already indicated and recommended in our guidelines for stable, monomorphic, wide complex tachycardia. Again, synchronized cardioversion (assuming you avoid shocking on the T-wave) is the only therapy which is both safe and effective among all etiologies in this category. However, adenosine is also a safe, indicated, and less invasive strategy in this situation, as it will not harm a patient with classic VT.

Bottom Line:

Given the considerations above, I propose two options for your practice, with opposite points of view, both of which reflect a high degree of forethought and reflection on this topic.
First, as these patients are usually quite stable, see if you can find any previous records to shed light on the diagnosis, and any previous successes or failures of conversion attempts.

Option #1: Honey Badger

With this option you basically ignore the existence of these idiopathic VTs, ensuring that you can never make a mistake as a result of misdiagnosing a rhythm as idiopathic VT which in fact is NOT idiopathic VT. The reasoning includes:
  1. “There are no reliable ways to differentiate idiopathic VT from VT, so I should always assume VT because this strategy is safer.”
  2. “Even if I could prove it was an idiopathic VT prospectively, there is poor evidence correlating the EKG patterns with effective treatment, and some of the questionable treatments you’re advising have potentially negative side effects”
  3. “The safest and most effective treatment for all the idiopathic VTs is electricity, so why go out of my way to diagnose something rare and less dangerous when the treatment will be the same regardless?”
  4. “Even if I were correct about the diagnosis and possible treatment, if anything went wrong in any way and my reasoning had been based on treating idiopathic VT, how could I protect myself when none of the guidelines’ tachycardia algorithms deal with idiopathic VT?”
  5. “Cardioversion is safe, effective, and fun.”

Option #2: Fancy Pants

In this option you adopt a practice in which you act on your experienced suspicion of IVT, but in a way that has been prospectively thought out to avoid the pitfalls and complications in the event that you’re wrong. You’ve thought out exactly when and why you’re going to use each medication. The reasoning includes:
  1. Adenosine: “As long as the wide complex tachycardia is monomorphic and regular, adenosine is safe and guideline-approved for a stable patient, and assuming I am prepared for the ever-present chance of unexpected adenosine-induced rhythm deterioration just like I would in a narrow complex SVT conversion, then there cannot be any error attributed to considering FVT in this situation.”  Dr. Smith would only give adenosine if RVOT is on the differential diagnosis, and that would be when there is RBBB pattern with inferior axis.
  2. Verapamil: This medication is slightly more problematic, because of the 2015 ACLS Guidelines’ contraindication for verapamil/diltiazem in the setting of possible VT (Class III, Level of evidence B). There are some practitioners who believe that calcium channel blockers are likely safe after a high quality bedside ultrasound shows normal cardiac contractility. If you’re in that camp, then you could argue that your plan for suspected verapamil-sensitive FVT will be: 1) ensure good contractility by bedside US + chart review, then 2) give verapamil while being prepared for small chance of deterioration +/- prophylactic voodoo including fluid bolus and calcium, etc.  Dr. Smith would always try electrical cardioversion first; however, it does not always work, or there is reversion to VT.  In such a case, he would try verapamil, but only if ultrasound shows a high ejection fraction (good LV function).
  3. “Sometimes electricity simply does not work. In these cases we must either rely on cardiologists to help or have an approach to these rare rhythms ourselves.”
  4. “If the rhythm can be diagnosed and treated easily with only a single medication push, we can prevent unnecessary sedation and cardioversion, as well as any time/effort/complications that comes from it.”
  5. “It is helpful prognostic and diagnostic information if the rhythm is successfully treated with adenosine/verapamil.”
Finally, many of these patients are rock stable and do not need to be converted right this second.  If the easy method of electrical cardioversion is not working, it can be very helpful to get consultation from your friendly cardiologist or electrophysiologist.  He/she may have some very good insights into the etiology of the tachycardia.

Cases to practice with:

A couple extra references on idiopathic VTs:

Comment by KEN GRAUER, MD (9/20/2018):
Excellent, thought-provoking post by Drs. Meyers, Smith and Weingart on evaluation and treatment of idiopathic VT. The fact that 2 approaches to practice are proposed (ie, Option #1 “Honey Badger” — vs — Option #2 “Fancy Pants”supports the clinical reality that there simply is no perfect answer. In the hope of offering additional perspective that for selected patients may fall in between the “Honey Badger” and “Fancy Pants” options — I’ll add the following thoughts.
  • There are occasions when you can definitively distinguish between VT vs SVT with either aberrant conduction or preexisting BBB (Bundle Branch Block). These include recognition of definite AV dissociation with capture and/or fusion beats. CAVEAT: In my experience, the phenomenon of AV dissociation is often thought to be present, when it in fact is not. But if it is truly there — then the rhythm is VT (See ECG Blog #133).
  • There are other occasions when you can with >95-98% certainty, tell that a rhythm is either VT or SVT. These very-high likelihood specificity situations are more common than is generally appreciated. Remember that one starts with ~80+% likelihood that a regular WCT ( = Wide-Complex Tachycardia) without clear sign of atrial activity is VT. This goes up to over 90% likelihood of being VT in older patients who have underlying ischemic or structural heart disease. Certain characteristics regarding QRS morphology and frontal plane axis may sometimes further enhance VT likelihood to ≥95% (See ECG Blog #42).
Aberrant Conduction in a WCT rhythm arises because one or more conduction fascicles are refractory due to the rapid rate. As a result — QRS morphology during aberrant conduction generally manifests some form of conduction block (ie, RBBB, LBBB, LAHB, LPHB, RBBB/LAHB, or RBBB/LPHB).
  • There are certain QRS morphologies that carry extremely high specificity for either aberrant conduction or a ventricular etiology. Thus, the finding of a completely typical RBBB pattern in lead V1 (ie, rsR’ with taller right-rabbit ear and S wave that descends below the baseline) — in association with a narrow upright R wave with wide terminal S waves in leads I and V6 — is virtually diagnostic of a supraventricular etiology.
  • In contrast — QRS morphology that is not suggestive of any form of conduction block moves the needle up from the starting point of ~90% likelihood, that a WCT without atrial activity in an older patient with heart disease is VT. For example — the LBBB + Inferior Frontal Plane Axis Morphology shown in the above discussion (which I’ve reproduced in Figure-1) is highly unlikely to represent an SVT with LBBB because, despite the monophasic R wave in lead V6 — it manifests the following features which are extremely atypical for a supraventricular etiology with LBBB conduction: ian all negative QRS in lead aVL; iia very wide initial positive deflection (r wave) in leads V1 and V2; and, iiiextremely early transition (with R>S already by lead V3), which is clearly not the pattern seen with LBBB conduction disorders, for which transition usually does not occur until after V4. CAVEAT: Anything is possible. Some patients (much more likely in those with severe underlying heart disease) may have very unusual QRS morphology on their baseline ECG, or may develop atypical morphologic aberrant forms. This is why >95% likelihood of VT based on morphologic characteristics is not the same as 100% likelihood.
Figure-1: While using QRS morphologic characteristics is not 100% specific — several features in this example of LBBB-like conduction strongly suggest that the rhythm is VT and not supraventricular (See text).
Generally Accepted Management Principles — Whatever clinical approach you favor — you’ll probably agree on the following:
  • If in doubt as to the etiology of a regular WCT rhythm without clear sign of atrial activity — then assume VT until proven otherwise. Treat accordingly. Remember, one has to prove that a WCT is supraventricular, rather than the other way around.
  • If the patient in question is at all hemodynamically unstable — then immediate electrical cardioversion is indicated regardless of the etiology of the rhythm.
  • A surprising number of patients who present in a sustained regular WCT rhythm may be hemodynamically stable. In this situation, one could either: iUse electricity ( = the “Honey Badger” approach); or, iiContemplate other options.
Clinical Considerations: Much of what follows is similar to Option #2 proposed above by Drs. Meyers, Smith, Weingart with a few additional thoughts:
  • Some patients with sustained VT may remain alert and hemodynamically stable for not only minutes, but for hours or longer. Therefore, an attempt at medical therapy is reasonable for such patients (with readiness to shock if at any time during the process the patient becomes unstable).
  • If clinical and ECG parameters suggest the patient has ischemic VT (ie, older patient; presence of underlying coronary or structural heart disease— then Adenosine is unlikely to work. This drug is probably best avoided in such cases.
  • A significant minority of patients with VT have idiopathic VT (ie,VT that occurs in a patient without underlying heart disease). Specific prevalence figures for the relative percentage of ischemic vs idiopathic forms of VT will vary, depending on age and characteristics of the population studied. The “good news” (as per the above Table by Dr. Meyers that compares Classic vs Idiopathic VTs) — is that in addition to being younger (often <40yo) — there is less risk of hemodynamic deterioration during idiopathic forms of VT, and these patients clearly have a better long term prognosis.
  • PEARL: Suspect that an idiopathic form of VT may be present when the patient is a younger adult without known coronary or structural heart disease — especially if this otherwise healthy and active individual develops the WCT during exercise or other strenuous effort.
  • NOTE #1: As per Dr. Meyers above — there are some adenosine-sensitive forms of VT (most notably RVOT VT). However, ECG appearance may not reliably predict all forms of idiopathic VT that might respond to Adenosine (See ECG Blog #35). This is the rationale for considering empiric use of Adenosine when confronted with a patient in a regular WCT in which the clinician is uncertain if the rhythm is SVT (with either preexisting BBB or aberrationor idiopathic VT. If the rhythm turns out to be a reentry SVT — then Adenosine will most probably convert the rhythm. And, this drug may also occasionally work if the rhythm turns out to be idiopathic VT, with little risk of clinical deterioration from Adenosine administration. NOTE #2: Because there are some adenosine-responsive forms of VT that are not always predictable from their ECG appearance — conversion to sinus rhythm following Adenosine administration does not prove that the WCT was supraventricular!
  • NOTE #3: Prior to general acceptance of Adenosine as a superb antiarrhythmic agent in this country — Verapamil was frequently used as a diagnostic/therapeutic trial when clinicians were confronted with a WCT of uncertain etiology. Unfortunately, a significant percentage of those patients who turned out to have ischemic VT immediately decompensated as a result of the vasodilating and negative inotropic effects of Verapamil. This is why Verapamil should not be used when there is reasonable possibility that a WCT is ischemic VT. On the other hand — Verapamil is the drug of choice for the idiopathic VT form known as Fascicular V(See ECG Blog #38).
  • When the ECG appearance and the clinical situation strongly suggest Fascicular VT (ie, younger adult patient; apparent absence of coronary or structural heart disease— then empiric Verapamil is perfectly reasonable. The ECG should show a QRS complex that is not overly wide during the WCT (ideally ≤0.13-0.14 second) — with QRS morphology consistent with a RBBB/LAHB-like pattern (less often a RBBB/LPHB pattern).
  • PEARL: The presence of somewhat atypical morphologic features for the conduction block during the WCT make it more likely that the rhythm is VT rather than SVT with aberrancy (See ECG Blog #85). That said, since you are avoiding Verapamil in patients likely to have ischemic VT (ie, older patients — those with suspected coronary or structural heart disease — and, with morphologic ECG features showing a wider QRS that does not resemble any form of conduction block) — use of Verapamil in those WCT patients who are thought to have either SVT or Fascicular VT is a win-win, since the drug is unlikely to harm in this situation, and it has a good chance to be effective for either arrhythmia.
Our thanks to Drs. Meyers, Smith and Weingart for this insightful discussion!


  1. Dr. Smith and co-

    Thank you for another great post, but I have a question from a prehospital perspective. I'm a paramedic, and while I read your blog (and others like it) regularly, not many of my colleagues do. Our protocols call for the typical ACLS anti-arrhythmics (e.g. Amiodarone, Lidocaine) to be given for all stable monomorphic wide-complex tachycardias, not just typical VT. Would these drugs be effective on idiopathic VTs?


    1. Doug,
      Glad you're reading the blog!
      Good question. No, they are generally not effective.
      Steve Smith

  2. I wonder how EPs and cardiologists will help any better in diagnosing the exact etiology BEDSIDE or can they?
    Very detailed information.. I guess I need to be careful to call a WCT; FVT or RVOT henceforth.
    So to be on safer side I would (in a stable patient) try Adenosine and then consider cardioversion as patients do not like getting shocked when we discuss about treatment plans with them.
    One question, does Adenosine works only in RVOT? what about Amiodarone? Could you write more on the treatment strategies? Thank you.

    1. Adenosine supposedly works in RVOT, and usually works in SVT with aberrancy. Amiodarone is indicated for wide complex regular tachycardia according to our ACC/AHA guidelines as an option, assuming you do not think it's SVT. I would say in general that, if you do not suspect a particular SVT with aberrancy or a particular idiopathic VT on the differential, then just revert back to your classic strategy for wide complex regular tachycardia. For many people, this includes drugs like amiodarone or procainamide (if you can get it easily), all vs. elective cardioversion. Remember, these idiopathic VTs are really only a consideration in stable patients with wide complex regular tachycardia for whom you have some time to think. Don't forget that the context for this is your regular SVT vs. VT paradigm.


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