EKG Myth - Ventricular tachycardia must have concordance

This is part of a series of posts detailing common electrocardiogram myths.


Myth: Ventricular Tachycardia must have precordial concordance

When differentiating a regular, wide-complex tachycardia some will look for precordial concordance to rule-in, or more importantly to rule-out ventricular tachycardia.

The absence of precordial concordance is not a reliable method of ruling out ventricular tachycardia:

Although the specificity of concordance for VT is high (>90%), the sensitivity is low (~20%)¹.

It is generally thought that positive concordance indicates a posteriobasal left ventricular origin and negative concordance indicates an anterioapical left ventricular origin. However, in the case of positive concordance, SVT with a left-posterior accessory pathway is a known cause.

Until recently, negative concordance has been thought to be "virtually diagnostic" of ventricular tachycardia². Multiple case reports have shown that certain configurations of accessory pathways can also cause negative concordance^3,4,5.

The key takeaway is while this criteria is a useful tool to rule-in ventricular tachycardia (i.e. high specificity), it is not a useful tool to rule-out ventricular tachycardia (i.e. low sensitivity).

Ventricular tachycardia without precordial concordance⁶.

Ventricular tachycardia without precordial concordance. (c) 2011 EMS 12-Lead Blog.

WPW and Atrial flutter with positive concordance⁷.

While positive or negative concordance may strongly suggest ventricular tachycardia, providers should not rule-out ventricular tachycardia in its absence.

1. Pellegrini CN, Scheinman MM. Clinical management of ventricular tachycardia. Curr Probl Cardiol. 2010; 35(9):453-504. [PubMed]
2. Goldberger ZD, Rho RW, Page RL. Approach to the Diagnosis and Initial Management of the Stable Adult Patient With a Wide Complex Tachycardia. Am J Cardiol. 2008; 101:1456-1466. [Full Text]
3. Pappas LK, et al. Wide QRS complex supraventricular tachycardia with negative precordial concordance. Am Heart Hosp J. 2009; 7(1):67-8. [PubMed]
4. Kappos KG, et al. Wide QRS Complex tachycardia with a negative concordance pattern in the precordial leads: Are the ECG criteria always reliable? Pacing Clin Electrophys. 2006; 29:63-6. [PubMed]
5. Volders PGA, et al. Wide QRS complex tachycardia with negative precordial concordance: Always a ventricular origin? J Cardio Electro. 2003; 14:109-111. [PubMed]
6. Garmel GM. Wide Complex Tachycardias: Understanding this Complex Condition Part 1 - Epidemiology and Electrophysiology. W J Emerg Med. 2008; 9(1):28-39. [Full Text]
7. Ibid. 1, Figure 3.

EKG Myth - "It's Too Fast for Ventricular Tachycardia"

This is part of a series of posts detailing common electrocardiogram myths.


Myth: Rate can help you rule out Ventricular Tachycardia

When differentiating a regular, wide-complex tachycardia some will look at the rate to rule out ventricular tachycardia. Studies have not found rate to be a predictive finding¹.

...regarding ventricular rate, significant overlap unfortunately exists between VT and SVT such that rate is not a helpful criterion to differentiate origins².

Ventricular tachycardia technically can range in rates from 100 bpm through 300 bpm. However, a practical definition of VT would place the lower bound around 120 bpm and the upper bound around 260 bpm³.

Common terminology includes rates slower than 120 as "Slow Ventricular Tachycardia", which most often is not true VT⁴. Rates upwards of 260 to 300 bpm are commonly termed "Ventricular Flutter"⁵.

Ventricular tachycardia at 130 bpm. (c) 2001 - 2011 Beth Israel Deaconess Medical Center.

Ventricular tachycardia at 206 bpm. (c) 2011 EMS 12-Lead Blog.

Ventricular tachycardia at 280 bpm. (c) 1994-2011 WebMD.

As a rule: a regular, wide-complex tachycardia should be treated as ventricular tachycardia in the field, until proven otherwise.

1. Griffith MJ, et al. Multivariate analysis to simplify the differential diagnosis of broad complex tachycardia. Br Heart J (1991); 66:166-74. [PubMed]
2. Hudson KB, et al. Electrocardiographic Manifestations: Ventricular Tachycardia. J Emerg Med (2003); 25:303-314. [PubMed]
3. Surawicz B, Knilans TK. Chou's Electrocardiography in Clinical Practice: Adult and Pediatric, 6th ed. Philadelphia, PA. Saunders, 2008. 
4. Mattu A. ECG PEARLS: Beware the Slow Mimics of Ventricular Tachycardia. Emergency Physicians Monthly, 24 August 2010. Retrieved Online 8 November 2011. [Free Full Text]
5. Gurevitz O, et al. Long-term prognosis of inducible ventricular flutter: not an innocent finding. Am Heart J (2004); 147(4):649-54. [PubMed]

Zebra Spotting

I'm sure we all received the following good advice at some point in our EMS education or careers:

"When you hear hoofbeats, think horses not zebras."

I propose we add the corollary:

"...but if you don't stay to watch, you won't know what you missed."

Remember, always err on the side of the patient.

An attempt at Video Education: Axis Determination

I'm a huge fan of the Khan Academy and regularly watch his videos when I have a question about something in mathematics. Usually it only takes five or so minutes into the video for me to recall how to accomplish the task, and I can move along. I've always wanted to see if I could do the same thing for ECG interpretation.
So here is my inaugural attempt; rapid axis determination using leads I and aVF (assuming you're ok with a ±5° difference):

Conclusion to 54 year old female CC: BLS intercept

As many readers noted, there is a lot of baseline wander. This is not the most helpful of 12-Leads. On scene the crew attempted multiple 12-Leads, however, the patient would not sit still and that was the best one. 

I think a close look at the Initial 12-Lead has enough information to make a field diagnosis.

Read the rest at EMS 12-Lead Blog: 54 year old female CC: BLS intercept - Conclusion!

New Case Study at EMS 12-Lead Blog

My first case study as an associate editor is up at the EMS 12-Lead Blog, so check it out: 54 year old female cc: BLS Intercept:

"It is just after 3am when you are called to intercept a BLS unit on scene with a 54 year old female with a low heart rate.

Upon your arrival, you find two EMT-Basics attending to a small woman lying in bed, who appears acutely ill..."

Also, I've done a brief review of atrioventricular blocks to help with identification of the rhythm in this case study!

Enjoy.

Unrecognized Limb Lead Misplacement?

Dr. Smith's ECG Blog has a new case up, "Reperfusion through collaterals associated with nitroglycerin, lateral MI with reciprocal T-wave inversion in lead III," with a pretty stark change in the initial 12-Leads. However, I have a hunch the stark change was really a change in the limb lead positions!

ECG 1 and ECG 2: Limb Leads Only

Look at leads I and II, notice how they "swap" positions between the two 12-Leads. Now look at aVL and aVF, notice how the "swap" positions too. Now take a look at lead III. It goes from inverted P's and T's with a Qr complex, to upright P's and T's with a Rs complex.

I propose that this change is due to a simple reversal of two leads. If we take a look at our friend Einthoven's Triangle (we covered this in a previous post on the S5 Lead) we can see that this makes sense!

LA/LL Swap: Einthoven's Triangle is "Flipped"

We can see that Lead I is actually looking at Lead II and Lead II is actually looking at Lead I; confirmed with ECG's 1 and 2. Lead III becomes an inverted Lead III; confirmed again in the original ECG's. This looks like a case of an unrecognized left arm and left leg lead reversal.

What I find most interesting is if you compare every ECG except the first, it appears to be a case with subtle posteriolateral changes that may have been missed had there not been the lead reversal!