Wide Complex Tachycardias

You are dispatched to the report of a sick case.  Upon arrival, you find a 52-year old male patient complaining of palpitations.  When pressed, he complains of very mild chest discomfort that he refuses to describe as “pain,” but is worth a two on the 0-10 scale. He has an irregular pulse rate of 130, a blood pressure of 116/70, and a respiratory rate of 16.  He is warm, pink, and dry and is completely awake and oriented with humor.

His ECG:

I started this post expecting to clear up misconceptions about the differentiation of wide complex tachycardias (WCTs).  I wanted to explain some of the main differentiation algorhythms with their reported sensitivity and specificity.  I was going to include algorhythms from Brugada (1), the American College of Cardiology (2), Verecki (3), and Griffith (4).  I’ve taught 12-lead ECG interpretation for more than 10 years, so this kind of topic is right in my wheelhouse.

I decided not to waste my time or your time.  The lesson is simpler than that: Prehospital and emergency differentiation of WCT is a waste of your time.

There are several issues with the differentiation of WCTs.  First, all of the algorhythms have low specificity.  Specificity is the percentage of cases that are negative for the condition and are found to be negative after applying the test – the true negative rate.  So, low specificity means that the test “pings” when the condition isn’t there.  Think of a radar detector in your windshield that alerts constantly, even when there is no speed trap.  Even the relatively higher sensitivity (true positive) ratings of the WCT algorhythms are only in the high 80% range.  That means you will get a false positive (read: be on the wrong path) about 10% of the time.

The second issue is that the algorhythms are complex - probably too complex for prehospital use, especially in front of a patient who needs your time and full attention.  For example, the ACC algorhythm has four main decisions, plus 13 morphology clues to remember.  How often will you practice using that?  A sub-point of this one is that most of the differentiation algorhythms involve precise measurements of R-wave to peak times, nadirs, and V_i/V_t ratios* that are difficult to measure accurately.

The third reason not to differentiate in the field is that there is no upside.  Every decision you make has a cost-benefit analysis, whether you overtly weigh the two sides or not.  The cost side doesn’t matter in this case because there is no upside to getting the differentiation right - the treatment (cardioversion or amiodarone) is the same for SVT and VT.  And you won’t look as cool as you think you will, like a paramedic Babe Ruth calling his shot.  Anyone that hears your ECG interpretation will assume that you just guessed right through chance, not skill.

The final reason is the most important: It does not matter! 

Cardioversion works for supraventricular tachycardia with aberrancy or with pre-existing bundle branch block.  Cardioversion works for ventricular tachycardia.  Amiodarone works for SVT.  Amiodarone works for ventricular tachycardia.  Adenosine can even convert ventricular tachycardia on occasion! (5)

Simplify!

Your decisions should revolve around whether or not the patient is stable or unstable.  Unstable patients get to ride the lightning – after a benzodiazepine, of course.  For me, the decision to cardiovert someone revolves around their level of responsiveness.  I am very hesitant to weld a patient who is awake, even with midazolam.  But other medics have a lower threshold and include chest pain as a sign of instability. 

If the patient is stable, your next decision is pretty much to think about adenosine, roll your eyes and skip the adenosine, and then start an amiodarone drip.  There are some decisions that revolve around whether the presenting rhythm is regular or irregular, but that decision is in the ACLS treatment algorhythm in order to avoid giving adenosine (or other AV node blockers) to atrial fibrillation with pre-excitation.  You can avoid those problems by just not giving adenosine.

The differentiation of WCTs can be a fun skill to have.  But you have to remember that it is a skill applied after you have dropped the patient off at the hospital.  It is a skill made for debating with your partner at the ED dock or in the front of a bus at post.  Not when you are in front of a patient. 

Instead of studying the ECG that your monitor just printed off, think about what else you could be doing.  Prioritize your actions.  The patient above, at the beginning of this post, has a pretty long list of required actions.  They include oxygen, IV access, possible blood draw, a complete physical exam, a complete history of the present illness, a complete health history, at least one 12-lead ECG, aspirin, consideration of nitrates, a phone call to the receiving hospital so that they are ready, considering/prepping an amiodarone infusion, repeat vital signs, constant monitoring, and extrication from wherever they are to the ambulance.  Pretty much all of those would take higher priority than ten minutes of studying a field ECG with a magnifying glass and a pair of calipers.

My heart-felt advice is to treat all wide complex tachycardias as wide complex tachycardias, rather than trying to differentiate whether it is a ventricular or supraventricular origin.

*V_i is the height/depth of the QRS after 40 milliseconds; V_t is the height/depth of the terminal 40 milliseconds.  Want to measure those while bouncing down the road, do you?

1. Brugada P, Brugada J, Mont L, Smeets J, Andries EW. A new approach to the differential diagnosis of a regular tachycardia with a wide QRS complex. Circulation. 1991; 83(5): 1649-1659.

2. Blomström-Lundqvist C, Scheinman MM, Aliot EM, Calkins H, Camm AJ, et al. ACC/AHA/ESC guidelines for the management of patients with supraventricular arrhythmias… J Am Coll Cardiol. 2003; 42(8): 1493-1531.

3. Vereckei A, Duray G, Szénási G, Altemose GT, Miller JM. Application of a new algorhythm in the differential diagnosis of wide QRS tachycardia. Eur Heart J. 2007; 28(5): 589-600.

4. Griffith MJ, Garratt CJ, Mounsey P, Camm AJ. Ventricular tachycardia as default diagnosis in broad complex tachycardia. Lancet. 1994; 343(8894): 386-388.
5. Marill KA, Wolfram S, Desouza IS, Nishijima DK, Kay D, Setnik GS, et al. Adenosine for wide-complex tachycardia: efficacy and safety. Crit Care Med. 2009; 37(9): 2512-2518.