Wednesday, August 03, 2011

Differential diagnosis of wide complex tachycardia

Over at the EMS 12-Lead blog there is a series of posts on this topic. The first post, available here, contains the links to the other five. These are not like the discussions you'll find in formal review articles or textbooks. They deal with real world situations encountered in the emergency setting. The author deemphasizes morphologic criteria and reminds readers of the adage “a wide complex tachycardia is VT until proven otherwise.” You'll make fewer mistakes if you start there. When you're under the gun in the emergency setting you don't want to waste too much precious time trying to make a fancy morphologic diagnosis. Later on when you have time to scratch your head, or in stable patients, you can do a detailed morphologic analysis. The most widely used criteria nowadays are the Brugada criteria. Those criteria are easily misunderstood. The original Brugada paper explains the nuances and limitations of the method. It also reviews and references the older more traditional morphologic criteria. The latter have serious limitations but may warrant consideration if the Brugada criteria fail to yield a definitive diagnosis.

Finally, it is increasingly being recognized that extracardiac causes, particularly hyperkalemia and drug overdose, can lead to some bizarre wide complex tachycardias. Although these do not fulfill criteria for SVT with aberrancy many are not VT.


mb said...

The easiest and most reliable criterion going is the aVR algorithm noted in the study "New algorithm using only lead aVR for differential diagnosis of wide QRS complex tachycardia" Vereckei et al. This is the only one I teach anymore because of incredible sensitivity and specificity. The criteria are simple, easy to remember and physiologically easy to grasp and explain. When the rhythm is fast, wide and regular, then look at aVR for: 1) Initial R wave (98.6% accurate), 2)Initial R or Q wave >40ms wide (87.8% accurate), 3)Notched descending limb of predominantly negative QRS (86.4%) When I compared other ECG's proven to be VTACH by other criteria(Brugada, morphology, axis, etc), the accuracy and agreement was nearly 100% and completed in about 1/10th the time.

R. W. Donnell said...

Thanks for this. I was not aware of that paper.