60-something with wide complex tachycardia: from where does the rhythm originate?

p.p1 {margin: 0.1px 0.0px 0.1px 0.1px; font: 9.0px Helvetica}An elderly woman with history of coronary disease presented with CP and SOB and hypotension by EMS.  EMS had attempted adenosine x 2 without success.Here is her ED ECG:Here is the ED physician ' s interpretation:IMPRESSIONUNCERTAIN REGULAR RHYTHM, wide complex tachycardia, likely p-waves.LEFT BUNDLE BRANCH BLOCK [120+ ms QRS DURATION, 80+ ms Q/S IN V1/V2, 85+ ms R IN I/aVL/V5/V6]Comparison Summary: LBBB and tachycardia are new.What do you think?Smith:  This is indeed a regular wide complex tachycardia.  I do not see P-waves.  Retrograde P-waves after the R-wave are possible (see lead II across the bottom).  This is clearly ventricular tachycardia.  It has a left bundle branch block morphology (small r-wave in V1 with deep S-wave), but the r-wave is wide and the RS interval is almost 100 ms.  LBBB should have a narrow r-wave and the RS interval should be no longer than 60-70 ms, unless there is also some other entity which widens the QRS, such as hyperkalemia or Na channel blocking medications.  That the VT is " LBBB-type " indicates that it originates in the right ventricle.  Since all inferior QRS axes are negative (going away from the inferior wall) and positive in I and aVL, (going towards I and aVL), the point of origin can be predicted to be in the inferior part of the right ventricle or the inferior and right side of the septum.  CourseThe medics...
Source: Dr. Smith's ECG Blog - Category: Cardiology Authors: Source Type: blogs