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Instructors' Collection ECG of the WEEK: Teaching Series - Tachycardia and Left Anterior Fascicular Block

Sat, 10/15/2016 - 15:48 -- Dawn

This series of three ECGs is from a 60-year-old man who was brought to the Emergency Department after being involved in a motor vehicle accident.  No injuries were found, but the patient was severely intoxicated by alcohol consumption.  He was conscious but agitated. 

ECG NO. 1     15:07:23

The first ECG was taken by fire-rescue personnel at the scene of the accident. His hemodynamic status was stable, and the rate was not addressed in the field. ECG No. 1 shows a supraventricular rhythm at 161 bpm, with a narrow QRS and P waves visible before each QRS. 

A notable feature of this ECG are the left axis deviation, by default diagnosed at left anterior hemiblock (left anterior fascicular block).  The .10 second QRS width is typical of LAHB, as is the rS pattern in Lead III.

Also  noted is the unusual R wave progression in the precordial leads.  The R waves are prominent in V2, and then fail to progress across the precordium, and the S waves persist. This is probably due to the hemiblock.  We do not know this patient’s medical history, except that he self-described as an “alcoholic”.  LAFB can be associated with coronary artery disease. 

ECG NO. 2      15:20:38

Now being evaluated in the Emergency Dept., we see the patient's heart rate is 163 bpm.  Some variability in the rate was noted with patient agitation and activity, so it was determined that the rhythm was probably sinus tachycardia.  There were no other significant changes in the ECG from the first one.  Unfortunately, we no longer have access to lab results, so we do not know his electrolyte or hydration status.  Labs confirmed ETOH intoxication. 

ECG NO. 3   15:43:26

After IV fluids and a short rest, the patient is much less agitated, and is conversant.  His heart rate is now 105 bpm.  This rate was reached by gradual increments, further evidence that this was SINUS TACHYCARDIA all along.  Reentrant rhythms (AVNT, AVNRT, atrial flutter) start and stop abruptly.  Some leads on ECG No. 3 may suggest an underlying atrial flutter (aVR, aVF), but the waves do not “march out”. 


At rates over 140 per minute, it can sometimes be difficult to differentiate sinus tach from reentrant tachycardias (PSVT).  Seeing gradual adjustments of the rate favors a diagnosis of sinus tach.  Also, seeing an obvious “cause” of sinus tach helps.  In this case, the patient was a chronic alcohol abuser who was intoxicated.  This is associated with sinus tachycardia, due to stimulation of catecholamine secretion and cell membrane alterations.  Also, he was agitated and possibly dehydrated.

Ventricular Systole

Click to open: 
Ventricular systole

This is an original illustration by Dawn Altman. It may be used free of charge for enhancement of classroom teaching materials. For commercial publication, please contact the artist at [email protected] 

ECG Basics: Second-degree AV Block With Characteristics of Type I and Type II

Thu, 09/01/2016 - 11:51 -- Dawn

This strip shows a second-degree AV block.  During most of the strip, 2:1 conduction is present.  At the beginning, however, two consecutive p waves are conducted, revealing progressive prolongation of the PR interval.  This usually represents a Type I , or nodal, block:  progressive refractoriness of the AV node.   However, the wide QRS ( possibly left bundle branch block), and the fact that the non-conducted p waves are "out in the open" where they should have conducted, points to Type II - an intermittant tri-fascicular block. Wenckebach periods in patients with LBBB can be caused by progressive conduction delay in the right bundle branch.

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1924:  Willem Einthoven wins the Nobel prize for inventing the electrocardiograph.

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