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Instructors' Collection ECG: Wide QRS Complex With First-degree AV Block

Fri, 06/07/2019 - 13:40 -- Dawn

The Patient:  This ECG was taken from a 73-year-old man with a history of heart failure with preserved ejection fraction, severe left ventricular hypertrophy, Type II diabetes, and stage 4 chronic kidney disease.  He also suffered deep vein thrombosis and is on anticoagulation.  He has a recent diagnosis of IgA myeloma.  He presented with a complaint of nausea and vomiting and was found to have a worsening of acute kidney infection.  There was suspicion of renal and cardiac amyloidosis, but the patient refused biopsy to confirm this.  He was started on chemotherapy for multiple myeloma and will be followed as an outpatient.

The ECG:  The rhythm is sinus at around 60 bpm, although the rate varies a little at the beginning of the strip.  The QRS complex is wide at .12 seconds, or 120 ms., representing interventricular conduction delay (IVCD).  The PR interval is .32 seconds, or 320 ms. This constitutes first-degree AV block.  There is left axis deviation in the frontal plane and poor R wave progression in the horizontal plane.

Wide QRS:   When confronted with wide QRS, there are many diagnostic possibilities.  We can rule out a ventricular origin for the beats, as there are P waves consistently before each QRS. There is no history given of the presence of electronic pacemaker, and no obvious spikes.  One of the most common forms of IVCD is left bundle branch block. In this ECG, V1 has the appearance of LBBB with it’s monophasic, wide QS pattern.  However Leads I and V6 do not have the typical LBBB pattern, which would be broad, positive QRS complexes. By ruling out obvious causes of the conduction delay, we are forced to simply call it “interventricular conduction delay (or defect)”.

Conduction delays below the level of the bundle of His can occur any place along the interventricular conduction system, and can even be a feature of the thickened or dilated left ventricle. One way to pinpoint the area of conduction delay is with electrophysiology studies.

In the past, patients who showed signs of LBBB (a bifascicular block) and first-degree AVB were said to have “trifascicular block”. This term is now outdated, and it is felt that it is preferable to just describe the conduction delays seen. The majority of first-degree AV blocks occur at the AV node level, but in the presence of LBBB, first-degree AVB can represent a conduction defect in the right bundle branch.  Of course, EP studies can make the naming of blocks and conduction delays much more accurate. A 1971 study explored the occurance and location of first-degree AVB in the setting of interventricular conduction delays.

Left Ventricular Enlargement:   (a term including hypertrophy and dilatation).  The QRS complexes on this ECG do not meet the Sokolov-Lyon criteria for LVH, but LVH is not diagnosed by ECG findings, which tend to be less than reliable. This patient’s known history of LVH is presumably confirmed by xray and echocardiogram. The slight ST elevations in V2, V3, and V4 are typical of wide-complex rhythms, in that they are “discordant” to the QRS direction, and proportional to the size of the QRS.  That is, the ST and T waves will point in a direction opposite that of the QRS, and there will be most notable ST elevation or depression in the leads with the tallest or deepest QRS complexes. For more on evaluation of ST elevation or depression in the presence of broad-complexes, see Dr. Smith’s work on the modified Sgarbossa criteria.

It is safe to say that this unfortunate patient has plenty of clinical history to have the ECG changes seen here, and that there are no acute ECG findings.  We want to thank Dr. Ahmad Nawid Latifi for sharing this most interesting case with us.

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