ECG of the Week - 19th September 2016 - Interpretation

This ECG is from an 88 yr old male with a history of ischaemic heart disease and PVD. I don't know what his presenting complaint to the Emergency Department was, but what does his ECG show ?

Click to enlarge

Rate:

• Ventricular rate 48 bpm
• Atrial rate 72 bpm

Rhythm:

• Regular atrial activity
• Group ventricular activity
• Wenckebach pattern
• Progressive PR prolongation
• Dropped QRS
• P:QRS 3:2 ratio

Rhythm Strip with P waves labelled
Click to enlarge

Axis:

• LAD

Intervals:

• PR
• Progressive PR prolongation
• Initial PR ~160ms
• Then PR ~340-360ms
• Then P wave with dropped QRS
• QRS - Prolonged (160ms)

Segments:

• Sgarbossa negative
• Discordant ST segment change

Additional:

• Typical LBBB morphology

Interpretation:

• LBBB - longstanding
• Type I 2nd Degree AV Block / Wenckebach

We've had several cases of Wenckebach features on the blog, links below:

• ECG of the Week - 3rd February 2014
• ECG of the Week - 1st April 2013
• Wenckebach Counter-Intuition - An explanation of why you get R-R shortening with PR progression

Most sources will sight Wenckebach as a benign AV block with a low chance of progression to complete heart block but intervention may still be indicated. 

The following is taken from the ACC/AHA/HRS 2008 Guidelines for Device-Based Therapy of Cardiac Rhythm Abnormalities (full text here).

Type I second-degree AV block is usually due to delay in the AV node irrespective of QRS width. Because progression to advanced AV block in this situation is uncommon, pacing is usually not indicated unless the patient is symptomatic. Although controversy exists, pacemaker implantation is supported for this finding..... However, it is not always possible to determine the site of AV block without electrophysiological evaluation, because type I second-degree AV block can be infranodal even when the QRS is narrow. If type I second-degree AV block with a narrow or wide QRS is found to be intra- or infra-Hisian at electrophysiological study, pacing should be considered.

What happened ?

The patient presented to the Emergency Department with progressive cardiac failure in the setting of NSTEMI. During inpatient telemetry he was found to alternate between atrial fibrillation, 2nd degree AV block and complete heart block, he underwent an uneventful pacemaker insertion.

References / Further Reading

Life in the Fast Lane

• 2nd Degree AV Block - Wenckebach / Mobitz I
• LBBB

Textbook

• Chan TC, Brady WJ, Harrigan RA, Ornato JP, Rosen P. ECG in Emergency Medicine and Acute Care. Elsevier Mosby 2005.