Man With Diverticulitis Undergoes Precolonoscopy Evaluation

ANSWER
This ECG shows probable ectopic rhythm with second-degree atrioventricular (AV) block and a nonspecific intraventricular conduction block.

The P-wave morphology is unusual; rather than being upright and positive in leads II and aVF, the P waves are biphasic and prolonged, suggesting they originate from an atrial source other than the sinus node.

The rhythm strip of lead I in this ECG isn’t of much help in determining the atrial rhythm, as the P waves are small. However, if you look at the strip beginning with either lead II or III and keep in mind that the strip is continuous even though the leads change (eg, lead III becomes lead aVF which becomes V3, etc), you can see an atrial complex immediately following the T wave that is very similar to the P wave prior to the QRS complex. The rate of the P waves is 84 beats/min, which is twice that of the QRS complex (42 beats/min) and therefore consistent with a 2:1 heart block.  

A nonspecific AV conduction block is evidenced by a QRS duration > 120 ms that does not have the appearance of a right or left bundle branch block.

Finally, while the QT interval of 514 ms is worrisome for long QT interval, it is normal when corrected for rate.