A 61 year old woman with a longstanding history of non-ischemic cardiomyopathy is seen in defibrillator clinic for routine follow-up.  She states that she has been somewhat more short of breath in the last several weeks.

• Underlying sinus rhythm 
• AV sequential pacing with adequate atrial sensing but no atrial capture, normal ventricular capture

Comment: Boxed “P” indicates underlying sinus rhythm P-waves and boxed “AP” indicates atrial pacing spikes which are not followed by a P waves, thus confirming loss of atrial capture.  Third and 8th paced QRS complexes occur early after a sensed P-wave confirming adequate atrial sensing.