Performing a routine ECG on an adolescent patient at the pediatric ICU the girl suddenly faints. She is lying in bed and does not respond for a few seconds. The ECG shows the following:
@ patient history: the girl underwent cardiac surgery 10 days ago, suffering from postoperative complete AV block. She has a temporary pacemaker (pacemaker wires sewed onto the heart during surgery). The ECG shows temporary exit block. I.e. the stimulus ( in this case output was set to 5mV) does not "capture" the myocardium, meaning it does not induce myocardial contractions.
The first 3 beats are "capturing", as you can spot a pacing spike prior to the QRS complex (best seen in aVR). With the following beats, you still see the pacing spike but there are no QRS complexes there. Only the P-waves appear regularly. Sinus node function seems to be intact.
Since this is a 25mm/s strip, the ventricular pause equals 3 seconds. Afterwards, the pacing continues to capture again.
Extended history revealed potentially loosening the ventricular lead through physical activity and possibly traction.
First measure was to increase the output to at least 10 mV, which resulted in permanent capture.
Usually, one would wait at least 10 to 14 days following cardiac surgery for the conduction system to spontaneously recover. Due to ongoing intermittent exit block despite up regulation of output we decided to go for permanent pacemaker implantation right away.
The girl is doing fine now, having a perfectly functioning trans venous dual chamber pacemaker.