a) Outline the advantages and disadvantages of the following modes of epicardial pacing post cardiac surgery.
A patient arrives ventilated to the ICU following a CABG and aortic valve replacement. They are on low dose noradrenaline and a native rate of 60 beats/minute in sinus rhythm. They have VVI epicardial pacing wires in situ with a pacemaker backup rate of 40 beats/minute.
You are called to the patient when the monitor trace below is demonstrated (see Figure 1.1)
b) State the pacing issue, and list the specific actions you would perform with the pacing box. (20% marks)
(Image removed from report.)
Advantages and disadvantages of various pacing modes is a topic that has come up in the past, specifically in the form of Question 20 from the first paper of 2007. To see it return in the 2020s is a positive sign - repeating questions about important topics is not a failure of SAQ design, but a way of emphasising important material (because assessment drives learning), and prevents a drift towards esoterica which can occur if the examiners intentionally avoid repeating SAQs.
The answer to that old SAQ is reproduced below with zero modification.
|AAI||atrial demand pacing||
|VVI||ventricular demand pacing||
|DDD||dual chamber demand pacing||
The other (20% mark) part of this question, which relates to the troubleshooting of the pacemaker circuit, is impossible to reconstruct from the wording of the question, because "(Image removed from report.)" The post-AVR patient described in the stem could theoretically develop any range of temporary pacing wire complications. For the purpose of keeping things simple, undersensing was used here, because it fits the scenario. So:
Pacing issue: undersensing. This is a situation where the pacemaker, instructed to inhibit itself whenever a viable P or QRS comes along, instead paces irresponsibly, ignoring normal cardiac activity. This pacemaker is in essence asynchronous.