Critical Care Medicine-Neurologic Disorders>>>>>Arrhythmias and Pacemaker
Question 5#

A 65-year-old patient with extensive adenocarcinoma of the lung is scheduled to undergo thoracotomy, left lower lobectomy, pericardiectomy, and pleurectomy. The patient has a medical history of hypertension, coronary artery disease, poorly controlled type II diabetes mellitus, a PPM due to a Mobitz type II AVB, and congestive heart failure with a left ventricular ejection fraction (LVEF) of 40% and mild diastolic dysfunction. Unfortunately, the available medical record does not contain any information about the PPM and the patient states that he had not seen a cardiologist in a few years. No pacing spikes are seen on the ECG.

Which of the following is the MOST appropriate way to proceed?

a. Obtain electrophysiology (EP) consult and ask for the PPM to be set to AAI with a backup rate at 60 bpm
b. Apply a magnet at the beginning of the case and convert PPM to VOO at a rate of 60 bpm
c. Obtain EP consult and ask for the PPM to be set to VVI at a rate of 60 bpm
d. Obtain EP consult and ask for the PPM to be set to AOO at a rate of 60 bpm
e. Obtain EP consult and ask for the PPM to be set to DOO at a rate of 60 bpm

Correct Answer is E


Correct Answer: E

Although applying a magnet may convert a PPM to an asynchronous mode (such as DOO or VOO), this would not be guaranteed in this case as little is known about the model of the PPM, the patient’s degree of dependence on the PPM, and the PPM’s battery function. Given that the patient had not seen a cardiologist in years, the least that should be done is to obtain an EP consult for PPM interrogation before this elective surgery. AAI and AOO are not ideal pacing modes for this patient given his high risk of progression to third-degree AV block. Both modes require intact AV conduction for proper functioning. Given the close proximity to the heart, electrocautery may inhibit PPM function in AAI and VVI modes.

DOO provides asynchronous atrial and ventricular pacing and thus atrioventricular coupling when compared with VOO. This confers hemodynamic benefits especially for patients with mild diastolic - dysfunction (impaired relaxation) in whom left ventricular filling is more dependent on atrial contraction than in patients with normal diastolic function or severe diastolic dysfunction. Both asynchronous modes (DOO and VOO) can cause an R-on-T phenomenon and trigger malignant ventricular tachyarrhythmias.


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