Pacemakers

In USA, over 3 million people have an implantable cardiac PM, and more than 400,000 PMs are implanted annually.

In addition to a right atrial and right ventricular lead, some PM pts with cardiomyopathy also have left ventricular pacing capability via a transvenous coronary sinus or epicardial lead (this configuration is called CRT-P).

Because all conventional ICDs provide antibradycardia pacing, that section of this book applies to these pts as well. ^∗

∗ MAGNET CAUTION : A magnet will never change the pacing mode or create asynchronous pacing in an ICD. Only ICDs from ELA (Sorin) will change the pacing rate (to 90 bpm if the battery is OK) upon magnet placement. For many ICDs (Boston Scientific and St Jude Medical), ^† the magnet switch can be programmed “OFF.” Only ICDs from Boston Scientific and its previous companies emit ongoing tones that identify correct placement of a magnet (except subcutaneous ICDs, which only emit a tone for 1 min following magnet application). Some older ICDs from Boston Scientific (with the “GDT” or “CPI” x-ray code) can undergo permanent disabling of tachy therapy by magnet placement.Boston Scientific owns the Guidant and CPI brands, and St Jude Medical owns the Pacesetter brand.

The incidence of pts with a PM or ICD (collectively called CIEDs) presenting for surgery is substantial.

Robust data are lacking; however, the presence of a PM might increase periop risk owing to

• Associated medical problems.

• Incorrect interpretation of device type (i.e., confusing a PM for an ICD) or events (i.e., pseudomalfunction).

• Inappropriate periop management, especially for the pacing-dependent pt.

• Lack of familiarity with new technology, such as LCP.

Intraop decrease in pacing rate and/or asystole from EMI: induced ventricular oversensing and pacing inhibition in the pacing-dependent pt.

Intraop increase in ventricular pacing owing to EMI entering a dual chamber PM and causing atrial lead oversensing and ventricular tracking

Intraop increases in pacing rates resulting from activation of the “exercise sensor,” whether because of direct mechanical stimulation (such as preparation of the chest) or pressure on the device (personnel leaning). Cause of this undesirable tachycardia: Possibly mistaken as inadequate anesthetic depth and inappropriately treated with antichronotropic agents

Failure to capture (i.e., pacing output without myocardial depolarization) because of inappropriate programmed parameters (i.e., inadequate safety margin), or abrupt increase in pacing threshold from myocardial ischemia/infarction, drug administration, or electrolyte shifts. (Note that any or all chambers can undergo failure to capture with possible hemodynamic derangement, even without apparent outright pacing failure.)

Hemodynamics being degraded by magnet ^∗ placement; magnet placement, which typically (but not always) produces asynchronous pacing at 85–100 bpm (depending upon the brand, model, and programming) and shortens the AV interval to 100 ms in some devices; magnet application to a Medtronic Micra leadless PM, which has no effect and is not programmable; magnet application to a St Jude Nanostim leadless PM, which will provide VOO (asynchronous ventricular) pacing at 100/min for 8 cycles, 90/min assuming the battery status normal, and 65/min if the battery status is “elective replacement indicated, assuming that the magnet sensor is programmed ‘ON’”

Thoracic central line placement in a pacing-dependent pt where the guidewire meets the ventricular lead causing over sensing and pacing inhibition; thoracic central line placement that could cause dislodgement of a new CIED lead because the procedure is relatively contraindicated for at least 6 wk following new lead implant. (Note that spontaneous dislodgement of coronary sinus leads occurs in over 10% of pts.)

Indications for permanent pacing: Symptomatic failure of impulse formation (sinoatrial disease), symptomatic failure of impulse conduction (AV block), hypertrophic or dilated cardiomyopathy, and long QT syndrome

Indications for temporary pacing (usually reversible issue): After cardiac surgery, treatment of drug toxicity resulting in dysrhythmias, certain dysrhythmias complicating MI, and bridge to permanent placement

Nomenclature: Five positions of the North American Society of Pacing and Electrophysiology (NASPE)/British Pacing and Electrophysiology Group (BPEG) generic pacing code, with the first position referring to the chamber(s) paced (A = atrium, V = ventricle, and D = both, O = none); the second position referring to the chamber(s) sensed (A, V, D, and O), the third position identifying the response to sensed events (I = inhibit, D = dual chamber pacing and tracking); the fourth position being “R” if the CIED increases its rate in response to “exercise” or “O” if rate responsiveness is programmed off; and the fifth position identifying a multisite (A = biatrial, V = biventricular, or D = both) CIED