PACEMAKER, AICDs AND THE ANESTHESIOLOGIST

• The need for cardiac pacing results from conduction disorders of the heart, which may or may not be associated with IHD.
• Permanent Pacemakers (PPM) are classified using a five letter code( See below)
• For example DDDR means atrial and ventricular sensing (I), atrial and ventricular pacing(II) with adaptive(III) rate(IV) response
• Most modern units work in DDD mode, and provide atrial pacing in the presence of atrial bradycardia and ventricular pacing after an endogenous/paced atrial depolarization, if a spontaneous ventricular beat is absent
• KEY PERIOPERATIVE QUESTIONS: 1. Indication for pacemaker and associated cardiac comorbidities 2. Type of pacemaker; also how does the rate modulation work in that pacemaker? Chest x-ray will help to find the pulse generator siting and lead placement (atrium/ventricle/both) and number 3. When it was last checked 4. Requirement of diathermy for the procedure 5.Whether anticipating any other factor/s interfering with pacemaker function? 6. Surgical site proximity to the pacemaker 7. What is your plan to avoid inappropriate pacemaker function (e.g. change from demand to fixed rate mode) in case of interference? Cardiology/ Pacemaker programmer support may be needed for the same
• WHAT ECG CAN TELL: 1. If native rhythm predominates--> patient not PPM dependent 2. If all beats preceeded by a pacemaker spike--> pacemaker dependent 3. No evidence of pacemaker activity--> magnet might be applied over the pulse generator to switch to fixed rate pacing. If pacemaker is activated by a magnet to pace at a fixed rate, spike may fall in the refractory period and fail to stimulate the ventricle 4. If pacemaker spike is not followed by p or QRS waves --> PPM malfunction
• The characteristics of a PPM can be changed externally by application of a magnet or using radiofrequency generators, usually for a change of demand to fixed rate. Application of a magnet over a non-programmable VVI pacemaker will convert it to VVO asynchronous mode. The modern reprogrammable units need a cautious approach to the use of magnets. In this case, there is a risk of reprogramming ( with inappropriate settings), but it will remain in the asynchronous fixed rate mode, until the magnet is removed, after which the 'inappropriate' reprogrammed mode may take over
• ABOUT THE RATE RESPONSE FUNCTION: Such PPMs may sense electrical activity or vibration (e.g. shivering) and cause a tachycardia in response. Some measure respiratory rate by sensing thoracic impedence and adjust HR accordingly. Some sense blood temperature and so may cause a tachycardia when warming a hypothermic patient. With hypokalemia, there is a risk of loss of pacing capture and with hyperkalemia, there is risk of VT or VF.
• INTRAOPERATIVE STEPS: 1. If possible, avoid surgical diathermy; but if unavoidable, bipolar is safer than unipolar diathermy. 2. Monopolar where necessary, should be used in short bursts with at as low energy levels as possible 3. Diathermy plate should be kept on the same side, as far away from the PPM as possible 4. Cables from diathermy equipment also should be kept away from the PPM 5. Confirm device functionality on completion of the surgery
• Surgical diathermy can cause 1. Ventricular fibrillation 2. 'Reprogramming' of programmable PPMs 3. Inhibition of demand function 4. Unit failure 5. Asystole
• AUTOMATIC IMPLANTABLE CARDIOVERTER DEFIBRILLATORS (AICDs) and THE ANESTHESIOLOGIST: They consist of a set of lead electrode systems for sensing-pacing-delivery of shocks for cardioversion/ defibrillation; modern units can also function as DDD pacemakers. All AICDs should be deactivated with a programming device before surgery to avoid inappropriate shock delivery during electrical interference; in modern AICDs, the anti-bradycardia function can be left activated (Consult the manufacturer for this). The effect of magnets are inconsistent across devices; but modern units are inhibited by magnets. If required, external pads can be placed over the patient with external defibrillators ready to attach, for use in case any tachyarrhythmias occur during this period. Take all precautions as in the case of PPM. Postoperatively, the ICD should be checked and reactivated.