What’s new in cardiology?
PACEMAKERS/ICD AND THE ANAESTHETIST
GD Young
Royal Adelaide Hospital, Adelaide, SA
For almost 50 years cardiac pacing has been the mainstay of therapy for intermittent or persistent bradycardia. Early devices were large, paced at a fixed rate and had limited longevity. Since that time there have been many improvements in pacemaker technology with the aim of restoring cardiac electrical activity to as close to the physiological state as possible. With increased sophistication has come increased complexity in programming and interpretation of cardiac pacemaker function. In many instances pacemakers are now inserted and followed by cardiologists with a full time practice in cardiac rhythm disturbances.
Over the last 20 years we have also seen the introduction and evolution of implantable cardiac defibrillator (ICD) therapy. ICD’s are now the standard therapy for patients who have survived a life threatening episode of ventricular arrhythmia. More recently they have also been shown to be of benefit in patients at high risk of sudden cardiac death who have not yet experienced a serious arrhythmia. With expanding indications for ICD therapy the rate of ICD implantation has increased from less than 20 per million population per annum in 1990 to in excess of 200 implants per million population per annum in 2005.
In assessing patients with a cardiac pacemaker or ICD prior to anaesthesia and surgery a number of issues need to be considered.
The first and foremost is the patients’ underlying cardiac status. Many patients undergoing pacemaker implantation have structurally normal hearts, although other recognised or undiagnosed cardiac pathology may be present. The vast majority of patients with an ICD in situ will have co-existent structural cardiac disease including significant left ventricular dysfunction. In many instances the underlying cardiac process (cardiac failure/CAD) poses a greater peri-operative risk to the patient than the presence of the pacemaker/ICD and potential problems with its function in the peri-operative period. In all instances an assessment of the patient’s functional status needs to be undertaken. Patients with symptomatic heart failure and/or angina with little provocation are at particular risk of perioperative cardiac complication.
The second issue that needs to be assessed is the indication for device implantation and the “dependency” of the patient. In many instances cardiac pacemakers are implanted for intermittent brachycardia and the patient has sufficient intrinsic cardiac activity such that device failure or inhibition would not be associated with disastrous consequences. In some case, particularly elderly patients with complete heart block, there is minimal underlying spontaneous cardiac electrical activity such that device inhibition/failure is associated with asystole. In many cases the dependency of the patient can only be established by formal device interrogation and temporary device inhibition. This information should be sought from the patient’s usual cardiologist. In the case of emergency surgery the facility for temporary transcutaneous cardiac pacing and cardiac defibrillation should be available. With elective surgery even in the pacemaker dependent patient temporary transvenous pacing is very rarely required, the major indication being surgery in close proximity to the pacing system where the leads or generator may be inadvertently damaged.
The final issue that needs to be considered is how the stress of surgery may impact specifically on the pacemaker/ICD patient. The most likely factor to be relevant is the use of electrocautery/diathermy. The effect of this on cardiac pacemakers and defibrillators is quite different. Diathermy, particularly unipolar configuration, is likely to cause temporary pacemaker inhibition. This is of particularly relevance to the pacemaker dependent patient. This risk can reduced by using bipolar diathermy, using the minimal power required and using short pulses of energy. It is now very uncommon for diathermy to cause permanent malfunction of a pacemaker (in most cases normal pacemaker function resumes as soon as the diathermy is ceased) although both pacemaker reprogramming and permanent inhibition/damage have been reported. In a pacemaker dependant patient who is having surgery where diathermy is required the best course of action is to program the pacemaker to an asynchronous mode. In this mode the pacemaker will continue to pace irrespective of intrinsic cardiac activity or external electromagnetic interference. This programming can be undertaken in a temporary fashion by applying a pacemaker magnet over the device or by the use of a transcutaneous pacemaker programming device.
For the ICD patient diathermy has a very different effect. The use of diathermy in an ICD patient has a high risk of causing inappropriate activation of the ICD. The ICD detects the diathermy current as representing a rapid ventricular arrhythmia. A shock delivered during the ventricular refractory period is likely to induce ventricular fibrillation. While the energy delivered is unlikely to cause serious discomfort or injury to the surgeon or assistant the involuntary muscular contraction that may be associated with an ICD discharge could have adverse consequences. It is recommended that all ICD’s are inactivated prior to elective surgery. This is best done using transcutaneous telemetry in the period immediately prior to surgery with reactivation of the device being undertaken as soon as possible post operatively. Continuous cardiac monitoring and external defibrillation capabilities are required for the period that the device is inactivated. The vast majority of ICDs can be temporarily inactivated by applying a magnet directly over the ICD generator (many devices will give a short audible signal when this is done).
There are a number of other factors that need consideration in the pacemaker/ICD patient having surgery. Any surgery in the region of the pacemaker/ICD generator and leads must be undertaken with caution. The pacing/defibrillation leads are very susceptible to damage from surgical instruments. If surgery is considered in close proximity to the device the implanting Cardiologist/Cardiac Surgeon should be consulted prior to the surgery. Finally programming changes to the pacemaker/ICD may be of assistance to improve the haemodynamic status of the patient in the perioperative period. In particular the patients with poor cardiac reserve and relatively fixed stroke volumes may benefit by a temporary increase in the pacing rate in the peri-operative period. Close liaison between surgeon, anaesthetist and cardiologist is likely to benefit the patient.
Time of Presentation
Saturday 13 May 2006 - 1030-1200
