Anaesthesia for patients with pacemakers and similar devices

Transcription

1 Anaesthesia for patients with pacemakers and similar devices Paul Diprose FRCS(A&E)Ed FRCA JM Tom Pierce MRCP FRCA Key points A detailed history, obtained from the patient and the notes, is important for safe anaesthesia The cardiovascular condition of the patient should be optimised pre-operatively Bipolar diathermy should be used in preference to unipolar Implantable cardioverter/ defibrillators should be disabled before surgery Back-up methods of pacing should always be available There are an estimated 300,000 patients who have a permanent pacemaker in the UK, with approximately 300 new implants per million population being inserted per year. In addition to this, there are increasing numbers of patients who are receiving implantable cardioverter/defibrillators (ICD). Approximately 1000 units were inserted in , but this number is increasing rapidly each year as the indications for insertion broaden. This article will review the important points for consideration prior to anaesthetising a patient with one of these devices. Permanent pacemakers Indications for the insertion of permanent pacemakers The American College of Cardiology guidelines for pacemaker implantation grade the indications from class I (evidence and/or general agreement for indication) to class III (evidence existing against the procedure). Class I indications for permanent pacing are summarised in Table 1. The majority of pacemakers in the UK are inserted for some form of acquired atrioventricular block in either of the first two circumstances indicated in Table 1. Most of the rest have evidence of sick sinus syndrome or chronic atrial fibrillation/flutter with associated bradycardia. Pacemaker technology and function The pacemaker box contains a battery (usually of lithium-iodide type) and microprocessors that contain both permanent and volatile memory. It is usually sited subcutaneously below the left clavicle with one or two leads passing current via electrodes to the myocardium and relaying information back to the box. All modern pacemakers exhibit a degree of programming ability via remote control that can enable alterations in pacing rate, energy output, sensitivity, mode of operation and other functions. Many also can relay information about rhythm, critical events and pacemaker function back to the operator. The current passing between anode and cathode will cause myocardial depolarisation if the energy applied exceeds the threshold for excitation of the local cells. Many factors will alter the energy required to exceed this threshold including fibrotic reactions around the catheter tip (commonly causing an increase in the threshold in the first 6 weeks after implantation). In addition, hypoxaemia, hypercarbia, acidosis, electrolyte abnormalites and drugs (especially anti-arrhythmics) may also influence the excitation threshold. Early pacemakers were unipolar with the electrode acting as a cathode and the pacemaker box Table 1 American College of Cardiology class I indications for permanent pacing Paul Diprose FRCS(A&E)Ed FRCA Specialist Registrar in Anaesthesia Royal Hampshire County Hospital Winchester, Hants SO22 5DG, UK JM Tom Pierce MRCP FRCA Consultant Cardiac Anaesthetist Shackleton Department of Anaesthesia Southampton General Hospital Tremona Road Southampton SO16 6YD, UK Acquired 3rd degree heart block associated with either bradycardia, other arrhythmias, periods of asystole, neuro-muscular disease, after catheter ablation of the AV junction Symptomatic acquired 2nd degree heart block, regardless of type and site Chronic bifascicular and trifascicular block may be the indications if 3 rd degree block occurs intermittently or if type II 2nd degree block occurs Post-myocardial infarction infranodal atrio-ventricular block and associated bundle branch block or persistent and symptomatic 2nd or 3rd degree heart block Sinus node dysfunction with symptomatic bradycardia and frequent sinus pauses or symptomatic chronotropic pauses Sustained ventricular tachycardia in which the efficacy of pacing has been documented thoroughly Hypersensitive carotid sinus syndrome Patients with hypertrophic cardiomyopathy or dilated cardiomyopathy who have sinus node dysfunction or atrioventricular block as described above After cardiac transplantation, if symptomatic bradyarrhythmias persist 166 British Journal of Anaesthesia CEPD Reviews Volume 1 Number The Board of Management and Trustees of the British Journal of Anaesthesia 2001

2 Table 2 The NASPE/BPEG Generic (NBG) Pacemaker Code Letter position I II III IV V Category Chamber paced Chamber sensed Response to sensing Programmability & Anti-tachyarrhythmia rate modulation functions Letters O = None O = None O = None O = None O = None A = Atrium A = Atrium T = Triggered P = Simple programmable P = Pacing V = Ventricle V = Ventricle I = Inhibited M = Multiprogrammable S = Shock D = Dual (A+V) D = Dual (A+V) D = Dual (T+I) C = Communicating D = Dual (P+S) R = Rate modulation acting as the anode. Modern systems are bipolar where the cathode and anode lie in close proximity. This has the effect of reducing the likelihood of electrical or environmental artefact disturbing pacemaker function. There are a number of ways that pacemakers can permit rate modulation. Commonly, this is via piezoelectric crystals measuring body vibration as a stimulus for an increased rate. However, these can be prone to respond to external vibration sources and its response to exercise is not always proportional to the intensity of the work performed. Their accuracy has been enhanced by the integrated use of accelerometers. Other forms of rate adaptation include sensors of minute ventilation, Q-T interval, temperature, oxygen saturation and myocardial contractility. Classification of pacemakers The North American Society of Pacing and Electrophysiology (NASPE) and the British Pacing and Electrophysiology Group (BPEG) have produced a generic code based on a system of five letters. The basic anti-bradycardia functions are described by the first three letters, the programmability (including rate modulation) by the fourth and any anti-tachycardia functions by the fifth (Table 2). It should be noted that the operator can program most modern pacemakers to many different modes. Problems and hazards in the hospital environment With the prevalence of more pacemakers with bipolar electrodes, the chances of interference from electromagnetic sources are much reduced. The pacemaker is further shielded inside a stainless steel or titanium case. However, the possible responses to external electromagnetic interference (usually of the radio frequency or microwave portion of the spectrum) include inappropriate inhibition/triggering of impulses, asynchronous pacing, reprogramming often to a backup mode (e.g. VOO) or permanent damage to the circuitry of the pacemaker. Mobile phones may represent one of these sources of electromagnetic interference and should not be placed directly over the device. However, there is no evidence of any clinically significant problems associated with their normal use in pacemaker patients. The most important source of potentially damaging electromagnetic radiation in hospitals is the magnetic resonance (MR) imaging scanner. MR imaging is contra-indicated in the patient with a pacemaker. Reported problems in patients who have been exposed to the investigation have included inhibition of pacing, rapid pacing induced by the radio frequency signal and heating of the electrode tip. Problems associated directly with surgery and anaesthesia Electromagnetic interference within the operating room will come principally from the use of monopolar diathermy. Generally, the pacemaker will respond to this interference with either inhibition (if the interference is sensed as cardiac activity) or will revert to a backup fixed rate mode (if overwhelming background noise is sensed). Lithotripsy may be used in patients with a pacemaker in situ, but the lithotriptor should be kept at least 6 inches away from the pacemaker. The lithotripsy pulses should be timed with the electrocardiogram and rate modulation should be de-activated. Patient positioning, shivering, alterations in heart size and positive pressure ventilation may all cause lead displacement which can result in loss of capture or increase in the pacing threshold. In addition, the shivering and fasciculation that may be associated with induction or emergence from anaesthesia can confuse rate modulators particularly those of the piezoelectric type. Peripheral nerve stimulators and transcutaneous electrical nerve stimulators (TENS) may potentially interfere with pacemaker function. However, in most circumstances, they are safe provided that the stimulator is placed a good distance away from the pacemaker and it is not in a vector parallel to that of the pacemaker current. Defibrillation is a theoretical cause of pacemaker reprogramming or damage. In practice, provided the defibrillating paddles are kept away from the pacemaker box, the risk of malfunction is slight. Anaesthetic management of the patient with a pacemaker Safe anaesthetic management of the patient with a pacemaker should start with a careful preoperative visit and review of the clinical records. Of particular note should be the original indication for pacemaker insertion, date of insertion and details of British Journal of Anaesthesia CEPD Reviews Volume 1 Number

3 recent follow-up pacemaker checks. The mode of action of the pacemaker should be noted. If the pacemaker has a rate modulator function, then this should be de-activated prior to anaesthesia. If the pacemaker can be switched between unipolar and bipolar modes, then the latter should be selected for the reasons discussed earlier. Direct enquiry from the patient may give clues as to recent pacemaker malfunction in terms of dizziness, syncope or heart failure. Almost certainly, these patients will have evidence of myocardial dysfunction. Any symptoms suggesting deterioration of the patients underlying heart disease should be managed aggressively before anaesthesia. Routine investigations Routine investigations should include the following: 1 12-lead ECG look for the underlying rhythm, any signs of pacemaker activity and evidence of electrical capture (i.e. intrinsic cardiac complexes following a pacing spike). 2 Chest X-ray this will show the position of the pacing box, the integrity of the leads and the position of the electrodes. Particularly important sites for lead fracture are at the junction with the pacing box, where the lead enters the subclavian vein or as the lead passes over the first rib. In addition, the chest X-ray may show evidence of cardiac failure. 3 Electrolytes electrolyte abnormalities may cause loss of capture and should be corrected pre-operatively. All monitoring should be attached prior to induction. ECG, pulse oximetry with plethysmography and non-invasive blood pressure monitoring are an absolute minimum. Serious consideration should be given to direct invasive arterial pressure monitoring to give additional beat-to-beat evidence of mechanical capture. Central venous catheters and pulmonary artery catheters may be used if indicated, but great care should be taken with their insertion if the pacemaker has been recently sited for fear of dislodging the electrodes and losing electrical capture. The technique of induction and maintenance of anaesthesia will depend upon the clinical circumstances. However, in general, the use of succinylcholine should be avoided to reduce the chances of over sensing following fasciculation. The risk of this problem is greater with unipolar pacing electrodes. Should succinylcholine need to be given to a patient with a sensor mode activated pacemaker, then a defasciculating dose of a non-depolarising agent should be given prior to its administration. Careful monitoring of the ECG is vital after any patient positioning or after commencement of mechanical ventilation to ensure that the pacemaker is still functioning appropriately. Diathermy If at all possible, only bipolar diathermy should be used during the operation. If unipolar diathermy must be used, then the diathermy and ground plate should be as far away from the pacemaker as possible and the current pathway from the forceps to plate should run at a right angle to the pacemaker leads. Additional pacing methods must be immediately to hand. Contingency plans For all patients undergoing anaesthesia, there should be some form of contingency plan in case of pacemaker dysfunction. Primitive but effective pacing can be achieved by regular thumps to the precordium (percussive pacing). Isoprenaline infusions may be used to improve rate and rhythm. However, the most rapid and effective backup system in most hospitals is non-invasive transthoracic pacing via external pads either positioned below the right clavicle and over the apex of the heart or over the left side of the chest in the antero-posterior position. Capture can usually be achieved at currents of about 80 ma. Alternatives to this include temporary transvenous and transoesophageal pacing, both of which will take longer to set up to achieve effective pacing. Magnets Magnets should NOT be placed over pacemakers during surgery. They have an unpredictable effect on the programming in modern pacemakers with potentially dangerous results. Previous advice to always have a magnet available, referred to a fixed rate magnet mode that some non-programmable pacemakers had in case of loss of sensing or over sensing. All modern pacemakers should be assumed to be programmable. Interestingly, there is a case report of pacemaker malfunction occurring after a magnetic sheet used for holding surgical instruments was placed over the box. The anaesthetist should be alert to any potential magnetic sources around the patient. Postoperative management Pacemaker function should be checked by technicians after the procedure, particularly if there have been any adverse events perioperatively. This will also permit the re-activation of rate modulation sensors and the re-institution of any specific pacing modes. New developments Pacemaker technology is improving all the time with improved battery efficiency and increasingly innovative ways of reducing battery use. The amount of retrievable volatile memory is also increasing. The potential indications for pacing are continuing to expand. Particular areas of interest at the moment are in the prevention of atrial fibrillation (an effect over and above that of just 168 British Journal of Anaesthesia CEPD Reviews Volume 1 Number

4 Table 3 The NASPE/BPEG Defibrillator (NBD) Code Position I II III IV Category Shock chamber Anti-tachycardia Tachycardia detection Anti-bradycardia pacing chamber pacing chamber Letters 0 = None 0 = None E = Electrocardiogram 0 = N one A = Atrium A = Atrium H = Haemodynamic A = Atrium V = Ventricle V = Ventricle V = Ventricle D = Dual (A&V) D = Dual (A&V) D = Dual (A&V) preventing the bradycardia associated with anti-arrhythmic treatment) and the treatment of congestive heart failure (by reducing mechanical atrio-ventricular dys-synchrony). Implantable cardioverter defibrillators The first implantable cardioverter defibrillator (ICD) was inserted in 1980 and they became commercially available by Since then, over 200,000 devices have been implanted world-wide. Initially bulky and capable of countershocks only, they have evolved into small sophisticated devices with multiple capabilities. Devices cost approximately 20,000 and implantation rates vary between countries (e.g. 17 per million per year in the UK, 197 per million per year in the US). Indications for insertion The National Institute for Clinical Excellence (NICE) has issued guidance advocating the increased use of ICDs to 50 per million per year, as pharmacological therapy alone provides insufficient suppression of clinically significant ventricular tachycardia (VT) or reduction in sudden cardiac death (SCD). In the UK, the indications for ICD insertion are similar to those of the Canadian Cardiovascular Society, who recommend ICD over drug therapy for: (i) ventricular fibrillation (VF) or SCD survivors; (ii) VT causing syncope not related to acute MI or other correctable causes; (iii) minimally symptomatic VT with left ventricular ejection fraction (LVEF) of <35%; (iv) patients with a previous myocardial infarction with LVEF <35%, asymptomatic spontaneous non-sustained VT with sustained VT/VF at electrophysiological study (EPS); (v) long QT syndrome with recurrent syncope or with a family history of SCD; (vi) the Brugada syndrome presenting with VT/VF or syncope with inducible VT at EPS; (vii) arrhythmogenic right ventricular dysplasia with documented sustained VT/VF or those with a family history of SCD; and (viii) hypertrophic cardiomyopathy with sustained VT/VF in the absence of a reversible cause or with a family history of SCD. Components, technology, implantation and magnet application An ICD includes a transvenous lead system with a pulse generator box containing a lithium iodide battery, capacitors and microprocessor memory to provide recent event chronology. In addition to the defibrillating function, ICDs may also have bipolar antibradycardia pacing (identical to permanent pacemakers) and anti-tachycardia pacing to pace-terminate VT. Once the heart rate exceeds a predetermined cut-off point for a predetermined detection time, a countershock is delivered. Various algorithms are incorporated to minimise inappropriate shocks (e.g. atrial sensing) to allow discrimination of SVT, AF and sinus tachycardia from VT. Programming is similar to permanent pacemakers. The vector of defibrillation is from right ventricle to both superior vena cava and the outer can of the pulse generator, i.e. the socalled triad configuration. The delivery of one shock shortens the battery life by 1 month. On average, lithium iodide batteries should operate for 5 9 years. There is no industry-wide standardization for the application of a magnet over an ICD. In the older devices, magnets would disable the defibrillation and anti-tachycardia functions. However, there can be an unpredictable effect to the application of a magnet with newer generation ICDs. There should be close consultation with the local cardiology services to determine whether a magnet may be of use during surgery. The combination of a magnet and diathermy has been shown to cause re-programming of ICDs. Classification Defibrillators are described by the NASPE/BPEG Defibrillator (NBD) Code (Table 3). Typically, the ICD code may be VVEV, i.e. ventricular shock chamber, ventricular anti-tachycardia chamber, ECG anti-tachycardia detection and ventricular anti-bradycardia pacing. The fourth letter may be replaced with the NBG Pacemaker code. In this example, VVE-VVIR. British Journal of Anaesthesia CEPD Reviews Volume 1 Number

5 Fig. 1 Schematic radiograph of an ICD.A, pulse generator box; B, tip of atrial sensing/pacing electrode; C, proximal defibrillation coil; D, distal defibrillation coil; E, ventricular bipolar sensing/pacing electrode. Environmental effects, problems and hazards The pacing leads are bipolar and less sensitive to external interference compared with unipolar leads. There are no reports of interference to countershock function from mobile telephones, although conventional wisdom states that they should not be placed over the ICD. MRI is contra-indicated and lithotripsy can cause damage. Anaesthetic management The indication for, and the history of, the ICD insertion and subsequent frequency of countershocks should be inquired into. Liaison with the ICD centre and interrogation of the device pre-operatively is valuable and should include the effect of magnet application. As with permanent pacemakers, many of these patients will have impaired left ventricular function. Anti-arrhythmic and anti-failure treatments should be continued and electrolyte abnormalities, including hypomagnesaemia, corrected pre-operatively. Other investigations should include ECG and chest X-ray (Fig. 1). The defibrillation and anti-tachycardia functions of the ICD should be de-activated pre-operatively if diathermy is to be used to avoid the ICD misinterpreting electrocautery as VF with a resultant counter shock. This is also particularly important in patients undergoing lithotripsy or electroconvulsive therapy. Patients should not receive TENS. The choice of anaesthetic technique and monitoring should be appropriate for the patient s medical and cardiac conditions and intended surgical procedure. Avoidance of stimuli known to aggravate arrhythmias (hypoxaemia, hypercapnia, acidosis, hypokalaemia) and myocardial depression is crucial. In the setting of poor LV function with VVI pacing, reliable pulse oximetry with plethysmography is mandatory in order to confirm mechanical capture. An external defibrillator should be available peri-operatively. Ideally, this should be attached to adhesive patches as this will permit external defibrillation without excessive disturbance of the operating field. If the vector of external applied defibrillation is perpendicular to the internal defibrillator electrodes, the ICD will be exposed to minimal induced current. In practice, this means cardiac apex to below the right clavicle. Resuscitative measures should follow the usual algorithms. Postoperatively, the patient should be managed in a highdependency area where continuous monitoring can be undertaken and full resuscitation equipment is to hand. ICD programming should be checked and verified after surgery and the device reactivated. Future developments ICDs capable of defibrillating atrial tachydysrhythmias and, more recently, atrial and ventricular defibrillators have become available. The results of on-going and future trials may widen the indications for ICD implantation. Acknowledgements The authors gratefully acknowledge the assistance of Dr Paul Roberts (Fellow in Cardiology) for his guidance with the manuscript and the Medical Illustration and Photographic Services, Southampton General Hospital for the figure. Key references Bourke ME. The patient with a pacemaker or related device. Can J Anaesth 1996; 43: Deroy R,Graham TR.Pacemakers and anaesthesia.curr Anaesth Crit Care 1995; 6: Glikson M, Hayes DL. Cardiac pacing a review. Med Clin North Am 2001; 85: Kam PCA. Anaesthetic management of a patient with an automatic implantable cardioverter defibrillator in situ. Br J Anaesth 1997; 78: See multiple choice questions British Journal of Anaesthesia CEPD Reviews Volume 1 Number