Simulation of Intraoperative Pacemaker Failure

DEMOGRAPHICS Patient Name: Peter Forrester Simulation Developer: Louie Wang, MD Date of Development: Friday, March 15, 2013 Target Audience: Staff anesthesiologists, junior and senior anesthesia residents, and CRNAs CURRICULAR INFORMATION Educational Rationale Nearly 3 million patients worldwide have an implanted pacemaker, and this number is increasing.1 It is not uncommon for a patient with a pacemaker to require surgery. There has been a proliferation of increasingly sophisticated implantable cardiac rhythm devices from various vendors, resulting in a wide diversity of functions. Although pacemakers are generally reliable, a malfunction rate of 0.4% has been reported.2 Electromagnetic interference (EMI) is known to cause problems with pacemaker function. Sources of EMI include the use of electrocautery during surgery, the magnetic field used in magnetic resonance imaging, and the electrical energy delivered from a defibrillator. In addition, acute intraoperative events such as myocardial ischemia, arrhythmias, acid-base imbalance, and electrolyte abnormalities may affect pacemaker function.3 The perioperative management of patients with these devices should be a collaborative process with the patients’ cardiac rhythm devices clinic or physician because of their increased complexity in management; however, these services may not be available after hours or in all locations 4. Thus, an understanding of pacemakers is important for learners in anesthesiology. Learning Objectives During this simulation session, the learner should demonstrate the following Royal College of Physicians and Surgeons of Canada CanMEDS core competencies: medical expert, communicator, collaborator, and scholar. By the end of the session, the learner will be able to: Preoperatively assess and optimize a patient with an implanted pacemaker Identify the patient who is pacemaker dependent Recognize the problems that EMI causes in a patient with an implanted pacemaker Diagnose and manage pacemaker-mediated tachycardia in a team setting Diagnose and manage failure of pacemaker capture in a team setting Safely administer a defibrillating shock to a patient with a pacemaker Actively participate in the debriefing process in a reflective, open, and respectful manner Guided Study Questions What preoperative laboratory and diagnostic studies are required for a patient with a pacemaker? Describe the intraoperative problems that may occur with rate-responsive pacemakers. What is an acceptable time from the last pacemaker interrogation before surgery? Under what conditions should a pacemaker be reprogrammed before surgery? How can one determine whether a patient is pacemaker dependent or not? What is the effect of placing a magnet on a pacemaker? What problems does EMI cause for pacemakers? What is the pathophysiology of pacemaker-mediated tachycardia? What are the causes of failure of pacemaker capture? Where should external pads be placed for defibrillation in a patient with a pacemaker? PREPARATION Location and Additional Information The scenario occurs in the orthopedic operating room with an anesthesia machine that has already undergone a machine check (Table 1). The mannequin is lying supine on the operating table and has 1 large bore intravenous line connected. An implantable pacemaker is simulated by a 2-to 3-inch diameter jar top cover placed under the mannequin’s outer skin an inch inferior to the left clavicle. Standard monitors (electrocardiography [ECG], noninvasive blood pressure cuff, and pulse oximeter) are in place. Airway equipment, standard anesthetic drugs, and intravenous fluids are available on the anesthetic cart.TABLE 1: Simulator Programming NotesAV sequential pacing can be simulated on the Laerdal SimMan 3G mannequin (Instructor Application software version 2.3 ver 020301\ build 12578). From the main control window of the Instructor Application, select the “Cardiac Controls” tab. Select the “Running” button, and the “Edit Running Rhythm” window will pop up. Locate the “Basic Rhythm” section, and scroll through until you find “Pacemaker A-V Seq.” Select the desired rhythm, set the heart rate using the “Heart Rate” slider bar, and then select “OK.” Monitors ECG Noninvasive blood pressure (BP) cuff Pulse oximeter Arterial line Central venous pressure Pulmonary artery catheter One peripheral intravenous line Other Equipment Anesthesia machine Infusion pump Defibrillator with cardiac arrest cart Magnet Electrocautery External air warmer and blanket Support Files Preoperative 12-lead ECG showing an AV sequentially paced rhythm (Fig. 1) FIGURE 1: Preoperative 12-lead ECG showing an AV sequentially paced rhythm.Actors Anesthesia assistant Circulating nurse Surgeon Time Duration Set-up: 10 minutes Simulation: 20 minutes Debrief: 15 minutes Case Stem You are providing a spinal anesthetic for a 75-year-old man undergoing a right total knee arthroplasty for osteoarthritis. He has a history of type 2 diabetes mellitus, hypertension, and an inferior myocardial infarction with subsequent triple coronary artery bypass grafting performed in 2000. In 2010, he presented to the hospital with presyncopal symptoms and was found to be in complete heart block. A DDDR pacemaker was inserted at that time. The pacemaker was found to be functioning normally on routine check 2 months ago. The patient was noted to be in a paced rhythm with an intrinsic rhythm of third degree AV block at 40 beats per minute. The consult letter from the cardiac rhythm devices Clinic recommends placing a magnet on the pacemaker if necessary during surgery, which will cause the pacemaker to pace in DOO mode at 80 beats per minute. Functional status is limited to less than 4 METS because of knee pain. Preoperative echocardiogram shows inferior akinesis, left ventricular ejection fraction of 45%, mild mitral regurgitation, mild aortic stenosis, and a patent foramen ovale. You have successfully placed a spinal anesthetic, and surgery is about to begin. Background and Briefing Information for Instructor’s Eyes Only This scenario involves a patient undergoing total knee arthroplasty who is pacemaker dependent. It is composed of 4 separate modules originating from a common stem: (a) cautery inhibition of the pacemaker, (b) pacemaker-mediated tachycardia caused by shivering, (c) loss of pacing capture, and (d) ventricular fibrillation arrest. It is recommended that the scenario focus on the first 2 modules for junior learners and the third and/or fourth modules can be added for more senior learners. Electromagnetic interference from the use of cautery in the operating room can lead to numerous problems. Electromagnetic interference can be sensed by the pacemaker, which can lead to inappropriate inhibition, asynchronous pacing, or resetting of the pacing mode.5 Electromagnetic interference has also been reported to cause direct myocardial injury and damage to the leads and device. The use of bipolar cautery can minimize the risk. If monopolar cautery is necessary, the current path should not cross the leads or generator, and the anode pad should be placed as far as possible from the pacemaker. To simulate the use of cautery during the scenario, the cautery machine should be set up to make a noise when in use. and the confederate surgeon should provide verbal cues that cautery is in use (eg, ask the confederate circulating nurse to increase the output of the cautery). Pacemaker-mediated tachycardia can develop in a patient who has a rate-responsive pacemaker. There are a variety of rate-responsive sensors including activity sensors, minute ventilation sensors, QT interval sensors, and contractility sensors.4 Perioperative events such as the use of an oscillating saw, excess patient movement, patient shivering, and mechanical ventilation may inadvertently trigger pacemaker-mediated tachycardia by activating the sensors.6 In addition, there are reports of tachycardia resulting from the interaction of minute ventilation sensor pacemakers and cardiac monitoring devices that measure respiratory rate.7,8 The increase in heart rate may be confused with light anesthesia and lead to inappropriate management. Other causes of pacemaker-mediated tachycardia include the following9: Presence of EMI Development of a reentrant loop in a patient with a dual chamber pacemaker Pacemaker tracking of an atrial tachyarrhythmia. To simulate shivering during the scenario, the mannequin should verbalize feeling cold and shivery, and the confederate circulating nurse should note that the mannequin is cold and shivering and suggest placing an external air warmer and blanket. There are several reasons for loss of pacemaker capture. Mechanical problems are unusual and include generator, battery, or lead malfunction. Myocardial causes result from events that lengthen the refractory period or increase the energy requirement for depolarization. These include myocardial ischemia or infarction, acid-base disturbances, electrolyte abnormalities, and abnormal levels of antiarrhythmia drugs.3 Management includes treatment of the underlying problem or reprogramming of the pacemaker. It may be necessary to replace the leads or the hardware or use the external pacing pads in some instances. Delivery of a defibrillating shock may damage or reprogram the pacemaker. To minimize the risk, the external pads should be placed in the anteroposterior positions so that the current is orthogonal to the leads and does not cross the battery pack.4,10 The pacemaker should be interrogated following the administration of an electrical shock. Debriefing Points Preoperative assessment4 Identify the type of device (pacemaker, implantable cardioverter-defibrillator (ICD), cardiac resynchronization device) and programming parameters. Identify and contact the patient’s cardiac rhythm devices clinic or physician. If unavailable: Review the patient’s medical chart and device identification card for information on the make and model of the pacemaker. All cardiac rhythm device manufacturers provide 24-hour technical support services. The presence of a shocking coil(s) on a chest radiograph distinguishes an ICD from a pacemaker. Characteristics of the device may also be seen to assist in identifying the make and model. Determine pacemaker dependency: The patient is unlikely to be highly pacemaker dependent if the ECG demonstrates an intrinsically conducted rhythm. Conversely, it is safest to assume the patient to be highly pacemaker dependent if the ECG demonstrates a paced rhythm all the time, in the absence of contrary information. Estimate the likelihood of EMI and pacemaker complications. Effect of a magnet placed over the pacemaker4: The device response to a magnet is manufacturer and model specific. Most modern pacemakers, but not all, will pace in an asynchronous mode. Effect is terminated immediately upon the removal of magnet. Rare incidences of device reprogramming associated with end-of-life battery condition, magnet movement, and EMI. Application of a magnet over an ICD will suspend tachyarrythmia detection and treatment (except when this function is programmed off) but does not modify the pacing mode of the device. Effect of electromagnetic interference (from cautery) on pacemaker function: Inappropriate inhibition Asynchronous pacing Reprogramming of device Damage to leads, generator Myocardial injury 2. Pros and cons of asynchronous pacing: Pro Avoid inappropriate inhibition by electromagnetic interference. Con Competition between paced and intrinsic rhythm may lead to symptomatic palpitations. Potential to induce arrhythmias including ventricular fibrillation. 4. Pathophysiology and management of pacemaker-mediated tachycardia: Perioperative events such as shivering, patient movement, mechanical ventilation, and attachment of some models of cardiac monitoring devices that measure respiratory rate cause inappropriate activation of sensors in patients with rate-responsive pacemakers. In DDD mode, atrial tachyarrhythmias can lead to pacemaker-mediated tachycardia. EMI from cautery and other sources. Development of a reentrant loop in patients with dual-chamber pacemakers. Management includes placing a magnet on the pacemaker, reprogramming the pacemaker, and treating the underlying arrhythmia. 5. Loss of pacemaker capture differential diagnosis: Myocardial ischemia Electrolyte abnormalities Acid-base imbalance Abnormal levels of antiarrhythmia drugs Hardware failure Lead failure 6. Defibrillation and pacemakers: Potential damage to pacemaker hardware. External pads should be placed in anteroposterior positions to minimize current transmission through leads or through the hardware. Need to interrogate the pacemaker following delivery of shock. PATIENT DATA BACKGROUND AND BASELINE STATE Review of Systems Central nervous system: alert and oriented, no distress Respiratory: normal Cardiovascular: as above Renal/hepatic: normal Gastrointestinal: normal Endocrine: type 2 diabetes mellitus Hematology/coagulation: normal Medications and Allergies Medications: metformin, glyburide, atorvastatin, ramipril, hydrochlorthiazide, ASA Allergies: eggs, shellfish Social History Forty pack year smoking history, quit in 2000. Social alcohol. Physical Examination Height and weight: 176 cm, 80 kg Vital signs: BP, 150/80; heart rate (HR), 70 (paced); SaO2, 97 General: alert and oriented, no distress Respiratory: clear breath sounds Cardiovascular: S1 and S2 normal, 2/6 systolic ejection murmur Abdominal: normal Laboratory Tests and Diagnostic Studies Complete blood cell count: hemoglobin 13.9 g/dL (139 g/L); white blood cell count, 5.7 x 103/µL; platelets, 220/µL Coagulation: international normalized ratio, 1.2; partial thromboplastin time, 29 seconds Electrolytes: Na, 139 mEq/L; K, 3.4 mEq/L; HCO3, 24 mEq/L; creatinine, 1.2 mg/dL (105 µmol/L) ECG: as attached

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