Fu Wai Cardiovascular Hospital, Cardiac Arrhythmia Center
Hua Wei, Wang Huan, Liu Zhimin, Wang Jing, Fan Xiaohan, Chen Ke Ping, Zhang Shu
Huawei, Department of Cardiovascular Medicine, Fu Wai Hospital, Beijing
The SureScan™ Pacing System (Medronic, Minnesota, USA) is a new pacing system for MRI examinations, which has been approved by FDA and marketed in the United States and approved by SFDA in China. FW Hospital has recently implanted this pacing system in two patients, which is the first case in China, and is summarized as follows.
Case 1: Male, 66 years old. He was admitted to the hospital with shortness of breath after activity for 4 years, which was aggravated for more than 2 months. After admission, the electrocardiogram indicated junctional zone escape with a heart rate of 55 beats/min. The 24-hour ambulatory electrocardiogram indicated sinus rhythm, junctional zone escape heart rate, intermittent 2nd degree sinus block with an average heart rate of 55 beats/min and a slowest heart rate of 40 beats/min (at night). The diagnosis was “restrictive cardiomyopathy, mitral valve prolapse (moderate to severe), mitral valve insufficiency (severe), tricuspid valve insufficiency (moderate), aortic valve insufficiency (mild), pulmonary hypertension (moderate), cardiac enlargement, arrhythmia, atrial flutter, intermittent second-degree sinus block, ventricular precontraction, short-onset ventricular tachycardia, junctional zone escape, complete right bundle branch block, cardiac function class II, hypertension class 3 (very high risk), and history of hyperlipidemia”. After admission, a consultation concluded that the patient had an indication for permanent pacemaker implantation.
Case 2: Male, 73 years old. He was admitted to the hospital with episodes of syncope for 8 days. The patient was diagnosed with third-degree atrioventricular block at a local hospital and was admitted to our hospital on an emergency basis after implantation of a temporary pacemaker. The patient had a previous history of hypertension for more than 10 years. He was admitted with the diagnosis of “arrhythmia, high degree AV block, post temporary pacemaker implantation, coronary artery disease, hypertension, and type 2 diabetes mellitus”. The patient’s indication for permanent pacemaker implantation was clear.
Considering that both patients were elderly males at risk of cerebrovascular accidents and might require MRI in the future, a regular pacemaker was a contraindication to MRI examinations. Therefore, Medtronic’s SureScan™ pacing system was implanted. On August 1, 2011 and August 2, 2011, respectively, the SureScan™ pacemaker was implanted under local anesthesia. The right subclavian vein was punctured with a conventional sterile towel and two 5086 CapSureFix MRI™ (Medronic, Minnesota, USA) active fixation electrodes were delivered and fixed to the right auricle and right ventricular outflow tract, respectively (see Figure 1). The leads and pacemakers are connected, the capsular bag is prepared, and the EnRhythm MRI™ SureScan™ pacemaker is placed. The wound is sutured. The patient was returned to the ward postoperatively.
Discussion: Epidemiological studies have shown that patients over 65 years of age are twice as likely to require MRI than younger patients1, while Kalin et al. showed that about 85% of pacemaker implant patients have more than 1 comorbidity and require a complete physical examination, and about 50-70% of pacemaker implant patients will require MRI during their lifetime2. Sakakibara et al3 showed that 17% of pacemaker implanted patients required MRI during the 1-year follow-up period. However, almost all major implantable pacemaker manufacturers’ websites list MRI as a contraindication and recommend avoiding MRI scans. The American College of Radiology (ACR) and the Radiological Society of North America (RSNA) warn that the magnetic fields generated by MR systems can cause pacemakers to malfunction and pose a direct risk to patients.
The effects of MRI on conventional pacemakers include the following: 1. It affects the pacemaker’s perception function, causing it to misperceive and inhibit the delivery of electrical stimulation, which can be life-threatening for pacemaker-dependent patients (see Figure 2), or it can cause the pacemaker to not perceive and deliver asynchronous stimulation signals, which can induce ventricular tachycardia or ventricular fibrillation. implanted patients underwent a total of 59 MRI examinations, with no change in pacing threshold before and after the examinations, but a small decrease in perceived amplitude and impedance; 7 scans showed significant ventricular asynchrony (>20 beats); 2. MRI magnetic fields may cause electrical resetting of the pacemaker. In the study by Sommer5 et al. 6.1% (7/115) of patients showed electrical resetting of the pacemaker after MRI. 3.1% (6/195) of leads showed an increase in pacing threshold; 3. The thermal effect of the MRI magnetic field may increase the temperature of the lead head end, damage the myocardium, increase the lead pacing threshold, and in severe cases may lead to myocardial perforation.Sommer6 et al. reported that in a magnetic field environment of 0.5 T, the temperature at the head end of the pacemaker lead can increase up to 8.9 °C at a SAR of 0.6 W/kg, and up to 23.5 °C at a SAR of 1.3 W/kg. This is bound to cause damage to the surrounding myocardium.4 In addition, magnetic fields can cause mechanical failures in pacemakers, such as: alternating magnetic field-mediated currents resulting in This can lead to poor sensing, poor pacing, damage to mechanical integrity due to magnetically generated torque or overheating of the housing, interference with program operation or electrical resetting due to alternating magnetic fields, damage to circuitry/components, dislocation of leads due to magnetic field-mediated vibration/magnetic forces, and mechanical damage to the housing. Thus, for patients with permanent pacemakers, the risks associated with MRI can be dangerous and fatal. The question of whether clinicians should aggressively implant pacemakers in patients who are likely to undergo MRI examinations is a troubling one for clinicians.
The SureScan™ Pacing System consists of the EnRhythm MRI™ SureScan™ Pacemaker and the 5086 CapSureFix MRI™ Electrode. The pacemaker effectively controls the reed switch to prevent electrical resetting due to electromagnetic interference and to reduce heating of the electrode leads due to RF fields (cross-conversion fields). The electrodes have been redesigned to reduce the interaction of the electrodes with the gradient magnetic field of MRI and the RF field, and to reduce the heating of the leads. Therefore, the entire pacing system is able to work properly in the MRI magnetic field environment. In a multicenter, randomized clinical study, 464 patients were implanted with the SureScan pacing system and randomized to either MRI scans (MRI group) or no MRI scans (control group) with MRI at the commonly used, clinically indicated scan intensity of 1.5T for a follow-up of 11.2 ± 5.2 months. The results of the study showed that the SureScan™ pacing system proved to be safe for MRI examinations in patients, with no MRI-related complications at all (n = 211, p < 0.001).9 While Sommer et al.7 reported no significant difference in lead pacing thresholds between the MRI-scanned and no MRI-scanned groups at the 4-month follow-up after the patients had undergone MRI. Certain conditions must be met to undergo MRI after implantation of the SureScan™ pacing system, starting with the implantation of both the EnRhythm MRI™ SureScan™ pacemaker and the accompanying 5086 CapSureFix MRI™ pacing electrode, in addition to the patient receiving an MRI scan 6 weeks after implantation of the pacemaker, with the pacemaker implanted in the chest, with a pacing threshold < 2.0 V @ 0.4 ms, and with a lead impedance between 200 and 1,500ohms, and the MRI SureScan mode must be programmed on.
The SureScan™ pacing system is the first safe pacing system under MRI to receive CE and FDA approval. For patients over 65 with indications for pacemaker implantation who have risk factors for stroke: hypertension, diabetes, etc., or a history of osteoarthritis, spine-related diseases and associated tumor risk factors, the possibility of MRI scanning after pacemaker implantation should be considered. The implantation of MRI-resistant pacing systems is recommended for such patients because of the possibility of MRI scans after pacemaker implantation. In addition, preimplantation of MRI-resistant pacing systems may be considered in patients with a history of MRI prior to pacemaker implantation or in younger patients in good general condition who require pacemaker support for the rest of their lives.