Safe performance of magnetic resonance of the heart in patients with magnetic resonance conditional pacemaker systems: the safety issue of the ESTIMATE study

Background

No published data exist about the safety of diagnostic magnetic resonance (MR) of the heart performed in a larger series of patients implanted with MR conditional pacemakers (PM). The purpose of our study is to analyse safety and potential alterations of electrical lead parameters in patients implanted with the EnRhythm/Advisa MRI SureScan PM with 5086MRI leads (Medtronic Inc.) during and after MR of the heart at 1.5 Tesla.

Methods

Patients enrolled in this single center pilot study who underwent non-clinically indicated diagnostic MR of the heart were included in this analysis. Heart MR was performed for analyses of potential changes in right and left ventricular functional parameters under right ventricular pacing at 80 and 110 bpm. Atrial/ventricular sensing, atrial/ventricular pacing capture threshold [PCT], and pacing impedances were assessed immediately before, during, and immediately after MR, as well at 3 and 15 months post MR.

Results

Thirty-six patients (mean age 69 ± 13 years; high degree AV block 18 [50%]) underwent MR of the heart. No MR related adverse events occurred during MR or thereafter. Ventricular sensing differed significantly between the FU immediately after MR (10.3 ± 5.3 mV) and the baseline FU (9.8 ± 5.3 mV; p < 0.05). Despite PCT [V/0.4ms] was not significantly different between the FUs (baseline: 0.84 ± 0.27; in-between MR scans: 0.82 ± 0.27; immediately after MR: 0.84 ± 0.24; 3-month: 0.85 ± 0.23; 15-month: 0.90 ± 0.67; p = ns), 7 patients (19%) showed PCT increases by 100% (max. PCT measured: 1.0 V) at the 3-month FU compared to baseline. RV pacing impedance [Ω/5V] differed significantly at the FU in-between MR scans (516 ± 47), and at the 15-month FU (482 ± 58) compared to baseline (508 ± 75).

Conclusion

The results of our study suggest MR of the heart to be safe in patients with the MR conditional EnRhythm/Advisa system, albeit although noticeable but clinically irrelevant ventricular PCT changes were observed.     

Cardiac biomarkers in patients with permanent pacemakers and implantable cardioverter-defibrillators undergoing an MRI scan

Background: Recent series suggest that magnetic resonance imaging (MRI) scanning can be performed safely in select patients with pacemakers or implantable cardioverter‐defibrillators (ICDs). Limited data have been reported on cardiac biomarker release following MRI scans in patients with pacemakers. The current study evaluated cardiac biomarkers pre‐ and postscan in patients with permanent pacemakers or ICDs undergoing MRI scanning of any body region without peak specific absorption rate (SAR) limit. Methods: Thirty‐seven patients with a total of 75 leads underwent a total of 40 MRI scans of both truncal and nontruncal regions using usual protocols with standard peak SAR settings for the scan. No patient was pacemaker dependent. Pacemaker magnet mode and ICD therapy were disabled during the scan. Baseline cardiac troponin‐I and myoglobin levels were obtained immediate pre‐ and 6–12 hours postscan. Pacemaker capture thresholds were measured immediately pre‐ and postscan. Results: The median peak SAR was 2.4 (1.3, 3.2) W/kg for all scans. Cardiac troponin‐I was unchanged following an MRI scan (0.01 (0.01, 0.02) versus 0.01 (0.01, 0.02) ng/mL, P = 0.90). Capture thresholds were no different pre‐ and postscan (0.67 (0.50, 0.80) versus 0.70 (0.50, 0.79) V at 0.5 ms, P = 0.50). Conclusions: The current series suggests that an MRI scan may be performed safely in carefully selected patients with close monitoring during the scan without limitation on peak SAR level or body landmark. Furthermore, it is unlikely that an MRI scan will produce sufficient tissue heating to cause enough myocardial cell necrosis to result in cardiac biomarker release.     

Force and torque effects of a 1.5-Tesla MRI scanner on cardiac pacemakers and ICDs

Magnetic resonance imaging (MRI) is a widely accepted tool for the diagnosis of a variety of disease states. However, the presence of an implanted pacemaker is considered to be a strict contraindication to MRI in a vast majority of centers due to safety concerns. In phantom studies, the authors investigated the force and torque effects of the static magnetic field of MRI on pacemakers and ICDs. Thirty-one pacemakers (15 dual chamber and 16 single chamber units) from eight manufacturers and 13 ICDs from four manufacturers were exposed to the static magnetic field of a 1.5-Tesla MRI scanner. Magnetic force and acceleration measurements were obtained quantitatively, and torque measurements were made qualitatively. For pacemakers, the measured magnetic force was in the range of 0.05-3.60 N. Pacemakers released after 1995 had low magnetic force values as compared to the older devices. For these devices, the measured acceleration was even lower than the gravity of the earth (< 9.81 N/kg). Likewise, the torque levels were significantly reduced in newer generation pacemakers (< or = 2 from a scale of 6). ICD devices, except for one recent model, showed higher force (1.03-5.85 N), acceleration 9.5-34.2 N/kg), and torque (5-6 out of 6) levels. In conclusion, modern pacemakers present no safety risk with respect to magnetic force and torque induced by the static magnetic field of a 1.5-Tesla MRI scanner. However, ICD devices, despite considerable reduction in size and weight, may still pose problems due to strong magnetic force and torque.     

In vitro determination of cardiac ventricular volumes using MRI at 1.0 T in a porcine heart model

Purpose: To determine the accuracy of a 1.0 T MR system with a standard gradient system for quantification of left and right ventricular volumes. A porcine heart model in vitro was used. Methods: In eight explanted porcine hearts the atria were removed and the aorta and the pulmonary truncus were cannulated. Defined volumes were injected into the ventricles. Magnetic resonance imaging (MRI): FFE-EPI (Multishot EPI) was used. Papillary muscles and trabeculae were excluded. True volumes and MR measurements were analysed separately for both ventricles and by both investigators. Results: The correlation of the true volumes and MR measurements was > 0.99. MRI was found to be investigator independent in assessing right and left ventricular volumes in vitro. Conclusions: MRI at 1.0 T using standard equipment can be used to quantitate cardiac ventricular volumes in vitro with high accuracy.     

Transthoracic pacing in cardiac asystole

A total of 139 patients had transthoracic pacemakers introduced via a subxiphoid approach for asystole during advanced CPR in the emergency department of a large urban teaching hospital over a calendar year. Two groups were examined retrospectively, A) 34 patients who presented asystolic, and B) 99 patients who presented with ventricular fibrillation that became asystole. Age, sex, and etiologies for cardiac arrest were similar in both groups; there were no survivors. The mean duration of asystole before pacemaker insertion was 4 min (group A) to 7 min (group B). Temporary electrical capture was obtained in six patients from group B, but electrical-mechanical association could not be achieved in any of these patients.     

Ectopy in Patients with Permanent Pacemakers and Implantable Cardioverter-Defibrillators Undergoing an MRI Scan

Background: Recent series suggest that magnetic resonance imaging (MRI) scanning can be performed safely in select patients with pacemakers or implantable cardioverter-defibrillators (ICDs). Limited data have been reported on ectopy during MRI scans in patients with pacemakers or ICDs. This study evaluated increased ectopy observed in patients with permanent pacemakers or ICDs undergoing MRI scanning of any landmark without peak specific absorption rate (SAR) limit.
Methods: Fifty-two patients with a total of 119 leads underwent a total of 59 MRI scans of any landmark using usual protocols with standard peak SAR settings for the scan. No patient was pacemaker dependent. All devices were programmed to single-chamber demand mode (VVI) or dual-chamber demand mode (DDI) with a lower rate of 40 bpm. Both telemetry and pulse oximetry plethysmographic waveform were observed continuously throughout the scans for ectopy.
Results: Increased ectopy was observed during seven scans. The ectopy in four scans was ventricular and had fixed coupling intervals of 1,500 and 3,000, and was likely due to device noise rejection behavior. The etiology of ectopy observed during the other three scans could not be determined. Ectopy could not be predicted by peak SAR, scan time duration, or landmark. No significant changes in pacing thresholds were seen postscan.
Conclusions: The current series suggests that a minority of patients with implanted pacemakers may have MRI-related ectopy. A significant proportion of this ectopy may arise from normal device behavior within the MRI environment.     

Pacing in high field cardiac magnetic resonance imaging:

Currently, cardiac MRI is contraindicated in patients with an implanted pacemaker or ICD due to safety hazards. However, MRI is promising to play a key role in cardiac diagnostics in near future. This study examined a rat with an implanted pacemaker pacing at a rate of 460/min with high field cardiac MRI. This study showed that pacing during cardiac imaging at 7 Tesla was possible. The pacemaker program was not disturbed by the high field or the strong gradients (maximum dB/dt 400 mT/s). The only noticeable effect on the MRI signal was a signal void of 2 cm around the device.     

心脏起搏器的历史进程及变迁

自1958年植入世界首例埋藏式人工心脏起搏器,50余年来心脏起搏器的进展日新月异.心脏起搏器不论从体积、使用寿命,还是性能、治疗领域全朝着轻巧、耐用、生理等方面发展.本文对心脏起搏器的发展史及起搏器技术的进展进行综述.     

Effects of transvenous pacing on cardiac troponin release

Cardiac troponins are invaluable tools for the detection of minimal myocardial injury. No study to date has analyzed the effect of permanent cardiac pacing on minimal myocardial injury detection by cardiac troponin I (cTnI) measurement. We investigated 76 clinically stable patients (mean age 75 years, range 31-93 years, 59% men) listed for elective endocardial permanent pacemaker insertion. Patients were required to have normal levels of cardiac cTnI, aspartate transaminase (AST) and creatinine kinase (CK) on a venous blood sample taken immediately prior to elective pacemaker implantation. Repeat measurements of AST, CK, and cTnI were performed at a mean of 19.2 post implantation. There was a detectable small rise in cTnI levels above normal in 21% of patients in a second blood sample taken 18-21 hours later (mean cTnI 0.39 +/- 0.37 microg/L, normal < 0.15 microg/L). The only factor that correlated with this rise was prolonged x ray screening time for lead implantation.     

Current clinical issues for MRI scanning of pacemaker and defibrillator patients

Dramatic increases in both magnetic resonance imaging (MRI) usage and cardiac device-based therapy have resulted in an estimated 50-75% probability of a patient being indicated for an MRI over the lifetime of their device. Some recent studies have demonstrated "safe procedures" and "no adverse events" in the limited populations, clinical situations, and specific devices and lead orientations tested. While these investigations are useful to help ascertain the hazards for patients with cardiac devices, they do not demonstrate clear freedom from risk. All components of active implantable systems must be engineered during the design stage to provide safety in current and evolving MR environments. Device manufacturers need to secure regulatory approval to confirm their products' safety under multiple clinical and technical variables.     

Long-term mortality and pacing outcomes of patients with permanent pacemaker implantation after cardiac surgery

Background: Approximately 20,000 permanent pacemakers (PPMs) are implanted annually for bradycardia or atrioventricular (AV) block after cardiac surgery. Little is known about the long‐term pacing and mortality outcomes and the temporal trends of these patients. Methods: We examined 6,268 consecutive patients who underwent cardiac surgery at the Minneapolis Veterans Administration Medical Center between 1987 and 2010. Patients who had a PPM within 30 days of cardiac surgery were identified. Pacemaker interrogation records were retrospectively reviewed and mortality was ascertained. Results: Overall, 141 (2.2%) patients underwent PPM implantation for high‐degree AV block (55%) and bradycardia (45%), 9 ± 6 days after surgery. Age, diuretic use, cardiopulmonary bypass time (CPBT), and valve surgery were independent predictors of PPM requirement. After 5.6 ± 4.2 years of follow‐up, 40% of the patients were PPM dependent. Longer CPBT (P = 0.03), PR interval >200 ms (P = 0.03), and QRS interval > 120 ms (P = 0.04) on baseline electrocardiogram predicted PPM dependency . In univariable analysis, PPM patients had a higher long‐term mortality than those without PPM (45% vs 36%; P = 0.02). However, after adjusting for age, sex, type of surgery, and CPBT, PPM requirement was not associated with long‐term mortality (hazard ratio 1.3; 95% confidence interval 0.9–1.9; P = 0.17). Compared to before, incidence of PPM implantation increased after the year 2000 (1.9% vs 2.6%; P = 0.04). Conclusion: The majority of patients who require PPM after cardiac surgery are not PPM dependent in the long term. Requiring a PPM after surgery is not associated with long‐term mortality after adjustment for patient‐related risk factors and cardiac surgical procedure. (PACE 2011; 34:331–338)     

Interference with Cardiac Pacemakers by Magnetic Resonance Imaging: Are There Irreversible Changes at 0.5 Tesla?

VAHLHAUS, C., et al. : Interference with Cardiac Pacemakers by Magnetic Resonance Imaging: Are There Irreversible Changes at 0.5 Tesla? The safety and feasibility of magnetic resonance imaging (MRI) in patients with cardiac pacemakers is an issue of gaining significance. The effect of MRI on patients' pacemaker systems has only been analyzed retrospectively in some case reports. Therefore, this study prospectively investigated if MRI causes irreversible changes in patients' pacemaker systems. The effect of MRI at 0.5 Tesla on sensing and stimulation thresholds, lead impedance and battery voltage, current, and impedance was estimated during 34 MRI examinations in 32 patients with implanted pacemakers. After measurements at baseline and with documentation of intrinsic rhythm and modification of the pacing mode, patients underwent MRI. The rest of the function time of the pacemaker was calculated. Measurements were again performed after 99.5 ± 29.6 minutes (mean ± SD), immediately after MRI examination, and 3 months later. Lead impedance and sensing and stimulation thresholds did not change after MRI. Battery voltage decreased immediately after MRI and recovered 3 months later. Battery current and impedance tended to increase. The calculated rest of function time did not change immediately after MRI. MRI affected neither pacemaker programmed data, nor the ability to interrogate, program, or use telemetry. Surprisingly, in the gantry of the scanner, temporary deactivation of the reed switch occurred in 12 of 32 patients when positioned in the center of the magnetic field. Missing activation of the reed switch through the static magnetic field at 0.5 Tesla is not unusual. MRI at 0.5 Tesla does not cause irreversible changes in patients' pacemaker systems.     

多参数心脏MRI用于急性心肌炎进展

心肌炎临床表现多样,可发展为急性心力衰竭、心源性休克和慢性扩张型心肌病,早期明确诊断对于改善预后至关重要。心脏MRI(CMRI)可显示心肌坏死、纤维化和水肿,已成为评估心肌炎的最佳影像学手段。本文就多参数CMRI用于急性心肌炎研究进展进行综述。     

Clinical validation of an automated boundary tracking algorithm on cardiac MR images

The goal of this research was to develop an automated algorithm for tracking the borders of the left ventricle (LV) in a cine-MRI gradient-echo temporal data set. The algorithm was validated on four patient populations: healthy volunteers and patients with dilated cardiomyopathy (DCM), left ventricular hypertrophy (LVH), or left ventricular aneurysm (LVA). A full tomographic set (11 slices/case) of short-axis images through systole was obtained for each patient. Initial endocardial and epicardial contours for the end-diastolic (ED) and end-systolic (ES) frames were manually traced on the computer by an experienced radiologist. The ED tracings were used as the starting point for the algorithm. The borders were tracked through each phase of the temporal data set, until the ES frame was reached (7 phases/slice). Peak gradients along equally spaced chords calculated perpendicular to a centerline determined midway between the endocardial and epicardial borders were used for border detection. This approach was tested by comparing the LV epicardial and endocardial volumes calculated at ES to those based on the manual tracings. The results of the algorithm compared favorably with both the endocardial (r ² = 0.72 – 0.98) and epicardial (r ² = 0.96 – 0.99) volumes of the tracer.     

不同起搏方式在高龄患者中的临床应用

目的　探讨心脏永久起搏器在高龄患者中的应用 ,并对生理性及非生理性两种起搏方式进行对比研究。方法　为 4 7例年龄≥ 75岁的高龄患者安置VVI型起搏器 2 5例 ,VDD型起搏器 3例 ,DDD型起搏器 19例。术后随访平均 3个月至 2年 ,了解患者自觉症状、生活质量、运动耐量、起搏器功能情况及测定左室射血分数 (EF)。结果　全组病例自觉症状、活动能力及生活质量均明显改善 ,起搏功能良好 ,患者平均心室率由术前的 (4 4± 11)次 /min提高到 (6 9± 16 )次 /min。生理性起搏组EF由 (5 1.7± 16 .8) %提高到 (6 2 .1± 15 .2 ) % (P <0 .0 1) ,1例发生房颤 ;非生理起搏组EF由 (4 8.5± 14 .8) %提高到 (6 0 .1± 16 .9) % (P <0 .0 1) ,2例发生房颤 ,3例出现起搏器综合征。结论　两种起搏方式均可改善高龄患者的生活质量 ,提高心室率 ,改善心功能 ,但生理性起搏可减少起搏器综合征及房颤的发生。     

Six-months of recombinant human GH therapy in patients with ischemic cardiac failure

Growth hormone therapy in patients with idiopathic dilated cardiomyopathy and ischemic cardiac failure has revealed varying effects on systolic function, probably related to the response in serum insulin-like growth factor I (IGF-I) levels. As diastolic function has not been studied thoroughly, we studied the effects of 6 months of recombinant human growth hormone (rh GH) treatment on systolic and diastolic function in patients with ischemic cardiac failure, using cardiovascular magnetic resonance (MR) imaging. Nineteen patients with ischemic cardiac failure (left ventricular ejection fraction (LVEF), <40%) were studied in a randomized trial. Nine patients received 6 months treatment with growth hormone (2 IU/day). Systolic and diastolic function were assessed at baseline and after 26 weeks by cardiovascular MR imaging. No differences were found in systolic and diastolic function between rh GH treated patients and controls. No change was observed in left ventricular mass index (LVMI), end-diastolic volume, end-systolic-volume and ejection fraction. The treated patients showed no clinical improvement. Six months of treatment with growth hormone therapy in ischemic cardiac failure has no favorable effects on LVMI, on systolic and diastolic function.     

脑干梗死MR成像的临床价值

目的：探讨脑干梗死的病理机理及MR表现特点。方法：本组72例，男42例，女30例，年龄21～86岁，平均66岁。采用GE 2．OT超导型磁共振仪。SE序列，T1加权，轴位；FSE序列，T2加权，轴位和冠状位。结果：72例中，中脑梗死16例，脑桥梗死52例（合并中脑梗死13例），延髓梗死4例。梗死灶在T1WI上表现为低信号、低～等信号或等信号，在T2WI上表现为高信号，随着病程的发展，T1和T2的延长愈明显，T2WI对脑干梗死灶最敏感。结论：MRI是诊断脑干梗死的最好检查方法，能够显示脑干梗死的部位、数目和大小。     

中老年人心肌淀粉样变性4例临床及其CMR表现

目的回顾性分析4例中老年心肌淀粉样变性的临床资料以及心脏磁共振成像特点,以提高诊断水平。材料与方法分析2010年8月至2016年12月在北京医院诊治并经病理证实的心肌淀粉样变性中老年患者4例,总结患者性别、年龄、临床表现、心脏核磁共振(cardiovascular magnetic resonance,CMR)影像特点和病理特点、治疗方式。结果患者平均年龄约68岁(57~72岁),病程较长(9~36个月),4例均出现血清N末端B型利钠肽原、肌钙蛋白增高并表现为不同程度的左心室收缩功能障碍,3例心律失常,2例低电压及病理Q波,3例血尿轻链水平增高。超声心动图4例可见心肌增厚,室间隔为著,诊断为非梗阻性肥厚性心肌病。CMR显示左心室心肌非对称性增厚,心肌质量明显增加,但心腔无扩大,心肌运动减低,3例收缩功能减低,左心室心肌呈弥漫心内膜下或透壁延迟强化,心腔暗血池及心肌较心腔提前抑制。4例经病理证实为原发性系统性淀粉样变性轻链型(AL型),3例通过心外组织活检、1例尸检,其心脏外受累主要表现为肾、肝、肠道、周围神经、皮肤。1例应用硼替佐米加地塞米松、马法兰加地塞米松方案化疗,无心脏不良事件发生;2例明确诊断但放弃治疗;1例明确诊断较晚,且未进行有效治疗,死亡。结论心肌淀粉样变性的心脏磁共振成像主要表现为心肌肥厚、心肌质量增加,增强扫描后心肌较心腔提前抑制,心腔呈暗血池,心肌延迟强化的特征表现为弥漫透壁或心内膜下强化,可提示临床难治性心衰的病因诊断,在诊断及鉴别诊断中起重要作用。