Assessing the Risks Associated with MRI in Patients with a Pacemaker or Defibrillator.

BACKGROUND: The presence of a cardiovascular implantable electronic device has long been a contraindication for the performance of magnetic resonance imaging (MRI). We established a prospective registry to determine the risks associated with MRI at a magnetic field strength of 1.5 tesla for patients who had a pacemaker or implantable cardioverter-defibrillator (ICD) that was "non-MRI-conditional" (i.e., not approved by the Food and Drug Administration for MRI scanning). METHODS: Patients in the registry were referred for clinically indicated nonthoracic MRI at a field strength of 1.5 tesla. Devices were interrogated before and after MRI with the use of a standardized protocol and were appropriately reprogrammed before the scanning. The primary end points were death, generator or lead failure, induced arrhythmia, loss of capture, or electrical reset during the scanning. The secondary end points were changes in device settings. RESULTS: MRI was performed in 1000 cases in which patients had a pacemaker and in 500 cases in which patients had an ICD. No deaths, lead failures, losses of capture, or ventricular arrhythmias occurred during MRI. One ICD generator could not be interrogated after MRI and required immediate replacement; the device had not been appropriately programmed per protocol before the MRI. We observed six cases of self-terminating atrial fibrillation or flutter and six cases of partial electrical reset. Changes in lead impedance, pacing threshold, battery voltage, and P-wave and R-wave amplitude exceeded prespecified thresholds in a small number of cases. Repeat MRI was not associated with an increase in adverse events. CONCLUSIONS: In this study, device or lead failure did not occur in any patient with a non-MRI-conditional pacemaker or ICD who underwent clinically indicated nonthoracic MRI at 1.5 tesla, was appropriately screened, and had the device reprogrammed in accordance with the prespecified protocol. (Funded by St. Jude Medical and others; MagnaSafe ClinicalTrials.gov number, NCT00907361 .).

Determining the risks of clinically indicated nonthoracic magnetic resonance imaging at 1.5 T for patients with pacemakers and implantable cardioverter-defibrillators: rationale and design of the MagnaSafe Registry.

BACKGROUND: Until recently, the presence of a permanent pacemaker or an implantable cardioverter-defibrillator has been a relative contraindication for the performance of magnetic resonance imaging (MRI). A number of small studies have shown that MRI can be performed with minimal risk when patients are properly monitored and device programming is modified appropriately for the procedure. However, the risk of performing MRI for patients with implanted cardiac devices has not been sufficiently evaluated to advocate routine clinical use. The aim of the present protocol is to prospectively determine the rate of adverse clinical events and device parameter changes in patients with implanted non-MRI-conditional cardiac devices undergoing clinically indicated nonthoracic MRI at 1.5 T. METHODS: The MagnaSafe Registry is a multicenter, prospective cohort study of up to 1500 MRI examinations in patients with pacemakers or implantable cardioverter-defibrillators implanted after 2001 who undergo clinically indicated nonthoracic MRI following a specific protocol to ensure that preventable potential adverse events are mitigated. Adverse events and changes in device parameter measurements that may be associated with the imaging procedure will be documented. RESULTS: Through August 2012, 701 MRI studies have been performed, representing 47% of the total target enrollment. CONCLUSIONS: The results of this registry will provide additional documentation of the risk of MRI and will further validate a clinical protocol for screening and the performance of clinically indicated MRI for patients with implanted cardiac devices.

Determining the risks of magnetic resonance imaging at 1.5 tesla for patients with pacemakers and implantable cardioverter defibrillators.

Conventional pacemaker and implantable cardioverter-defibrillator product labeling currently cautions against exposure to magnetic resonance imaging (MRI). However, there is a growing clinical need for MRI, without an acceptable alternative imaging modality in many patients with cardiac devices. The purpose of this study was to determine the risk of MRI at 1.5 T for patients with cardiac devices by measuring the frequency of device failures and clinically relevant device parameter changes. Data from a single-center retrospective review of 109 patients with pacemakers and implantable cardioverter-defibrillators (the MRI group) who underwent 125 clinically indicated MRI studies were compared to data from a prospective cohort of 50 patients with cardiac devices who did not undergo MRI (the control group). In the MRI group, there were no deaths, device failures requiring generator or lead replacement, induced arrhythmias, losses of capture, or electrical reset episodes. Decreases in battery voltage of ≥0.04 V occurred in 4%, pacing threshold increases of ≥0.5 V in 3%, and pacing lead impedance changes of ≥50 Ω in 6%. Although there were statistically significant differences between the MRI and control groups for the mean change in pacing lead impedance (-6.2 ± 23.9 vs 3.0 ± 22.1 Ω) and left ventricular pacing threshold (-0.1 ± 0.3 vs 0.1 ± 0.2 V), these differences were not clinically important. In conclusion, MRI in patients with cardiac devices resulted in no device or lead failures. A small number of clinically relevant changes in device parameter measurements were noted. However, these changes were similar to those in a control group of patients who did not undergo MRI.

A novel technique for ultra-low contrast administration during angiography or intervention.

Contrast-induced nephropathy (CIN) after coronary angiography or intervention is associated with substantial morbidity. The data supporting various prophylactic measures and adjunctive therapies to prevent this complication are conflicting. However, contrast volume is clearly related to CIN after percutaneous coronary intervention (PCI), and the risk of CIN has been shown to be directly related to contrast dose. Therefore, minimizing contrast exposure is a primary method to reduce the risk of CIN, especially in at-risk patients. We report a novel technique designed to deliver ultra-low (<15 cm(3)) volume contrast to patients with chronic kidney disease undergoing coronary angiography and PCI.

A randomized controlled trial of angiography versus intravascular ultrasound-directed bare-metal coronary stent placement (the AVID Trial).

BACKGROUND: AVID (Angiography Versus Intravascular ultrasound-Directed stent placement) is a multicenter, randomized controlled trial designed to assess the effect of intravascular ultrasound (IVUS)-directed stent placement on the 12-month rate of target lesion revascularization (TLR). METHODS AND RESULTS: After elective coronary stent placement and an optimal angiographic result (<10% stenosis), 800 patients were randomized to Angiography- or IVUS-directed therapy. Blinded IVUS was performed in the Angiography group without further therapy. In the IVUS group, IVUS criteria for optimal stent placement (<10% area stenosis, apposition, and absence of dissection) were applied. Final minimum stent area was 6.90+/-2.43 mm(2) in the Angiography group and 7.55+/-2.82 mm(2) in the IVUS group (P=0.001). In the IVUS group, only 37% with inadequate expansion (<90%) received further therapy. The 12-month TLR rate was 12.0% in the Angiography group and 8.1% in the IVUS group (P=0.08, 95% confidence level [CI], [-8.3% to 0.5%]). When vessels with a distal reference diameter <2.5 mm by core laboratory angiography measurement were excluded from analysis, the 12-month TLR rate was 10.1% in the Angiography group and 4.3% in the IVUS group (P=0.01, 95% CI, [-10.6% to -1.2%]). With a pre-stent angiographic stenosis of > or =70%, the TLR rate was lower in the IVUS group compared with the Angiography group (3.1% versus 14.2%; P=0.002; 95% CI, [-18.4% to -4.2%]). CONCLUSIONS: IVUS-directed bare-metal stent placement results in larger acute stent dimensions without an increase in complications and a significantly lower 12-month TLR rate for vessels > or =2.5 mm by angiography and for vessels with high-grade pre-stent stenosis. However, for the entire sample analyzed on an intention-to-treat basis, IVUS-directed bare-metal stent placement does not significantly reduce the 12-month TLR rate when compared with stent placement guided by angiography alone. In addition, IVUS evaluation of adequate stent expansion is underutilized by experienced operators.

Coronary artery overexpansion increases neointimal hyperplasia after stent placement in a porcine model.

OBJECTIVE: To determine if an aggressive approach to coronary revascularisation with oversized balloons is counterproductive, we studied the effect of increasing balloon-to-artery (B:A) ratio on neointimal hyperplasia following primary stent placement using a non-atherosclerotic porcine coronary overstretch model. METHODS: 60 vessels in 33 Yorkshire swine were randomly assigned to one of five B:A ratios between 1.0:1 and 1.4:1. Intravascular ultrasound (IVUS) imaging was performed before bare-metal stent placement to accurately determine vessel size, after stent placement, and at 28 days. RESULTS: The mean prestent vessel diameter was 3.05 (0.31) (SD) mm. In-stent neointimal volume, in-stent volume stenosis and cross-sectional area stenosis at the stent minimum lumen diameter increased significantly with increasing achieved B:A ratio (multilevel regression test for slope, p<0.001, p = 0.002 and p<0.001, respectively) and were independent of vessel size. Even minor vessel overstretch at an achieved B:A ratio of 1.1:1 resulted in significant neointimal hyperplasia. Larger B:A ratios were also associated with more neointima beyond the stent edges (p = 0.008). For vessels from the same animal, neointimal response at a given B:A ratio was dependent upon the animal treated. CONCLUSIONS: In a porcine model of IVUS-guided coronary primary stent placement, vessel overexpansion is counterproductive. Neointimal hyperplasia at 28 days is strongly associated with increasing B:A ratio. In addition, vessels do not respond independently of each other when multiple stents are placed within the same animal using a range of B:A ratios.

Five-year clinical follow-up after intracoronary radiation: results of a randomized clinical trial.

BACKGROUND: Several clinical trials indicate that intracoronary radiation is safe and effective for treatment of restenotic coronary arteries. We previously reported 6-month and 3-year clinical and angiographic follow-up demonstrating significant decreases in target lesion revascularization (TLR) and angiographic restenosis after gamma radiation of restenotic lesions. The objective of this study was to document the clinical outcome 5 years after treatment of restenotic coronary arteries with catheter-based iridium-192 (192Ir). METHODS AND RESULTS: A double-blind, randomized trail compared 192Ir to placebo sources in patients with restenosis after coronary angioplasty. Over a 9-month period, 55 patients were enrolled; 26 were randomized to 192Ir and 29 to placebo. At 5-year follow-up, TLR was significantly lower in the 192Ir group (23.1% versus 48.3%; P=0.05). There were 2 TLRs between years 3 and 5 in patients in the 192Ir group and none in patients in the placebo group. The 5-year event-free survival rate (freedom from death, myocardial infarction, or TLR) was greater in 192Ir-treated patients (61.5% versus 34.5%; P=0.02). CONCLUSIONS: Despite apparent mitigation of efficacy over time, there remains a significant reduction in TLR at 5 years and an improvement in event-free survival in patients treated with intracoronary 192Ir. The early clinical benefits after intracoronary gamma radiation with 192Ir seem durable at 5-year clinical follow-up.

Centered versus noncentered source for intracoronary artery radiation therapy: a model based on the Scripps Trial.

BACKGROUND: The Scripps Trial was a randomized study of intracoronary artery radiation therapy with iridium 192 used to treat restenotic vessels. We used the intravascular ultrasound data from the Scripps Trial to investigate whether a lumen-centered gamma or beta radiation source would reduce radiation dose heterogeneity compared with the noncentered source position used. METHODS: Analysis included 28 patients with stent placement in 20 native vessels and 8 saphenous vein grafts enrolled in this trial. Radiation dosimetry for gamma radiation was calculated to deliver 800 cGy to the far field target, provided the maximum dose to the near field target did not exceed 3000 cGy. Prescribed dosimetry for beta radiation by use of yttrium 90 was 1600 cGy at 2 mm distance from the source. RESULTS: The calculated average minimum source to target distance by use of a lumen-centered source increased by 0.18 mm from 1.70 +/- 0.25 to 1.88 +/- 0.36 mm, whereas the maximum distance decreased by 0.17 mm from 3.64 +/- 0.60 to 3.47 +/- 0.43 mm (P <.05). On the basis of these distances, the maximum radiation dose, as well as radiation dose heterogeneity (ratio of maximum to minimum), would have been reduced in 22 of 28 patients by use of a lumen-centered gamma or beta source (P <.005). The reduction in dose heterogeneity was substantially greater with a beta source compared with a gamma source (48% vs 16% reduction). CONCLUSIONS: Centering of the intracoronary artery radiation therapy delivery catheter within the vessel lumen can significantly reduce radiation dose heterogeneity when compared with a noncentered source position. This dose reduction is substantially greater for a beta compared with a gamma source.