Real-Time Magnetic Resonance Imaging-Guided Transarterial Aortic Valve Implantation In-Vivo Evaluation in Swine

Real-time magnetic resonance imaging (rtMRI) is considered attractive for guiding transarterial aortic valve implantation (TAVI). Compared with X-ray fluoroscopy, rtMRI offers unrestricted scan plane orientation and an unsurpassed soft-tissue contrast with simultaneous device visualization, potentially allowing enhanced positioning accuracy together with online monitoring of cardiac function and immediate detection of complications. Additionally, MRI offers noninvasive assessment of cardiovascular anatomy and function for preinterventional screening as well as immediate morphologic and functional assessment of the implanted prothesis and may, thus, be envisioned as a single comprehensive imaging modality for TAVI. We, therefore, sought to assess the preclinical feasibility of entirely rtMRI-guided TAVI in a swine model (female domestic pigs weighing 70.5 to 86.5 kg) using the original CoreValve (Medtronic, Minneapolis, Minnesota) prosthesis without alterations in conjunction with a modified, MRI-compatible delivery device (1).

rtMRI-guided transfemoral (n = 2) and transsubclavian (n = 6) TAVI was performed in a 1.5-T whole-body MRI scanner (Magnetom Avanto, Siemens Healthcare Sector, Erlangen, Germany). Conventional x-ray fluoroscopy and angiography were performed for comparison. After pre-interventional evaluation using standard steady-state free-precession imaging with electrocardiographic gating and time-resolved retrospective image reconstruction (cine-TrueFISP retro) (TR, 40 ms; TE, 1.1 ms; flip angle, 62°; FOV, 380 x 330 mm2; matrix, 192 x 168; slice thickness, 6 mm; bandwidth, 930 Hz/pixel; image acquisition time, 15 s for a single slice acquired over 20 phases of the cardiac R-R interval) and electrocardiography-triggered, flow-sensitive, phase-contrast sequences (TR, 62 ms; TE, 3.5 ms; flip angle, 30°; FOV, 320 x 220 mm2; matrix, 192 x 132; bandwidth, 555 Hz/pixel; acquisition time, 1 min 52 s; velocity encoding value, 100 cm/s), TAVI was performed using rtMRI fluoroscopy based on a commercially available interactive real-time projection reconstruction TrueFISP sequence with radial k-space filling during free breathing and without cardiac triggering that was modified to achieve a frame rate of 7 frames per second (TR, 3.0 ms; TE, 1.5 ms; flip angle, 70°; FOV, 360 x 360 mm2; matrix, 192 x 192; bandwidth, 1530 Hz/pixel; slice thickness, 6 mm). Images were displayed without delay inside the scanner room and could be adapted interactively according to the operator’s (P.K.) needs while the sequence was running. After TAVI, real-time TrueFISP, cine-TrueFISP retro, and flow-sensitive phase-contrast sequences were used to verify procedural success. Autopsies were performed to validate MRI findings.

Three-point localizer sequences allowed for rapid detection (11 ± 3 min) of all scan planes required for preinterventional evaluation, procedural guidance, and post-procedural validation. High-resolution TrueFISP retro sequences enabled detailed visualization of all procedurally relevant anatomic landmarks and allowed precise measurements (aortic annulus diameter in long axis, 17 ± 3 mm; aortic arch diameter, 21 ± 4 mm; distance from aortic annulus to left and right coronary ostium, 9 ± 3 and 10 ± 2 mm; access vessel diameter, 6.9 ± 1.2 mm) in good accordance with measurements on previous angiographic images (mean error, 0.4 ± 0.3 mm; p = NS) and during autopsy (mean error, 0.5 ± 0.2 mm; p = NS).

Passive device visualization using real-time TrueFISP sequences provided reliable imaging guidance during TAVI superior to fluoroscopy. Mild susceptibility artifacts confined to the loaded stent valve enabled adequate determination of the position of stent valve and delivery system in relation to the surrounding anatomy without undue image distortion, allowing a precise, real-time anatomic orientation during device navigation through the vasculature, aortic valve passage, positioning and deployment of the prosthesis, and catheter withdrawal.

In 6 of 8 animals, an oversized 26-mm CoreValve prosthesis was successfully placed across the aortic annulus without dislocation, coronary artery obstruction, or impairment of the mitral valve, as confirmed by autopsy (rtMRI acquisition time, 4 ± 2 min) (Fig. 1). However, 2 implant failures occurred. The first was a result of unsuccessful aortic arch passage due to insufficient support by the initially used MRI-compatible, soft polymer guidewire and led to a controlled deployment of the stent valve in the thoracic aorta, which is sometimes required in clinical application when the prosthesis dislocates into the ascending aorta during deployment. As a consequence, we continued our experiments without guidewire support and focused on the straighter transsubclavian access route. The second implant failure occurred due to perforation of the left ventricular apex caused by the delivery device, which was inadvertently pushed with too much force, this complication being immediately detected by rtMRI. Both cases indicate that rtMRI might improve both precision and safety of the TAVI procedure.

Postprocedural TrueFISP retro sequences allowed precise structural evaluation of the procedural result in good accordance with autopsy findings. Flow-sensitive, electrocardiography-triggered, phase-contrast sequences with imaging planes placed approximately 1 cm below and above the nitinol stent frame confirmed good systolic transvalvular blood flow without diastolic regurgitation. The current study demonstrates the preclinical feasibility of entirely MRI-guided TAVI. As a single imaging modality, MRI offered comprehensive diagnostic evaluation of the relevant cardiac and vascular anatomy for adequate interventional planning, real-time procedural guidance with excellent anatomic orientation, immediate evaluation of procedure-related complications, and post-interventional validation of treatment success with a total procedure time of 61 ± 13 min. Complementary to reduction of radiation exposure and nephrotoxic contrast media, rtMRI guidance, therefore, provides clinically relevant advantages over conventional X-ray-fluoroscopy and warrants further attention. These advantages should encourage future efforts to translate rtMRI-guided TAVI into clinical application using commercial but modified or entirely novel devices (2,3) and to overcome remaining obstacles such as the development of suitable, MRI-compatible guidewires.

PMID: 22222083

Utility of Cardiovascular Magnetic Resonance in Identifying Substrate for Malignant Ventricular Arrhythmias

OBJECTIVES: Sudden cardiac death (SCD) and sustained monomorphic ventricular tachycardia (SMVT) are frequently associated with prior or acute myocardial injury. Cardiovascular magnetic resonance (CMR) provides morphological, functional, and tissue characterization in a single setting. We sought to evaluate the diagnostic yield of CMR-based imaging versus non-CMR-based imaging in patients with resuscitated SCD or SMVT.

METHODS: Eighty-two patients with resuscitated SCD or SMVT underwent routine non-CMR imaging, followed by a CMR protocol with comprehensive tissue characterization. Clinical reports of non-CMR imaging studies were blindly adjudicated and used to assign each patient to 1 of 7 diagnostic categories. CMR imaging was blindly interpreted using a standardized algorithm used to assign a patient diagnosis category in a similar fashion. The diagnostic yield of CMR-based and non-CMR-based imaging, as well as the impact of the former on diagnosis reclassification, was established.

RESULTS: Relevant myocardial disease was identified in 51% of patients using non-CMR-based imaging and in 74% using CMR-based imaging (P=0.002). Forty-one patients (50%) were reassigned to a new or alternate diagnosis using CMR-based imaging, including 15 (18%) with unsuspected acute myocardial injury. Twenty patients (24%) had no abnormality by non-CMR imaging but showed clinically relevant myocardial disease by CMR imaging.

CONCLUSIONS: CMR-based imaging provides a robust diagnostic yield in patients presenting with resuscitated SCD or SMVT and incrementally identifies clinically unsuspected acute myocardial injury. When compared with non-CMR-based imaging, a new or alternate myocardial disease process may be identified in half of these patients.

PMID: 22038987

Patient Management After Noninvasive Cardiac Imaging – Results From SPARC (Study of Myocardial Perfusion and Coronary Anatomy Imaging Roles in Coronary Artery Disease)

OBJECTIVES: This study examined short-term cardiac catheterization rates and medication changes after cardiac imaging. Noninvasive cardiac imaging is widely used in coronary artery disease, but its effects on subsequent patient management are unclear.

METHODS: We assessed the 90-day post-test rates of catheterization and medication changes in a prospective registry of 1,703 patients without a documented history of coronary artery disease and an intermediate to high likelihood of coronary artery disease undergoing cardiac single-photon emission computed tomography, positron emission tomography, or 64-slice coronary computed tomography angiography.

RESULTS: Baseline medication use was relatively infrequent. At 90 days, 9.6% of patients underwent catheterization. The rates of catheterization and medication changes increased in proportion to test abnormality findings. Among patients with the most severe test result findings, 38% to 61% were not referred to catheterization, 20% to 30% were not receiving aspirin, 35% to 44% were not receiving a beta-blocker, and 20% to 25% were not receiving a lipid-lowering agent at 90 days after the index test. Risk-adjusted analyses revealed that compared with stress single-photon emission computed tomography or positron emission tomography, changes in aspirin and lipid-lowering agent use was greater after computed tomography angiography, as was the 90-day catheterization referral rate in the setting of normal/nonobstructive and mildly abnormal test results.

CONCLUSIONS: Overall, noninvasive testing had only a modest impact on clinical management of patients referred for clinical testing. Although post-imaging use of cardiac catheterization and medical therapy increased in proportion to the degree of abnormality findings, the frequency of catheterization and medication change suggests possible undertreatment of higher risk patients. Patients were more likely to undergo cardiac catheterization after computed tomography angiography than after single-photon emission computed tomography or positron emission tomography after normal/nonobstructive and mildly abnormal study findings.

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Simultaneous Right and Left Heart Real-Time, Free-Breathing CMR Flow Quantification Identifies Constrictive Physiology

PMID: 22239888

Pulmonary Hypertension: How the Radiologist Can Help

Pulmonary hypertension is defined as an abnormal elevation of pressure in pulmonary circulation, with a mean pulmonary arterial pressure higher than 25 mmHg, regardless of the underlying mechanism. The clinical classification system for pulmonary hypertension was updated at the fourth World Symposium on Pulmonary Hypertension in Dana Point, California, in 2008. In patients with suspected pulmonary hypertension, the diagnostic approach includes four stages: suspicion, detection, classification, and functional evaluation. It is crucial to understand the advantages and disadvantages of the different imaging tools available for the diagnostic work-up and follow-up of patients with pulmonary hypertension. Many conditions that cause pulmonary hypertension have suggestive findings at multidetector computed tomography or magnetic resonance imaging; some causes may be surgically treatable, whereas others may demonstrate adverse reactions to vasodilator therapies used during the course of treatment. Therefore, the radiologist plays an important role in evaluating patients with this disease.

PMID: 22236891

Anomalous Origin of the Right Coronary Artery from the Left Coronary Sinus With an Interarterial Course: Subtypes and Clinical Importance

OBJECTIVES: To classify anomalous origins of the right coronary artery (RCA) from the left coronary sinus (AORL) with an interarterial course into two subtypes and to evaluate the clinical importance of each.

METHODS: Institutional review board approval was obtained for this retrospective study, and informed consent was waived. Through a retrospective review of 22 925 consecutive cardiac computed tomographic (CT) scans, 124 cases of AORL with an interarterial course were identified. These anomalies were classified into two subtypes according to the location of the anomalous RCA ostium: high interarterial course (between the aorta and the pulmonary artery) and low interarterial course (between the aorta and the right ventricular outflow tract). The clinical records were evaluated, and differences in prevalence of typical angina and major adverse cardiac events (MACEs) between the subtypes were analyzed through the χ(2) contingency tables or Fisher exact test.

RESULTS: After excluding patients with combined cardiac disease, 87 patients (51 [59%] men, 36 [41%] women; mean age, 56.0 years) were enrolled. Of the 87 patients, 53 had a high interarterial course and 34 had a low interarterial course. A significant difference in the prevalence of typical angina (high [43%] vs low [6%], P = .001) and MACE (high [28%] vs low [6%], P = .012) was observed between the two subtypes. For patients with a high interarterial course, the odds ratio for typical angina was 12.3 (95% confidence interval: 2.7, 56.6), and the odds ratio for MACE was 6.3 (95% confidence interval: 1.3, 29.7).

CONCLUSIONS: The prevalence of typical angina and that of MACE were significantly higher in patients with a high interarterial course than in those with a low interarterial course.

PMID: 22056684

Cardiovascular Magnetic Resonance and Single-Photon Emission Computed Tomography for Diagnosis of Coronary Heart Disease (CE-MARC): A Prospective Trial

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CT for Evaluation of Myocardial Cell Therapy in Heart Failure A Comparison With CMR Imaging

OBJECTIVES: The aim of this study was to use multidetector computed tomography (MDCT) to assess therapeutic effects of myocardial regenerative cell therapies. Cell transplantation is being widely investigated as a potential therapy in heart failure. Noninvasive imaging techniques are frequently used to investigate therapeutic effects of cell therapies in the preclinical and clinical settings. Previous studies have shown that cardiac MDCT can accurately quantify myocardial scar tissue and determine left ventricular (LV) volumes and ejection fraction (LVEF).

METHODS: Twenty-two minipigs were randomized to intramyocardial injection of phosphate-buffered saline (placebo, n = 9) or 200 million mesenchymal stem cells (MSC, n = 13) 12 weeks after myocardial infarction (MI). Cardiac magnetic resonance and MDCT acquisitions were performed before randomization (12 weeks after MI induction) and at the study endpoint 24 weeks after MI induction. None of the animals received medication to control the intrinsic heart rate during first-pass acquisitions for assessment of LV volumes and LVEF. Delayed-enhancement MDCT imaging was performed 10 min after contrast delivery. Two blinded observers analyzed MDCT acquisitions.

RESULTS: MDCT demonstrated that MSC therapy resulted in a reduction of infarct size from 14.3 ± 1.2% to 10.3 ± 1.5% of LV mass (p = 0.005), whereas infarct size increased in nontreated animals (from 13.8 ± 1.3% to 16.5 ± 1.5%; p = 0.02) (placebo vs. MSC; p = 0.003). Both observers had excellent agreement for infarct size (r = 0.96; p < 0.001). LVEF increased from 32.6 ± 2.2% to 36.9 ± 2.7% in MSC-treated animals (p = 0.03) and decreased in placebo animals (from 33.3 ± 1.4% to 29.1 ± 1.5%; p = 0.01; at week 24: placebo vs. MSC; p = 0.02). Infarct size, end-diastolic LV volume, and LVEF assessed by MDCT compared favorably with those assessed by cardiac magnetic resonance acquisitions (r = 0.70, r = 0.82, and r = 0.902, respectively; p < 0.001).

CONCLUSIONS: This study demonstrated that cardiac MDCT can be used to evaluate infarct size, LV volumes, and LVEF after intramyocardial-delivered MSC therapy. These findings support the use of cardiac MDCT in preclinical and clinical studies for novel myocardial therapies.

PMID: 22172785

3D Echo Systematically Underestimates Right Ventricular Volumes Compared to Cardiovascular Magnetic Resonance in Adult Congenital Heart Disease Patients With Moderate or Severe RV Dilatation

OBJECTIVES: Three dimensional echo is a relatively new technique which may offer a rapid alternative for the examination of the right heart. However its role in patients with non-standard ventricular size or anatomy is unclear. This study compared volumetric measurements of the right ventricle in 25 patients with adult congenital heart disease using both cardiac magnetic resonance (CMR) and three dimensional echocardiography.

METHODS: Patients were grouped by diagnosis into those expected to have normal or near-normal RV size (patients with repaired coarctation of the aorta) and patients expected to have moderate or worse RV enlargement (patients with repaired tetralogy of Fallot or transposition of the great arteries). Right ventricular end diastolic volume, end systolic volume and ejection fraction were compared using both methods with CMR regarded as the reference standard

RESULTS: Bland-Altman analysis of the 25 patients demonstrated that for both RV EDV and RV ESV, there was a significant and systematic under-estimation of volume by 3D echo compared to CMR. This bias led to a mean underestimation of RV EDV by -34% (95%CI: -91% to + 23%). The degree of underestimation was more marked for RV ESV with a bias of -42% (95%CI: -117% to + 32%). There was also a tendency to overestimate RV EF by 3D echo with a bias of approximately 13% (95% CI -52% to +27%).

CONCLUSIONS: Statistically significant and clinically meaningful differences in volumetric measurements were observed between the two techniques. At the current time, three dimensional echocardiography is not interchangeable with CMR for volumetric assessment of ACHD patients who have more than mild RV dilatation.

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Prognostic Importance of Late Gadolinium Enhancement Cardiovascular Magnetic Resonance in Cardiomyopathy

Cardiovascular magnetic resonance has revolutionised the diagnosis of cardiomyopathy, particularly through the use of late gadolinium enhancement imaging which provides the unique opportunity to assess myocardial fibrosis in vivo. More recently, the prognostic capability of cardiovascular magnetic resonance to predict outcomes has been assessed. Traditional risk markers do not at present adequately predict outcomes in either dilated cardiomyopathy or hypertrophic cardiomyopathy, which are the two most common causes of primary heart muscle disease. Many of these existing markers reflect underlying disease severity. Given the important role fibrosis is thought to play in the pathogenesis and sequelae of these cardiomyopathies, the presence and amount of fibrosis has been proposed as a potential novel risk factor for adverse events. This paper reviews the evidence for late gadolinium enhancement as a prognostic marker in dilated and hypertrophic cardiomyopathy and highlights the challenges ahead.

PMID: 22128204

Prognostic Value of Routine Cardiac Magnetic Resonance Assessment of Left Ventricular Ejection Fraction and Myocardial Damage: An International, Multicenter Study

OBJECTIVES: Cardiac magnetic resonance (CMR) is considered the reference standard for assessment of left ventricular ejection fraction (LVEF) and myocardial damage.  However, few studies have evaluated the relationship between CMR findings and patient outcome, and of these, most are small and none multicenter.  We performed an international, multicenter study to assess the prognostic importance of routine CMR in patients with known or suspected heart disease.

METHODS: From 10 centers in 6 countries, consecutive patients undergoing routine CMR assessment of LVEF and myocardial damage by cine and delayed-enhancement imaging (DE-CMR), respectively, were screened for enrollment.  Clinical data, CMR protocol information, and findings were collected at all sites and submitted to the data coordinating center for verification of completeness and analysis.  The primary end point was all-cause mortality.

RESULTS: A total of 1560 patients (age, 59±14 years; 70% men) were enrolled.  Mean LVEF was 45±18%, and 1049 (67%) patients had hyperenhanced tissue (HE) on DE-CMR indicative of damage.  During a median follow-up time of 2.4 years (interquartile range, 1.2, 2.9 years), 176 (11.3%) patients died.  Patients who died were more likely to be older (P<0.0001), have coronary disease (P=0.004), have lower LVEF (P<0.0001), and have more segments with HE (P<0.0001).  In multivariable analysis, age, LVEF, and number of segments with HE were independent predictors of mortality.  Among patients with near-normal LVEF (≥50%), those with above-median HE (>4 segments) had reduced survival compared to patients with below- or at-median HE (P=0.02).

CONCLUSIONS: Both LVEF and amount of myocardial damage as assessed by routine CMR are independent predictors of all-cause mortality.  Even in patients with near-normal LVEF, significant damage identifies a cohort with a high risk for early mortality.

PMID: 21911738

Exercise-Induced Right Ventricular Dysfunction and Structural Remodelling in Endurance Athletes

PMID:

Percutaneous Transvenous Melody Valve-in-Ring Procedure for Mitral Valve Replacement

OBJECTIVES: The purpose of this study was to demonstrate the feasibility of percutaneous transvenous mitral valve-in-ring (VIR) implantation using the Melody valve in an ovine model. The recurrence of mitral regurgitation following surgical mitral valve (MV) repair in both adult and pediatric patients remains a significant clinical problem. Mitral annuloplasty rings are commonly used in MV repair procedures and may serve as secure landing zones for percutaneous valves.

METHODS: Five sheep underwent surgical MV annuloplasty (24 mm, n = 2; 26 mm, n = 2; 28 mm, n = 1). Animals underwent cardiac catheterization with VIR implantation via a transfemoral venous, transatrial septal approach 1 week following surgery. Hemodynamic, angiographic, and echocardiographic data were recorded before and after VIR.

RESULTS: VIR was technically successful and required <1 h of procedure time in all animals. Fluoroscopy demonstrated securely positioned Melody valves within the annuloplasty ring in all animals. Angiography revealed no significant MV regurgitation in 4 and moderate central MV regurgitation in the animal with the 28-mm annuloplasty. All animals demonstrated vigorous left ventricular function, no outflow tract obstruction, and no aortic valve insufficiency.

CONCLUSIONS: This study demonstrated the feasibility of a purely percutaneous approach to MV replacement in patients with preexisting annuloplasty rings. This novel approach may be of particular benefit to patients with failed repair of ischemic mitral regurgitation and in pediatric patients with complex structural heart disease.

PMID: 22133846

Post-Mortem Imaging as an Alternative to Autopsy in the Diagnosis of Adult Deaths: A Validation Study

OBJECTIVES: Public objection to autopsy has led to a search for minimally invasive alternatives. Imaging has potential, but its accuracy is unknown. We aimed to identify the accuracy of post-mortem CT and MRI compared with full autopsy in a large series of adult deaths.

METHODS: This study was undertaken at two UK centres in Manchester and Oxford between April, 2006, and November, 2008. We used whole-body CT and MRI followed by full autopsy to investigate a series of adult deaths that were reported to the coroner. CT and MRI scans were reported independently, each by two radiologists who were masked to the autopsy findings. All four radiologists then produced a consensus report based on both techniques, recorded their confidence in cause of death, and identified whether autopsy was needed.

RESULTS: We assessed 182 unselected cases. The major discrepancy rate between cause of death identified by radiology and autopsy was 32% (95% CI 26-40) for CT, 43% (36-50) for MRI, and 30% (24-37) for the consensus radiology report; 10% (3-17) lower for CT than for MRI. Radiologists indicated that autopsy was not needed in 62 (34%; 95% CI 28-41) of 182 cases for CT reports, 76 (42%; 35-49) of 182 cases for MRI reports, and 88 (48%; 41-56) of 182 cases for consensus reports. Of these cases, the major discrepancy rate compared with autopsy was 16% (95% CI 9-27), 21% (13-32), and 16% (10-25), respectively, which is significantly lower (p<0·0001) than for cases with no definite cause of death. The most common imaging errors in identification of cause of death were ischaemic heart disease (n=27), pulmonary embolism (11), pneumonia (13), and intra-abdominal lesions (16).

CONCLUSIONS: We found that, compared with traditional autopsy, CT was a more accurate imaging technique than MRI for providing a cause of death. The error rate when radiologists provided a confident cause of death was similar to that for clinical death certificates, and could therefore be acceptable for medicolegal purposes. However, common causes of sudden death are frequently missed on CT and MRI, and, unless these weaknesses are addressed, systematic errors in mortality statistics would result if imaging were to replace conventional autopsy.

PMID: 22112684

Improved Detection of Myocardial Involvement in Acute Inflammatory Cardiomyopathies Using T2 Mapping

OBJECTIVES: T2-weighted cardiac magnetic resonance (CMR) is useful in diagnosing acute inflammatory myocardial diseases such as myocarditis and tako-tsubo cardiomyopathy (TTCM). We hypothesized that quantitative T2 mapping could better delineate myocardial involvement in these disorders vs. T2-weighted imaging.

METHODS: Thirty patients with suspected myocarditis or TTCM referred for CMR who met established diagnostic criteria underwent myocardial T2 mapping. T2 values were averaged in involved and remote myocardial segments, both defined by a reviewer blinded to T2 data.

RESULTS: In myocarditis, T2 was 65.2±3.2ms in the involved myocardium vs. 53.5±2.1 in remote myocardium (p0.05 for all). T2 maps provided diagnostic data even in patients with difficulty breath-holding. A T2 cutoff of 59ms identified areas of myocardial involvement with sensitivity and specificity of 94% and 97%, respectively. T2 mapping revealed regions of abnormal T2 beyond those identified by wall motion abnormalities or LGE-positivity. Conventional T2-weighted short tau inversion recovery (T2W-STIR) images were uninterpretable in 7 patients due to artifact and unremarkable in 2 who had elevated T2 values. T2-prepared steady state free precession (T2p-SSFP) images showed areas of signal hyperintensity in only17/30 patients.

CONCLUSIONS: Quantitative T2 mapping reliably identifies myocardial involvement in patients with myocarditis and TTCM. T2 mapping delineated greater extent of myocardial disease in both conditions compared to that identified by wall motion abnormalities, T2W-STIR, T2p-SSFP or LGE. Quantitative T2 mapping warrants consideration as a robust technique to identify myocardial injury in patients with acute myocarditis or TTCM.

PMID: 22038988