Mitral Valve Flow and Myocardial Motion Assessed with Dual-Echo Dual-Velocity Cardiac MRI

Purpose

To develop a dual-echo phase-contrast (DEPC) MRI approach with which each echo is acquired by using a different velocity sensitivity within one repetition time (TR) and demonstrate the feasibility of this approach to measure transmitral blood flow (E) and myocardial tissue (E _m) velocities.

Materials and Methods

The flow across tubes of known diameter was measured by using the proposed DEPC method and compared with flowmeter measurements and theoretic predictions. Then, with both the DEPC MRI sequence and the conventional single-echo phase-contrast (SEPC) MRI sequence, E, E _m, and E/E _m were measured in six healthy volunteers (mean age, 49 years ± 13 [standard deviation]) and eight patients (mean age, 54 years ± 15) being evaluated for cardiac disease. Differences between the DEPC and conventional SEPC MRI methods were assessed by percent error, Pearson correlation, and Bland-Altman analyses.

Results

Velocities measured in vitro and in vivo by using the SEPC and DEPC MRI approaches were well correlated (r ² > 0.97), with negligible bias (<0.5 cm/sec) and comparable velocity-to-noise ratios. Imaging times were approximately 19% shorter with the DEPC method (TR, 5.7 msec) than with the SEPC method (TR, 2.8 msec ± 4.2) (P < .05).

Conclusion

The proposed DEPC method was sensitive to two velocity regimes within a single TR, resulting in a shorter imaging time compared with the imaging time in conventional SEPC MRI. Preliminary human study results suggest the feasibility of using this approach to estimate E/E _m.Supplemental material is available for this article.© RSNA, 2020.

Left Ventricular Noncompaction Detected by Cardiac Magnetic Resonance Screening: A Reexamination of Diagnostic Criteria

In a previous cross-sectional screening study of 5,169 middle and high school students (mean age, 13.1 ± 1.78 yr) in which we estimated the prevalence of high-risk cardiovascular conditions associated with sudden cardiac death, we incidentally detected by cardiac magnetic resonance (CMR) 959 cases (18.6%) of left ventricular noncompaction (LVNC) that met the Petersen diagnostic criterion (noncompaction:compaction ratio >2.3). Short-axis CMR images were available for 511 of these cases (the Short-Axis Study Set). To determine how many of those cases were truly abnormal, we analyzed the short-axis images in terms of LV structural and functional variables and applied 3 published diagnostic criteria besides the Petersen criterion to our findings. The estimated prevalences were 17.5% based on trabeculated LV mass (Jacquier criterion), 7.4% based on trabeculated LV volume (Choi criterion), and 1.3% based on trabeculated LV mass and distribution (Grothoff criterion). Absent longitudinal clinical outcomes data or accepted diagnostic standards, our analysis of the screening data from the Short-Axis Study Set did not definitively differentiate normal from pathologic cases. However, it does suggest that many of the cases might be normal anatomic variants. It also suggests that cases marked by pathologically excessive LV trabeculation, even if asymptomatic, might involve unsustainable physiologic disadvantages that increase the risk of LV dysfunction, pathologic remodeling, arrhythmias, or mural thrombi. These disadvantages may escape detection, particularly in children developing from prepubescence through adolescence. Longitudinal follow-up of suspected LVNC cases to ascertain their natural history and clinical outcome is warranted.

Myocardial Stress Perfusion MRI: Experience in Pediatric and Young-Adult Patients Following Arterial Switch Operation Utilizing Regadenoson

Dextro-transposition of the great arteries (D-TGA) is one of the most common cyanotic heart lesions. The arterial switch operation (ASO) is the preferred surgical palliation for D-TGA. One of the primary concerns following the ASO is complications arising from the coronary artery transfer. There is a need for myocardial perfusion assessment within ASO patients. There is no report on the utility of regadenoson as a stress agent in children following ASO. Our objective was to observe the safety and feasibility of regadenoson as a pharmacologic stressor for perfusion cardiac MR in a pilot cohort of pediatric and young-adult patients who have undergone ASO. We reviewed our initial experience with regadenoson stress cardiac MR in 36 pediatric and young-adult patients 15.1 ± 4.5 years (range 0.2-22 years) with history of ASO. The weight was 61.6 ± 21.5 kg (range 3.8-93 kg). All patients underwent cardiac MR because of concern for ischemia. Subjects' heart rate and blood pressure were monitored and pharmacologic stress was induced by injection of regadenoson. We evaluated their hemodynamic response and adverse effects using changes in vital signs and onset of symptoms. A pediatric cardiologist and radiologist qualitatively assessed myocardial perfusion and viability images. All stress cardiac MR examinations were completed without adverse events. Resting heart rate was 72 ± 13 beats per minute (bpm) and rose to peak of 120 ± 17 bpm (95 ± 50% increase, p < 0.005) with regadenoson. Image quality was considered good or diagnostic in all cases. A total of 11/36 (31%) patients had a perfusion defect on the stress FPP images. 14 of the 36 patients (39%) underwent cardiac catheterization within 6 months of the CMR and the findings showed excellent agreement. Regadenoson may be a useful coronary hyperemia agent to utilize for pediatric patients following arterial switch procedure when there is concern for ischemia. The ability to administer as a single bolus with one IV makes it advantageous in pediatrics. In a limited number of cases, regadenoson stress perfusion showed excellent agreement with cardiac catheterization.

High-Risk Cardiovascular Conditions in Sports-Related Sudden Death: Prevalence in 5,169 Schoolchildren Screened via Cardiac Magnetic Resonance

Improving preparticipation screening of candidates for sports necessitates establishing the prevalence of high-risk cardiovascular conditions (hr-CVC) that predispose young people to sudden cardiac death (SCD). Our accurate, novel protocol chiefly involved the use of cardiac magnetic resonance (CMR) to estimate this prevalence. Middle and high school students from a general United States population were screened by means of questionnaires, resting electrocardiograms, and CMR to determine the prevalence of 3 types of hr-CVC: electrocardiographic abnormalities, cardiomyopathies, and anomalous coronary artery origin from the opposite sinus with intramural coronary course (ACAOS-IM). We examined the range of normal left ventricular size and function in the main study cohort (schoolchildren 11-14 yr old). We defined diagnostic criteria for hr-CVC and compared the cardiac measurements of these younger participants with those of older children whom we examined (age, 15-18 yr). From 5,169 completed diagnostic studies (mean participant age, 13.06 ± 1.78 yr), CMR results revealed 76 previously undiagnosed cases of hr-CVC (1.47% of the total cohort): 11 of dilated cardiomyopathy (14.5%), 3 of nonobstructive hypertrophic cardiomyopathy (3.9%), 23 ACAOS-IM cases (30.3%; 6 left-ACAOS and 17 right-ACAOS), 4 Wolff-Parkinson-White patterns (5.3%), 34 prolonged QT intervals (44.7%), and 1 Brugada pattern (1.3%). Cardiomyopathies were significantly more prevalent in the older children. Of note, we identified 959 cases (18.5%) of left ventricular noncompaction. If our estimate is accurate, only 1.47% of school-age sports participants will need focused secondary evaluations; the rest can probably be reassured about their cardiac health after one 30-minute screening study.

Two-center clinical validation and quantitative assessment of respiratory triggered retrospectively cardiac gated balanced-SSFP cine cardiovascular magnetic resonance imaging in adults

BACKGROUND

Breath-hold (BH) requirement remains the limiting factor on the spatio-temporal resolution and coverage of the cine balanced steady-state free precession (bSSFP) cardiovascular magnetic resonance (CMR) imaging. In this prospective two-center clinical trial, we validated the performance of a respiratory triggered (RT) bSSFP cine sequence for evaluation of biventricular function.

METHODS

Our study included 23 asymptomatic healthy subjects and 60 consecutive patients from Institute A (n = 39) and Institute B (n = 21) referred for a clinically indicated CMR study. We implemented a RT sequence with a respiratory synchronized drive to steady state (SS) of bSSFP signal, before the commencement of image data acquisition with prospective cardiac arrhythmia rejection and retrospectively cardiac gated reconstruction in real-time. Left (LV) and right (RV) ventricular function and LV mass were evaluated by using RT-bSSFP and conventional BH-bSSFP sequences with one cardiac cycle for SS preparation keeping all the imaging parameters identical. The performance of the sequences was evaluated by using quantitative and semi-quantitative metrics.

RESULTS

Global LV and RV functional parameters and LV mass obtained from the RT-bSSFP and BH-bSSFP sequences were in good agreement. Quantitative metrics designed to capture fluctuation in SS signal intensity showed no significant difference between sequences. In addition, blood-to-myocardial contrast was nearly identical between sequences. The combined clinical score for image quality was excellent or good for 100% of cases with the BH-bSSFP and 83% of cases with the RT-bSSFP sequence. The de facto image acquisition time for RT-bSSFP was statistically significantly longer than that for conventional BH-bSSFP (7.9 ± 3.4 min vs. 5.1 ± 2.6 min).

CONCLUSIONS

Cine RT-bSSFP is an alternative for evaluating global biventricular function with contrast and spatio-temporal resolutions that are similar to those attained by using the BH-bSSFP sequence, albeit with a modest time penalty and a small reduction in image quality.

Hypertrophy Regression With N-Acetylcysteine in Hypertrophic Cardiomyopathy (HALT-HCM): A Randomized, Placebo-Controlled, Double-Blind Pilot Study

RATIONALE

Hypertrophic cardiomyopathy (HCM) is a genetic paradigm of cardiac hypertrophy. Cardiac hypertrophy and interstitial fibrosis are important risk factors for sudden death and morbidity in HCM. Oxidative stress is implicated in the pathogenesis of cardiac hypertrophy and fibrosis. Treatment with antioxidant N-acetylcysteine (NAC) reverses cardiac hypertrophy and fibrosis in animal models of HCM.

OBJECTIVE

To determine effect sizes of NAC on indices of cardiac hypertrophy and fibrosis in patients with established HCM.

METHODS AND RESULTS

HALT-HCM (Hypertrophy Regression With N-Acetylcysteine in Hypertrophic Cardiomyopathy) is a double-blind, randomized, sex-matched, placebo-controlled single-center pilot study in patients with HCM. Patients with HCM, who had a left ventricular wall thickness of ≥15 mm, were randomized either to a placebo or to NAC (1:2 ratio, respectively). NAC was titrated ≤2.4 g per day. Clinical evaluation, blood chemistry, and 6-minute walk test were performed every 3 months, and electrocardiography, echocardiography, and cardiac magnetic resonance imaging, the latter whenever not contraindicated, before and after 12 months of treatment. Eighty-five of 232 screened patients met the eligibility criteria, 42 agreed to participate; 29 were randomized to NAC and 13 to placebo groups. Demographic, echocardiographic, and cardiac magnetic resonance imaging phenotypes at the baseline between the 2 groups were similar. WSE in 38 patients identified a spectrum of 42 pathogenic variants in genes implicated in HCM in 26 participants. Twenty-four patients in the NAC group and 11 in the placebo group completed the study. Six severe adverse events occurred in the NAC group but were considered unrelated to NAC. The effect sizes of NAC on the clinical phenotype, echocardiographic, and cardiac magnetic resonance imaging indices of cardiac hypertrophy, function, and extent of late gadolinium enhancement-a surrogate for fibrosis-were small.

CONCLUSIONS

Treatment with NAC for 12 months had small effect sizes on indices of cardiac hypertrophy or fibrosis. The small sample size of the HALT-HCM study hinders from making firm conclusions about efficacy of NAC in HCM.

CLINICAL TRIAL REGISTRATION

URL: http://www.clinicaltrials.gov. Unique identifier: NCT01537926.

Identification of established arrhythmogenic right ventricular cardiomyopathy mutation in a patient with the contrasting phenotype of hypertrophic cardiomyopathy

Background

Advances in the nucleic acid sequencing technologies have ushered in the era of genetic-based “precision medicine”. Applications of the genetic discoveries to practice of medicine, however, are hindered by phenotypic variability of the genetic variants. The report illustrates extreme pleiotropic phenotypes associated with an established causal mutation for hereditary cardiomyopathy.

Case presentation

We report a 61-year old white female who presented with syncope and echocardiographic and cardiac magnetic resonance (CMR) imaging findings consistent with the diagnosis of hypertrophic cardiomyopathy (HCM). The electrocardiogram, however, showed a QRS pattern resembling an Epsilon wave, a feature of arrhythmogenic right ventricular cardiomyopathy (ARVC). Whole exome sequencing (mean depth of coverage of exons 178X) analysis did not identify a pathogenic variant in the known HCM genes but identified an established causal mutation for ARVC. The mutation involves a canonical splice accepter site (c.2146-1G > C) in the PKP2 gene, which encodes plakophillin 2. Sanger sequencing confirmed the mutation. PKP2 is the most common causal gene for ARVC but has not been implicated in HCM. Findings on echocardiography and CMR during the course of 4-year follow up showed septal hypertrophy and a hyperdynamic left ventricle, consistent with the diagnosis of HCM. However, neither baseline nor follow up echocardiography and CMR studies showed evidence of ARVC. The right ventricle was normal in size, thickness, and function and there was no evidence of fibro-fatty infiltration in the myocardium.

Conclusions

The patient carries an established pathogenic mutation for ARVC and a subtle finding of ARVC but exhibits the classic phenotype of HCM, a contrasting phenotype to ARVC. The case illustrates the need for detailed phenotypic characterization for patients with hereditary cardiomyopathies as well as the challenges physicians face in applying the genetic discoveries in practicing genetic-based “precision medicine”.

Electronic supplementary material

The online version of this article (doi:10.1186/s12881-017-0385-8) contains supplementary material, which is available to authorized users.

High-Performance Hybrid Bismuth-Carbon Nanotube Based Contrast Agent for X-ray CT Imaging

Carbon nanotubes (CNTs) have been used for a plethora of biomedical applications, including their use as delivery vehicles for drugs, imaging agents, proteins, DNA, and other materials. Here, we describe the synthesis and characterization of a new CNT-based contrast agent (CA) for X-ray computed tomography (CT) imaging. The CA is a hybrid material derived from ultrashort single-walled carbon nanotubes (20-80 nm long, US-tubes) and Bi(III) oxo-salicylate clusters with four Bi(III) ions per cluster (Bi₄C). The element bismuth was chosen over iodine, which is the conventional element used for CT CAs in the clinic today due to its high X-ray attenuation capability and its low toxicity, which makes bismuth a more-promising element for new CT CA design. The new CA contains 20% by weight bismuth with no detectable release of bismuth after a 48 h challenge by various biological media at 37 °C, demonstrating the presence of a strong interaction between the two components of the hybrid material. The performance of the new Bi₄C@US-tubes solid material as a CT CA has been assessed using a clinical scanner and found to possess an X-ray attenuation ability of >2000 Hounsfield units (HU).

Endovascular therapy in patients with genetically triggered thoracic aortic disease: applications and short- and mid-term outcomes

OBJECTIVES

For patients with genetically triggered thoracic aortic disease, the morbidity and mortality associated with reoperation are high, making endovascular treatment an appealing option. We evaluated the short- and mid-term outcomes of different applications of endovascular intervention in such patients.

METHODS

Between January 2003 and April 2013, 60 patients received endovascular or hybrid treatment for genetically triggered thoracic aortic disease. The inclusion criteria were based on those devised by the National Registry of Genetically Triggered Thoracic Aortic Aneurysms and Cardiovascular Conditions. We included patients with thoracic aneurysm or dissection not due to trauma in a patient aged ≤50 years (n = 30), bicuspid aortic valve (BAV) and coarctation (n = 11), Marfan syndrome (n = 10), BAV with thoracic aneurysm (n = 4), Loeys-Dietz syndrome (n = 3), familial thoracic aneurysm or dissection (n = 3) and genetic mutations (n = 2). Some patients met more than one inclusion criterion. Forty-one (68.3%) patients were treated with only endovascular stent grafting. Nineteen (31.7%) patients underwent a hybrid procedure with open proximal or total arch replacement and concomitant endovascular stenting of the aortic arch or the descending thoracic aorta. Twenty-nine (48.3%) had previous cardiovascular operations (mean ± SD, 1.9 ± 1.4) before undergoing hybrid or endovascular therapy. The median follow-up was 2.3 years (interquartile interval 25-75%, 1.4-4.6 years).

RESULTS

The technical success rate was 100%. In-hospital mortality was 3.3% (n = 2) and neurological events occurred in 2 patients; 1 (1.6%) had a stroke and 1 (1.6%) suffered paraparesis with partial recovery. Fifteen repeat open or endovascular interventions were required in 10 surviving patients (17.2%). Overall survival during follow-up was 94.8% (55/58).

CONCLUSIONS

Endovascular technology can be helpful in treating selected young patients with genetically triggered thoracic aortic disease. Long-term studies and further evolution of endovascular technology will be necessary for it to be incorporated into the armamentarium of surgical options for this challenging patient population.

Coarctation-associated aneurysms: a localized disease or diffuse aortopathy

BACKGROUND

We evaluated the occurrence and treatment of aortic aneurysms in coarctation patients.

METHODS

During 1962 to 2011, 943 cases of coarctation were repaired. Aortic aneurysms were identified in 55 patients (5.8%). Forty-eight had prior coarctation repair (median 23 years earlier, interquartile range 18 to 26 years). Forty-two aneurysms were found in the descending thoracic aorta (76.4%), 18 in the ascending aorta (32.7%), 8 in the left subclavian artery (14.5%), and 1 each (1.8%) in the abdominal aorta, iliac artery, and innominate artery. Twenty-three patients (41.8%) had multiple aneurysms. Twenty-five patients (45.4%) had a bicuspid aortic valve.

RESULTS

Fifty-three patients' aneurysms were treated surgically. Thirty-five (66.0%) had descending thoracic aortic repair, of whom 11 had aorto-left subclavian bypass. Aortic cross-clamping alone was used in 23 patients, left heart bypass in 4, and circulatory arrest in 8. Eleven patients underwent endovascular repair (20.8%). Proximal aortic aneurysms were repaired in 7 patients (13.2%); 1 had simultaneous antegrade endostent delivery. Four patients had ascending-to-descending aortic bypass (7.3%). Concomitant valve-sparing root repair was performed in 2 patients, Bentall in 4, aortic valve replacement in 3, and coronary artery bypass in 1. One 30-day death occurred (1.9%). Three patients (5.7%) had transient neurologic deficits, 2 (3.8%) required tracheostomy, and 11 (20.8%) had vocal cord paralysis.

CONCLUSIONS

Coarctation is a marker for aortic aneurysm formation in adults and merits long-term surveillance. Anatomic complexity and associated conditions can complicate the surgical repair. Various open, extra-anatomic, and endovascular techniques may be used.

Bismuth@US-tubes as a Potential Contrast Agent for X-ray Imaging Applications

The encapsulation of bismuth as BiOCl/Bi₂O₃ within ultra-short (ca. 50 nm) single-walled carbon nanocapsules (US-tubes) has been achieved. The Bi@US-tubes have been characterized by high-resolution transmission electron microscopy (HR-TEM), energy-dispersive X-ray spectroscopy (EDS), thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. Bi@US-tubes have been used for intracellular labeling of pig bone marrow-derived mesenchymal stem cells (MSCs) to show high X-ray contrast in computed tomography (CT) cellular imaging for the first time. The relatively high contrast is achieved with low bismuth loading (2.66% by weight) within the US-tubes and without compromising cell viability. X-ray CT imaging of Bi@US-tubes-labeled MSCs showed a nearly two-fold increase in contrast enhancement when compared to unlabeled MSCs in a 100 kV CT clinical scanner. The CT signal enhancement from the Bi@US-tubes is 500 times greater than polymer-coated Bi₂S₃ nanoparticles and several-fold that of any clinical iodinated contrast agent (CA) at the same concentration. Our findings suggest that the Bi@US-tubes can be used as a potential new class of X-ray CT agent for stem cell labeling and possibly in vivo tracking.

Use of magnetic resonance imaging to assess myocardial perfusion after transmyocardial laser revascularization

BACKGROUND

Transmyocardial laser revascularization (TMLR) is an alternative treatment modality for patients with refractory angina who are not candidates for conventional surgical or percutaneous revascularization. Clinical studies of TMLR have not shown one-to-one correlation between increased myocardial perfusion and improved clinical status.

METHODS

Three patients (51, 53, and 70 years old) with severe, diffuse coronary artery disease not amenable to conventional surgical revascularization and with angina (Canadian Cardiovascular Society [CCS] class 3-4) refractory to maximal medical therapy underwent TMLR with a CO2 laser. Preoperative and postoperative cardiac magnetic resonance imaging (MRI) were performed to assess left ventricular perfusion and wall-motion changes in the laser-treated areas. Postoperative MRIs were performed within 6 months of TMLR and at 12 months. Angina status was assessed with the Seattle Angina Questionnaire.

RESULTS

Postoperative adenosine stress myocardial perfusion imaging with MRI revealed improved overall perfusion and a reduction in subendocardial hypoperfused areas when compared to preoperative images. In all patients, an improvement in CCS class was consistent with an improvement in perfusion.

CONCLUSIONS

Cardiac MRI can be used to assess improved subendocardial perfusion after TMLR treatment. In our study, we found that endocardial perfusion was maintained over a 12-month period.