Aortic distensibility after aortic root replacement assessed with cardiovascular magnetic resonance

BACKGROUND AND AIM OF THE STUDY: The changes in geometry of the aortic root during the cardiac cycle are thought to be essential for optimal valve function, both in terms of leaflet stress and dynamic behavior. Using cardiac magnetic resonance (CMR), the study aim was to determine aortic root distensibility of the homograft (group H) and the Medtronic Freestyle xenograft (group F) after aortic root replacement, from a prospective randomized trial. METHODS: CMR was performed in 15 patients (six homografts, nine Freestyle) at six months and one year after surgery. Percentage change in aortic radius (PCR) and pressure strain elastic modulus (PSEM) were measured as indices of distensibility, and results related to left ventricular mass (LVM). RESULTS: At six months after surgery, mean PCR was 12+/-2.5 in group H and 12.9+/-6.1 in group F (p = NS), and PSEM was 428.5+/-69.8 and 493.5+/-72.7 g/cm2, respectively (p = NS). PCR was reduced to 10+/-1.7% in group H, and by 8.5+/-2.8% in group F (p = NS), while PSEM was increased to 520.5+/-87.3 and 825+/-420.4, respectively (p = NS) at the one-year follow up. Regression analysis showed a correlation between PCR and LVM (r = 0.52, p = 0.08) and LVM index (r = 0.46, p = 0.14), respectively. In addition, there was a relationship between PSEM, LVM and LVM index, suggesting that the stiffer the root wall, the higher the postoperative LVM. CONCLUSION: Up to one year after aortic root replacement, the wall of both the allogenic and xenogenic valves retained near-normal distensibility. For the first time, a correlation was demonstrated between the elastic properties of the aortic root and LVM. The longer-term behavior and clinical implications of these findings require further investigation.     

T-wave and its association with myocardial fibrosis on cardiovascular magnetic resonance examination

Background

Risk stratification in non-ischemic myocardial disease poses a challenge. While cardiovascular magnetic resonance (CMR) is a comprehensive tool, the electrocardiogram (ECG) provides quick impactful clinical information. Studying the relationships between CMR and ECG can provide much-needed risk stratification. We evaluated the electrocardiographic signature of myocardial fibrosis defined as presence of late gadolinium enhancement (LGE) or extracellular volume fraction (ECV) ≥29%.

Methods

We evaluated 240 consecutive patients (51% female, 47.1 ± 16.6 years) referred for a clinical CMR who underwent 12-lead ECGs within 90 days. ECG parameters studied to determine association with myocardial fibrosis included heart rate, QRS amplitude/duration, T-wave amplitude, corrected QT and QT peak, and Tpeak-Tend. Abnormal T-wave was defined as low T-wave amplitude ≤200 µV or a negative T wave, both in leads II and V5.

Results

Of the 147 (61.3%) patients with myocardial fibrosis, 67 (28.2%) had ECV ≥ 29%, and 132 (54.6%) had non-ischemic LGE. An abnormal T-wave was more prevalent in patients with versus without myocardial fibrosis (66% versus 42%, p < .001). Multivariable analysis demonstrated that abnormal T-wave (OR 1.95, 95% CI 1.09–3.49, p = .03) was associated with myocardial fibrosis (ECV ≥ 29% or LGE) after adjustment for clinical covariates (age, gender, history of hypertension, and heart failure). Dynamic nomogram for predicting myocardial fibrosis using clinical parameters and the T-wave was developed: https://normogram.shinyapps.io/CMR_Fibrosis/ .

Conclusion

Low T-wave amplitude ≤ 200 µV or negative T-waves are independently associated with myocardial fibrosis. Prospective evaluation of T-wave amplitude may identify patients with a high probability of myocardial fibrosis and guide further indication for CMR.

     

Quantification of regurgitant fraction in mitral regurgitation by cardiovascular magnetic resonance: comparison of techniques

BACKGROUND AND AIM OF THE STUDY: Cardiovascular magnetic resonance (CMR) assessment of mitral regurgitant volume from the subtraction of the right ventricular stroke volume (RVSV) from left ventricular stroke volume (LVSV) has commonly been performed using volumetric techniques. This is sensitive to errors in RVSV visualization and regurgitation of other heart valves, and therefore subtracting aortic flow volume from LVSV may be preferable. The study aim was to compare both techniques in a single CMR examination. METHODS: Twenty-eight patients with isolated mitral regurgitation underwent left ventricular (LV) and right ventricular (RV) volumetry and aortic flow volume measurements. Mitral regurgitant fraction (RF) was calculated as either RF(VOL) = [LVSV - RVSV] or RF(FLOW) = [LVSV - aortic flow volume], both expressed as a fraction of LVSV. The agreement of the measurements was assessed as a measure of robustness in clinical practice. RESULTS: There was good agreement between aortic and pulmonary flow (mean +/- SD difference -0.8 +/- 8.1 ml), and aortic flow volume and RVSV by volumetry (mean difference -2.6 +/- 11.8 ml). Intra- and interobserver variability (SD) of aortic flow volume (+/-6.6 ml and +/-5.3 ml) was superior to that of the RVSV (+/-8.5 ml and +/-12 ml). The intra- and inter-observer variability (SD) of RF(FLOW) was lower (+/-4.8% and +/-7.7%) than by RF(VOL) (+/-6.7% and +/-8.8%). CONCLUSION: The RF(FLOW) technique maximized intra- and inter-observer agreement, and is the optimal CMR technique to quantify mitral regurgitation. RF(FLOW) also has the advantage of allowing correction for aortic regurgitation when it is present, and is potentially independent of the effects of tricuspid and pulmonary regurgitation.     

Doppler-echocardiographic assessment of pulmonary regurgitation in adults with repaired tetralogy of Fallot: comparison with cardiovascular magnetic resonance imaging

Aims

The purpose of this study was to compare the noninvasive assessment of severity of pulmonary regurgitation with Doppler echocardiography versus cardiovascular magnetic resonance imaging (CMR) in adult patients with repaired tetralogy of Fallot (rTOF).

Methods

We studied 52 (22 females) consecutive patients (aged 32 ± 2 years, 23 ± 5 years after rTOF) using Doppler echocardiography and compared these findings with CMR. From the continuous-wave Doppler trace, the duration of pulmonary regurgitation and of total diastole was measured and the ratio between the 2 was defined as pulmonary regurgitation index (PRi). Pulmonary regurgitant fraction (PRF) was assessed with flow phase velocity mapping with CMR.

Results

Patients were divided into 2 groups according to the median value (24.5%) of PRF measured by CMR: Group I (26 patients) with PRF ≤24.5% and Group II with PRF >24.5%. There was no difference between patients' age, sex, or age at repair between the 2 groups. More patients from Group II had a right ventricular outflow or transannular patch repair compared to Group I (12/26 [46%] vs 6/26 [23%], P < .01). Mean pulmonary regurgitation time was shorter (340 ± 60 vs 440 ± 135 ms, P = .001) and PRi was lower (0.61 ± 0.11 vs 0.91 ± 0.11, P < .001) in Group II compared to Group I. Color Doppler regurgitant jet was also broader in Group II (1.4 ± 0.4 vs 0.7 ± 0.5 cm, P < .001), signifying more severe pulmonary regurgitation. Doppler-measured PRi correlated closely with CMR regurgitant fraction (r = −0.82, P < .001) and with color Doppler pulmonary regurgitant jet width (r = −0.66, P < .001); the latter correlated with PRF assessed with CMR (r = 0.72, P < .001). A PRi <0.77 had 100% sensitivity and 84.6% specificity for identifying patients with pulmonary regurgitant fraction >24.5%, with a predictive accuracy of 95%. Furthermore, echocardiographically-assessed right ventricular end-diastolic dimensions correlated with CMR end-diastolic volume index (r = 0.49, P < .001 ).

Conclusions

Pulmonary regurgitation is common in asymptomatic adults with rTOF. Severity of pulmonary regurgitation and its effects on right ventricular dimensions in these patients can be assessed noninvasively by Doppler echocardiography and CMR, with reasonable agreement between the 2 techniques.     

Comparison of severity of aortic regurgitation by cardiovascular magnetic resonance versus transthoracic echocardiography

Transthoracic echocardiography is the current standard for assessing aortic regurgitation (AR). AR severity can also be evaluated by flow measurement in the ascending aorta using cardiac magnetic resonance (CMR); however, the optimal site for flow measurement and the regurgitant fraction (RF) severity grading criteria that best compares with the transthoracic echocardiographic assessment of AR are not clear. The present study aimed to determine the optimal site and RF grading criteria for AR severity using phase-contrast flow measurements and CMR. A prospective observational study was performed of 107 consecutive patients who were undergoing CMR of the thoracic aorta. Using CMR, the AR severity and aortic dimensions were measured at 3 levels in the aorta (the sinotubular junction, mid-ascending aorta, and distal ascending aorta). The results were compared to the transthoracic echocardiographic grade of AR severity using multiple qualitative and quantitative criteria (grade 0, none; I+, mild; II+, mild to moderate; III+, moderate to severe; and IV+, severe). The mean RF values were significantly greater at the sinotubular junction than at the distal ascending aorta (13 ± 13.3% vs 9.4 ± 12.6%, respectively; p <0.001). The RF values that best defined AR severity using phase-contrast CMR were as follows: grade 0 to I+, <8%; grade II+, 8% to 19%; grade III+, 20 to 29%; and grade IV+, 30%) at the sinotubular or mid-ascending aorta. In conclusion, the quantitative RF values of AR severity using phase-contrast flow are best assessed in the proximal ascending aorta and differ from recognized quantitative echocardiographic criteria.     

The emerging clinical role of cardiovascular magnetic resonance imaging

Starting as a research method little more than a decade ago, cardiovascular magnetic resonance (CMR) imaging has rapidly evolved to become a powerful diagnostic tool used in routine clinical cardiology. The contrast in CMR images is generated from protons in different chemical environments and, therefore, enables high-resolution imaging and specific tissue characterization in vivo, without the use of potentially harmful ionizing radiation.CMR imaging is used for the assessment of regional and global ventricular function, and to answer questions regarding anatomy. State-of-the-art CMR sequences allow for a wide range of tissue characterization approaches, including the identification and quantification of nonviable, edematous, inflamed, infiltrated or hypoperfused myocardium. These tissue changes are not only used to help identify the etiology of cardiomyopathies, but also allow for a better understanding of tissue pathology in vivo. CMR tissue characterization may also be used to stage a disease process; for example, elevated T2 signal is consistent with edema and helps differentiate acute from chronic myocardial injury, and the extent of myocardial fibrosis as imaged by contrast-enhanced CMR correlates with adverse patient outcome in ischemic and nonischemic cardiomyopathies.The current role of CMR imaging in clinical cardiology is reviewed, including coronary artery disease, congenital heart disease, nonischemic cardiomyopathies and valvular disease.     

Advances in clinical applications of cardiovascular magnetic resonance imaging

Cardiovascular magnetic resonance (CMR) is an evolving technology with growing indications within the clinical cardiology setting. This review article summarises the current clinical applications of CMR. The focus is on the use of CMR in the diagnosis of coronary artery disease with summaries of validation literature in CMR viability, myocardial perfusion, and dobutamine CMR. Practical uses of CMR in non-coronary diseases are also discussed.     

Aortic root abscess. Initial experience using magnetic resonance imaging

The detection of aortic root abscess by magnetic resonance imaging has not been described previously. We report a patient with an aortic root abscess that was successfully diagnosed by magnetic resonance imaging and echocardiography. Computed tomography failed to detect the abscess. The patient recovered with antibiotic therapy. Based on this case and other reports in the literature, we advocate treating similar patients without surgery. We recommend magnetic resonance imaging as an investigational method where the diagnosis of aortic root abscess is ambiguous.     

Toward clinical risk assessment in hypertrophic cardiomyopathy with gadolinium cardiovascular magnetic resonance

OBJECTIVES: We sought to assess whether hyperenhancement by gadolinium cardiovascular magnetic resonance (CMR) occurs in hypertrophic cardiomyopathy (HCM) and correlates with the risk of heart failure and sudden death. BACKGROUND: The myocardial interstitium is abnormal in HCM at post-mortem. Focally increased interstitial myocardial space appears as hyperenhancement with gadolinium CMR. METHODS: In a blinded, prospective study, HCM patients were selected for the presence (n = 23) or absence (n = 30) of an increased clinical risk of sudden death and/or progressive adverse left ventricular (LV) remodeling. Gadolinium-enhanced CMR was performed. RESULTS: Myocardial hyperenhancement was found in 42 patients (79%), affecting 10.9% (range 0% to 48%) of the LV mass. There was a greater extent of hyperenhancement in patients with progressive disease (28.5% vs. 8.7%, p < 0.001) and in patients with two or more risk factors for sudden death (15.7% vs. 8.6%, p = 0.02). Improved discrimination was seen in patients >40 years old (29.6% vs. 6.7%, p < 0.001) for progressive disease and for patients <40 years old for risk factors for sudden death (15.7% vs. 2.1%, p = 0.002). Patients with diffuse rather than confluent enhancement had two or more risk factors for sudden death (87% vs. 33%, p = 0.01). CONCLUSIONS: Gadolinium CMR reveals myocardial hyperenhancement in HCM. The extent of hyperenhancement is associated with progressive ventricular dilation and markers of sudden death.     

Gadolinium delayed enhancement cardiovascular magnetic resonance correlates with clinical measures of myocardial infarction

OBJECTIVES: The current study tested the hypothesis that gadolinium delayed enhancement assessment of infarct size correlates with clinical indices of myocardial infarction (MI) in humans. Acute infarct mass by cardiac magnetic resonance (CMR) was compared with peak troponin I, acute and chronic left ventricular (LV) systolic function, and chronic infarct mass in patients imaged after recent acute MI. BACKGROUND: Cardiac magnetic resonance accurately determines myocardial viability in patients with chronic ischemic heart disease but is not well validated for recent MI. METHODS: Patients with first acute MI (n = 33) or chronic MI (n = 10) underwent cine CMR followed by gadolinium delayed enhancement imaging. A follow-up CMR scan was performed on 20 of the 33 acute MI patients and all of the chronic MI patients. RESULTS: In patients with acute percutaneous coronary intervention, acute MI mass correlated with peak troponin I (r = 0.83, p < 0.001, n = 23). In the 20 acute infarct patients with follow-up CMR scans, the acute infarct size correlated well with the follow-up LV ejection fraction (r = 0.86, p < 0.001). The transmural extent of delayed enhancement imaged acutely correlated inversely with wall thickening measured acutely (p < 0.001) and at follow-up (p < 0.001). Although chronic infarct size was reproducible (11 +/- 4% vs. 12 +/- 7%, p = NS), acute infarct size decreased from 16 +/- 12% to 11 +/- 9% (p < 0.003). CONCLUSION: In humans imaged shortly after acute MI, gadolinium delayed enhancement acute CMR infarct size correlates with acute and chronic indices of infarct size but will appear to diminish in size on follow-up.     

A clinical cardiovascular magnetic resonance service: operational considerations and the basic examination

Cardiovascular magnetic resonance (CMR) is now considered the "gold standard" for the assessment of regional and global systolic function, myocardial infarction and viability, and congenital heart disease. At specialized centers, CMR has become a clinical workhorse for the evaluation of ischemic heart disease and for heart failure and cardiomyopathies. Despite this versatility, general acceptance of CMR in cardiovascular medicine has progressed slowly. This article provides a basic understanding of important operational considerations when starting a CMR service and describes a conceptual framework of the components of a CMR examination.     

Clinical cardiovascular magnetic resonance imaging

Magnetic resonance imaging (MRI) is a powerful tool providing high-resolution images of the heart and great vessels without the use of ionizing radiation or contrast agents. MRI systems currently in use at many hospitals can be used effectively in the routine, clinical evaluation of many forms of cardiovascular disease, including great vessel disease, ischemic cardiac disease and congenital cardiac disease. Moreover, quantitative and cine MRI techniques are now available, which provide highly accurate measures of chamber size, wall motion and wall thickening. Recent developments in the areas of myocardial tagging, high-speed imaging and MR assessments of flow and perfusion suggest potential for an increasing role of MRI in the clinical evaluation of the cardiovascular system.