Cardiac magnetic resonance imaging in valvular heart disease

Aortic stenosis assessment from the 3-chamber cine: Ratio of balanced steady-state-free-precession (bSSFP) blood signal between the aorta and left ventricle predicts severity

BACKGROUND

Cardiovascular magnetic resonance (CMR) imaging is an important tool for evaluating the severity of aortic stenosis (AS), co-existing aortic disease, and concurrent myocardial abnormalities. Acquiring this additional information requires protocol adaptations and additional scanner time, but is not necessary for the majority of patients who do not have AS. We observed that the relative signal intensity of blood in the ascending aorta on a balanced steady state free precession (bSSFP) 3-chamber cine was often reduced in those with significant aortic stenosis. We investigated whether this effect could be quantified and used to predict AS severity in comparison to existing gold-standard measurements.

METHODS

Multi-centre, multi-vendor retrospective analysis of patients with AS undergoing CMR and transthoracic echocardiography (TTE). Blood signal intensity was measured in a ∼1 cm2 region of interest (ROI) in the aorta and left ventricle (LV) in the 3-chamber bSSFP cine. Because signal intensity varied across patients and scanner vendors, a ratio of the mean signal intensity in the aorta ROI to the LV ROI (Ao:LV) was used. This ratio was compared using Pearson correlations against TTE parameters of AS severity: aortic valve peak velocity, mean pressure gradient and the dimensionless index. The study also assessed whether field strength (1.5 T vs. 3 T) and patient characteristics (presence of bicuspid aortic valves (BAV), dilated aortic root and low flow states) altered this signal relationship.

RESULTS

314 patients (median age 69 [IQR 57-77], 64% male) who had undergone both CMR and TTE were studied; 84 had severe AS, 78 had moderate AS, 66 had mild AS and 86 without AS were studied as a comparator group. The median time between CMR and TTE was 12 weeks (IQR 4-26). The Ao:LV ratio at 1.5 T strongly correlated with peak velocity (r = -0.796, p = 0.001), peak gradient (r = -0.772, p = 0.001) and dimensionless index (r = 0.743, p = 0.001). An Ao:LV ratio of < 0.86 was 84% sensitive and 82% specific for detecting AS of any severity and a ratio of 0.58 was 83% sensitive and 92% specific for severe AS. The ability of Ao:LV ratio to predict AS severity remained for patients with bicuspid aortic valves, dilated aortic root or low indexed stroke volume. The relationship between Ao:LV ratio and AS severity was weaker at 3 T.

CONCLUSIONS

The Ao:LV ratio, derived from bSSFP 3-chamber cine images, shows a good correlation with existing measures of AS severity. It demonstrates utility at 1.5 T and offers an easily calculable metric that can be used at the time of scanning or automated to identify on an adaptive basis which patients benefit from dedicated imaging to assess which patients should have additional sequences to assess AS.

Electrocardiographic QRS duration reflects right ventricular remodeling in patients undergoing corrective surgery for isolated tricuspid regurgitation: a comparative study with cardiac magnetic resonance imaging

BACKGROUND

The role of electrocardiogram (ECG) is unclear for the longitudinal follow-up of patients who undergo corrective surgery for isolated severe tricuspid regurgitation (TR).

HYPOTHESIS

This study sought to investigate the usefulness of changes in QRS duration of ECG after TR surgery in predicting right ventricular (RV) reverse remodeling as determined by cardiac magnetic resonance imaging (CMR).

METHODS

We enrolled 30 consecutive TR patients (27 women, aged 57.8 ± 9.6 years) who had undergone prior left-sided valve surgery. A computer-assisted analysis was performed for objective calculation of QRS duration before and after surgery.

RESULTS

At a median CMR follow-up of 27.5 months postsurgery, QRS duration was cut by 14.6%, from 110.4 ± 14.6 msec to 96.9 ± 11.9 msec (P < 0.001), while CMR showed a decrease in RV end-diastolic volume index (RV-EDVI) from 179.5 ± 59.7 to 119.1 ± 30.4 mL/m(2) (P < 0.001). QRS duration correlated significantly with RV-EDVI and RV end-systolic volume index (r = 0.65, P < 0.001 and r = 0.53, P < 0.001, respectively), and a percent change in QRS duration was significantly correlated with a percent change in RV-EDVI (r = 0.40, P = 0.03). When significant RV reverse remodeling was defined as a reduction in RV-EDVI ≥20% following TR surgery, the sensitivity and specificity for significant RV reverse remodeling were 75% and 78%, respectively, with a 9% reduction in QRS duration (P = 0.01, area underneath the receiver operator curve [AUC] = 0.81).

CONCLUSIONS

The extent of changes in postoperative QRS duration can be used as a useful, inexpensive, and simple index reflecting the occurrence of significant RV reverse remodeling in patients undergoing corrective TR surgery.

Four-dimensional phase contrast MRI with accelerated dual velocity encoding

PURPOSE

To validate a novel approach for accelerated four-dimensional phase contrast MR imaging (4D PC-MRI) with an extended range of velocity sensitivity.

MATERIALS AND METHODS

4D PC-MRI data were acquired with a radially undersampled trajectory (PC-VIPR). A dual V(enc) (dV(enc) ) processing algorithm was implemented to investigate the potential for scan time savings while providing an improved velocity-to-noise ratio. Flow and velocity measurements were compared with a flow pump, conventional 2D PC MR, and single V(enc) 4D PC-MRI in the chest of 10 volunteers.

RESULTS

Phantom measurements showed excellent agreement between accelerated dV(enc) 4D PC-MRI and the pump flow rate (R(2) ≥ 0.97) with a three-fold increase in measured velocity-to-noise ratio (VNR) and a 5% increase in scan time. In volunteers, reasonable agreement was found when combining 100% of data acquired with V(enc) = 80 cm/s and 25% of the high V(enc) data, providing the VNR of a 80 cm/s acquisition with a wider velocity range of 160 cm/s at the expense of a 25% longer scan.

CONCLUSION

Accelerated dual V(enc) 4D PC-MRI was demonstrated in vitro and in vivo. This acquisition scheme is well suited for vascular territories with wide ranges of flow velocities such as congenital heart disease, the hepatic vasculature, and others.

Current developments in the tissue engineering of autologous heart valves: moving towards clinical use

The use of tissue-engineering methods to create autologous heart valve constructs has the potential to overcome the fundamental drawbacks of more traditional valve prostheses. Traditional mechanical valves, while durable, increase the risk for endocarditis and thrombogenesis, and require the recipient to continue lifelong anticoagulant therapy. Homograft or xenograft heart valve prostheses are associated with immune reaction and progressive deterioration with limited durability. Most importantly, neither option is capable of growth and remodeling in vivo and both options place the patient at risk for valve-related complications and reoperation. These shortcomings have prompted the application of tissue-engineering techniques to create fully autologous heart valve replacements. Future clinically efficacious tissue-engineered autologous valves should be nonthrombogenic, biocompatible, capable of growth and remodeling in vivo, implantable with current surgical techniques, hemodynamically perfect, durable for the patient’s life and most importantly, significantly improve quality of life for the patient. In order to meet these expectations, the nature of the ideal biochemical milieu for conditioning an autologous heart valve will need to be elucidated. In addition, standardized criteria by which to quantitatively evaluate a tissue-engineered heart valve, as well as noninvasive analytical techniques for use in long-term animal models, will be required. This article highlights the advances, challenges and future clinical prospects in the field of tissue engineering of autologous heart valves, focusing on progress made by studies that have investigated a fully autologous, tissue-engineered pulmonary valve replacement in vivo.

B-type natriuretic Peptide in isolated severe tricuspid regurgitation: determinants and impact on outcome

BACKGROUND

The plasma B-type natriuretic peptide (BNP) level is a useful prognostic marker in heart failure and valvular heart disease. In patients with isolated severe tricuspid regurgitation (TR), little is known about the determinants of plasma BNP levels and the correlation with future outcome. The purpose of this study was to identify the determinants of plasma BNP levels in patients with isolated severe TR and the value of the BNP level in predicting postoperative outcomes after corrective surgery.

METHODS

We prospectively enrolled 39 patients with isolated, severe TR undergoing corrective surgery. A plasma BNP assay and cardiac magnetic resonance (CMR) imaging were performed before surgery. The combined end-point was the occurrence of cardiac death or readmission due to heart failure.

RESULTS

Linear regression analysis showed that the left ventricular ejection fraction and right ventricular end systolic volume were the most important determinants of the BNP levels (p = 0.002, R(2) = 0.315). Based on the receiver operating characteristics (ROC) curve, we were able to derive an optimal cutoff value (200 pg/mL) to predict postoperative cardiac death with a sensitivity of 80% and a specificity of 85%. The one-year survival rate was 96% in patients with a BNP < 200 pg/mL and 53% in patients with a BNP ≥ 200 pg/dL (p = 0.001).

CONCLUSION

An elevation in the BNP level is determined by the functional status of the right and left ventricles in patients with isolated, severe TR. An elevated BNP predicts adverse events after corrective surgery. Therefore, the BNP level should be included in the clinical evaluation and risk stratification of patients with isolated TR.

Assessment of haemodynamic effects of surgical correction for severe functional tricuspid regurgitation: cardiac magnetic resonance imaging study

AIMS

There has been growing attention for the development of functional tricuspid regurgitation (TR) long after left-sided valve surgery. We attempted to determine the long-term haemodynamic effects of corrective surgery for severe functional TR in patients who had prior left-sided valve surgery using cardiac magnetic resonance imaging (CMR).

METHODS AND RESULTS

Thirty-one patients with severe functional TR (TR fraction of 46.0+/-16.2% by CMR) were analysed. CMR was performed within 1 month before and at a median 27.0 months after surgery. Long after TR surgery, 28 of the 31 patients had no or mild residual TR, two had mild-to-moderate TR, and one showed moderate TR. Remarkable reductions in the right ventricular (RV) end-diastolic volume index (RV-EDVI) (177.4+/-59.1 mL/m(2) vs. 118.2+/-31.2 mL/m(2), P<0.001) and end-systolic volume index (RV-ESVI) (88.5+/-30.1 mL/m(2) vs. 67.2+/-31.0 mL/m(2), P=0.002) were observed, whereas RV ejection fraction (RV-EF) showed no change (49.7+/-8.3% vs. 44.9+/-12.5%, P=0.09). Pre-operative RV-EDVI (R=-0.86, P<0.001) and RV-ESVI (R=-0.55, P=0.001) were significantly associated with their respective changes after corrective surgery. Post-surgery, a normal RV-EF was achieved in 14 patients (42.5%). Pre-operative RV-EDVI of 164 mL/m(2) effectively discriminated patients with normal RV-EF from those without post-surgery, with a sensitivity of 77% and a specificity of 72% (P=0.01). A significant rise in the left ventricular (LV) EDVI and cardiac index (CI) was found after surgery (from 92.9+/-24.4 to 123.2+/-31.6 mL/m(2) for LV-EDVI, P<0.001; from 3.8+/-1.3 to 4.2+/-0.8 L/min/m(2) for CI, P=0.03). Functional capacity as assessed by NYHA class showed a significant improvement from 2.7+/-0.6 before surgery to 2.0+/-0.6 long after surgery (P<0.001).

CONCLUSION

Successful TR surgery can remarkably reduce RV volumes and preserve RV systolic function. In addition, successful TR surgery led to a significant rise in LV preload and CI, which may significantly contribute to a significant amelioration in the functional capacity of the patients. It seems that RV volume measurement by CMR is helpful for determining optimal timing for TR surgery.