Nick G. Bellenger

IN VITRO AND PRELIMINARY IN VIVO VALIDATION OF ECHO PARTICLE IMAGE VELOCIMETRY IN CAROTID VASCULAR IMAGING

Noninvasive, easy-to-use and accurate measurements of wall shear stress (WSS) in human blood vessels have always been challenging in clinical applications. Echo particle image velocimetry (Echo PIV) has shown promise for clinical measurements of local hemodynamics and wall shear rate. Thus far, however, the method has only been validated under simple flow conditions. In this study, we validated Echo PIV under in vitro and in vivo conditions. For in vitro validation, we used an anatomically correct, compliant carotid bifurcation flow phantom with pulsatile flow conditions, using optical particle image velocimetry (optical PIV) as the reference standard. For in vivo validation, we compared Echo PIV-derived 2-D velocity fields obtained at the carotid bifurcation in five normal subjects against phase-contrast magnetic resonance imaging (PC-MRI)-derived velocity measurements obtained at the same locations. For both studies, time-dependent, 2-D, two-component velocity vectors; peak/centerline velocity, flow rate and wall shear rate (WSR) waveforms at the common carotid artery (CCA), carotid bifurcation and distal internal carotid artery (ICA) were examined. Linear regression, correlation analysis and Bland-Altman analysis were used to quantify the agreement of different waveforms measured by the two techniques. In vitro results showed that Echo PIV produced good images of time-dependent velocity vector maps over the cardiac cycle with excellent temporal (up to 0.7 ms) and spatial (∼0.5 mm) resolutions and quality, comparable with optical PIV results. Further, good agreement was found between Echo PIV and optical PIV results for velocity and WSR measurements. In vivo results also showed good agreement between Echo PIV velocities and phase contrast MRI velocities. We conclude that Echo PIV provides accurate velocity vector and WSR measurements in the carotid bifurcation and has significant potential as a clinical tool for cardiovascular hemodynamics evaluation.

Haemodynamic significance of ostial side branch nipping following percutaneous intervention at bifurcations: a pressure wire pilot study

Stenting of a coronary artery narrowing across a bifurcation with a side branch artery may result in a significant angiographic stenosis (nipping) of the side branch. If this causes symptoms of chest pain or ischaemic ECG changes at the time of the procedure, additional angioplasty (with or without stent insertion) through the stent struts is usually undertaken to improve blood flow into the side branch, but this increases subsequent risks of restenosis and stent thrombosis in the main vessel. In the absence of symptoms or ECG abnormalities, the functional significance of side branch nipping is uncertain and opinion on whether to treat a nipped side branch remains divided.1–4 The coronary pressure-derived fractional flow reserve (FFR) is a lesion-specific means of determining the functional significance of coronary artery narrowings, but its value in assessing side branch nipping is not known. This pilot study aimed to assess the correlation between the FFR across nipped side branch arteries that have been crossed by main vessel stents, with the degree of angiographic narrowing at the side branch ostium. The potential role of the coronary pressure wire in guiding treatment of the nipped side branch is considered. This study was registered with Southampton University NHS Trust R&D Department and approved by the local ethics committee. All patients gave written informed consent. All patients were scheduled for elective percutaneous intervention (PCI) for symptoms of chronic stable …

The relationship between the contralateral collateral supply and myocardial viability on cardiovascular magnetic resonance: Can the angiogram predict functional recovery?

BACKGROUND A collateral circulation which supplies a myocardial territory, subtended by a chronic total occlusion (CTO), may be observed at invasive coronary angiography. The prognostic and protective role of such collateralisation is well demonstrated suggesting that a good collateral circulation may be a predictor of myocardial viability, but current evidence is discrepant. The aim of this study is to assess the relationship between collateralisation from the contralateral epicardial vessels and myocardial viability by cardiovascular magnetic resonance (CMR). METHOD Consecutive patients with CTO having had both CMR and invasive coronary angiography were retrospectively identified. The collateral circulation was graded with the Cohen and Rentrop classification. CMR images were graded per segment for wall motion (1: normal/hyperkinetic, 2: hypokinetic, 3: akinetic, or 4: dyskinetic) and wall motion score index (WMSI) was calculated. The segmental transmurality of late gadolinium enhancement was scored as 1 (0%), 2 (1-25%), 3 (26-50%), 4 (51-75%) and 5 (76-100%). RESULTS A good collateral circulation was more likely to supply viable myocardium (p=0.01). There was no relationship between collateral circulation supply and wall motion score index (WMSI), however, increasing transmurality of LGE was significantly associated with higher mean WMSI representing increasing dysfunctional myocardium (p<0.001). CONCLUSION The presence of collateral coronary circulation at angiography predicts the presence of viability on cardiovascular MRI, with a gradation of greater viability associated with improving Rentrop grade. A collateral circulation at angiography should, therefore, prompt more formal assessment of viability and consideration of revascularisation in order for the patient to obtain the associated functional and prognostic improvement.

Safety and feasibility of dobutamine stress cardiac magnetic resonance for cardiovascular assessment prior to renal transplantation.

Aims Current guidelines recommend cardiovascular risk assessment prior to renal transplantation. There is currently no evidence for the role of cardiovascular magnetic resonance (CMR) in this population, despite an established evidence base in the non-chronic kidney disease (CKD) population. Our aim is to determine the feasibility and safety of dobutamine stress CMR (DSCMR) imaging in the risk stratification of CKD patients awaiting renal transplantation. Methods CKD patients who were deemed at high risk for coronary artery disease (CAD) and awaiting renal transplantation underwent DSCMR. Results Forty-one patients whose median age was 56 years (range 28–73 years) underwent DSCMR. Nineteen were undergoing haemodialysis, 10 peritoneal dialysis and 12 pre-dialysis. The aetiology of the renal failure was diabetes mellitus in 29%, glomerulonephritis in 24%, hypertension in 22% and autosomal dominant polycystic kidney disease in 10%. Thirty-eight patients (93%) achieved the end point, either positive for ischaemia or negative, achieving at least 85% of age-predicted heart rate. Two of them did not achieve target heart rate and one was discontinued because of severe headache. Of the 38 patients who achieved the end point, 35 (92%) were negative for inducible wall motion abnormalities and four (10%) were positive. There were no serious adverse effects. Conclusion DSCMR is a well tolerated and viable investigation for the cardiovascular risk stratification of high-risk CKD patients prior to renal transplantation. DSCMR already has an established evidence base in the non-CKD population with superiority over other non-invasive techniques. Larger studies with outcome data are now required to define its true utility in the CKD population.

In Vivo Validation of Echo Partical Image Velocimetry (Echo PIV) in Human Carotid Arteries Using Phase-Contrast MRI

Accurate non-invasive measurements of dynamic wall shear stresses (WSS) in the cardiovascular system should allow clinicians to evaluate the progression of atherosclerosis, estimate vulnerability of plaques, and assess hemodynamic changes in the proximity of implants such as vascular grafts and stents that may contribute to restenosis. Although computational methods have been used to obtain blood flow characteristics from patients, these methods are difficult to apply in routine fashion, are prone to errors due to incorrect application of boundary conditions and are time and resource intensive. Ultrasound Doppler methods [1] allow simple measurement of blood flow velocities but are not acceptable for shear measurements because they do not provide multiple-component velocity vectors, are prone to angulation error and have relatively poor spatial resolution. Phase contrast magnetic resonance imaging (PC-MRI) velocimetry [2] does provide good spatial resolution and multiple-component velocity vectors in vivo and is considered the gold-standard. However, PC-MRI is expensive, time consuming and possesses relatively poor temporal resolution.Copyright

Cardiac imaging to investigate suspected cardiac pain in the post-treadmill era

Symptomatic cardiovascular disease is one of the leading causes of hospital admissions in the UK; along with emergency attendances, over 100,000 patients are investigated using treadmill testing via rapid access chest pain clinics each year. With the introduction of new technologies, clinicians have a wide choice of investigations including nuclear perfusion scanning, dobutamine stress echocardiography, cardiac computed tomography and stress cardiac magnetic resonance imaging. These imaging modalities have their strengths and weaknesses, which depend not only on the pre-test likelihood of significant coronary artery disease but also the clinical characteristics of the patient. This article will review the differing imaging modalities, the patient experience, accuracy, prognostic data and future prospects for cardiac computed tomography and magnetic resonance imaging.

Cardiac magnetic resonance imaging is established in cardiomyopathies.

Raju and colleagues did not elaborate on the established role of cardiac magnetic resonance imaging in their clinical review of inherited cardiomyopathies.1 In hypertrophic cardiomyopathy such imaging allows accurate measurement of wall thickness, location of …

Cardiac magnetic resonance directed intervention following right ventricular infarction

A 45 year old man presented 30 hours after suffering an inferior ST elevation myocardial infarction (MI). On admission he was in cardiogenic shock with signs of severe right ventricular compromise, a junctional rhythm and acute renal failure. Initial creatine kinase …