Benjamin Clayton

Transcatheter aortic valve insertion (TAVI): a review

The introduction of transcatheter aortic valve insertion (TAVI) has transformed the care provided for patients with severe aortic stenosis. The uptake of this procedure is increasing rapidly, and clinicians from all disciplines are likely to increasingly encounter patients being assessed for or having undergone this intervention. Successful TAVI heavily relies on careful and comprehensive imaging assessment, before, during and after the procedure, using a range of modalities. This review outlines the background and development of TAVI, describes the nature of the procedure and considers the contribution of imaging techniques, both to successful intervention and to potential complications.

Assessment of the myocardium with cardiac computed tomography

The imaging of myocardial disease is of increasing importance for cardiologists from all subspecialties, for diagnosis, risk stratification, or to facilitate therapy. While the gold standard modalities for such assessment are cardiac magnetic resonance and echocardiography, these are not universally suitable. Cardiac computed tomography (CT), well-established for the assessment of coronary artery disease (CAD), can be of value in the assessment of myocardial pathology, due to excellent patient compatibility and tolerability, high spatial resolution, and acceptable tissue characterization. This review considers the value and limitations of CT in the assessment of the myocardial sequelae of CAD, and for patients with a variety of other cardiomyopathic diseases, depicts some of the common findings, and considers current developments in this area.

Diagnostic accuracy of high-definition CT coronary angiography in high-risk patients.

AIM To assess the diagnostic accuracy of computed tomography coronary angiography (CTCA) using a combination of high-definition CT (HD-CTCA) and high level of reader experience, with invasive coronary angiography (ICA) as the reference standard, in high-risk patients for the investigation of coronary artery disease (CAD). MATERIALS AND METHODS Three hundred high-risk patients underwent HD-CTCA and ICA. Independent experts evaluated the images for the presence of significant CAD, defined primarily as the presence of moderate (≥ 50%) stenosis and secondarily as the presence of severe (≥ 70%) stenosis in at least one coronary segment, in a blinded fashion. HD-CTCA was compared to ICA as the reference standard. RESULTS No patients were excluded. Two hundred and six patients (69%) had moderate and 178 (59%) had severe stenosis in at least one vessel at ICA. The sensitivity, specificity, positive predictive value, and negative predictive value were 97.1%, 97.9%, 99% and 93.9% for moderate stenosis, and 98.9%, 93.4%, 95.7% and 98.3%, for severe stenosis, on a per-patient basis. CONCLUSION The combination of HD-CTCA and experienced readers applied to a high-risk population, results in high diagnostic accuracy comparable to ICA. Modern generation CT systems in experienced hands might be considered for an expanded role.

Safety of intravenous β-adrenoceptor blockers for computed tomographic coronary angiography.

AIMS To assess the safety of our clinical practice using off-label intravenous metoprolol to facilitate computed tomographic (CT) coronary angiography. METHODS A retrospective analysis of scan reports and hospital admissions data was conducted to identify adverse events occurring following CT coronary angiography in patients who had received intravenous metoprolol prior to the scan. RESULTS A total of 3098 patients were included, of whom 1871 received intravenous metoprolol. Nine hundred and one patients received more than 15 mg and 129 patients received metoprolol despite a resting heart rate <65 beats min(-1) . There was a single adverse incident, comprising transient loss of consciousness. CONCLUSIONS The use of intravenous metoprolol to facilitate cardiac CT scanning appears safe. Dose limits recommended for other indications, generally in acutely unwell patients, may not need to be as stringent in this population.

CT coronary angiography in atrial fibrillation: a comparison of radiation dose and diagnostic confidence with retrospective gating vs prospective gating with systolic acquisition

OBJECTIVE To compare unmodulated, retrospective electrocardiographic (ECG) gating to prospective ECG gating with systolic acquisition for CT coronary angiography (CTCA) in patients with atrial fibrillation (AF), considering the radiation dose and the diagnostic confidence achieved with each technique. METHODS A retrospective service evaluation was conducted before and after prospective gating with systolic acquisition replaced retrospectively gated imaging for patients with AF undergoing CTCA at our institution. 25 consecutive patients were examined in each group. The scan parameters and radiation dose information had been collected in a prospective fashion. The image sets were read by blinded, expert readers who rated their diagnostic confidence using a 5-point Likert scale. RESULTS The radiation dose received by patients was significantly greater in the retrospectively gated group than those being scanned using prospective gating (21 vs 5.9 mSv, p < 0.01). The prospective gating technique was also associated with greater diagnostic confidence (mean, per-patient score 3.09 vs 3.78, p = 0.02). CONCLUSION Prospective gating with systolic acquisition appears to improve diagnostic confidence at a significantly reduced radiation dose compared with retrospective gating in patients with AF. ADVANCES IN KNOWLEDGE The use of prospective gating with systolic triggering significantly reduces the radiation exposure to patients in AF undergoing CTCA. The same protocol also appears to improve diagnostic confidence.

Primary Percutaneous Coronary Intervention for Refractory Cardiac Arrest

The identification and treatment of reversible causes is paramount to the success of resuscitation in cardiac arrest, particularly when standard therapy has failed. Acute coronary occlusion is one such cause, and the introduction of primary percutaneous coronary intervention services may provide an opportunity for emergency revascularization in this setting. This article describes 2 patients with cardiac arrest as a result of coronary occlusion, in which standard therapeutic measures proved futile. The first patient had refractory ventricular fibrillation, and the second had an episode of ventricular fibrillation followed by true pulseless electrical activity: total cessation of ventricular activity. In both examples, external mechanical compression and primary percutaneous coronary intervention facilitated coronary revascularization and achieved return of spontaneous circulation, leading to survival to hospital discharge.

118 Single Source, Dual Energy CT for the Assessment of Calcified Coronary Artery Disease

Introduction Arterial calcification can limit the visualisation of vessel lumen at CT coronary angiography (CTCA). Dual energy CT (DECT) using two x-ray spectra of differing energy, either from distinct sources or using novel detectors and a single source, offers novel approaches to this problem. It allows the generation of images depicting objects as if they have been subjected to a specific photon energy (keV) rather than a polychromatic beam (virtual monochromatic images). With improved material identification, based on its attenuation coefficient at each keV and transformation into a linear combination of the two basis materials (material decomposition), it may also be possible to subtract materials from each other, such as calcium from iodine. Single source DECT, using two energy spectra from a single anode almost simultaneously using rapid tube voltage switching, requires novel detector technology capable of distinguishing signals 0.25 ms apart without artefact from detector artefact. To date, this has not been evaluated in patients with coronary calcification. This feasibility study examined potential benefits and limitations of virtual monochromatic and material decomposition images for assessing calcified coronary arteries, and their potential diagnostic accuracy compared to invasive angiography. Methods The study was approved by the National Research Ethics Service. Patients gave informed, written consent. Thirty patients undergoing invasive angiography on clinical grounds, with evidence of coronary calcification, underwent CTCA with a single-source DECT scanner. The results of each test were assessed by experienced, independent, blinded readers and compared in per-segment, per-vessel and per-patient analyses. Results 403 segments in 86 vessels were analysed. The median Agatston score was 964. The accuracy of virtual monochromatic imaging is outlined in Table 1. Overall the accuracy for the identification of moderate and severe stenosis was 0.88 and 0.88 on a per-segment basis, 0.84 and 0.86 per vessel, and 0.93 and 0.97 per-patient. The weighted kappa score between invasive and CT angiography was 0.71 suggesting good agreement.Abstract 118 Table 1 Per segment Per vessel Per patient >50% stenosis Sensitivity 0.76 (0.66–0.84) 0.78 (0.64–0.89) 0.93 (0.76–0.99) Specificity 0.92 (0.89–0.95) 0.93 (0.80–0.98) 1.00 (0.19–1.00) PPV 0.76 (0.66–0.84) 0.92 (0.79–0.98) 1.00 (0.86–1.00) NPV 0.92 (0.89–0.95) 0.79 (0.65–0.90) 0.50 (0.08–0.92) >70% stenosis Sensitivity 0.73 (0.60–0.83) 0.78 (0.61–0.90) 1.00 (0.85–1.00) Specificity 0.91 (0.87–0.93) 0.94 (0.84–0.98) 0.83 (0.36–0.97) PPV 0.58 (0.47–0.70) 0.90 (0.74–0.98) 0.96 (0.79–0.99) NPV 0.95 (0.92–0.97) 0.86 (0.74–0.94) 1.00 (0.48–1.00) The per-segment sensitivity, specificity, PPV and NPV (and 95% confidence intervals) of the material decomposition images were 0.67 (0.57–0.76), 0.82 (0.77–0.86), 0.54 (0.45–0.63) and 0.88 (0.84–0.92) respectively for moderate stenosis, and 0.70 (0.57–0.80), 0.79 (0.75–0.83), 0.40 (0.31–0.49) and 0.93 (0.89–0.96) respectively for severe stenosis. Overall accuracy was 0.78 for both moderate and severe stenosis. Calcium subtraction was highly inconsistent, mainly due to image noise with resultant misidentification of calcium and excessive subtraction. Conclusions The study suggests that single source DECT is feasible in patients with severe coronary calcification, and virtual monochromatic imaging may improve accuracy compared to conventional CT. A larger study comparing standard and DECT is merited.

Pacing via a patent foramen ovale: computed tomographic identification of unusual lead positioning

A 55-year-old woman underwent computed tomography (CT) coronary angiography to investigate atypical chest pain. Sixteen years ago she had undergone DDDR pacemaker insertion via a persistent left-sided superior vena cava (SVC) for Mobitz I with syncope. At implantation, acceptable pacing parameters were …

115 HIGH DEFINITION CT CORONARY ANGIOGRAPHY FOR THE PRIMARY INVESTIGATION OF CHEST PAIN AFTER REVASCULARISATION

Background NICE Diagnostics Guidance DG3 recommends ‘new generation’ cardiac CT scanners ‘for first-line evaluation of disease progression, to establish the need for revascularisation, in people with known coronary artery disease in whom imaging with earlier generation CT scanners is difficult’. This has previously been challenging due to artefact from stent metal and heavy calcification in the native vessels of patients who have undergone coronary artery bypass grafting (CABG). High-definition CT coronary angiography (HD-CTCA) aims to address the shortcoming of conventional technology by improving spatial resolution and reducing calcium blooming artefact. We evaluated the accuracy of HD-CTCA in patients presenting with chest pain after previous coronary revascularisation as part of an HD-CTCA accuracy trial. Methods Patients with high pre-test probability and established coronary artery disease were prospectively enrolled into our HD-CTCA accuracy trial. We present the interim results of 64 consecutive, previously revascularised patients (40 PCI, 24 CABG) who underwent HD-CTCA within 30 days following invasive coronary angiography (ICA). Anonymised ICA and HD-CTCA studies were evaluated separately and results compared with ICA as the reference standard. Grafts were not assessed. Results HD-CTCA studies were acquired using prospective gating, 100 kV tube voltage and optimum radiation reduction strategies. The male: female ratio was 3.9:1 and the median age and BMI of patients at the time of scanning were 68 years, 26.4 kg/m2 respectively. The median calcium score of patients without stents was 1715 (53–5389). The median radiation dose was 190 mGy cm (36–350) representing effective doses of 5.3 mSv (1–8.4) using a cardiac specific conversion factor (0.028). Compared to ICA, the per-coronary segment sensitivity and specificity of HD-CTCA for 70% stenosis were 99.0% and 97.7% respectively. The negative predictive value was 99.5% and positive predictive value 95.1%. The κ statistic was 0.95 implying very good agreement between imaging methods. Discussion Interventional cardiologists with direct access to HD-CTCA increasingly use this modality for first-line investigation of patients re-presenting following revascularisation. There has previously been little data to justify this trend although conventional CTCA is well established for the evaluation of coronary bypass grafts. The NICE Guidance supports this trend and this study defines the level of accuracy that can be anticipated with a non-invasive approach to coronary angiography for these patients. Conclusions In expert hands, HD-CTCA is highly accurate with remarkably similar angiographic findings to ICA for the assessment of the native coronary arteries in patients with prior revascularisation. These findings have significant implications for how sophisticated CTCA is integrated into the diagnostic algorithms of those re-presenting with IHD and previous revascularisation. Figure 1 Figure 2