Pain perception during baroreceptor unloading by lower body negative pressure.

BACKGROUND: People with high blood pressure have reduced sensitivity to pain, known as blood pressure hypoalgesia. One proposed mechanism for this is altered baroreceptor sensitivity. In healthy volunteers, stimulating the carotid baroreceptors causes reduced sensitivity to acute pain; however, this effect may be confounded by a rise in blood pressure due to baroreflex stimulation. The present study tests whether baroreceptor unloading contributes to the physiological mechanism of blood pressure-related hypoalgesia. METHODS: In the present study, pain perception to thermal stimulation of the forearm was studied in 20 healthy volunteers during baroreceptor unloading by lower body negative pressure (LBNP) at -5 and -20 mmHg. Blood pressure and heart rate were measured continuously throughout. To address issues relating to stimulation order, the sequence of LBNP stimulation was counterbalanced across participants. RESULTS: Increased heart rate was observed at a LBNP of -20 mmHg, but not -5 mmHg, but neither stimulus had an effect on blood pressure. There was no change in warm or cold sensory detection thresholds, heat or cold pain thresholds nor perceived pain from a 30s long thermal heat stimulus during LBNP. CONCLUSION: Therefore, baroreceptor unloading with maintained systemic blood pressure did not alter pain perception. The current study does not support the hypothesis that an altered baroreflex may underlie the physiological mechanism of blood pressure-related hypoalgesia. SIGNIFICANCE: This work provides evidence that, when measured in normotensive healthy young adults, the baroreflex response to simulated hypovolaemia did not lead to reduced pain sensitivity (known as blood pressure hypoalgesia).

CT pulmonary angiography: optimising acute thoracic imaging by fixed-timing contrast medium delivery with a modified breathing instruction.

AIM: To compare the thoracic vascular opacification achieved using the standard bolus-tracking protocol (BTP) with a fixed-timing protocol (FTP) with a modified breathing instruction during computed tomography pulmonary angiography (CTPA) examinations. MATERIALS AND METHODS: A single-centre review of CTPA examinations performed between July 2018 and January 2019 using the BTP or FTP and weight-based contrast dosing of 20 mg iodine/kg body weight/s for 20 seconds at 100 kV tube potential. Radiodensity (in Hounsfield units) was analysed in the right ventricle, main pulmonary artery (MPA), left atrium, left ventricle, and ascending and descending thoracic aorta (DTA). A p-value of <0.05 was considered significant. RESULTS: Of 782 examinations, 88 BTP and 90 FTP examinations were included. Mean attenuation of the MPA was similar in the FTP (396 ± 106 HU) and BTP (362 ± 119 HU; p=0.06); however, good-quality (≥250 HU) MPA opacification was achieved in more FTP examinations (87/90, 96.7%) compared to the BTP (73/88, 82.9%; p=0.002). Mean attenuation of the DTA was better in the FTP (325 ± 72 HU) than the BTP (228 ± 75 HU; p <0.0001), with good-quality opacification (≥250 HU) in 76/90 (84.4%) FTP examinations compared with 36/88 (40.9%) BTP examinations (p <0.001). CONCLUSION: The FTP achieves better opacification of the MPA and DTA compared to the BTP.

Computed tomography-derived fractional flow reserve (FFRCT) has no additional clinical impact over the anatomical Coronary Artery Disease - Reporting and Data System (CAD-RADS) in real-world elective healthcare of coronary artery disease.

AIM: To evaluate the impact of computed tomography-derived fractional flow reserve (FFRCT) compared to the anatomical Coronary Artery Disease - Reporting and Data System (CAD-RADS) in the elective assessment of coronary artery disease in real-world cardiology practise. MATERIALS AND METHODS: A retrospective review was undertaken of 1,239 coronary CT examinations from August 2018 to December 2019 with a minimum follow-up period of 1 year. Coronary disease was classified according to the CAD-RADS system. A non-occlusive ≥30% maximum diameter stenosis was considered eligible for FFRCT. Lesion-specific FFRCT and FFR were considered positive if ≤ 0.80. The patients were followed up using the hospital radiology information system and the electronic patient record. A positive outcome was defined by a subsequent invasive angiogram (ICA) showing disease requiring revascularisation or FFR ≤0.80 or a positive stress test or medical therapy for angina in CAD-RADS 4. RESULTS: Of the 1,145 analysable studies (mean follow up 618 ± 153 days) the incidence of a positive result was 7% with a 5.4% elective revascularisation rate. Two hundred and forty-five patients (CAD-RADS 2-4) had FFRCT. FFRCT reduced the accuracy of the CAD-RADS grade from 91% to 78.4% (p<0.001). In CAD-RADS 2, the accuracy is reduced from 99% to 90.7% (p=0.005), and in CAD-RADS 3 from 93.9% to 67.7% (p<0.001). In CAD-RADS 4, FFRCT increases accuracy from 69.4% to 75.5% (p=0.025), but 89.8% of FFRCT are positive and specificity is low (26.7%). CONCLUSION: In the present "real-world" practise, FFRCT does not improve standard radiological assessment of coronary disease graded by the CAD-RADS alone.

A quality-improvement project to enhance systemic arterial contrast opacification in CT for trans-catheter aortic valve implantation.

AIM: To assess improvement in arterial opacification by optimising the contrast medium dosing protocol for computed tomography (CT) prior to trans-catheter aortic valve implantation (TAVI). MATERIALS AND METHODS: A wide variation in arterial opacification was observed in the initial CT TAVI protocol (standard protocol). The practice was optimised by considering the time required for the examination and optimising contrast medium flux. This became the optimised protocol with a 30-second contrast medium bolus of iodine flux 15-19 mg iodine/kg body weight/second (mg/kg/s). Attenuation (mean HU) in (a) the ascending aorta (gated systolic acquisition) and (b) the ascending, descending thoracic (at carina), infra-renal abdominal aorta, and right common iliac artery (non-gated acquisition) was measured. Thirty-one sequential optimised examinations were compared to 31 prior standard protocol examinations. RESULTS: There was no difference between the standard and optimised groups regarding age, sex, weight, body mass index (BMI), or voltage. The mean bolus durations were 24.9±4.4 seconds for the standard and 30±0.3 seconds for the optimised protocols (p<0.001). Although there was no difference in the attenuation in the gated ascending aorta (p>0.99), there was improvement at all other anatomical points in the non-gated examinations of the optimised protocol (p<0.002). CONCLUSION: Optimising contrast medium flux and matching bolus duration to the CT technology dramatically improves the vascular access component of TAVI planning and provides a reliable method to achieve objectively enhanced arterial opacification. This work highlights how to obtain good arterial contrast medium opacification in haemodynamically fragile patients without excessive contrast medium volumes.

The effect of left ventricular longitudinal strain on left atrial function and ventricular filling in hypertension.

AIM: To assess the relationship of global longitudinal strain during left atrial (LA) and left ventricular (LV) filling and emptying. MATERIALS AND METHODS: Using magnetic resonance imaging in 47 hypertensive patients, biplane global LV longitudinal strain was evaluated and related to LA and LV filling and emptying (by volumetric analysis), and to pulmonary vein and trans-mitral flow (by phase-contrast imaging). The results were compared to normal subjects. RESULTS: In hypertensive patients, reduced global longitudinal LV strain was associated with reduced LA reservoir (47 ± 10 versus 53 ± 9%, p<0.05), reduced LA conduit function (21 ± 9 versus 32 ± 11%, p<0.004), reduced LA early peak emptying rate (150 ± 77 versus 230 ± 88 ml/s, p=0.007), and slower early LV filling (373 ± 141 versus 478 ± 141 ml/s, p=0.03). LA peak filling rate showed a positive correlation to LV peak emptying rate (R=0.331, p=0.02). CONCLUSION: In hypertensive heart disease, impaired LV longitudinal systolic function causes reduced LA filling and emptying, and this leads directly to impaired LV filling and diastolic dysfunction.

Electrocardiography-gated CT for acute aortic syndrome: quantifying the potential impact of subspecialty national recommendations on emergency general radiology reporting.

AIM: To evaluate the detection of acute aortic syndrome (AAS) and the prevalence of alternative diagnoses that may explain the presentation or require follow-up. MATERIALS AND METHODS: This was a retrospective, blinded re-evaluation of consecutive electrocardiography (ECG)-gated computed tomography (CT) aortic studies by a cardiovascular radiologist performed between September 2019 and May 2020 in a tertiary-referral cardiothoracic centre. RESULTS: There were 118 identified examinations, six examinations were excluded leaving 112 (mean age = 61 ± 17; 56% male). Three cases of AAS were present (prevalence 2.7%); only one was reported on initial review. There were no false-positive diagnoses of AAS. The heart was mentioned in 79 (70.5%) reports and 73 (65.2%) of reviews revealed a total of 114 new observations; 111 (97.4%) of these were cardiovascular with 44/112 (39.3%) patients potentially having a significant previously unsuspected cardiovascular diagnosis. CONCLUSION: The implementation of national clinical guidance to increase testing and improve image quality led to a series of challenges. The real value of ECG-gated CT may lie in detecting other diseases that mimic AAS. With the additional workload, increased subspecialty expertise is required but there needs to be a willingness to learn with an adequate support infrastructure.

The design and use of a simple device for the MRI assessment of changes in cardiovascular function by lower-body negative-pressure-simulated reduction of central blood volume.

AIM: To use a locally designed and simple lower-body negative-pressure (LBNP) device and 1.5 T magnetic resonance imaging (MRI) to demonstrate the ability to assess changes in cardiovascular function during preload reduction. These effects were evaluated on ventricular volumes and great vessel flow in healthy volunteers, for which there are limited published data. MATERIAL AND METHODS: After ethical review, 14 volunteers (mean age 33.9 ± 7 years, mean body mass index [BMI] 23.1 ± 2.5) underwent LBNP prospectively at 0, -5, -10, and -20 mmHg pressure, using a locally designed LBNP box. Expiratory breath-hold biventricular volumes, and free-breathing flow imaging of the ascending aorta and main pulmonary artery were acquired at each level of LBNP. RESULTS: At -5 mmHg, there was no change in aortic flow or left ventricular volumes versus baseline. Right ventricular output (p=0.013) and pulmonary net flow (p=0.026) decreased. At -20 mmHg, aortic and pulmonary net flow (p<0.001) decreased, as were left and right ventricular end diastolic volume (p<0.001) and left and right end systolic volumes (p=0.038 and p=0.003 respectively). CONCLUSIONS: Use of a MRI-compatible LBNP device is feasible to measure changes in ventricular volume and great arterial flow in the same experiment. This may enhance further research into the effects of preload reduction by MRI in a wide range of important cardiovascular pathologies.

Electrocardiographic detection of hypertensive left atrial enlargement in the presence of obesity: re-calibration against cardiac magnetic resonance.

Left atrial enlargement (LAE) has adverse prognostic implications in hypertension. We sought to determine the accuracy of five electrocardiogram (ECG) criteria for LAE in hypertension relative to cardiac magnetic resonance (CMR) gold standard and investigate the effect of concomitant obesity. One hundred and thirty consecutive patients (age: 51.4±15.1 years, 47% male, 51% obese, systolic blood pressure (BP): 171±29 mm Hg, diastolic BP: 97±15 mm Hg) referred for CMR (1.5 T) from a tertiary hypertension clinic were included. Patients with concomitant cardiac pathology were excluded. ECGs were assessed blindly for the following: (1) P-wave >110 ms, (2) P-mitrale, (3) P-wave axis <30°, (4) area of negative P-terminal force in V1 >40 ms.mm and (5) positive P-terminal force in augmented vector left (aVL) >0.5 mm. Left atrial volume ≥55 ml m-2, measured blindly by CMR, was defined as LAE. Sensitivity, specificity, positive predictive value, negative predictive value, accuracy and area under the receiver operator curve were calculated. The prevalence of LAE by CMR was 26%. All the individual ECG LAE criteria were more specific than sensitive, with specificities ranging from 70% (P-axis <30o) to 99% (P-mitrale). Obesity attenuated the specificity of most of the individual ECG LAE criteria. Obesity correlated with significant lower specificity (48% vs 65%, P<0.05) and a trend towards lower sensitivity (59 vs 43%, P=0.119) when ≥1 ECG LAE criteria were present. Individual ECG criteria of LAE in hypertension are specific, but not sensitive, at identifying LAE. The ECG should not be used to excluded LAE in hypertension, particularly in obese subjects.

Comparison between a fixed-dose contrast protocol and a weight-based contrast dosing protocol in abdominal CT.

AIM: To compare a fixed-dose intravenous iodinated contrast medium protocol with weight-based dosing protocols for abdominal computed tomography (CT). MATERIALS AND METHODS: Fifty patients were scanned using a fixed-dose protocol, 50 patients were scanned using a full-dose weight-based contrast dosing protocol, and 13 patients were scanned using a reduced dose weight-based protocol. Radiodensity was measured at the portal vein, aorta, spleen, and liver. These values were plotted against contrast medium dose per unit weight. Images from all patients were anonymised and presented to two independent consultants who subjectively assessed contrast enhancement using a five-point Likert scale. RESULTS: Using a fixed-dose protocol, there was a statistically significant negative correlation and trend between patient weight and radiodensity at the portal vein, aorta, spleen, and liver. Using a full-dose weight-based contrast dosing protocol, there was no longer a statistically significant correlation or trend implying a more consistent degree of enhancement over a spectrum of patient weights. In addition, when the full-dose weight-based contrast dosing protocol was used, there was a statistically significant increase in the number of scans subjectively assessed as having ideal enhancement and a statistically significant decrease in the number of scans felt to have excessive enhancement when compared to a fixed-dose protocol. The weight-based dosing protocol used less contrast medium than the fixed-dose protocol and there was no evidence of contrast-induced acute kidney injury (CIAKI) in any of the patients that received a greater dose than that which they would have received using a fixed-dose protocol. The reduced-dose weight-based protocol showed less objective enhancement of the portal vein, abdominal aorta, spleen, and liver compared to the full-dose protocol and a reduction in the number of scans perceived as showing ideal enhancement. There was, however, no increase in the number of scans with poor or non-diagnostic enhancement. CONCLUSION: Weight-based contrast medium dosing has been shown to objectively provide more consistent vessel and solid-organ enhancement and subjectively improve image quality across a spectrum of weights. Depending on mean patient mass, it has also been shown to reduce overall contrast medium dose, and there is no evidence of CIAKI in patients that receive larger doses. This study also postulates that a standardised approach to contrast medium dose reduction in patients with renal impairment may be a viable strategy.

Application of TWIST MR angiography to aid successful central venous access in challenging patients: initial single-centre experience.

AIM: To investigate whether time-resolved angiography with interleaved stochastic trajectories (TWIST) with GeneRalised Autocalibrating Partially Parallel Acquisitions (GRAPPA) parallel acquisition could be used successfully to non-invasively and efficiently image patients with more complex vascular access issues. MATERIALS AND METHODS: TWIST magnetic resonance angiography (MRA) in the GRAPPA algorithm was performed on 15 patients at our centre using the 1.5 T Siemens Magnetom Avanto MRI system. Images were interpreted by cardiac radiologists. RESULTS: TWIST provided excellent dynamic imaging of the venous system, demonstrating venous occlusion, stenoses, and collaterals, as well as providing good anatomical detail. CONCLUSION: TWIST MRA enables successful identification of candidate sites for central/tunnelled line access, whilst diagnosing complications of long-term access such as venous thrombosis or congenital venous anomalies.

The safe practice of CT coronary angiography in adult patients in UK imaging departments.

Computed tomography coronary angiography is increasingly used in imaging departments in the investigation of patients with chest pain and suspected coronary artery disease. Due to the routine use of heart rate controlling medication and the potential for very high radiation doses during these scans, there is a need for guidance on best practice for departments performing this examination, so the patient can be assured of a good quality scan and outcome in a safe environment. This article is a summary of the document on 'Standards of practice of computed tomography coronary angiography (CTCA) in adult patients' published by the Royal College of Radiologists (RCR) in December 2014.

The effect of obesity on electrocardiographic detection of hypertensive left ventricular hypertrophy: recalibration against cardiac magnetic resonance.

Electrocardiograph (ECG) criteria for left ventricular hypertrophy (LVH) are a widely used clinical tool. We recalibrated six ECG criteria for LVH against gold-standard cardiac magnetic resonance (CMR) and assessed the impact of obesity. One hundred and fifty consecutive tertiary hypertension clinic referrals for CMR (1.5 T) were reviewed. Patients with cardiac pathology potentially confounding hypertensive LVH were excluded (n=22). The final sample size was 128 (age: 51.0±15.2 years, 48% male). LVH was defined by CMR. From a 12-lead ECG, Sokolow-Lyon voltage and product, Cornell voltage and product, Gubner-Ungerleidger voltage and Romhilt-Estes score were evaluated, blinded to the CMR. ECG diagnostic performance was calculated. LVH by CMR was present in 37% and obesity in 51%. Obesity significantly reduced ECG sensitivity, because of significant attenuation in mean ECG values for Cornell voltage (22.2±5.7 vs 26.4±9.4 mm, P<0.05), Cornell product (2540±942 vs 3023±1185 mm • ms, P<0.05) and for Gubner-Ungerleider voltage (18.2±7.1 vs 23.3±1.2 mm, P<0.05). Obesity also significantly reduced ECG specificity, because of significantly higher prevalence of LV remodeling (no LVH but increased mass-to-volume ratio) in obese subjects without LVH (36% vs 16%, P<0.05), which correlated with higher mean ECG LVH criteria values. Obesity-specific partition values were generated at fixed 95% specificity; Cornell voltage had highest sensitivity in non-obese (56%) and Sokolow-Lyon product in obese patients (24%). Obesity significantly lowers ECG sensitivity at detecting LVH, by attenuating ECG LVH values, and lowers ECG specificity through changes associated with LV remodeling. Our obesity-specific ECG partition values could improve the diagnostic performance in obese patients with hypertension.

Tube potential can be lowered to 80 kVp in test bolus phase of CT coronary angiography (CTCA) and CT pulmonary angiography (CTPA) to save dose without compromising diagnostic quality.

OBJECTIVES: The purpose of this study was to determine whether performing the test bolus (TB) of computed tomography coronary angiography (CTCA) and computed tomography pulmonary angiography (CTPA) at 80 kVp reduces dose without compromising diagnostic quality. METHODS: An 80 kVp TB protocol for CTCA and CTPA was retrospectively compared to standard TB protocol (non-obese: 100 kVp, obese: 120 kVp). CT angiogram parameters were unchanged between cohorts. Thirty-seven consecutive 80 kVp TB CTCA images were compared to 53 standard CTCA images. Fifty consecutive CTPAs from each protocol were analysed. Diagnostic quality of the CT angiogram was assessed by: mean attenuation, signal-to-noise ratio (SNR) in the ascending aorta (AA) in CTCA and in the main pulmonary artery (MPA) in CTPA, diagnostic rate, and number of repeated monitoring scans. Mean effective dose was estimated using the dose-length product. RESULTS: Mean TB effective doses were significantly lower (P < 0.0001) for 80 kVp scans compared to the standard in non-obese CTCA (0.15 ± 0.04 mSv Vs 0.33 ± 0.09 mSv), obese CTCA (0.17 ± 0.06 mSv Vs 0.57 ± 0.12 mSv), and CTPA patients (0.07 ± 0.03 mSv Vs 0.15 ± 0.06 mSv). No difference was demonstrated in mean attenuation, SNR (AA), SNR (MPA), diagnostic rates, or number of repeated monitoring scans between protocols. CONCLUSIONS: Routinely performing TB at 80 kVp, regardless of body habitus, in CTCA and CTPA results in a small but significant dose reduction, without compromising CT angiogram diagnostic quality. KEY POINTS: • CT coronary angiography is performed to exclude the presence of significant coronary atherosclerosis. • CT pulmonary angiography is performed to diagnose pulmonary thromboembolism. • This retrospective study showed dose reduction by performing test bolus at 80 kVp. • Diagnosis can be made with reduced exposure to ionising radiation.

Transcatheter and endovascular stent graft management of coarctation-related pseudoaneurysms.

OBJECTIVE: Surgical correction of congenital aortic coarctation can lead to a number of important problems including late pseudoaneurysm formation. Redo surgery has a significant risk. Endovascular stent graft repair is increasingly used but there are limited data regarding this indication. We describe the experience of two UK congenital referral centres. DESIGN: Retrospective analysis of patients treated with endovascular aortic stent grafting for late pseudoaneurysms. SETTING: Two UK congenital heart centres, Bristol Heart Institute and Leeds General Infirmary. PATIENTS: 17 patients were treated 2006-2012. This represents all patients treated with this technique. MAIN OUTCOME MEASURES: Procedural and postprocedure success and complications. RESULTS: The average time from index repair to endovascular repair of pseudoaneurysm was 24.6 years. The majority (70.6%) had patch aortoplasty as the original surgical procedure and 41.2% were not under follow-up or discharged. Stent grafting procedural success rate was 100%. Median hospital stay postprocedure was 3 days. There was no procedural mortality or immediate complication. There were four minor early and three minor late complications. Imaging follow-up was available for an average of 31.6 months (range 6-65 months). All patients have demonstrated positive remodelling of the pseudoaneurysm with no incidence of continued expansion or stent graft failure up to 5 years following implant. CONCLUSIONS: Endovascular stent graft treatment of pseudoaneurysms show promising results in a population who have a high risk of surgical re-intervention. Complication rates appear to be low and recovery is quick. Longer-term data remain essential to scrutinise stent graft performance in this situation.

Presence of left atrial diverticula, accessory appendages, and normal variant pulmonary venous anatomy diagnosed using MDCT and adverse outcomes following radiofrequency catheter ablation therapy in patients with drug-refractory atrial fibrillation: an exploratory study.

AIM: To determine the frequency of normal variation left atrial anatomy (NVLAA) (diverticula, accessory appendages) and normal variation pulmonary venous anatomy (NVPVA) in patients with atrial fibrillation (AF), and to determine whether the presence of these entities is associated with an increased recurrence of atrial arrhythmias following radiofrequency catheter ablation (RFCA). MATERIALS AND METHODS: All cardiac MDCT images performed prior to RFCA between November 2009 and May 2011 in patients with drug-refractory AF were retrospectively evaluated. The presence, type, and location of NVLAA and NVPVA, and outcome of RFCA were recorded. Success was defined as restoration of sinus rhythm. RESULTS: Forty-six consecutive patients with a mean age of 59.8 (±9.7) years (76.1% male) underwent cardiac MDCT for anatomical planning prior to RFCA procedures. Fourteen (30.4%) patients had NVLAA, 35% of patients had NVPVA. Thirty (65%) patients had successful RFCA: 57% of these had a NVLAA, 67% had NVPVA. Sixteen (35%) patients had unsuccessful RFCA: 63% of these had a NVLAA, 56% had NVPVA. There was no significant association between the presence of NVLAA (p = 0.699), NVPVA (p = 0.197), or "NVLAA in the presence of normal pulmonary venous anatomy" (p = 0.589) and the outcome of RFCA. CONCLUSION: The presence of NVLAA and NVPVA appears unrelated to adverse outcome in patients undergoing RFCA for the treatment of drug-refractory AF.