Coronary CT radiation dose reduction strategies at an Australian Tertiary Care Center - improvements in radiation exposure through an evidence-based approach.

INTRODUCTION: Coronary CT Angiography (CCTA) is a rapidly increasing technique for coronary imaging; however, it exposes patients to ionising radiation. We examined the impact of dose reduction techniques using ECG-triggering, kVp/mAs reduction and high-pitch modes on radiation exposure in a large Australian tertiary CCTA service. METHODS: Data on acquisition modes and dose exposure were prospectively collected on all CCTA scans from November 2009 to March 2014 at an Australian tertiary care centre. A dose reduction algorithm was developed using published techniques and implemented with education of medical staff, radiographers and referrers. Associations of CCTA acquisition to radiation over time were analysed with multivariate regression. Specificity in positive CCTA was assessed by correlation with invasive coronary angiography. RESULTS: 3333 CCTAs were analysed. Mean radiation dose decreased from 8.4 mSv to 5.3, 4.4, 3.7, 2.9 and 2.8 mSv (P < 0.001) per year. Patient characteristics were unchanged. Dose reduction strategies using ECG-triggering, kVp/mAs reduction accounted for 91% of the decrease. High-pitch scanning reduced dose by an additional 9%. Lower dose was independently related to lower kVp, heart rate, tube current modulation, BMI, prospective triggering and high-pitch mode (P < 0.01). CCTA specificity remained unchanged despite dose reduction. CONCLUSION: Implementation of evidence-based CCTA dose reduction algorithm and staff education programme resulted in a 67% reduction in radiation exposure, while maintaining diagnostic specificity. This approach is widely applicable to clinical practice for the performance of CCTA.

Quantitation of mitral regurgitation after percutaneous MitraClip repair: comparison of Doppler echocardiography and cardiac magnetic resonance imaging.

OBJECTIVE: Percutaneous valve intervention for severe mitral regurgitation (MR) using the MitraClip is a novel technology. Quantitative assessment of residual MR by transthoracic echocardiography (TTE) is challenging, with multiple eccentric jets and artifact from the clips. Cardiovascular magnetic resonance (CMR) is the reference standard for left and right ventricular volumetric assessment. CMR phase-contrast flow imaging has superior reproducibility for quantitation of MR compared to echocardiography. The objective of this study was to establish the feasibility and reproducibility of CMR in quantitating residual MR after MitraClip insertion in a prospective study. METHODS: Twenty-five patients underwent successful MitraClip insertion. Nine were excluded due to non-magnetic resonance imaging (MRI) compatible implants or arrhythmia, leaving 16 who underwent a comprehensive CMR examination at 1.5 T (Siemens Aera) with multiplanar steady state free precession (SSFP) cine imaging (cine CMR), and phase-contrast flow acquisitions (flow CMR) at the mitral annulus atrial to the MitraClip, and the proximal aorta. Same-day echocardiography was performed with two-dimensional (2D) visualization and Doppler. CMR and echocardiographic data were independently and blindly analyzed by expert readers. Inter-rater comparison was made by concordance correlation coefficient (CCC) with 95% confidence intervals (CIs), and Bland-Altman (BA) methods. RESULTS: Mean age was 79 years, and mean LVEF was 44%±11% by CMR and 54%±16% by echocardiography. Inter-observer reproducibility of echocardiographic visual categorical grading by expert readers was poor, with a CCC of 0.475 (-0.7, 0.74). Echocardiographic Doppler regurgitant fraction reproducibility was modest (CCC 0.59, 0.15-0.84; BA mean difference -3.7%, -38% to 31%). CMR regurgitant fraction reproducibility was excellent (CCC 0.95, 0.86-0.98; BA mean difference -2.4%, -11.9 to 7.0), with a lower mean difference and narrower limits of agreement compared to echocardiography. Categorical severity grading by CMR using published ranges had good inter-observer agreement (CCC 0.86, 0.62-0.95). CONCLUSIONS: CMR performs very well in the quantitation of MR after MitraClip insertion, with excellent reproducibility compared to echocardiographic methods. CMR is a useful technique for the comprehensive evaluation of residual regurgitation in patients after MitraClip. Technical limitations exist for both techniques, and quantitation remains a challenge in some patients.

Clinical value of supine and upright myocardial perfusion imaging in obese patients using the D-SPECT camera.

PURPOSE: We have assessed whether additional upright imaging increases the confidence of interpretation of stress only supine myocardial perfusion imaging (MPI) in obese patients. METHODS AND RESULTS: Tc-MIBI stress MPI of 101 consecutive patients (M = 49, 62 ± 12 years) with BMI ≥30 scanned on the D-SPECT cardiac camera were assessed. Images were interpreted as diagnostic or equivocal and the need for a rest study was recorded. Stress supine MPI was interpreted first, then gated and finally upright data were added. Defects on supine but not on upright were defined as artefacts and defects seen on both as abnormal. The total perfusion deficit (TPD) was also quantified. There were 27 normal, 22 abnormal, and 52 equivocal supine scans. The median EF was 52%, unaffecting the need for rest imaging. Upright imaging reclassified 32/52 (62%) equivocal studies as normal and 6/52 (11%) as abnormal (P < 0.001). Rest scan was deemed needed in 74/101 patients on supine vs 42/101 on supine/upright (P < 0.001). Supine TPD was normal in 53 and supine/upright TPD was normal in 70 patients (P < 0.001). CONCLUSION: Supine stress MPI is inadequate in obese patients. The addition of upright imaging significantly increases the ability to interpret scans as diagnostic and may reduce considerably the need for rest imaging.

Initial multicentre experience of high-speed myocardial perfusion imaging: comparison between high-speed and conventional single-photon emission computed tomography with angiographic validation.

PURPOSE: High-speed (HS) single-photon emission computed tomography (SPECT) with a recently developed solid-state camera shows comparable myocardial perfusion abnormalities to those seen in conventional SPECT. We aimed to compare HS and conventional SPECT images from multiple centres with coronary angiographic findings. METHODS: The study included 50 patients who had sequential conventional SPECT and HS SPECT myocardial perfusion studies and coronary angiography within 3 months. Stress and rest perfusion images were visually analysed and scored semiquantitatively using a 17-segment model by two experienced blinded readers. Global and coronary territorial summed stress scores (SSS) and summed rest scores (SRS) were calculated. Global SSS ≥3 or coronary territorial SSS ≥2 was considered abnormal. In addition the total perfusion deficit (TPD) was automatically derived. TPD >5% and coronary territorial TPD ≥3% were defined as abnormal. Coronary angiograms were analysed for site and severity of coronary stenosis; ≥50% was considered significant. RESULTS: Of the 50 patients, 13 (26%) had no stenosis, 22 (44%) had single-vessel disease, 6 (12%) had double-vessel disease and 9 (18%) had triple-vessel disease. There was a good linear correlation between the visual global SSS and SRS (Spearman's ρ 0.897 and 0.866, respectively; p < 0.001). In relation to coronary angiography, the sensitivities, specificities and accuracies of HS SPECT and conventional SPECT by visual assessment were 92% (35/38), 83% (10/12) and 90% (45/50) vs. 84% (32/38), 50% (6/12) and 76% (38/50), respectively (p < 0.001). The sensitivities, specificities and accuracies of HS SPECT and conventional SPECT in relation to automated TPD assessment were 89% (31/35), 57% (8/14) and 80% (39/49) vs. 86% (31/36), 77% (10/13) and 84% (41/49), respectively. CONCLUSION: HS SPECT allows fast acquisition of myocardial perfusion images that correlate well with angiographic findings with overall accuracy by visual assessment better than conventional SPECT. Further assessment in a larger patient population may be needed to confirm this observation.

Comparison of radiation dose and the effect of operator experience in femoral and radial arterial access for coronary procedures.

Radial access coronary procedures are associated with fewer access site complications compared to femoral access. There is controversy regarding greater radiation exposure to patient and operator using radial access. We aimed to compare radiation dose during coronary procedures for the 2 access routes and assess the effect of operator experience with radial access on radiation dose. Fluoroscopy time (FT) and dose-area product (DAP) were recorded for all radial access and femoral access procedures during default femoral access, transition phase (femoral access and early radial access), and default radial access. Femoral access cases (n = 848, 412 diagnostic, 436 percutaneous coronary interventions [PCIs]) and radial access cases (n = 965, 459 diagnostic, 506 PCIs) were assessed. For diagnostics, median FT for radial access was longer than for femoral access (4.43 minutes, interquartile range [IQR] 2.55 to 8.18, vs 2.34 minutes, IQR 1.49 to 4.18, p <0.001) and associated with larger DAP (radial access 1,837 µGy·m(2), IQR 1,172 to 2,783, vs femoral access 1,657 µGy·m(2), IQR 1,064 to 2,376, p <0.001). For PCI, FT was longer for radial access (median 12.02 minutes, IQR 7.57 to 17.54, vs femoral access 9.36 minutes, IQR 6.13 to 14.27, p <0.001)-this did not translate into an increased DAP (femoral access median 3,392 µGy·m(2), IQR 2,139 to 5,193, vs radial access 3,682 µGy·m(2), IQR 2,388 to 5,314, p = NS). For diagnostic radial access, FT decreased from the transition phase (n = 134) to the default radial access phase (n = 323, 5.12 minutes, IQR 3.07 to 9.40, vs 4.21 minutes, IQR 2.49 to 7.52, p = 0.03). This was not observed for PCI. In conclusion, transition from femoral access to radial access for diagnostics and PCI increased FT. DAP increased for diagnostic radial access but not PCI compared with femoral access. FTs for radial access diagnostic cases decreased with experience.

Early detection of acute posterior myocardial infarction using body surface mapping and SPECT scanning.

BACKGROUND: Many patients with non-ST elevation myocardial infarction (NSTEMI) may have posterior STEMI, which should be emergently treated with reperfusion strategies but is difficult to identify by 12-lead ECG. OBJECTIVES: To compare the initial ECG and body surface map (BSM) for the diagnosis of posterior MI as verified by single-photon emission computed tomography (SPECT) and cTroponin T. METHODS: Patients with chest pain greater than 20 min at rest with either ST depression of at least 0.1 mV in at least one of leads I, aVL or V1-V6 on ECG or STE at least 0.05 mV in at least one posterior lead on the BSM which underwent early SPECT scan. RESULTS: Sixty patients (87%, 60 out of 69 with interpretable SPECT) had a posterior wall perfusion defect, all had cTroponinT (>0.09 ng/ml) and thus had posterior MI. Initial ECG showed STE in 24 (40%, 24 out of 60): 36 were non-diagnostic (60%, 36 out of 60). STE on BSM identified inferior MI in seven patients (12%, 7 out of 60), posterior in 32 patients (53%, 32 out of 60), and nine patients had right ventricular (15%, 9 out of 60). Twelve had no STE (20%, 12 out of 60). Of the patients with posterior MI and non-diagnostic ECGs, 53% (19 out of 36) were posterior MI by the BSM and six (17%, 6 out of 36) right ventricular MI only. The BSM correctly identified 53% (32 out of 60) (95% confidence interval 40-66%) of posterior MI. Of the 60 patients with posterior MI, 60% (36) had non-diagnostic ECGs: the BSM identified 42% (25) either as posterior MI or right ventricular MI only. CONCLUSION: We have shown that the BSM diagnoses significantly more posterior MI than the 12-lead ECG, allowing early identification of these patients so that maximum benefit from early reperfusion strategies can be gained.

Myocardial wall motion and thickening assessment in early gated SPECT images of acute coronary syndrome patients likely to have inferolateral perfusion defects.

The purpose of this study was to compare semi-quantitative visual scores of perfusion, motion and thickening with an automated hypoperfusion index (HI) in patients with suspected acute inferolateral perfusion defects. In the absence of perfusion defects motion and thickening abnormalities were assessed. Sixty-eight patients with chest pain at rest and either ST depression ≥0.1 mV in ≥1 of leads I, aVL, V1-V6 on 12-lead ECG or ST elevation ≥0.05 mV in ≥1 posterior lead on the body surface map comprised the study population. A rest gated perfusion scan was performed within 24 h of symptoms. Scans were scored for perfusion, motion and thickening semi-quantitatively. The scores were compared to the automated HI. A 12 h Troponin T >0.09 ng/ml indicated myocardial infarction (MI). Sixty-five patients (96%, 65/68) had MI. The summed perfusion score correlated well with the HI (ρ = 0.90, P < 0.01) and agreement between scorers was good (κ = 0.77, 95% CI = 0.57-0.94). The summed motion score correlated with the HI (ρ = -0.61, P < 0.01) and agreement between scorers was moderate (κ = 0.65, 95% CI = 0.52-0.79). Summed thickening score correlated with HI (ρ = -0.67, P < 0.01) and agreement between scorers was good (κ = 0.74, 95% CI = 0.64-0.88). Of the 1156 segments assessed (68 × 17), 542 had normal perfusion. Of these normally perfused segments, 113 (21%, 113/542) had a motion abnormality and 102 (19%, 102/542) had a thickening abnormality. Three patients with proven myocardial infarction had normal myocardial perfusion (HI ≤ 5) but exhibited wall motion and thickening abnormalities. In conclusion, assessment of wall motion and thickening in addition to perfusion in acute myocardial perfusion imaging may improve the diagnostic sensitivity for acute MI. Of the scores addressing motion and thickening, interobserver agreement was better for the summed thickening score.

Predictors of excess mortality after myocardial infarction in women.

BACKGROUND: Research suggests that women have higher mortality after acute myocardial infarction (AMI) than men. Potential factors to explain this disparity include delay to presentation, less aggressive interventional strategies, and more severe disease at coronary angiography in women. METHODS: Consecutive patients (n=663) presenting to coronary care between Jan 2002 and Jan 2005 with ischemic type chest pain and AMI (troponin T >0.09ng/ml) were recruited. Details of the presentation and management were obtained from the medical notes. The primary endpoint was three month all cause mortality. RESULTS: Of these patients 31% (205/663) were female. Mean age of women was 70 (SD 11) and 63 (SD 13) for men (p<0.001). There was no difference between the sexes for delay in presentation or treatment or for ST elevation infarction site. Women had prior hypertension more than men (49% 100/205 vs. 38% 174/458, p=0.008). Women were less likely to have diagnostic catheterisation (67% 137/205 vs. 80% 365/458 p<0.001). Both genders had similar coronary artery disease extent and frequencies of LV impairment (EF<45%) and were equally likely to undergo revascularisation (79% 108/137 vs. 81% 295/365 p=NS). There was an excess 3 month mortality among women (11% 23/205 vs. 5% 24/458 in men p=0.006). INDEPENDENT: predictors of 3 month mortality by logistic regression analysis were age (OR 1.06, 95% CI 1.03 -1.09, p<0.001) and LV impairment (OR 0.28, 95% CI 0.13-0.56, p<0.001). CONCLUSION: As LV impairment was comparable in men and women, the excess mortality identified is due to older age at presentation of women.

Risk stratification of chest pain patients in the emergency department by a nurse utilizing a point of care protocol.

OBJECTIVE: Risk stratification of patients with ischaemic type chest pain assessed in the emergency department utilizing a point of care (POC) protocol. METHODS: Patient demographics, cardiac biomarkers, management and follow-up at 6 months were reviewed for patients seen over 20 months. RESULTS: Out of 546 patients, 351 (64%) were admitted. The diagnoses after admission were confirmed as acute myocardial infarction in 59 patients and unstable angina, (cTroponin T<0.09 ng/ml) in 92 patients. The c-statistic of the receiver operating curves for myocardial infarction (myocardial infarction, cTroponinT at 12 h >0.09 ng/ml) as determined by the POC assay was cTroponin I=0.884, CK-MB=0.883, myoglobin=0.845 and beta-type natriuretic peptide (BNP)=0.755. The c-statistic for the same sample assessed by the hospital laboratory was cTroponin T=0.893: for CK-MB within 12 h of admission it was 0.918; the 12 h cTroponin T was 0.982 and within 24 h of admission NT pro-BNP was 0.789. POC BNP in patients admitted was 68 ng/l (median) vs. 24 ng/l (median) for those not admitted, (P<0.001). POC BNP for patients admitted with unstable angina (12 h cTroponin T <0.09 ng/ml) was 47 ng/l (median, P<0.001). At 6 months, 14 patients had died; five during admission, two within 30 days and seven up to 6 months. During admission two died from heart failure, two with respiratory tract infection and one from carcinoma. Of those not admitted one had died from asbestosis. CONCLUSION: Risk stratification by a specialist nurse utilizing a POC protocol is an appropriate means of assessing patients with chest pain.

ST segment elevation in lead aVR during exercise testing is associated with LAD stenosis.

PURPOSE: To evaluate, in patients with chest pain, the diagnostic value of ST elevation (STE) in lead aVR during stress testing prior to (99m) Tc-sestamibi scanning correlating ischaemic territory with angiographic findings. METHODS: Consecutive patients attending for (99m) Tc-sestamibi myocardial perfusion imaging (MPI) completed a treadmill protocol. Peak exercise ECGs were coded. STE >or=0.05 mV in lead aVR was considered significant. Gated perfusion images and findings at angiography were assessed. RESULTS: STE in lead aVR occurred in 25% (138/557) of the patients. More patients with STE in aVR had a reversible defect on imaging compared with those who had no STE in aVR (41%, 56/138 vs 27%, 114/419, p=0.003). Defects indicating a left anterior descending artery (LAD) culprit lesion were more common in the STE in aVR group (20%, 27/138 vs 9%, 39/419, p=0.001). There was a trend towards coronary artery stenosis (>70%) in a double vessel distribution involving the LAD in those patients who had STE in aVR compared with those who did not (22%, 8/37 vs 5%, 4/77, p=0.06). Logistic regression analysis demonstrated that STE in aVR (OR 1.36, p=0.233) is not an independent predictor of inducible abnormality when adjusted for STD >0.1 mV (OR 1.69, p=0.026). However, using anterior wall defect as an end-point, STE in aVR (OR 2.77, p=0.008) was a predictor even after adjustment for STD (OR 1.43, p=0.281). CONCLUSION: STE in lead aVR during exercise does not diagnose more inducible abnormalities than STD alone. However, unlike STD, which is not predictive of a territory of ischaemia, STE in aVR may indicate an anterior wall defect.