J. Rivers

Measures of radiation exposure in cardiac imaging and the impact of case complexity.

BACKGROUND Although it is important for a patients radiation related risks to be considered when recommending a cardiac imaging procedure, few clinicians appreciate the level of exposure involved. This paper provides a comprehensive set of radiation exposure metrics for common angiography procedures highlighting links to factors that influence radiation dose. METHODS Radiation use metrics and various clinical findings for diagnostic procedures and number of lesions treated, vessels treated and stents deployed for interventional cases were analysed. RESULTS Data relating to 1088 coronary angiography (CA), 256 angioplasty and 167 CA/angioplasty procedures were examined. The median effective dose (E) (mSv) for these procedures (including inter-quartile range) were, respectively, 3.3 (2.1-5.1), 7.5 (4.5-14.1) and 11.6 (6.9-16.1). For CA, E varied with the number of vessels (p<0.01) while for angioplasty E was linked to the number of vessels (p<0.01), lesions (p<0.01) and stents (p<0.01). CONCLUSION Radiation exposure metrics for common cardiac angiography imaging procedures have been documented and linked to procedure complexity. This has implications for performance monitoring when comparing radiation usage between users, facilities, times and technologies.

Reassessment of Radiation Risks from Electrophysiology Procedures Compared to Coronary Angiography

BACKGROUND Electrophysiology (EP) procedures have been reported to carry a significantly greater radiation risk than that of coronary angiography (CA). This is largely due to numerous reports linking severe deterministic radiation effects to long procedure and fluoroscopy times (FTs). This study documents low radiation doses achieved by strategies involving operator training and education as well as equipment and technique optimisation to reduce radiation risks. METHODS Records relating to 732 diagnostic EP and 1744 therapeutic EP procedures performed between January 2002 and December 2007 were analysed. Data from 1458 diagnostic only CA procedures performed in 2006 was used for comparison. For each procedure type, FT, number of digital frames acquired and estimated effective dose (E) were compared. RESULTS Although the FT for CA procedures is significantly less than for therapeutic EP procedures (FT for diagnostic EP being similar), EP procedures generally are associated with lower E, the exception being procedures for atrial fibrillation (AF). CONCLUSION Through the application of a comprehensive exposure minimisation strategy, the radiation risk to patients undergoing diagnostic and, therapeutic EP procedures (except AF ablation procedures) is significantly less than that faced by patients undergoing CA. E, however, is heavily dependent on procedure type and as such care must be taken in undertaking generalised comparisons for audit and benchmarking purposes.

The role of quantitative feedback in coronary angiography radiation reduction

OBJECTIVE To evaluate the benefits of radiation education with and without feedback reporting in altering clinician radiation use behaviour in performing coronary angiography (CA). DESIGN A retrospective review of radiation use (fluoroscopy time) in coronary angiograms performed between July 1996 and December 2005 by 10 cardiologists to assess the impact of various interventions aimed at minimizing radiation risk. The impact of interventions such as education and audit/feedback was correlated against radiation use using cumulative sum and cumulative expected minus observed charts. SETTING Private Hospital in Brisbane, Australia. PARTICIPANTS Ten cardiologists. INTERVENTION Education and audit/feedback. RESULTS Baseline radiation use subject to standard guidelines was stable. Group performance charts show a modest transient improvement in radiation use associated with an education intervention alone. However, regular detailed personalized feedback comparing an individuals radiation use to group and external benchmarks was successful in achieving sustained reduction in overall radiation use. For individual participants, significant improvement was noted in 7 of 10 cardiologists. CONCLUSION Although an improved theoretical understanding of effective radiation hygiene strategies might contribute to reduced radiation use, this study suggests that regular detailed quantitative feedback supporting education is an effective tool in altering radiation use in CA. Understanding triggers that stimulate change in clinician behaviour is critical to the design of systems to optimize clinical performance. Confidentially reported benchmarking systems may be a useful tool to alter clinician behaviour.

Performance Monitoring in Cardiac Surgery: Application of Statistical Process Control to a Single-site Database

BACKGROUND Graphical Statistical Process Control (SPC) tools have been shown to promptly identify significant variations in clinical outcomes in a range of health care settings. We explored the application of these techniques to quantitatively inform the routine cardiac surgical (CAS) morbidity and mortality (M&M) review processes at a single site. METHODS Baseline clinical and procedural data relating to 5265 consecutive cardiac surgical procedures, performed at St Andrews War Memorial Hospital (SAWMH) between the 1st January 2003 and the 30th April 2012, were retrospectively evaluated. A range of appropriate clinical outcome indicators (COIs) were developed and evaluated using a combination of Cumulative Sum charts, Exponentially Weighted Moving Average charts and Funnel Plots. Charts were updated regularly and discussed at the cardiac surgery units bi-monthly M&M meetings. Risk adjustment (RA) for the COIs was developed and validated for incorporation into the charts to improve monitoring performance. RESULTS Discrete and aggregated measures, including blood product/reoperation, major acute post-procedural complications, cardiopulmonary bypass duration and Length of Stay/Readmission < 28 days have proved to be valuable measures for monitoring outcomes. Instances of variation in performance identified using the charts were examined thoroughly and could be related to changes in clinical practice (e.g. antifibrinolytic use) as well as differences in individual operator performance (in some instances, driven by case mix). CONCLUSIONS SPC tools can promptly detect meaningful changes in clinical outcome thereby allowing early intervention to address altered performance. Careful interpretation of charts for group and individual operators has proven helpful in detecting and differentiating systemic versus individual variation.

Radiation risk reduction in cardiac electrophysiology through use of a gridless imaging technique.

AIMS It has been previously demonstrated that use of appropriate frame rates coupled with minimal use of high-dose digital acquisition can limit radiation risk to patients undergoing diagnostic and therapeutic electrophysiology (EP). Imaging without the anti-scatter grid has been proposed as a means of achieving further radiation reduction. We evaluate application of a gridless imaging technique to deliver further reductions in radiation risk to both patients and personnel. METHODS AND RESULTS Radiation and clinical data for EP procedures performed for 16 months from March 2012 were monitored. The period was divided into three phases: Phase 1 (March 2012-June 2012) provided a performance baseline (radiation output modelling and procedural risk adjustment calibration), Phase 2 (July 2012-September 2012) confirmation of performance with the grid, and Phase 3 (September 2012-June 2013) gridless imaging period. Statistical process control (SPC) charts were used to monitor for changes in radiation use and clinical outcomes (procedural success). Imaging without the grid halved the levels of radiation delivered in undertaking EP procedures. Although there was a perceptible impact on image quality with the grid removed. Review of the SPC chart monitoring procedural outcomes did not identify any discernable adverse impact on success rates. Selected use of the gridless technique is recommended with re-introduction of the grid in larger patients or during aspects of the procedure where image quality is important (e.g. transeptal punctures). CONCLUSION Use of a gridless imaging technique can contribute to a significant reduction in radiation risk to both patients and operators during cardiac EP procedures.

Evaluation of coronary angiographic projections to balance the clinical yield with the radiation risk

OBJECTIVE Radiation safety principles dictate that imaging procedures should minimise the radiation risks involved, without compromising diagnostic performance. This study aims to define a core set of views that maximises clinical information yield for minimum radiation risk. Angiographers would supplement these views as clinically indicated. METHODS An algorithm was developed to combine published data detailing the quality of information derived for the major coronary artery segments through the use of a common set of views in angiography with data relating to the dose-area product and scatter radiation associated with these views. RESULTS The optimum view set for the left coronary system comprised four views: left anterior oblique (LAO) with cranial (Cr) tilt, shallow right anterior oblique (AP-RAO) with caudal (Ca) tilt, RAO with Ca tilt and AP-RAO with Cr tilt. For the right coronary system three views were identified: LAO with Cr tilt, RAO and AP-RAO with Cr tilt. An alternative left coronary view set including a left lateral achieved minimally superior efficiency (<5%), but with an ~8% higher radiation dose to the patient and 40% higher cardiologist dose. CONCLUSION This algorithm identifies a core set of angiographic views that optimises the information yield and minimises radiation risk. This basic data set would be supplemented by additional clinically determined views selected by the angiographer for each case. The decision to use additional views for diagnostic angiography and interventions would be assisted by referencing a table of relative radiation doses for the views being considered.

Risk Modelling in Quality Clinical Registries: Monitoring Lesion Treatment Failure Rate in Percutaneous Coronary Interventions

AIMS This paper describes the development of a risk adjustment (RA) model predictive of individual lesion treatment failure in percutaneous coronary interventions (PCI) for use in a quality monitoring and improvement program. METHODS AND RESULTS Prospectively collected data for 3972 consecutive revascularisation procedures (5601 lesions) performed between January 2003 and September 2011 were studied. Data on procedures to September 2009 (n=3100) were used to identify factors predictive of lesion treatment failure. Factors identified included lesion risk class (p<0.001), occlusion type (p<0.001), patient age (p=0.001), vessel system (p<0.04), vessel diameter (p<0.001), unstable angina (p=0.003) and presence of major cardiac risk factors (p=0.01). A Bayesian RA model was built using these factors with predictive performance of the model tested on the remaining procedures (area under the receiver operating curve: 0.765, Hosmer-Lemeshow p value: 0.11). Cumulative sum, exponentially weighted moving average and funnel plots were constructed using the RA model and subjectively evaluated. CONCLUSION A RA model was developed and applied to SPC monitoring for lesion failure in a PCI database. If linked to appropriate quality improvement governance response protocols, SPC using this RA tool might improve quality control and risk management by identifying variation in performance based on a comparison of observed and expected outcomes.