Our Visible and Invisible Friends and Foes

In the realm of interventional cardiology, the combination of radiopaque contrast and fluoroscopy serves as our visual apparatus, thereby making possible the wide array of intravascular procedures we perform. When used in excess though, these “eyes” can become our enemy, producing significant adverse events such as kidney impairment and skin and subcutaneous injury. In this month’s Journal of Invasive Cardiology, Maccagni et al have described their experience with contrast use and radiation exposure in transcatheter aortic valve replacement (TAVR) procedures over certain time intervals.¹ They convincingly demonstrate steady improvement in their ability to limit both contrast volume and radiation dose in parallel with improvements in imaging technology and operator experience, even while optimizing outcomes in TAVR. They examined the records of consecutive patients undergoing TAVR at their institution and divided them into three cohorts based on time period and technology. The first cohort was treated using an older image-intensifier based fluoroscopic system and earlier-generation TAVR devices. The second cohort was treated using flat-panel detector technology and improved TAVR devices. The third cohort witnessed the introduction of multidetector computed tomography (MDCT) for improved co-planar angle prediction as well as ever-improving operator experience and TAVR devices. From their first cohort to their third cohort, they found an approximately 44% reduction in contrast volume, 30% reduction in kerma area product (KAP), and 48% reduction in effective radiation dose to their patients. 

These results are most likely representative of many large-volume TAVR centers around the world. The question is: Of what importance are these findings? The key to answering that question lies in understanding the risks inherent in contrast-induced kidney injury and focal thoracic radiation damage. From the world of percutaneous coronary intervention (PCI), we possess a wealth of information on these topics. 

In a 2014 article, Tsai et al examined the National Cardiovascular Data Registry (NCDR) Cath-PCI dataset for 2009-2011 to better understand the incidence and consequences of acute kidney injury (AKI) in patients undergoing PCI.² They found that 7.1% of PCI patients experienced AKI (based on the Acute Kidney Injury Network [AKIN)] criteria), with 0.3% requiring dialysis. Occurrence of AKI or need for dialysis were associated with a substantial increase in the in-hospital mortality, rising from 0.5% for those without AKI to 9.7% for those with AKI, and to 34% for those requiring dialysis. Contrast-induced nephropathy, therefore, is far from benign. We also have an excellent grasp on the contrast volumes that are associated with kidney injury. In a 2011 article, Gurm et al examined the relationship between contrast volume, calculated creatinine clearance, and AKI.³ They found that a contrast volume to creatinine clearance ratio >2 resulted in an increased incidence of AKI, with an exponential rise in AKI once the contrast volume to creatinine clearance ratio exceeded 3. Both the Tsai and Gurm papers noted a common set of risk factors for AKI, which included baseline impairment in renal function, congestive heart failure, and hemodynamic compromise – a set of circumstances frequently found in patients with severe aortic stenosis undergoing TAVR. 

There are smaller-scale data in the setting of TAVR confirming the link between contrast volume, AKI, and mortality. In a single-center study of 165 patients, Barbash et al noted a 14.6% incidence of AKI based on the Valve Academic Research Consortium (VARC) definition of AKI post-TAVR.⁴ Furthermore, in keeping with Tsai’s findings in the setting of PCI procedures, they noted that patients who developed AKI suffered both higher in-hospital morality (21% vs 4%) and 30-day mortality (29% vs 7%) versus TAVR patients without AKI. Perhaps what is required now is a larger-scale analysis of material from the Transcatheter Valve Therapeutics (TVT) registry similar to analyses of PCI databases, in order to better understand the impact of contrast volumes on outcomes post TAVR. 

The risks of excessive radiation exposure to patients are obvious in that radiation-induced skin injury is something we all fear. On the other hand, the risks of more subtle radiation exposure to both patients and operators over time are less well understood. TAVR patients are typically older and are frequently burdened with multiple other co-morbidities including coronary artery disease (CAD). Many in fact will have a history of prior angiography and/or PCI. Some analyses suggest that significant CAD may be present in anywhere from 25%-50% of patients with severe aortic stenosis.⁵ What the additive impact over time might be from radiation exposure after multiple PCI procedures followed by TAVR is difficult to study and understand. Furthermore, as interventionalists now routinely perform not only PCI and TAVR but a myriad of other structural heart interventions, the additive impact of greater radiation exposure on operators is poorly understood at present. Efforts to reduce radiation exposure to both patients and operators are laudable. In a small study in Great Britain, Sharma et al compared radiation exposure in patients undergoing TAVR using standard radiographic settings versus modified settings aimed at conserving radiation.⁶ They were able to show a roughly 25% reduction in radiation exposure for the experimental group. 

Simple measures such as reduction in frame rate, use of MDCT angle prediction, and fluoroscopy storage rather than cineangiography, as the study by Maccagni et al has demonstrated, should result in substantial radiation savings. Probably most important in avoiding both excessive radiation as well as contrast usage is the avoidance of complications. It seems intuitive that cases in which complications occur, particular major vascular complications, are precisely the cases in which contrast volumes and radiation doses climb potentially to harmful levels. Meticulous preprocedure planning, intraprocedural management, and postprocedure care are therefore absolutely necessary to avoid complications as well as the contrast-induced and radiation-induced injuries that may follow. The longitudinal experience offered by Maccagni et al nicely demonstrates the learning curve and evolution of technique and technology that allows for safer and better TAVR procedures. As our discipline evolves to include more varied and complex pathology, we must always remember our visible and invisible friends and foes. 

References

1.    Maccagni D, Gotino C, Latib A, et al. Radiation exposure and contrast agent reduction during transcatheter aortic valve implantation: an ongoing experience. J Invasive Cardiol. 2016;28:459-465.

2.    Tsai TT, Patel UD, Chang TI, et al. Contemporary incidence, predictors, and outcomes of acute kidney injury in patients undergoing percutaneous coronary interventions: insights from the NCDR Cath-PCI Registry. JACC Cardiovasc Interv. 2014;7:1-9.

3.    Gurm HS, Dixon SR, Smith DE, et al. Renal function-based contrast dosing to define safe limits of radiographic contrast media in patients undergoing percutaneous coronary intervention. J Am Coll Cardiol. 2011;58:907-914.

4.    Barbash IM, Ben-Dor I, Dvir D, et al. Incidence and predictors of acute kidney after tanscatheter aortic valve replacement. Am Heart J. 2012;163:1031-1036.

5.    Goel SS, Ige M, Tuzcu EM, et al. Severe aortic stenosis and coronary artery disease — implications for management in the transcatheter aortic valve replacement era: a comprehensive review. J Am Coll Cardiol. 2013;62:1-10.

6.    Sharma D, Ramsewak A, O’Conaire S, et al. Reducing radiation exposure during transcatheter aortic valve implantation (TAVI). Catheter Cardiovasc Interv. 2015;85:1256-1261.

From the University of Texas Health Science Center Houston, Memorial Hermann Heart & Vascular Institute, Texas Medical Center, Houston, Texas.

Disclosure: The authors have completed and returned the ICMJE Form for Disclosure of Potential Conflicts of Interest. The authors report no conflicts of interest regarding the content herein.

Address for correspondence: H. Vernon Anderson, MD, Cardiology Division, University of Texas Health Science Center, McGovern Medical School, 6431 Fannin, Suite 1.246, Houston, TX 77030. Email: h.v.anderson@uth.tmc.edu