How fractional flow reserve coronary artery computer tomography angiography is a sea change for patients with congenital heart defects
The field of radiology is evolving at a breakneck pace. New technologies are dramatically improving our ability to diagnose, treat and heal patients. At Phoenix Children’s, a hospital system that embraces innovation and entrepreneurism, our opportunities to improve and ultimately transform pediatric practice are truly boundless.
For example, we are using 3-D imaging technology to measure tumor volume with real precision, a breakthrough considering the significant margin of error with traditional x-y-z measurement. In addition, our providers are investigating the use of Amide Proton Transfer MRI as a possible alternative to the use of contrast in pediatric brain tumor imaging. This MR sequence is an improvement over traditional MRI, where post-operative changes can be confused for residual tumor.
Perhaps most exciting, our hospital is the first in the world to offer a drug-induced CT stress test for children and young adults who cannot complete traditional treadmill-based EKGs due to heart anomalies. While such testing is used in adults with acquired coronary diseases, our radiology and cardiology teams worked together to author the protocol for pediatrics.
Until recently, few children with heart defects lived into adulthood, but medical advances in diagnosis and treatment have given many of these patients a normal life expectancy. It’s a miraculous turn of events for these children and their families, but it presents a practical challenge: only a small number of providers are trained to treat adults with congenital heart defects, and there are few established protocols for caring for this patient population.
Adapting the Procedure
It invites the question: what will happen to congenital heart patients when they grow up? For Phoenix Children’s cardiologist, Dr. Tabitha Moe, and pediatric radiologist, Dr. Dianna Bardo, this question drove them to seek a solution in hopes of safeguarding the long-term health of such patients. They came to me with a novel idea: to adapt the Fractional Flow Reserve Coronary Artery Computed Tomography Angiography (FFR CTTA) procedure for pediatric patients. FFR CCTA was approved in 2011 for use in adult patients; our team knew it could prove a valuable diagnostic tool for pediatric heart patients, too.
Working together, we were successful in modifying the FFR CCTA, a nonsurgical procedure that allows us to evaluate the hemodynamic significance of coronary artery stenosis and its physiological effects in patients with arterial switch, Kawasaki disease and other congenital heart conditions.
In many of these patients, coronary arteries arise from the wrong place. Other patients have undergone surgery to repair a congenital defect, creating scar tissue. Such issues often compromise the blood supply to the myocardium. When blood flow is limited, the perfusion of the myocardium is not maintained, putting patients at risk of ischemia or a heart attack. Abnormal perfusion gets worse during periods of exercise or stress, making it impossible for these patients to have a normal, exercise-based CT result.
With FFR CCTA, we use medication to dilate blood vessels just before the second coronary artery CT. We perform an examination when the patient is at rest, and then compare the amount of blood flow through the coronary arteries and in the myocardium to determine whether an abnormality exists. At the same time, we collect anatomic and physiologic data, constrict and dilate the blood vessels, and examine blood flow with and without stress, all while collecting 256 high-resolution images per second.
The images are processed in our 3-D Innovation Lab, where our technicians color the coronaries and remove the other structures from the image, allowing us to focus on the coronary tree to evaluate the blood flow at stress and rest. From here, we determine what action we must take to address the issue.
This procedure offers several critical advantages over other imaging modalities like stress echocardiography and myocardial profusion imaging (MPI). While the stress echo allows us to obtain images in patients with complex heart disease, there are no standards for using the data and no understanding of the impacts of testing over time. Likewise, there’s scant information about MPI, which also exposes the patient to ionizing radiation. In fact, its results are so poorly understood that only one study has been published on this modality.
Conversely, FFR CCTA provides a real sense of the risk of ischemia in pediatric patients and allows us to determine whether surgery is required to correct coronary insufficiencies, thus avoiding the current gold-standard method of invasive cardiac catheterization with coronary angiography.
Just as important, the dose of ionizing radiation in FFR CCTA is drastically lower than other modalities. For example, the amount of exposure from FFR CCTA is only 1/20th that of MPI.
Radiation dose is a consideration for all providers whose patients must undergo multiple scans, but the concern in pediatrics is even greater. When you consider that children with congenital heart anomalies and other complex conditions will require imaging throughout their lives, you must take into account the cumulative lifetime dose. This makes FFR CCTA an especially good option for pediatric heart patients.
It’s truly a win on all counts.
The road ahead is an exciting one. As we continue to use this procedure and build upon our knowledge and expertise, we believe FFR CCTA will create a sea change in the diagnosis and treatment of congenital heart conditions and improve outcomes for children worldwide.