MR angiography (MRA) has matured into an extremely reliable, accurate, and valuable diagnostic vascular tool. Accurate imaging of excellent quality, using MRA for both cardiac and noncardiac applications, is now available in many medical centers equipped with state-of-the-art, high-performance gradients and fast pulse sequences.
This has led to a virtual explosion of research and application development in the field of MRA, the fruits of which we and our patients are beginning to enjoy today. One can now successfully acquire diagnostic angiograms of all major vascular territories with MRA replacing conventional angiography. In coronary applications, promising work is being done for the visualization of coronary arteries with and without using contrast injections.
These clinical applications encompass the lion’s share of traditional invasive angiography as experienced in a busy vascular suite. MRA is inexpensive relative to invasive angiography, is almost risk free, and uses no ionizing radiation or nephrotoxic contrast. In addition, MRA results can be rendered as a three-dimensional volume, allowing visualization of the vasculature in any obliquity with a single acquisition of data. Areas of research and development that have produced methods nearing clinical approval include faster imaging sequences and blood-pool agents for arterial and venous applications. Real-time MRI is already available; with further refinement, it will allow for a true real-time fluoroscopic evaluation of the vasculature by tracking small boluses of contrast through the body. MRI-guided endovascular interventions will be a clinical reality soon (once MRI-compatible catheters and balloons are approved for use in the noncoronary circulation). Application of interventional techniques to the coronary circulation will take longer, but its impact on the diagnosis of coronary disease will be significant. Plaque characterization and assessment of stability will be possible using dedicated intravascular coils and catheters. At the same time, cardiac applications are developing at a rapid paceand so is the technology, in order to keep up with the demands of physicians. The provocative concept of a single cardiovascular screening examination, a one-stop cardiovascular assessment performed in 30 to 40 minutes is rapidly becoming a reality (and has, in fact, been demonstrated in some centers in Europe). It is therefore possible, using a single noninvasive modality, to provide imaging of cardiac anatomy, function, and perfusion; coronary-artery anatomy; and the entire peripheral vascular circulation, all in one examination! This paradigm shift, which is only beginning, has significant clinical and financial ramifications, since MRA is safer, cheaper, and far more convenient for our patients than invasive angiography.
What might this mean to vascular interventionalists and interventional cardiologists? Cardiovascular MRI will continue to become a critical point of entry into the health care system for many patients with cardiovascular disease. Those physicians who participate stand to be the beneficiaries of the potential interventions that follow, analogous to the pattern now seen for noninvasive vascular laboratories, echocardiography, and stress testing. The dissemination and accessibility of health information will continue to empower patients, as well as their physicians, to rightfully resist an invasive study and demand the safer, more comprehensive, convenient, and elegant alternative cardiovascular work-up.
Even today, we have the obligation to inform our patients about MRA as an excellent alternative prior to obtaining consent for invasive diagnostic studies in the periphery. Soon, a similar necessity may arise for coronary angiography. In addition, the quality of MRA has developed to the point that it should no longer be reserved for patients who have renal insufficiency. MRA could be used as a primary imaging modality in any patients who do not have absolute contraindications for MRI examinations. For cardiac applications, MRI and MRA already have great value for assessing cardiac chambers and function, congenital heart abnormalities, flow dynamics, myocardial function, and coronary-artery anatomy, with rapid advances being made in all areas.
For those of us performing invasive procedures, particularly in the periphery but also in the coronary circulation, the shift away from the need for invasive diagnostic angiography will have a significant effect. In addition to MRA, CT angiography, particularly for coronary artery circulation, offers the opportunity to obtain highly detailed images of the coronary arterial tree. While still requiring ionizing radiation and contrast, fast multidetector and other fast CT examinations offer the potential to visualize the coronary arterial tree in great detail. Clearly, the future direction of diagnostic angiography is one of diminished need for invasive angiography for cardiac, coronary, and peripheral angiography.
Anticipating the resulting shift in workload and, particularly, technological shifts that may have an impact on practice patterns is extremely important to the stability of provider organizations. One of the advantages of the multidisciplinary collaboration present at Miami Cardiac & Vascular Institute is the need for us to anticipate the future and to begin developing plans for dealing with the effects of technology shifts on practice patterns. If diagnostic angiography is eliminated and replaced by an imaging modality that is totally noninvasive and can be performed by staff from a variety of disciplines, how does this affect interventional cardiologists? Similarly, if all diagnostic angiography of the peripheral circulation were to disappear, what would be the effect on invasive radiologists and those in other disciplines involved in peripheral vascular intervention?
These questions may seem, to some, irrelevant at this time, but the future will bring the need for this discussion. Therefore, at Miami Cardiac & Vascular Institute, we have begun to consider some of these issues (and, in particular, to develop collaborative efforts to optimize both technology and image-interpretation quality). Avoiding major work shifts and involving disciplines from different specialties generally has the effect of increasing overall volume and allowing the participation of a diverse group of people.
The impact of less invasive imaging on invasive imaging is going to be significant over the next several years. Both MRI and fast CT applications will greatly reduce the need for diagnostic invasive angiography for both cardiac and peripheral circulations. Since this is an area of interest to both radiology and cardiology, now is the time to consider and develop good working relationships between the disciplines whose members have a primary interest in the imaging of the cardiovascular system. Clearly, for cardiologists who are interested in participating in MRI, dedicated training will be required, especially if dedicated cardiovascular magnets are developed and implemented. In large cardiovascular centers, it may make sense to begin looking at installing dedicated magnets for cardiovascular diagnosis and placing them within the interventional environment, directly adjacent to angiography suites. This has been implemented at the Miami Cardiac & Vascular Institute already and has promoted integration of technology and physicians.
The future of noninvasive imaging is bright, and the need for invasive techniques to image the heart and circulatory tree will diminish. Experience in several centers has already demonstrated that the increasing use of noninvasive techniques can result in a significant increase in intervention, and we anticipate that this will happen. The current role of the diagnostic vascular specialist should be reassessed, and perhaps additional training should be obtained to ensure that the use of a noninvasive imaging modality is woven into the mainstream of cardiovascular diagnosis.
Barry T. Katzen, MD
Miami Cardiac & Vascular Institute