May 16, 2019
5 min read

Complex CAD: Ambiguity in Definition Can Influence Treatment Decisions

Clarifying the definition of complex CAD may elucidate when PCI, CABG or medical therapy is the best option.

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CVD remains the leading cause of death in the United States, with CAD being the most common cause of death attributable to CVD. Rates of CAD have been on the rise in the United States in conjunction with many risk factors for CAD, including diabetes and chronic renal insufficiency, which have been temporally associated with a notable rise in the complexity of CAD.

However, rates of revascularization therapy for CAD including PCI and CABG have been on the decline. Several trials, including COURAGE and ORBITA, have called into question the value of coronary revascularization in additional to optimal medical therapy in patients with stable CAD, which may have contributed to the decreasing rates of revascularization. However, patients enrolled in these trials make up an increasingly smaller fraction of cases seen in today’s catheterization lab, which can make extrapolation of these results to this expanding patient group with complex CAD difficult at best. One impediment of extrapolating trial data to real-time patient care in this group is our current ambiguous definition of “complex CAD.”

Competing Definitions

Complex CAD has been defined in multiple different ways. One definition for patients with multivessel CAD is the SYNTAX score, which is based on anatomy. The SYNTAX score was designed around the principle that the number of diseased coronary vessels is not the only marker for CAD severity. The location of the lesions and their impact on blood flow, the degree of vessel stenosis, lesion classification, and the diameter and calcification of the vessel are also important factors that affect the technical feasibility of performing PCI. While the findings from this trial are broad, the fundamental finding was that more complex CAD had superior outcomes when treated with CABG, while less complex anatomy had equivalent outcomes between PCI and CABG. As more attention was directed toward a population with increasingly complex CAD, many of the clinical comorbidities that made both revascularization procedures higher-risk became increasingly recognized, culminating in the SYNTAX II score, which takes many of these comorbidities into account, and showed improved discrimination over the original SYNTAX score regarding revascularization strategies in this group. Other mortality risk scores for PCI include the National Cardiovascular Data Registry (NCDR) and Mayo models.

Robert F. Riley

A second definition of complex CAD from a percutaneous revascularization standpoint could focus around the spectrum of periprocedural risk. The NCDR risk calculators estimate a baseline mortality risk of less than 1% for routine elective PCI, though this goes up in the presence of diabetes, chronic renal insufficiency, increasing age, acute vs. elective presentation, chronic obstructive pulmonary disease (COPD) and peripheral vascular disease. These risk factors have a synergistic effect with more complex anatomical subsets as defined by periprocedural 30-day mortality risk: left main PCI (1%), chronic total occlusions (0.9%), lesions with significant calcification that require atherectomy (2.3%), device-assisted PCI (7.6%), patients turned down for CABG (7%), and age at least 80 years (3.2%). However, while these prospective studies and trials illustrate the elevated procedural risk for these patient subsets, they also show that PCI can be performed safely and efficiently in these groups, particularly utilizing modern techniques and current second-generation drug-eluting stents, as demonstrated by the SENIOR and CONSISTENT CTO trials, among others. Many of these studies illustrate that our best understanding of complex CAD involves anatomical complexity, physiologic parameters (cardiac index/power, ejection fraction) and comorbidities.


A final definition of complex CAD could revolve around what it is not, which can be inferred by the exclusion criteria from COURAGE and ORBITA (Table). These exclusions are the exact patient population described above as complex and do not fit the headlines associated with publication of these trials.

Unfortunately, these trials dissuade treatment of the very patients most likely to receive the most benefit, resulting in omission of care for many of these patients, with PCI being viewed as a procedure of last result. Regardless of our definition, however, there is clear impetus to continue to develop technologies and techniques for the percutaneous treatment of these lesions, as those patients at highest procedural risk also have the most to gain in terms of long-term MACE reduction compared with those at lower risk.

Mixed Messages

This direct relationship between CAD complexity and appropriateness for revascularization is reflected in societal guidelines and appropriate use criteria for PCI. However, it should be noted that the definition of complex CAD in these documents only focuses on anatomic complexity and does not take into account the previously mentioned physiologic characteristics and comorbidities that clearly influence the risk-reward relationship for patients with significant CAD considering revascularization.

This underscores how messages originating from sensationalized trials in the media can come into direct conflict with the daily treatment of patients, especially when documents aimed to guide practice omit key variables in complex decision-making.

Future guidelines should focus on the growing complexity of caring for this patient group and offer guidance on utilizing the growing wealth of prospective study and trial data supporting the treatment of this group. Concurrently, efforts should be made to offer readily available risk-stratification tools that incorporate known variables that contribute to procedural risk so that this can be discussed with patients as part of formulating an individualized treatment plan. Efforts in technical education should be combined with increasing awareness of treatment therapy so that the data can be properly and safely utilized to treat patients, as seen at many recent societal meetings such as TCT through live cases and hands-on proctoring.

However, given that annual volume of complex PCI and outcomes are directly related (and indirectly related to rates of complications), efforts should be made to refer patients to high-volume centers and individuals trained to care for these patients until broader educational efforts can overcome the current limitations in care delivery.


Disclosure: Riley reports he serves on the speakers’ bureau for Abbott Vascular, Asahi Intec, Boston Scientific and Philips; serves on the advisory board for Abbott Vascular and Boston Scientific; and received honoraria from Abbott Vascular, Asahi Intec, Boston Scientific and Philips.