Research overview
About CTOs
Cardiovascular disease remains the leading cause of mortality in the western world. Chronic total occlusions (CTOs), defined as arterial occlusions more than six weeks old, are extremely common. Angiographic studies have shown total occlusions in about 30% of patients with coronary artery disease and more than 50% patients with peripheral arterial disease. Successful revascularization of coronary CTOs significantly improves angina and left ventricular function. Coronary total occlusions are also a significant component of peripheral arterial disease, which afflicts 12% to 20% of people aged over 65 years. Peripheral CTOs lead to conditions such as claudication (limping), limb ischemia, ulcers and sometimes to amputation.
According to studies, only 12% of patients with coronary CTO and 13% of patients with peripheral CTO are treated with percutaneous interventions (that is, those done through the skin). Remaining patients are either referred for bypass surgery (23% with coronary artery disease, 2% with peripheral arterial disease) or persist with medical therapy and/or exercise regimens (65% coronary, 82% peripheral).
Bypass surgery and medical therapy have significant limitations:
- Bypass surgery is more invasive than percutaneous revascularization, requires a longer time in hospital and for recovery, and is associated with significant morbidity including cerebral vascular complications (strokes and persistent cognitive dysfunction).
- Medical therapy is frequently ineffective, leaving patients with restricted lifestyles.
Successful percutaneous revascularization requires passing a small (360 μm diameter for coronary arteries) guidewire through tissue obstructing the lumen of the occlusion, a procedure called CTO crossing. Difficulty in safely reaching the distal arterial bed with the guidewire is the most common technical challenge in this procedure. This hurdle, along with prolonged radiation exposure, high contrast loads (with risk of contrast nephropathy) associated with X-ray guidance, and the potential for vascular perforations, all contribute to physician reluctance to consider percutaneous coronary interventions. As a result, CTO crossing represents less than 8% of all attempted percutaneous coronary interventions, despite its benefits when successful. Even in cases where percutaneous revascularization was successful in CTOs, the long-term outcomes with conventional bare metal stents was limited by prohibitively high restenosis rates. However, major advances that have dramatically lowered restenosis rates in coronary lesions, including CTOs, have now established CTOs as the main priority of interventional cardiology.
Importance of studying CTOs
Studying CTOs is important, because there is huge gap in our knowledge of the current status of CTO therapy in Canada. The patient factors and demographics that influence the decision of a particular therapy for any given CTO are unknown. There is also surprisingly little information about the pathophysiology of CTOs and why some CTOs can be crossed while others are unsuccessful. An examination of the natural history and direct characterization of the structure, composition and physiology of a CTO during intervention with new imaging approaches could play a major role in treatment planning, device guidance and outcome assessment. Moreover, putting new CTO strategies into routine cardiac practice will also require knowledge of the status of CTO therapy in Canada (e.g., information on regional variations) and identifying subgroups of CTOs that could derive the greatest potential clinical benefit from less invasive percutaneous coronary interventions.
