The Chronic Total Occlusion
Anthony Fung
Jaap N. Hamburger
Percutaneous transluminal coronary angioplasty (PTCA) has established itself as an important alternative to coronary artery bypass surgery in the treatment of coronary artery disease (CAD). The continuing development of tools and techniques has led to an increase in the number and complexity of cases performed annually (1,2). In current angioplasty practice, the treatment of saphenous vein bypass graft disease, small-diameter coronary arteries, and multivessel disease is considered as routine rather than as the exception. The explosive increase in the use of intracoronary stents certainly played a major role in this shift of former angioplasty boundaries (3), which was further enhanced by the successful introduction of drug-eluting stents (DES) (4, 5, 6). However, recanalization and maintenance of blood flow through a previously chronically occluded coronary artery still is a major challenge. Initially, low success rates (7, 8, 9, 10) and high recurrence rates (11, 12, 13) hampered percutaneous attempts at the recanalization of chronic occlusions. Consequently, in the 1977-1981 angioplasty registry compiled by the National Heart Lung and Blood Institute (NHLBI), chronic total occlusions (CTO) represented a mere 2% of all lesions attempted. In the 1985-1986 registry, this number had increased to 10%. It was only after the introduction of improved guidewire technology (14, 15, 16) and the demonstration of a positive influence of intracoronary stent implantation on long-term vessel patency (17, 18, 19, 20, 21, 22), that the percutaneous treatment of chronic occlusions became an acceptable alternative for surgical treatment. Three randomized trials of primary stent placement versus balloon angioplasty (BA) alone, enrolling at least 100 patients, have been reported (SICCO, GISSOC, and TOSCA-1) (17, 18, 19). Although the trials varied in inclusion criteria, design, antithrombotic regimen, and endpoints, their results were substantially concordant in demonstrating reduced restenosis and reduced reocclusion when a strategy of routine stenting of recanalized nonacute occlusions was followed. In addition to technological improvements, indications for attempting CTO recanalization may broaden substantially over the next several years to include a large reservoir of asymptomatic patients currently treated medically. It is now recognized that asymptomatic occluded infarct-related coronary arteries identified during convalescence from myocardial infarction (MI) are associated with progressive left ventricular dilatation and dysfunction, reduced cardiac electrical stability, and higher long-term rates of cardiac death. The benefit of routinely seeking and opening such occlusions is being tested definitively in the NIH-NHLBI-funded Open Artery Trial (OAT) and its angiographic substudy TOSCA-2. This strategy, if proven effective, will increase greatly the number of nonacute coronary occlusions treated percutaneously.
In this chapter we discuss:
The use of noninvasive imaging for patient selection and preprocedural evaluation of coronary anatomy
A technical approach to recanalization and adjunctive angioplasty procedures
Currently available dedicated angioplasty hardware
The use of guidance for optimization of procedural results
THE RATIONALE
Before the Procedure I
The decision to subject a patient with a chronic total occlusion
to an attempt at percutaneous recanalization can be as much of a challenge as performing the procedure itself. The absence of (large) randomized trials unequivocally documenting a long-term clinical benefit, the nonurgent character, and the relatively high procedural costs force the responsible operator to carefully balance the benefits and potential downsides of an attempt at recanalizing a CTO. Clearly, myocardial salvage, such as in direct percutaneous intervention for patients with acute MI, is not the issue.
to an attempt at percutaneous recanalization can be as much of a challenge as performing the procedure itself. The absence of (large) randomized trials unequivocally documenting a long-term clinical benefit, the nonurgent character, and the relatively high procedural costs force the responsible operator to carefully balance the benefits and potential downsides of an attempt at recanalizing a CTO. Clearly, myocardial salvage, such as in direct percutaneous intervention for patients with acute MI, is not the issue.
For symptomatic patients, successful recanalization could result in relief of angina. This indeed has been documented in various publications (7, 8, 9, 10, 11, 12, 13,20,21). For asymptomatic patients, or for patients with heart failure symptoms, the goal of recanalization could be an improvement of left ventricular function and/or improved survival rates.
Using dobutamine stress echocardiography, Rambaldi et al. (23) reported early recovery of left ventricular function within 24 hours of successful recanalization of chronic occlusion, whereas other investigators reported on medium long-term (24,25) improvement of ventricular function based on left ventricular angiography analyses. This is in contrast to the outcome of The Open Artery Trial (TOAT) study. In this study, 66 patients with total occlusion of the LAD 1 month following anterior MI were randomized to percutaneous coronary intervention (PCI) versus medical therapy. Patients with a persistent open artery 12 months following successful recanalization surprisingly showed a larger end systolic volume (ESV) (26). Although recovery of regional and/or global ventricular function is a desirable endpoint, recanalization may confer benefits that extend beyond functional recovery. One potential benefit is that of attenuation of progressive ventricular dilatation. Regional contraction is secondary to thickening of the inner layers of myocardium, which can be damaged in patients with nontransmural, subendocardial infarctions. In such patients, preserved viability of the outer layers can prevent progressive dilatation, despite the lack of any improvement in resting function following revascularization. Senior et al. studied 56 patients with severe ischemic cardiomyopathy (27). They assessed viability with nitrate-enhanced thallium single photon emission computed tomography (SPECT) before physician-directed revascularization or medical therapy. In patients with a large amount of viable tissue (>5 segments in a 12-segment model), revascularization was associated with prevention of remodeling and improvement in left ventricular ejection fraction.
Several investigators reported on long-term survival rates in patients following an attempt at recanalization, comparing long-term outcome of successful procedures with continued medical therapy in those patients in whom an attempt had failed (28, 29, 30). These retrospective patient series strongly suggest a correlation between successful recanalization and improved survival rates. Two separate cohort studies assessed the correlation of preprocedural assessment of ischemia by means of positron emission tomography (PET) scan and clinical outcome (31,32). These studies showed that, among patients with a large amount of dysfunctional but viable myocardium, the survival rate was significantly higher with revascularization than with medical therapy.
This correlation was further corroborated by the findings of meta-analyses by Bax et al. (33) and Allman et al. (34): 24 studies with a total of 3,088 patients. The latter analysis demonstrated a strong association between myocardial viability on noninvasive testing and improved survival after revascularization in patients with chronic CAD and left ventricular dysfunction. Absence of viability was associated with no significant difference in outcomes, irrespective of treatment strategy.
Accordingly, procedural efficacy, long-term outcome, and cost-effectiveness could be optimized by improvement of case selection based on noninvasive imaging techniques. In patients with CAD and dysfunctional myocardium, impaired regional myocardial function may be secondary to scarring, stunning, or hibernation. Imaging could help differentiate between scarred and dysfunctional, but otherwise viable tissue, where—obviously—only viable tissue would have a potential for functional improvement. Potentially useful techniques would include radionuclide SPECT imaging with thallium201 or Tc99m-sestamibi to evaluate myocardial perfusion and cellular integrity, dobutamine echocardiography to interrogate inotropic reserve, 2-[18F] fluoro-2-deoxy-D-glucose PET (FDG-PET) scanning to evaluate metabolic activity, and delayed-enhancement magnetic resonance imaging (MRI) to differentiate between myocardial scar and viability.
In summary, basic guidelines when using the results of noninvasive testing for case selection include:
For relief of angina, even smaller vessels may be reasonable targets. However, if the goal is improvement of left ventricular function, then only larger vessels supplying a significant segment of myocardium should be considered.
The affected territory must show impaired regional function in order for improvement to occur.
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