Coronary Chronic Total Occlusions

INTRODUCTION

Chronic total occlusion (CTO) is a term used to describe a coronary artery that is completely blocked for at least 3 months.¹ CTO’s are very prevalent as they are documented in up to 20% of diagnostic angiograms.² Major coronary arteries with CTO’s are sometimes supported via complex networks of collateral blood vessels from the remaining patent coronary arteries. Although arteries with a collateralized CTO are often receiving enough arterial blood flow via the collateral network to prevent complete infarction in the territory fed by the artery with the CTO, patients often experience exertional angina or dyspnea because the myocardium is still ischemic due to suboptimal arterial blood flow.

Percutaneous coronary intervention (PCI) of CTO’s is very challenging. The initial step required during percutaneous coronary intervention involves advancing an intracoronary guidewire across the blockage. The guidewire provides a platform over which balloons, stents, and any other ancillary equipment can be safely advanced into the coronary artery to treat the blockage. During CTO PCI, this initial step is usually difficult and sometimes impossible to achieve. The CTO is often densely fibrotic and impassable. Additionally, it is sometimes difficult for the interventional cardiologist to understand which direction the guidewire should be directed because the distal coronary artery is not adequately visualized (due to the more proximal CTO preventing flow to the distal segments of the artery). Because of these challenges, percutaneous coronary interventions in CTO’s are often regarded as the “final frontier” in the field of percutaneous coronary intervention. Recent advances such as the hybrid CTO algorithm have been developed to help interventional cardiologists conquer this “final frontier” in the field of percutaneous coronary intervention. A link to a video presentation of this article is attached below:

BENEFITS OF CTO PCI

Successful CTO PCI provides numerous benefits. These benefits are listed below and the scientific evidence that supports this list is summarized in the paragraphs that follow:

1. Reducing anginal symptoms such as chest pain and/or dyspnea.

2. Decrease the need for coronary artery bypass graft surgery.

3. Decrease the need for anti-anginal medications.

4. Reduce mortality (compared to patients with failed CTO PCI).

5. Improve left ventricular function.

6. Decrease the risk for arrhythmias.

7. Improve tolerance to acute coronary syndromes that may occur in the future.

Successful CTO PCI can decrease or eliminate angina, ^3,4 non-anginal symptoms, ⁵ and improve exercise capacity. ⁶ A large meta-analysis that compared patients in whom CTO PCI failed versus those in whom CTO PCI was successful demonstrated that a successful CTO PCI produced significant reductions in recurrent angina during 6 years of follow up.⁴

CTO PCI may reduce the need for patients to undergo coronary artery bypass graft surgery. In patients with stable coronary disease, the SYNTAX trial demonstrated coronary artery bypass graft surgery reduces mortality and the risk of myocardial infarction compared to PCI in patients with very complex disease (high SYNTAX scores), but outcomes are similar in patients with less complex disease (SYNTAX score < 23). ⁷ Many patients decline coronary artery bypass graft surgery due concerns regarding complications and recovery. Other patients are at increased risk for complications with coronary artery bypass graft surgery due to multiple medical comorbidities, age, and/or the need to undergo a redo coronary artery bypass graft surgery. CTO PCI provides additional treatment options for many of these patients. Additionally, CTO PCI is preferable to coronary artery bypass graft surgery in patients with single vessel disease involving a CTO who have refractory angina, and in patients with prior coronary artery bypass graft surgery who re-present with angina and are found to have a patent left internal mammary artery bypass graft to the left anterior descending coronary artery with an unprotected CTO due to failed saphenous vein bypass grafts.

Successful CTO PCI decreases the need for anti-anginal medications. Many patients prefer eliminating medications whenever possible to eliminate possible side effects and costs. Additionally, eliminating the chronic use of long acting nitrates enables many male patients to use phosphodiesterase inhibitors such as sildenafil, varenafil, or tadalifil to treat erectile dysfunction (a medical problem that has a high prevalence amongst male patients with coronary artery disease).

Whether or not CTO PCI improves survival is arguable. Many observational studies have shown better survival among patients with successful versus failed CTO PCI even though bare metal stents were used in many of those studies.^{4, 8, 9} Another recently published, large, multicenter analysis not only revealed that successful CTO PCI was associated with improved survival, it also revealed that the surivival benefit was present regardless of the vessel that was treated (left anterior descending, circumflex, and right coronary artery CTO PCI all provided mortality benefit).¹⁰ Complete revascularization has been associated with lower risk for death, myocardial infarction, and revascularization compared to incomplete revascularization.¹¹ The presence of a CTO is strongly associated with incomplete revascularization,¹² which in turn is associated with an unfavorable outcome.^{13, 14} In another study of 301 patients who underwent myocardial perfusion imaging before and after CTO PCI, a baseline ischemic burden of greater than 12.5% was optimal in identifying patients most likely to have a significant decrease in ischemic burden post successful CTO PCI. Hence, the highest benefit of CTO PCI is most likely to be achieved in patients with significant baseline myocardial ischemia.¹⁵ It should also be noted that a well-developed collateral circulation to the CTO target vessel does not necessarily suggest that ischemia is absent. When fractional flow reserve (FFR) was measured in 92 patients immediately after wire crossing, FFR was < .80 in all patients.¹⁶ Similar findings were present in another study of 50 patients with CTO who were all found to demonstrate ischemia regardless of the presence of collateral circulation.¹⁷

Successful CTO PCI has been shown to improve left ventricular systolic function in numerous studies.^18-26 Improvement of left ventricular systolic function is only expected to occur if the CTO supplied myocardium is viable, ^{23, 26} and the vessel remains patent during follow-up.^{21, 22}

It has been hypothesized that CTO PCI may reduce the risk for life threatening arrhythmias. Ischemia may predispose to ventricular arrhythmias. Among 162 patients with ischemic cardiomyopathy who received an implantable cardiac defibrillator, 44% had at least one CTO.²⁷ During a median follow-up of 26 months, the presence of CTO was associated with higher rates of ventricular arrhythmias and death.²⁷ Currently, there are no prospective studies demonstrating that CTO PCI decreases the risk for ventricular arrhythmias but this is likely to be an area of future research.

Experts also propose that successful CTO PCI may improve a patient’s tolerance for future acute coronary syndrome.¹ Patients with a CTO who develop an acute coronary syndrome have much worse outcomes than those who do not have a CTO (including patients with multivessel coronary artery disease). ^28-31 Although there are no prospective studies demonstrating that prophylactic CTO PCI can improve the outcomes of future acute coronary syndrome, a retrospective study showed improved long-term outcomes in patients with successful CTO PCI versus those with failed CTO PCI after presenting for primary PCI due to acute ST elevation myocardial infarction.³²

THE HYBRID ALGORITHM

The challenges associated with coronary CTO percutaneous coronary intervention have traditionally resulted in a more conservative strategy regarding their management. In patients with multivessel coronary artery disease who are found to have a coronary CTO, the presence of the CTO is often the primary factor that leads to referral for coronary artery bypass surgery. In patients with single vessel coronary artery disease found to have a coronary CTO, percutaneous coronary intervention attempts have typically been reserved for those patients who demonstrate severe angina despite optimized medical therapy. Recently developed advances with the hybrid algorithm suggest that the historic paradigm used to refer patients with coronary CTO for PCI needs modification.

The optimal approach to CTO PCI continues to evolve. In January 2011, several high volume CTO operators met in Bellingham, Washington and created a consensus algorithmic approach to CTO PCI. ³³ This approach was named the “hybrid algorithm.” It integrates all possible wire crossing strategies (antegrade wire escalation, antegrade dissection/reentry, and retrograde). The algorithm directs physicians to the safest, most effective, and most efficient strategy based on the anatomy of the CTO. A fundamental principle of the hybrid algorithm requires that operators master all the skillsets of CTO PCI and be able to alternate between these techniques during the same CTO PCI procedure in order to recanalize the CTO.¹

The first and most important step of the hybrid approach to CTO PCI is to perform simultaneous dual guide catheter coronary angiography. Dual guide catheter angiography allows complete anatomic assessment of the CTO. The hybrid algrorithm requires operators to assess four anatomic characteristics of the CTO:

1. Clear or ambiguous proximal cap anatomy

2. Lesion length (< or > 20 mm length)

3. Quality of the distal target

4. Presence or absence of “interventional” collaterals

By incorporating these four anatomic characteristics of the CTO, the hybrid algorithm directs the operator to the best initial crossing strategy and also provides guidance for subsequent strategies that may be utilized if the initial strategy is not successful. For example, a CTO with a clearly defined (tapered) proximal cap, 15 mm length, good distal target, and absent “interventional” collaterals (too small or tortuous for retrograde crossing) is best approached with an initial strategy involving antegrade wire escalation, and a secondary strategy involving antegrade dissection/reentry. On the other hand, a CTO with an ambiguous proximal cap, 25 mm length, poor distal target, and good “interventional” collaterals is best approached with an initial retrograde dissection/reentry strategy.

Alternating between different CTO strategies is at the heart of the hybrid algorithm.¹ Should one approach fail, another approach should be utilized. Every CTO case is unique and may require a different set of strategies for success.

IMPACT OF THE HYBRID CTO ALGORITHM

The hybrid CTO algrorithm has made a major impact on the dissemination and application of CTO PCI techniques in recent years.¹ An initial single operator experience with the hybrid CTO algorithm was presented at a professional meeting in 2013 and reported a procedural success rate of 90.4% during 73 consecutive PCI cases. ³⁴ This success rate was much better than the previously expected success rate expected during CTO PCI that had historically approximated 75%. ³⁵ Shortly thereafter, a “hybrid registry” of 144 cases performed by five different centers was presented at a CTO summit meeting and reported a procedural success rate of 94% using the hybrid algorithm. ³⁶ Recently, several publications in peer reviewed medical journals confirm overall procedural success rates that exceed 90% with low complication rates using the hybrid CTO algorithm. ^37-39 The CTO PCI procedural success rates reported in the studies utilizing the hybrid CTO alogorithm seem to far exceed those reported during the same era performed without the hybrid algorithm. ⁴⁰

CASE EXAMPLES

Video links for several examples of complex CTO cases performed by Dr. Raj Chandwaney are demonstrated below.

CONCLUSION

Coronary CTO’s have a high prevalence amongst patients with coronary artery disease. Successful CTO PCI may have numerous benefits such as reducing angina symptoms, decreasing the need for angina medications, reducing the need for coronary artery bypass graft surgery, improving systolic function, and possibly reducing mortality. The hybrid CTO algorithm integrates antegrade and retrograde CTO techniques to optimize patient safety and improve procedural success rates during CTO PCI. Recently published data appear to confirm that the hybrid CTO algorithm will continue to improve the outcomes for patients with coronary artery disease who have a CTO that may have previously been declared irreparable. The highly skilled physicians at Oklahoma Heart Institute will continue to monitor and master this rapidly evolving area of cardiology so that we may continue to offer our patients the most progressive treatments available.

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