Coronary lesions are chronic total occlusions (CTOs) when
- there is no anterograde filling of the distal vessel
- angiographic or clinical evidence of an occlusion duration of more or equal to 3 months (1).
Approximately one-third of all significant coronary stenoses at angiography are CTOs, but only 10-15% of them are treated with percutaneous coronary intervention (PCI) while the majority is treated medically or referred for surgery (2).
As for stable lesions, indication for revascularisation of CTO is justified
- in cases of angina
- demonstrable silent ischemia involving myocardium supplied by the occluded vessel.
The main cause of the large discrepancy between the prevalence of CTO and lesions treated percutaneously is not lack of indications but the perception that CTO revascularisation has low immediate success, a high periprocedural complication rate and that it offers poor long-term clinical benefit.
On the contrary, unlike treatment of nonocclusive lesions for stable angina, successful reopening of CTO has been shown not only to alleviate anginal symptoms but also to improve left ventricular ejection fraction, decrease the need for coronary bypass graft surgery (CABG) and improve long-term survival.
If collateral development eliminates ischaemia…Just wait for the collaterals
Opening a CTO in the presence of well-developed collaterals may not be required if the distal myocardium is believed to be receiving a sufficient blood supply. An elegant study using Doppler and flow wires was designed to test collateral function and functional reserve in patients with CTO and its response to pharmacological stress (3). It revealed that only 7% of patients had a sufficient increase in collateral flow during stress to reach a normal coronary flow reserve of >2 while a reduction in absolute flow during hyperaemia occurred in one-third of patients. These results suggest that even in “well-collateralised” CTOs, maximal hyperaemic distal flow is functionally insufficient so recanalization provides extra benefit.
OAT and COURAGE’s conclusions do not apply to CTO lesions
The OAT trial (4) tested in 2166 patients, the hypothesis that routine PCI for total occlusion of the infarct-related artery 3 to 28 days after acute myocardial infarction would reduce the composite end point of death, reinfarction or advanced heart failure. The trial demonstrated no effect of PCI on outcome and a trend to more frequent reinfarction and higher 4-year cumulative event rate.
The conclusions of this trial, however do not apply to real CTO lesions because patients enrolled had recent occlusions (8 days median duration), functional (TIMI 1) and complete occlusions. The trial had an unexpectedly low recanalisation success rate of 87% and excluded patients symptomatic or patients with large areas of viable myocardium at risk. In low risk patients (young, small area of myocardium at risk, single vessel disease and preserved LVEF) it is obviously impossible to find differences between hard end-points such as death or myocardial infarction.
The COURAGE trial (5) was a strategy-driven trial randomizing 2287 patients to optimal medical therapy with or without PCI. The main result revealed no difference by treatment in the primary end point of death or MI for a median follow-up of 4.6 years. Several points related to patient-selection bias and PCI procedure weaken these conclusions and limit their generalisation to CTO cases.
As the OAT trial, COURAGE excluded more than 90% of the patients who were evaluated, suggesting a super-selected study population. In particular, cases with revascularisation within the previous 6 months and coronary anatomy unsuitable for PCI (i.e most CTOs) were excluded. Additionally, in the randomised patients, revascularisation was incomplete: two thirds of the patients had multivessel disease but 59% received only one stent in the PCI group. The ischaemic burden measured by stress myocardial perfusion single photon emission computed tomography (MPS) was measured in selected patients in a recently published post hoc analysis (6) showing that ischaemia reduction was greater in the PCI group. In the patients with more severe pre-treatment ischaemia, a lower unadjusted risk for death or MI was observed.
Recanalisation of CTOs , with proper testing, can have beneficial effects on myocardial function
The long-term effect of percutaneous revascularisation of CTO on left ventricular ejection fraction (LVEF) and remodeling results are promising, even though the information available is still insufficient .
Chung MC et al (7) repeated ventriculograghy six months after PCI of CTO and showed a significant improvement in-global LVEF (4% on average), but a higher increase (8%) in the group of patients without previous MI in the territory of distribution of the opened CTO. Longer follow-up (3 years) and more accurate cardiac imaging tests (8), showed a significant reduction in LV volumes, an increase in segmental wall thickening and a trend to improved LVEF.
The practical message is that both early and late improvements in regional LV function can be expected in the distribution territory of CTO lesions if patients are properly selected with myocardial viability testing and the extension of transmural scar testing.
Reopening CTOs improves prognosis
Recent reports add evidence to the initial studies of Hoye et al (9) who evaluated a total of 874 CTO patients for the occurrence of major adverse cardiac events (MACE) including death, myocardial infarction (MI) and the need for repeat revascularisation. Procedural success rate was 65.1% and stents were used in 81%. At 5 years, survival was 93.5% after successful recanalisation vs 88% after failed recanalisation. Freedom of MACE was also significantly higher in patients with successful PCI.
Aziz et al (10) reported the results obtained in 543 CTO cases with a 69.4% rate of success and compared survival rates in patients with successful revascularisation and in patients with failed revascularisation. After nearly two years of follow up, the mortality rate was 2.5% in patients with successful recanalisation versus 7.3% in those who failed recanalisation. The crude hazard ratio for death with CTO failure was 3.92 (95% confidence intervals 1.56-10.07; P = 0.004). The rate of CABG was significantly lower in the successful PCI group (3.2% vs 21.7%, p<0.001).
Procedural success depends on favourable predictive factors and highly-experienceed CTO-operators
A number of predictors of procedural success have been reported in literature. Blunt occlusion stumps, heavy calcification, proximity to a side branch, presence of bridging collaterals, and indeterminate occlusion duration seem to impact the likelihood of procedural success unfavorably (11-14).
To evaluate the trends in procedural success, in-hospital and long-term outcomes after PCI for CTO over the last 25 years in the Mayo Clinic (15), 1262 patients were divided into 4 groups according to the period the intervention was performed. They considered group 1 (percutaneous transluminal angioplasty), group 2 (early stent era), group 3 (BMS era) and group 4 (DES era). The procedural success rates increased between PTCA only and all the stent groups (51% versus 72%, 73% and 70%, respectively). In-hospital mortality (2%, 1%, 0.4% and 0%, p<0.009), emergency CABG and rates of major adverse cardiac events were significantly lower in the 2 most recent cohorts compared with those treated before. Compared with the present era, in-hospital major adverse cardiac events and 1-year TVR rates have declined by approximately 50%.
The main reason for failure is the impossibility of a guide-wire or balloon to pass through the occlusion and many methods are being described to improve success rates, from better selection of guiding support catheters to the development of dedicated guidewires or alternative devices and complex CTO techniques.
Today, the procedural success rate varies widely from <60-70% in the presence of one or more unfavourable predictive factors to >90% with favourable characteristics and highly experienced CTO-operators (1,16).
The complication rate is not prohibitive
Many complications have been described including vessel perforation, impairment of collateral flow, retrograde dissection with branch occlusion or perforation, guidewire entrapment, and those derived from contrast overload and high radiation dose.
However Suero et al (17), have shown that total in-hospital complications were similar among the CTO patients (n=2007) compared to a matched non-CTO cohort. New-generation wire perforation occurred in 4 out of 420 consecutive cases (1.5%), two contained and two requiring pericardiocentesis due to cardiac tamponade. Also in the Mayo Clinic Registry (15) and according to the time of intervention, a significant improvement over time of in-hospital outcome was observed when a successful PCI was completed. In-hospital mortality (2%, 1%, 0.4%, and 0%, p = 0.009), emergency coronary artery bypass grafting (15%, 3%, 2%, and 0.7%, p < 0.001), and rates of major adverse cardiac events (8%, 5%, 3%, and 4%, p = 0.052) decreased over time.
CTO often reocclude after recanalisation – maybe not
The long term success after implantation of bare metal stents (BMS) for CTO has been limited by high rates of restenosis and re-occlusion. A large amount of data has demonstrated that drug-eluting stents (DES) are effective in reducing restenosis compared to BMS in various patient and lesion subsets.
Sirolimus-eluting stents (SES) showed a significantly lower in-stent (7% vs 36%, p<0.001) and in-segment restenosis (11% vs 41%, p<0.00001) rate at 6-months of follow-up leading to a lower target lesion revascularisation (TLR) and vessel revascularisation (TVR) rate compared to BMS in a randomised trial. Reocclusion rates, described in 8% of CTO versus 1.8% of non-CTO, has shown a significant decrease (p<0.04) with sirolimus-eluting stents from 13% (BMS) to 4% (18).
After a follow-up of 18 months, the composite endpoint of death, MI or TLR was significantly lower (p=0.005) in the DES group (8.1%) than in BMS group (21.6%) and the difference was due to the reduction in TLR (19).
Different authors (20,21) tried to explain the OAT trial results and hypothesised that recanalisation could lead to loss of previously developed collaterals and re-exposure the myocardial area to future reinfarctions. Because the OAT trial included patients with 1- or 2-vessel coronary disease, and PCI on the noninfarct-related arteries was permitted, >85% of patients in the intervention group had no coronary arteries with significant obstructions after PCI, a situation that would cause the functional regression of existing collaterals. In cases of subsequent plaque rupture and total occlusion of any of the 3 coronary arteries occurred (expected in 5% to 15% of patients with acute coronary syndromes over the first 1 to 2 years), the impaired collateral flow after new acute occlusion would immediately predispose to greater myocardial reinfarction, which could explain the negative effects of the OAT study.
The content of this article reflects the personal opinion of the author/s and is not necessarily the official position of the European Society of Cardiology.
Conclusion:
Conclusions
Management of patients with chronic total occlusions remains challenging. Most of these patients have multivessel coronary artery disease, have undergone previous revascularisation and have other complex target lesions usually considered unsuitable for percutaneous intervention.
Lifestyle modifications and aggressive control of other cardiovascular risk factors (statins, betablockers and ACE inhibitors) are mandatory. With the exception of the most obvious indications, magnetic resonance imaging or myocardial perfusion scans should be performed to evaluate the extension and severity of inducible ischemia in the CTO related myocardium, stratify the patients and guide therapeutic decision making.
In this setting, percutaneous coronary intervention of CTO by well-experienced operators has been shown to alleviate anginal symptoms, improve left ventricular function, reduce redo surgery and improve long-term survival.
Proven and Potential Benefits of Opening a Chronic Total Occlusion of a territory with ischaemia and viability
Alleviate anginal symptoms (13, 15)
Improved global and segmental left ventricular systolic function (7,8)
Reduced left ventricular volumes (8)
Reduced need of further coronary artery bypass grafting (15)
Prolonged survival (9,10)
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