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LEFT MAIN DISEASE - SURGERY OR ANGIOPLASTY
Thomas Alexander
Senior Consultant Cardiologist, Kovai Heart Centre, Coimbatore.
INTRODUCTION
Since the first clinical description of left main coronary artery (LMCA) disease by Herrick in 1912, [1] numerous studies have shown that stenosis of the left main is of critical prognostic importance. LMCA disease poses special management problems due to the extensive myocardial territory at risk during the revascularisation procedure. Histological differences including the increased elastic tissue within the LMCA also makes their management different.
Angiographically significant left main stenosis has been defined as diameter stenosis greater than 50%. The prevalence of significant LMCA disease in patients with coronary artery disease (CAD) varies from 2.5 to 10% in various published studies. [2,3] The mortality and morbidity of this condition depends on various factors including the severity of the LMCA stenosis, associated disease in the other coronaries including the RCA, left dominance and LV function.MEDICAL VS SURGICAL TREATMENT
Patients with LMCA stenosis who are managed medically have a poor prognosis. Elliot [4] in an analysis of patients with LMCA stenosis awaiting surgery, found a one year mortality of 21% and an event free survival at one year of only 46%. In the earlier landmark studies that looked at medical vs. surgical treatment of LMCA stenosis, the three year survival for medical treatment was 60% in the VACSS, [5] 69% in the CASS, [6] and 82% in the ECASS, [7] where the patients were younger and with better LV function. The comparative surgical survival was 82%, 91% and 91% respectively. This benefit has been shown in the CASS [8] study to persist in the long term with a median survival in the surgical group being 13.3 years against 6.6 years in the medical group.
Most of these studies, which were carried out in an earlier era, had an operative mortality, which ranged from 3.5 to 12%. Majority of these patients received vein grafts rather than mammary arteries. With the improvement in operative techniques, the current operative mortality rates are below 3%. Furthermore with the use of the mammary artery even in these high-risk patients, the long-term results should be even better.
Thus any new technique of intervention should be compared against the current gold standard of surgical treatment before being put into common use.ROLE OF ANGIOPLASTY
Since the introduction of PTCA, intervention of the LMCA has been an attractive target. However the acute catastrophic emergencies of dissection with abrupt vessel closure and the high restenosis rate has been the major problems with this procedure.
Percutaneous revascularisation of patients with significant LMCA stenosis was first described by Gruntzig [9] in his original report on PTCA. Due to procedural difficulties and an early cardiac death, he stated that LMCA stenosis was a contraindication for balloon angioplasty. The largest experience of LMCA balloon angioplasty was reported by O’Keefe-et al. [10] In this series of 127 procedures, 33 were performed on an unprotected LMCA stenosis. Despite the initial success of 94%, there was a 9.1% procedural mortality with only 35% surviving to 3 years. The authors concluded angioplasty was technically feasible but the results were inferior to the surgical procedure.
With the advent of newer interventional devices, particularly the coronary stent, the risk of acute closure has been significantly reduced and therefore there has been a renewed interest in percutaneous intervention. Even so, until there are controlled double blind studies comparing surgical revascularisation, the indications for percutaneous interventions will remain tightly restricted.
These now include:
- Those who refuse surgery.
- Those at too high a risk for surgery - advanced renal, pulmonary or hepatic disease.
- Those with limited life expectancy.
- Those with acute MI and in cardiogenic shock.
- Protected left main disease.
In dealing with LMCA stenosis there are certain important factors that need to be considered. These include:
1. Prognostic factors
- Protected vs Unprotected LMCA stenosis
- Emergency vs Elective intervention.
2. Technical considerations depending on the location of stenosis
UNPROTECTED LMCA ANGIOPLASTY
- Aorto-ostial :Left main trunk
- Distal bifurcation
There are few studies that have looked at angioplasty in patients with unprotected LMCA stenosis. The initial data of plain balloon angioplasty in LMCA stenosis were uniformly unfavourable. In January 1994, a multicentre registry (Unprotected left main trunk intervention multicentre assessment - ULTIMA [11]) was started to assess the results of LMCA intervention. Data from this and the single centre experience of Park et al [12] have been useful to evaluate the results with the newer devices. These results are shown in Table 1.
The registry data showed 12% in hospital mortality and a further 17% mortality within 12 months. The event free survival was also very poor. The single centre experience of Park et al[12] was better and this was attributed to more of isolated LMCA stenosis, less of distal bifurcation lesions and better LV function. The important points from the various studies are summarised below:
- Plain balloon angioplasty is inadequate and stenting is invariably required.
- Debulking followed by stenting may be better in certain situations.
- Good LV function reduces in-hospital mortality to less than 2%
- Support devices like IABP were used in about 50% of patients.
- Due to the high incidence of late death, close follow up is required with a very low threshold for re-angio. Mandatory follow up angiography is required at 4-6 weeks and probably again at 6 months. 3D echocardiography of the LMCA may be an alternative especially if the lesion was ostial.
- IVUS may be an important adjuvant for optimal LMCA stenting.
- Restenosis should be treated by CABG.
Table 1 No. Follow up (months) Success (%) In-hospital mortality
Late mortality Event free survival Restenosis rates Ellis11 91 12 99 12 17 68 17 Park12 42 10 100 0 2 78 22 Protected LMCA stenosiss
This has been defined as stenosis of the left main with at least one of the arteries distal to the left main protected by a graft or excellent collaterals. Most studies show that the immediate success rates and long term results are good. This is especially so when compared with the higher risks associated with re-do CABG. Various studies [13] have shown technical success rates of over 95% and one year event free survival of above 75%. However restenosis still remains high at around 35%.Emergency Intervention
Acute closure of LMCA can result in sudden cardiac death or cardiogenic shock. Acute stenting of flow limiting dissections during diagnostic coronary angiography or during angioplasty have been reported with good results. This is the best option in that situation. Unprotected LMCA intervention in the setting of acute myocardial infarction (AMI) is difficult and carries a high risk. However in the setting of cardiogenic shock, this may be the only option. In the ULTIMA [11] registry, of the 16 patients with AMI and unprotected LMCA stenosis, there was a 68.8% in-hospital mortality with 81.3% requiring IABP or CPS.Aorto-ostial stenosis
This is technically difficult. The guiding catheter cannot be fully engaged and so catheters with side holes may be preferred. Advancing and centering the balloon, retracting the guiding catheter proximal to the balloon and short inflation times are mandatory. Perfusion balloons can also be used for added safety. Stenting with tubular stents with reasonable radio-opacity is required with the stent protruding into the aorta by 1-2 mm. If there issignificant ostial calcium, then debulking with a rotablator followed by stenting may be required. This can make the procedure very demanding.Left main trunk stenosis
This is technically easier to perform. If the stenosis is not very tight, then primary stenting without predilatation is a reasonable option.Distal LMCA / Bifurcation stenosis
This is again technically more difficult. Often debulking with DCA or rotablator is required before stenting. Stenting across a circumflex artery can result in plaque shift and ostial narrowing. Therefore bifurcation stenting using a coil and tubular stent with or without debulking, may be the optimum strategy. Restenosis rates are probably higher for this type of lesions.Present status and future directions
Advances in angioplasty techniques and optimum anti-thrombotic regimen have made percutaneous intervention of LMCA stenosis feasible. However the risk of acute death, significant late death and restenosis are the major drawbacks of this procedure. Furthermore about 50% of patients have associated triple vessel disease and so complete revascularisation may be better achieved surgically. Debulking procedures, stenting and probably brachytherapy have addressed some of these concerns. However the gold standard for comparison continues to be surgical treatment and until randomised trials show that percutaneous intervention is at least comparable, its role should continue to be restricted to carefully selected patients.REFERENCES
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