Coronary artery stenting

From Ganfyd

Survival curves for first year after index myocardial infarction in New Jersey over the last 16 years. The crude mortality has decreased acutely for both weekday and weekend admissions (prefixed WE), but after 1999 some factor seems to have increased mortality after 180 days. From Table 3^[1]

The coronary artery stents are currently either bare metal or drug-eluting. The relative merits of the two (and different drugs that are eluted) are currently subject to controversy with financial implications. The drug eluting ones are less likely to re-occlude than the plain ones in the long term^[2], but until the endothelium has regrown over them - the process the eluted drugs retard - they are more prone to clotting and occluding.^[3][4]

In multivessel disease generally coronary-artery bypass grafting has better outcomes than either plain^[5] or drug-eluting stents^[6] in the domains of:

1. Mortality rates
2. Myocardial infarction
3. Repeat revascularization
4. Those with diabetes and more than 2 vessel disease^[7]

Much of the benefit seems to be in reduced long term complication rate^[8] and in selected subgroups such as those with severe left ventricular dysfunction drug-eluting stents are likely to offer better outcome^[9]

Dual antiplatelet therapy

At the time of stent insertion, particularly with primary PCI the patient is likely to have a special, probably triple therapy loading regime.

Stent occlusion is opposed by aspirin and a thienopyridine which it is very important to continue for a suitable period, currently given as 6 months to a year for the drug eluting stent, and notably shorter for the plain metal one. If you run into bleeding issues, try not to stop antiplatelet therapy and if you do have to stop it, only the cardiologist is likely to be able to estimate accurately the risk of so doing in terms of stent thrombosis, as it will be a stent specific function of time since implantation.

The combination of aspirin and clopidogrel may be accompanied by bruising, sometimes impressive (particularly if it is sub-conjunctival), but ceasing treatment is a serious decision to be made only with the utmost caution.

Combined antiplatelet and anticoagulation therapy

This is likely to be indicated in acute coronary syndrome when the patient is already on anticoagulation for another indication at the time of presentation. ESC consensus guidelines now exist^[10]. Essentially in patients at low to moderate bleeding risk, and a good indication anticoagulation (warfarin) is continued with the antiplatelet agents covering the highest risk period of stent thrombosis. Thus elective metal stents get 1 month of triple therapy, elective 'olimus coated stents get 3 months triple therapy and to 12 months an antiplatelet and anticoagulant, while elective paclitaxel coated stents get 6 months triple therapy, then up to 12 months an antiplatelet and anticoagulant. This last regime also applies to all stents used in primary PCI. If risk of haemorrhage is high use bare metal stents in all indications and up to 4 weeks of triple therapy, then in elective patients revert to warfarin but in primary PCI ACS patients give 6 months antiplatelet and anticoagulant before reverting to anticoagulation alone.

Brief overview

The intensive analysis of the clinical trial data suggests:

• Diabetic patients and those with acute coronary syndrome may be better off with a bare metal stent^[11][12]
• The extensive take up of drug eluting stents based on short term studies showing benefit for easily measured primary cardiac outcome measures rather than awaiting total mortality and cardiac event rates over several years was premature^[13]. Not all drug eluting stents are equivalent and indeed the drug of choice is definitely evolving.
• Patients need to be selected for stent type and this selection needs to consider multiple patient parameters, the cost of the therapy and cost and convenience of long term drug prophylaxis.
• In patients with stable coronary artery disease on optimal medical therapy of antiplatelet agent, betablockers, calcium channel blockers, nitrates, ACE inhibitors (or proven Angiotensin II inhibitors) and statins the COURAGE trial has confirmed previous studies that the addition of percutaneous coronary intervention (PCI) with stents:
  • reduction myocardial infarction and death is unlikely to be benefical
  • symptom control of angina is likely to be beneficial for the first 3 years but unlikely to be benefical after this with PCI^[14]
• Early stent thrombosis after PCI is associated with^[15]:
  • Acuteness of PCI
  • Complexity lesions
  • Left ventricular function less than 40%
  • Diabetes mellitus
  • Use of proton pump inhibitors
  • Lower clopidogrel loading doses
  • CYP2C19
  • ABCB1 genotype
  • ITGB3 genotype
• The risk of plain stent thrombosis is associated with^[16]:
  • Discontinuing clopidogrel therapy
    • First 30 days after the index PCI hazard ratio = 36 (8 - 168)
    • 30 days to 6 months after the index PCI hazard ratio = 4.6 (1.4 - 15.3)
    • Beyond 6 months hazard ratio = 5.9 (1.7 to 19.8)
  • Undersizing of the coronary stent
  • Poor flow through stent and other technical issues like lesion at arterial bifurcation
  • Concurrent malignancy
  • Coronary artery disease proximal and distal to the stent
  • Dissection
  • No aspirin
  • Ejection fraction <30%
  • Younger age
• The risk of drug-eluting stent thrombosis is associated with^[17][18]:
  • Premature antiplatelet therapy discontinuation
  • Renal failure
  • Lower ejection fraction
  • Acute coronary syndrome at presentation
  • Diabetes mellitus
• Few doctors, including most cardiologists would have the time to navigate the massive amount of information published in the last few years and translate it into advice that is objective and not subject to selection or other bias.

References