Opening that blocked artery

Heart attack patients need to bear a few things in mind when undergoing percutaneous coronary intervention (PCI).

If you have a major heart attack, it is very likely that your doctor will advise you to undergo a procedure called coronary angiography (CAG) followed by percutaneous coronary intervention (PCI).  CAG involves inserting a plastic tubing inserted into your leg or wrist artery under local anaesthesia and injecting iodine contrast agents into your heart arteries then taking pictures using X-ray machines. PCI involves the insertion of wires, balloon catheters, and cylindrical meshes through the plastic tubing inserted into your limb artery to reach the blocked segment of the heart artery to open it. Most of the time, the diagnosis of a significantly blocked heart artery occurs in a non-emergency setting, allowing more time for understanding and assessment of the heart condition. What are the facts that you should know about PCI to obtain the best long term outcomes?

Heart attack

In October 2015, the American Heart Association (AHA) and American College of Cardiology Foundation (ACCF) released an update to the guidelines on emergency PCI for those with a major heart attack. In the past, the guidelines had recommended that only the heart artery causing the heart attack should be opened during the PCI and even if there are significant blockages in other heart arteries, this should not be performed within the same time or same hospitalisation. Unfortunately, this stand has resulted in patients who have had emergency PCI during a heart attack suffer a second heart attack from another heart artery occlusion shortly after being discharged from hospital.

Current data including randomised controlled studies have shown that opening multiple blockages during the emergency PCI or as a second staged procedure during the same hospitalisation may be beneficial during a heart attack when compared to just opening the culprit blockage.  When comparing the opening of multiple blockages within the same hospitalisation as compared to opening only the culprit blockage, the  data from the PRAMI (Preventive Angioplasty in Acute Myocardial Infarction) trial (death and heart attacks in 9% versus 22%), CvLPRIT (Complete Versus Culprit-Lesion Only Primary PCI) trial (death and heart attack in 10% versus 21%) and  the DANAMI 3 PRIMULTI (Third Danish Study of Optimal Acute Treatment of Patients with ST-segment Elevation Myocardial Infarction) trial (death, heart attacks and repeat procedures of 13% versus 22%) support the approach to treat the significant major heart artery blockages within the same hospitalisation rather than just the culprit blockage.

Elective PCI

Most PCIs are non-emergency procedures and the right decisions can help you to obtain the best outcome.

The widening of the narrowed segment by the implantation of cylindrical meshes (stents) during PCI causes damage to the inner lining of the heart artery. If there is significant scar tissue during healing, the lumen may re-narrow. To overcome the problem of scar tissue formation, stents have drugs coated onto them, either directly or through drugs embedded into polymer coatings of the stents. The drugs are used to reduce the likelihood of scar formation. Studies have shown that genetic resistance to drugs that prevent scar formation and hypersensitivity reactions to the polymer coating have resulted in re-narrowing as a result of scar formation.

Newer stents use better drugs to reduce scar formation and polymers which are biologically more compatible or polymers that completely absorbed by the body from the metal surface.  For example, one of the newer stents has a bioabsorbable polymer coating that is applied only to the abluminal surface (stent surface in direct contact with the arterial wall) of the stent.

Pre-planning the PCI

As CAG only allows visualisation of the arterial lumen and not the arterial wall, in patients with widespread disease, it is difficult to know what is the “normal” size of the artery as there is no normal reference segment for comparison. Hence the stent size or length may be underestimated resulting in incomplete coverage of the diseased arterial segment. This is an important cause of poorer outcomes. Computed tomography (CT) scan of the heart arteries prior to the PCI can provide 3 dimensional images of the heart arteries and allow pre-planning of the PCI to assess the tortuosity of the arteries, the amount and extent of calcification which will stiffen the arterial segment, and the extent of the plaque.

Choice of stents

The real truth is that not all the stents are the same. Newer generation stents use alloys to allow them to have thinner metallic struts with adequate radial strength so that they can pass more easily through segments that are tortuous or highly calcified. The likelihood of damage to the polymer coating or removal of drug coating from the stent will be reduced. When inflating the stent to a high pressure to ensure that the stent is fully expanded, the polymer coating can be damaged and in certain stents, the entire polymer coating on the luminal surface may be almost completely damaged. As the heart is a constantly moving structure, the stent strut is subjected to constant mechanical stresses and may fracture in stents with closed cell design (each strut in the mesh cell of the stent is fixed in length).

New generation thin strut stents with open cell design (stent with mesh cell that can be expanded without breaking the individual mesh cell of the stent) and with newer drugs in a bioabsorbable polymer coating on the abluminal surface of the stent means that the stent can be passed into tortuous segments of the heart artery with minimal damage – there will be no risk of polymer damage to the luminal surface.  In addition, the thin struts allow more rapid healing and coverage of the metallic struts with a new cell layer in the vessel lumen within weeks to months and hence it may be possible to stop blood thinning medications as the metallic stent struts are no longer exposed to the blood.

In another development in recent years, bioabsorbable polymer stents have been used to open blocked heart arteries and as they contain no metallic meshes, they are completely absorbed by the body in 3 years leaving the artery in its natural state without the need for long term blood thinning medication. These polymer “stents” have limited sizes and require cardiologists who are experienced in using these polymer “stents” to achieve good results.

Stent implantation

In the “Stent deployment Techniques on cLinicaL outcomes of patients treated with the cypheR stent (STLLR) study”, it was found that in almost two thirds of the procedures, the stent did not fully cover  the  injured or diseased narrowed segment of the heart artery (termed as geographical miss or GM). Routinely, in most PCI procedures, the narrowed segment is initially widened with a balloon dilatation before a stent can be passed through. The injured segment is due to the balloon induced trauma to the vessel wall when it was inflated to widen the channel. At 1-year follow-up, the incidence of repeat heart procedures was more than 2-fold (5.1% versus 2.5%) and there was a 3-fold increase in heart attacks (2.4% versus 0.8%) in patients with GM compared to those with no GM. As discussed earlier, pre-planning with CT scan can ensure choosing a stent of appropriate length and hence avoid the complications associated with GM.

Getting the best outcomes

Get the best outcomes with the following key pointers : –

• For emergency PCI, if there is severe blockage of multiple heart arteries, same hospitalisation PCI, where feasible, gives the best outcomes. “Incomplete” PCI may increase your risk of a heart attack and death;

• If you are suspected to have significant heart artery disease, a non-invasive CT scan of the heart arteries is a less costly and safer alternative to CAG. The CT scan will allow better pre-planning to reduce complications and avoid GM;

• Wherever possible, you should consider using a stent that will allow you to avoid lifelong blood thinning medications;

• If you are young, a bioabsorbable polymer “stent” should be considered;

• Current data shows that the larger the number of PCIs performed by the doctors annually, the lower the risk of complications.  The 2013 AHA and ACCF Clinical Competence Statement on Coronary Artery Interventional Procedures recommend that cardiologists perform 50 or more PCIs a year to maintain competency. Where possible, especially if there are multiple blockages in multiple heart arteries, a highly experienced cardiologist with good outcomes should be considered for complex procedures;

• Non-compliance with blood thinning medications can lead to clot formation in the stents and even occlusion of the stents.  Poor control of risk factors such as high cholesterol, diabetes mellitus, high blood pressure and smoking can lead to progression of disease. Amongst these risk factors, the presence of diabetes mellitus consistently increases the risk of re-narrowing of the heart arteries. Hence, compliance with medication and good risk factor control will contribute to good outcomes.

2017-06-22T11:12:48+00:00