New developments in percutaneous coronary intervention
Percutaneous coronary intervention has become a more common procedure than coronary artery bypass surgery in many countries, and the number of procedures continues to rise. In one day an interventionist may treat four to six patients with complex, multivessel disease or acute coronary syndromes. Various balloons, stents, and other devices are delivered by means of a 2 mm diameter catheter introduced via a peripheral artery. The success rate is over 95%, and the risk of serious complications is low. After a few hours patients can be mobilised, and they are usually discharged the same or the next day. Even the spectre of restenosis is now fading.
coronary intervention.Triple vessel disease is no longer a surgical preserve, and particularly
good results are expected with drug eluting stents. In this case, lesions in
the left anterior descending (LAD), circumflex (Cx), and right coronary
arteries (RCA) (top row) are treated easily and rapidly by stent (S)
implantation (bottom row).coronary intervention
Refinements of existing techniques
The present success of percutaneous procedures is largely because of refinement of our “basic tools” (intracoronary guidewires and low profile balloons), which have greatly contributed to the safety and effectiveness of procedures. However, the greatest technological advance has been in the development of stents. These are usually cut by laser from stainless steel tubes into a variety of designs, each with different radial strength and flexibility. They are chemically etched or electropolished to a fine finish and sometimes coated. Digital angiography is a great advance over cine-based systems, and relatively benign contrast media have replaced the toxic media used in early angioplasty. Although magnetic resonance and computed tomographic imaging may become useful in the non-invasive diagnosis of coronary artery disease, angiography will remain indispensable to guide percutaneous interventions for the foreseeable future.Interventional devices and their uses
| Device | Use (% of cases) | Types of lesion |
| Balloon catheter | 100% | Multiple types |
| Stent | 70-90% | Most types |
| Drug eluting stent | 0-50% | High risk of restenosis(possibly all) | Cutting balloon | 1-5% | In-stent restenosis, ostial lesions |
| Rotablator | 1-3% | Calcified, ostial, undilatable lesions |
| Brachytherapy | 1-3% | In-stent restenosis |
| Atherectomy | < 1% | Bulky, eccentric, ostial lesions | Stent graft | < 1% | Aneurysm, arteriovenous malformation, perforation |
| Thrombectomy | < 1% | Visible thrombus |
| Laser | < 1% | Occlusions, in-stent restenosis |
| Distal protection | < 1% | Degenerate vein graft |
Performance of percutaneous coronary intervention
General statistics| Success rate of procedure | > 95% |
| Symptoms improved after procedure | 90% |
| Complications* | 2% |
| Restenosis | 15% (range 5-50%) |
| Duration of procedure | 15 minutes-3 hours |
| Access point: | |
| Femoral artery | 95% |
| Radial or brachial artery | 5% |
| Time in hospital after procedure: | |
| Overnight | 60% |
| Day case | 20% |
| Longer | 20% |
| Intravenous contrast load | 100-800 ml |
| X ray dose to patient | 75 Gy/cm2† |
| Success of direct procedure for acute myocardial infarction | > 95% |
| Success for chronic ( > 3 month) occluded vessel | 50-75% |
| Mortality for procedure in severe cardiogenic shock | 50% |
| Restenosis: | |
| Vessels < 2.5 mm in diameter, > 40 mm length | 60% |
| Vessels > 3.5 mm diameter, < 10 mm length | 5% |
| Lesion recurrence later than 6 months after procedure | < 5% |
| Re-restenosis: | |
| After repeat balloon dilatation | 30-50% |
| After brachytherapy | < 15% |
†Equivalent to 1-2 computed tomography scans
New device technology
Pre-eminent among new devices is the drug eluting (coated) stent, which acts as a drug delivery device to reduce restenosis. The first of these was the sirolimus coated Cypher stent.Sirolimus is one of several agents that have powerful antimitotic effects and inhibit new tissue growth inside the artery and stent. In a randomised controlled trial (RAVEL) this stent gave a six month restenosis rate of 0% compared with 27% for an uncoated stent of the same design. A later randomised study (SIRIUS) of more complex stenoses (which are more prone to recur) still produced a low rate of restenosis within stented segments (9% v 36% with uncoated stents), even in patients with diabetes (18% v 51% respectively). Other randomised studies such as ASPECT and TAXUS II have also shown that coated stents (with the cytotoxic agent paclitaxel) have significantly lower six month restenosis rates than identical uncoated stents (14% v 39% and 6% v 20% respectively). By reducing the incidence of restenosis (and therefore recurrent symptoms), drug eluting stents will probably alter the balance of treating coronary artery disease in favour of percutaneous intervention rather than coronary artery bypass surgery. However, coated stents will not make any difference to the potential for percutaneous coronary intervention to achieve acute success in any given lesion; nor do they seem to have any impact on acute and subacute safety.
Although coated stents may, paradoxically, be too effective at altering the cellular response and thus delay the desirable process of re-endothelialisation, there is no evidence that this is a clinical problem. However, this problem has been observed with brachytherapy (catheter delivered radiotherapy over a short distance to kill dividing cells), a procedure that is generally reserved for cases of in-stent restenosis. This may lead to late thrombosis as platelets readily adhere to the “raw” surface that results from an impaired healing response. This risk is minimised by prolonged treatment with antiplatelet drugs and avoiding implanting any fresh stents at the time of brachytherapy.
Other energy sources may also prove useful. Sonotherapy (ultrasound) may have potential, less as a treatment in its own right than as a facilitator for gene delivery, and is “benign” in its effect on healthy tissue. Photodynamic therapy (the interaction of photosensitising drug, light, and tissue oxygen) is also being investigated but is still in early development. Laser energy, when delivered via a fine intracoronary wire, is used in a few centres to recanalise blocked arteries.
Names of trials
Angiograms showing severe,
diffuse, in-stent restenosis in the
left anterior
descending artery and
its diagonal branch (L and D, left).coronary intervention
This was treated
with balloon dilatation
and brachytherapy with irradiation
(Novoste) from
a catheter (Br, centre),
with an excellent final result (right)coronary intervention
coronary intervention.Angiogram of an aortocoronary vein graft with an aneurysm and stenoses (A and S, left). Treatment by implantation of a membrane-covered stent excluded the aneurysm and restored a tubular lumen (right)
New work practices
Twenty years ago, a typical angioplasty treated one proximally
located lesion in a single vessel in a patient with good left
ventricular function. Now, it commonly treats two or three vessel
disease, perhaps with multiple lesions (some of which may be
complex), in patients with impaired left ventricular function,
advanced age, and comorbidity. Patients may have undergone coronary artery bypass surgery and be unsuitable for further
heart surgery. Isolated left main stem and ostial right coronary
artery lesions, though requiring more experience and
variations on traditional techniques, are also no longer a
surgical preserve.
coronary intervention.Unprotected left main stem stenoses (LMS, top) may, with careful selection,be treated by stent implantation (S, bottom).Best results (similar to coronary artery bypass surgery) are achieved in stable patients with good left ventricular function and no other disease.Close follow up to detect restenosis is important.(LAD=left anterior descending artery, Cx=circumflex coronary artery)
Right coronary artery containing large,
lobulated thrombus (T, left)
on a substantial
stenosis.
After treatment with glycoprotein
IIb/IIIa inhibitor,
the lesion was stented
successfully (St, right)coronary intervention
Role of percutaneous coronary intervention
The role of percutaneous intervention has extended to the
point where up to 70% of patients treated have acute coronary
syndromes. Trial data now support the use of a combination of
a glycoprotein IIb/IIIa inhibitor and early percutaneous
intervention to give high risk patients the best long term results.
The same applies to acute myocardial infarction, where
percutaneous procedures achieve a much higher rate of arterial
patency than thrombolytic treatment. Even cardiogenic shock,
the most lethal of conditions, may be treated by an aggressive
combination of intra-aortic balloon pumping and percutaneous
intervention.
The potential for percutaneous procedures to treat a wide
range of lesions successfully with low rates of restenosis raises
the question of the relative roles of percutaneous intervention
and bypass surgery in everyday practice. It takes time to
accumulate sufficient trial data to make long term
generalisations possible.
Early trials comparing balloon angioplasty with bypass
surgery rarely included stents and few patients with three vessel
disease (as such disease carried higher risk and percutaneous
intervention was not as widely practised as now). The long term
results favoured bypass surgery, but theses trials are now
outdated. In the second generation of studies, stents were used
in percutaneous intervention, improving the results. As in the
early studies, surgery and intervention had similarly low
complications and mortality. The intervention patients still had
more need for repeat procedures because of restenosis than the
bypass surgery patients, but the differences were less.
The major drawback of all these studies was an exclusion
rate approaching 95%, making the general clinical application
of the findings questionable. This was because it was unusual at
that time to find patients with multivessel disease who were
technically suitable for both methods and thus eligible for
inclusion in the trials. Now that drug eluting stents are available,
more trials are under way: the balance will now probably tip in
favour of percutaneous coronary intervention. Meanwhile, the
decision of which treatment is better for a patient at a given
time is based on several factors, including the feasibility of
percutaneous intervention (which is generally considered as the
first option), completeness of revascularisation, comorbidity,
age, and the patient’s own preferences.
Implications for health services
These issues are likely to pose major problems for health
services. Modern percutaneous techniques can be used both to
shorten patients’ stay in hospital and to make their treatment
minimally hazardous and more comfortable. They can also be
used in the first and the last (after coronary artery bypass
surgery) stages of a patient’s “ischaemic career.”
On the other hand, for the role of percutaneous coronary
intervention in acute infarction to be realised, universal
emergency access to this service will be needed. However, most
health systems cannot afford this—the main limiting factor
being the number of interventionists and supporting staff
required to allow a 24 hour rota compatible with legal working
hours and the survival of routine elective work.
General roles of percutaneous coronary intervention (PCI) and coronary artery bypass surgery (CABG)
| Condition | 1993 | 2003 | CABG |
| Acute presentation | |||
| Acute coronary syndrome | ++ | +++ | ++ |
| Cardiogenic shock | +/- | + | +/- |
| Acute full thickness myocardial infarction | + | +++ | - |
| Bailout after failed thrombolysis | + | ++ | - |
| Chronic presentation | |||
| Impaired left ventricle with left main stem stenosis and blocked right coronary artery | -- | - | +++ |
| Impaired left ventricle and 3 vessel disease | + | ++ | +++ |
| Impaired left ventricle and 3 vessel disease with >1 occlusion | - | + | +++ |
| Diabetes and 3 vessel disease | + | ++ | +++ |
| Good left ventricle and 3 vessel disease | + | ++ | +++ |
| 2 occluded vessels | - | - | ++ |
| Good left ventricle and 2 vessel disease | + | +++ | ++ |
| Repeat revascularisation after PCI | ++ | +++ | ++ |
| Good left ventricle and 1 vessel disease | +++ | +++ | + |
| 2-3 vessel diffuse or distal disease | + | ++ | + |
| Repeat revascularisation after CABG | + | ++ | + |
| Palliative partial revascularisation | + | ++ | - |
| Revascularisation of frail patient or with severe comorbidity | + | ++ | - |
The future for percutaneous coronary intervention
Will percutaneous coronary intervention exist in 20 years time, or, at least, be recognisable as a logical development of today’s procedures? Will balloons and stents still be in use? It is likely that percutaneous procedures will expand further, although some form of biodegradable stent is a possibility. A more “biological” stent might also be able to act as an effective drug or gene reservoir, which may extend local drug delivery into new areas of coronary artery disease.We may find ourselves detecting inflamed (“hot”) plaques with thermography catheters and treating these before they rupture.We may even be able to modify the natural course of coronary artery disease by releasing agents “remotely” (possibly using an external ultrasound trigger) or by injecting an agent that activates the molecular cargo in a stent.A persistent challenge still limiting the use of percutaneous coronary intervention is that of chronic total occlusions, which can be too tough to allow passage of an angioplasty guidewire. An intriguing technique is percutaneous in situ coronary artery bypass. With skill and ingenuity, a few enthusiasts have anastomosed the stump of a blocked coronary artery to the adjacent cardiac vein under intracoronary ultrasound guidance, thereby using the vein as an endogenous conduit (with reversed flow). This technique may assist only a minority of patients. More practical, we believe, is the concept of drilling through occlusions with some form of external guidance, perhaps magnetic fields.
“Direct” myocardial revascularisation (punching an array of holes into ischaemic myocardium) has had a mixed press over the past decade. Some attribute its effect to new vessel formation, others cite a placebo effect. Although the channels do not stay open, they seem to stimulate new microvessels to grow. Injection of growth factors (vascular endothelial growth factor and fibroblast growth factor) to induce new blood vessel growth also has this effect, and percutaneous injection of these agents into scarred or ischaemic myocardium is achievable. However, we need a more thorough understanding of biological control mechanisms before we can be confident of the benefits of this technology.
Challenges to mechanical revascularisation
Deaths from coronary artery disease are being steadily reduced in the Western world. However, with increasing longevity, it is unlikely that we will see a reduction in the prevalence of its chronic symptoms. More effective primary and secondary prevention; antismoking and healthy lifestyle campaigns; and the widespread use of antiplatelet drugs, blockers, statins, and renin-angiotensin system inhibitors may help prevent, or at least delay, the presentation of symptomatic coronary artery disease. In patients undergoing revascularisation, they are essential components of the treatment “package.” More effective anti-atherogenic treatments will no doubt emerge in the near future to complement and challenge the dramatic progress being made in percutaneous coronary intervention.The coronary artery imaging was provided by John Bowles, clinical specialist radiographer, and Nancy Alford, clinical photographer, Sheffield Teaching Hospitals NHS Trust, Sheffield.