Percutaneous coronary intervention.I: History and development
The term “angina pectoris” was introduced by Heberden in1772 to describe a syndrome characterised by a sensation of“strangling and anxiety” in the chest. Today, it is used for chestdiscomfort attributed to myocardial ischaemia arising fromincreased myocardial oxygen consumption. This is ofteninduced by physical exertion, and the commonest aetiology isatheromatous coronary artery disease. The terms “chronic” and“stable” refer to anginal symptoms that have been present for atleast several weeks without major deterioration. However,symptom variation occurs for several reasons, such as mentalstress, ambient temperature, consumption of alcohol or largemeals, and factors that may increase coronary tone such asdrugs and hormonal change.
Classification
The Canadian Cardiovascular Society has provided a gradedclassification of angina which has become widely used. Inclinical practice, it is important to describe accurately specificactivities associated with angina in each patient. This shouldinclude walking distance, frequency, and duration of episodes.History of myocardialrevascularisation
In the management of chronic stable angina, there are twoinvasive techniques available for myocardial revascularisation:coronary artery bypass surgery and catheter attached devices.Although coronary artery bypass surgery was introduced in1968, the first percutaneous transluminal coronary angioplastywas not performed until September 1977 by AndreasGruentzig, a Swiss radiologist, in Zurich. The patient, 38 yearold Adolph Bachman, underwent successful angioplasty to a leftcoronary artery lesion and remains well to this day. After thesuccess of the operation, six patients were successfully treatedwith percutaneous transluminal coronary angioplasty in thatyear.By today’s standards, the early procedures usedcumbersome equipment: guide catheters were large and couldeasily traumatise the vessel, there were no guidewires, andballoon catheters were large with low burst pressures. As aresult, the procedure was limited to patients with refractoryangina, good left ventricular function, and a discrete, proximal,concentric, and non-calcific lesion in a single major coronaryartery with no involvement of major side branches orangulations. Consequently, it was considered feasible in only10% of all patients needing revascularisation.
Canadian Cardiovascular Society classification of angina
Class I- No angina during ordinary physical activity such as walking orclimbing stairs
- Angina during strenuous, rapid, or prolonged exertion
- Slight limitation of ordinary activity
- Angina on walking or climbing stairs rapidly; walking uphill;walking or climbing stairs shortly after meals, in cold or wind, whenunder emotional stress, or only in the first few hours after waking
- Angina on walking more than two blocks (100-200 m) on the levelor climbing more than one flight of stairs at normal pace and innormal conditions
- Marked limitation of ordinary physical activity
- Angina on walking one or two blocks on the level or climbing oneflight of stairs at normal pace and in normal conditions
- Inability to carry out any physical activity without discomfort
- Includes angina at rest
Modern ballooncatheter: its low
profile facilitateslesion crossing, the
flexible shaft allowstracking down
tortuous vessels, andthe balloon
can beinflated to highpressures
withoutdistortion or rupture
Developments in percutaneousintervention
During 1977-86 guide catheters, guidewires, and ballooncatheter technology were improved, with slimmer profiles andincreased tolerance to high inflation pressures. As equipmentimproved and experience increased, so more complex lesionswere treated and in more acute situations. Consequently,percutaneous transluminal coronary angioplasty can now beundertaken in about half of patients needing revascularisation(more in some countries), and it is also offered to high-riskpatients for whom coronary artery bypass surgery may beconsidered too dangerous.Although percutaneous transluminal coronary angioplastycauses plaque compression, the major change in lumengeometry is caused by fracturing and fissuring of the atheroma,extending into the vessel wall at variable depths and lengths.This injury accounts for the two major limitations ofpercutaneous transluminal coronary angioplasty{acute vesselclosure and restenosis.
Acute vessel closure—This usually occurs within the first 24hours of the procedure in about 3-5% of cases and followsvessel dissection, acute thrombus formation, or both. Importantclinical consequences include myocardial infarction, emergencycoronary artery bypass surgery, and death.
Restenosis occurring in the first six months after angioplastyis caused largely by smooth muscle cell proliferation andfibrointimal hyperplasia (often called neointimal proliferation),as well as elastic recoil. It is usually defined as a greater than50% reduction in luminal diameter and has an incidence of25-50% (higher after vein graft angioplasty). Furtherintervention may be indicated if angina and ischaemia recur.
Micrographs showing arterialbarotrauma caused by coronaryangioplasty.percutaneous transluminal coronary angioplasty. Top left: coronaryarterial dissection with large flap.Top right: deep fissuring withincoronary artery wall atheroma.Bottom: fragmented plaque tissue(dark central calcific plaquesurrounded by fibrin andplatelet-rich thrombus), which mayembolise in distal arterioles to causeinfarction
Tools for coronary atherectomy. Top:the Simpson atherocath has a cutter ina hollow cylindrical housing. The cutterrotates at 2000 rpm, and excisedatheromatous tissue is pushed into thedistal nose cone. Left: the Rotablatorburr is coated with 10 m diamondchips to create an abrasive surface. Theburr, connected to a drive shaft and aturbine powered by compressed air,rotates at speeds up to 200 000 rpm
Coronary stents. Top: Guidant Zeta stent. Middle: BiodivYsio AS stent coatedwith phosphorylcholine, a synthetic copy of the outer membrane of redblood cells, which improves haemocompatibility and reduces thrombosis.Bottom: the Jomed JOSTENT coronary stent graft consists of a layer ofPTFE (polytetrafluoroethylene) sandwiched between two stents and is usefulin sealing perforations, aneurysms, and fistulae
Drills, cutters, and lasers
In the 1980s, two main developments aimed at limiting theseproblems emerged. The first were devices to remove plaquematerial, such as by rotational atherectomy, directional coronaryatherectomy, transluminal extraction catheter, and excimerlaser. By avoiding the vessel wall trauma seen duringpercutaneous transluminal coronary angioplasty, it wasenvisaged that both acute vessel closure and restenosis rateswould be reduced.However, early studies showed that, although acute closurerates were reduced, there was no significant reduction inrestenosis. Moreover, these devices are expensive, notparticularly user friendly, and have limited accessibility to moredistal stenoses. As a result, they have now become niche toolsused by relatively few interventionists. However, they may havean emerging role in reducing restenosis rates when used asadjunctive treatment before stenting (especially for largeplaques) and in treating diffuse restenosis within a stent.
Coronary angiogram showingthree lesions (arrows) affectingthe left anterior descendingartery (top left). The lesionsare stented withoutpre{dilatation (top right), withgood results (bottom)
Unequivocal indications for use of coronary stents
- Acute or threatened vessel closure during angioplasty
- Primary reduction in restenosis in de novo lesions in arteries> 3.0 mm in diameter
- Focal lesions in saphenous vein grafts
- Recanalised total chronic occlusions
- Primary treatment of acute coronary syndromes
Intracoronary stents
The second development was the introduction of intracoronarystents deployed at the site of an atheromatous lesion. Thesewere introduced in 1986 with the objective of tacking downdissection flaps and providing mechanical support. They alsoreduce elastic recoil and remodelling associated with restenosis.The first large randomised studies conclusively showed thesuperiority of stenting over coronary angioplasty alone, both inclinical and angiographic outcomes, including a significant 30%reduction in restenosis rates. Surprisingly, this was not due toinhibition of neointimal proliferation—in fact stents mayincrease this response. The superiority of stenting is that theinitial gain in luminal diameter is much greater than afterangioplasty alone, mostly because of a reduction in elasticrecoil.Although neointimal proliferation through the struts of thestent occurs, it is insufficient to cancel out the initial gain,leading to a larger lumen size and hence reduced restenosis.Maximising the vessel lumen is therefore a crucial mechanismfor reducing restenosis. “Bigger is better” is the adage followedin this case.
Early stent problemsAs a result of initial studies, stents were predominantly usedeither as “bail out” devices for acute vessel closure duringcoronary angioplasty (thus avoiding the need for immediatecoronary artery bypass surgery) or for restenosis afterangioplasty.
Thrombosis within a stent causing myocardial infarctionand death was a major concern, and early aggressiveanticoagulation to prevent this led to frequent complicationsfrom arterial puncture wounds as well as major systemichaemorrhage. These problems have now been overcome by theintroduction of powerful antiplatelet drugs as a substitute forwarfarin. The risk of thrombosis within a stent diminishes whenthe stent is lined with a new endothelial layer, and antiplatelettreatment can be stopped after a month. The recognition thatsuboptimal stent expansion is an important contributor tothrombosis in stents has led to the use of intravascularultrasound to guide stent deployment and high pressureinflations to ensure complete stent expansion.
Current practiceA greater understanding of the pathophysiology of stentdeployment, combined with the development of more flexiblestents (which are pre-mounted on low-profile catheterballoons), has resulted in a massive worldwide increase in stentuse, and they have become an essential component of coronaryintervention. Low profile stents have also allowed “direct”stenting—that is, implanting a stent without the customaryballoon dilatation—to become prevalent, with the advantages ofeconomy, shorter procedure time, and less radiation fromimaging. Most modern stents are expanded by balloon andmade from stainless steel alloys. Their construction and design,metal thickness, surface coverage, and radial strength varyconsiderably.
Stents are now used in most coronary interventions and in awide variety of clinical settings. They substantially increaseprocedural safety and success, and reduce the need foremergency coronary artery bypass surgery. Proceduresinvolving stent deployment are now often referred to aspercutaneous coronary interventions to distinguish them fromconventional balloon angioplasty (percutaneous transluminalcoronary angioplasty).
A major recent development has been the introduction ofdrug eluting stents (also referred to as “coated stents”), whichreduce restenosis to very low rates. Their high cost currentlylimits their use, but, with increasing competition amongmanufacturers, they will probably become more affordable.