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(BQ) Part 2 book Practical cardiology presentation of content: The revascularisation patient, the patient with palpitations, the patient with dyspnoea, the patient with a murmur, other problems. (BQ) Part 2 book Practical cardiology presentation of content: The revascularisation patient, the patient with palpitations, the patient with dyspnoea, the patient with a murmur, other problems.
C H A P T E R 5 THE REVASCULARISATION PATIENT The rather grand term revascularisation refers to the use of coronary angioplasty or surgery to improve myocardial blood supply Angioplasty Balloon dilatation of coronary artery stenoses was first performed in the late 1970s by Andreas Grunzig The technique has undergone many refinements and is now widely used for the treatment of angina not responding to medical treatment Angioplasty has not been shown to improve the prognosis of patients with stable angina Coronary artery bypass grafting (CABG) has similarly not been shown to prolong life for most stable angina patients However, both treatments are very successful in relieving the symptoms of angina The COURAGE Trial compared optimal medical treatment of angina with angioplasty but excluded patients with symptoms refractory to medical treatment.1 Not surprisingly, this group of stable mild angina patients had a similar outcome with angioplasty and medical treatment The trial suggests that compared with optimal medical treatment, angioplasty is a safe and slightly more effective treatment for stable angina Patients can make an informed choice between these two treatments The majority of patients treated with angioplasty in Australia have acute coronary syndromes and here there is good evidence of prognostic benefit with angioplasty compared with medical treatment In many centres one-, two- and complicated three-vessel disease are managed this way It has been shown to be as effective as coronary surgery for these patients but at the price of a higher rate of re-intervention This is because the greatest limitation of angioplasty is the rate of restenosis in vessels that have been dilated Restenosis Restenosis has been reported in as many as 40% of balloon angioplasties where a coronary stent (p 199) has not been used—plain old balloon angioplasty (POBA) Re-dilatation is usually possible but a similar risk of restenosis occurs after a second dilatation Renarrowing of these vessels is caused by the elastic recoil that occurs over the weeks after dilatation POBA is also associated with a relatively high risk of acute closure of the artery This may result from dissection of the arterial wall during dilatation, leading to thrombus formation or occlusion of the vessel by the dissection flap Coronary stents The introduction of coronary stents has revolutionised angioplasty (Fig 5.1) These folded metal structures are crimped onto a balloon catheter They are made from stainless steel or, more recently, cobalt alloys Alloy stents have thinner struts, which make them more flexible and may reduce the rate of restenosis within the stent Dilatation of the balloon expands the stent up against the intima of the artery The stent has enough radial strength to prevent elastic recoil It will also seal a dissection flap back into place Dissection occurs when damage to the intima separates it from the media This can occur as a result of splitting of the intima following balloon 188 • T H E R E V A S C U L A R I S A T I O N P A T I E N T 189 a b c Figure 5.1 (a) A drawing of a coronary stent during balloon dilatation (b) Stents crimped onto their balloons (c) A model of an expanded stent dilatation or from entry of the guide wire beneath the intimal layer Blood enters the dissection and forces the intima and media further apart The use of stents has dramatically reduced the complication rate of angioplasty Dissection and acute closure of the vessel that would previously have led to immediate coronary artery surgery can usually be repaired Figure 5.2 and video clips 20–22 show an example of dissection of the left main coronary artery The need for urgent coronary artery bypass grafting has fallen from about 5% of cases to much less than 1% In addition, more complicated lesions can be treated safely Sometimes long segments of arteries are stented (video clip 23), although at the cost of a higher risk of restenosis Numerous randomised trials have shown improvement in restenosis rates and in the need for re-intervention when stents are used.2 Angioplasty is increasingly being performed in hospitals without cardiac surgical back-up There remains some controversy about this approach Bare metal stents Although stents have eliminated the problem of elastic recoil, restenosis can still occur in up to 30% of patients The mechanism of restenosis within a stent is different from that which occurs after angioplasty It has been shown that stents become lined with new endothelial cells within 190 PRACTICA L C A R D I O L O G Y a b c d Guide wire in circumflex Figure 5.2 (a) This 55-year-old man was admitted for a routine angioplasty to a mid-LAD lesion (arrow) He had exertional chest pain The proximal LAD was calcified (b) As the stent was being positioned across the lesion, left main dissection caused by the guiding catheter became apparent (arrow) This can be seen extending to the level of the first diagonal branch The patient had no symptoms The origin of the circumflex was not compromised (c) A guide wire has been placed in the circumflex and a long stent is being positioned across the left main and into the LAD (arrows) (d) The final result after stenting of the left main and the LAD and balloon dilatation through the stent struts into the circumflex A follow-up angiogram at six months showed no restenosis and the patient was asymptomatic four weeks of being implanted Some of these cells migrate through the struts of the stent from the arterial media For reasons not fully understood, in a proportion of patients they continue to grow into the lumen of the vessel (neo-intimal proliferation) and gradually cause narrowing that leads to a return of symptoms This is rarely associated with an acute coronary syndrome or infarct This phenomenon occurs within six months of the stent insertion and it is rare for restenosis to occur after this time Although up to 30% of stents show evidence of restenosis, if patients have routine follow-up angiograms only about 10% develop symptomatic restenosis Certain risk factors for restenosis have been identified (Table 5.1) • T H E R E V A S C U L A R I S A T I O N P A T I E N T 191 Table 5.1 Risk factors for restenosis Diabetes Previous restenosis in that stent A long lesion (and stent) (> 18 mm) A narrow stent (< mm) Dilatation and stenting in a saphenous vein bypass graft A stent not adequately dilated and deployed Drug-eluting stents The realisation that restenosis is a neoproliferative process has led to the development of drugeluting stents (DESs) These stents are coated with anti-proliferative drugs The drug is held within a polymer bonded to the metal Drug elution occurs over about four weeks after implantation The two drugs currently available are sirolimus and paclitaxel Sirolimus is used for the prevention of renal transplant rejection It blocks G1 to S cell cycle progression Paclitaxel is an anti-proliferative agent that stabilises microtubules and prevents cell division These drugs have almost no systemic absorption when implanted with a stent The restenosis rate has been reduced dramatically by using these stents Clinical restenosis rates of 2% or 3% are commonly obtained These stents are now implanted in 90% of angioplasty patients in the United States In Australia the cost of these devices (four to five times that of a bare metal stent) has kept the implantation rate much lower, but usage varies from state to state Cardiac surgeons note that the cost of CABG for a patient becomes less than that of angioplasty once more than three or four drug-eluting stents are used In many hospitals DESs are reserved for patients with a high risk of restenosis They have not been shown to improve mortality compared with bare metal stents Alloy stents There is some evidence that the thickness of the stent struts is a factor in the risk of restenosis Cobalt alloy stents have thinner struts and are more flexible than stainless steel ones They can be easier to deploy and may have a lower restenosis rate Bio-absorbable stents Studies are underway with stents made of materials that are completely absorbed over a period of months after implantation These include magnesium stents Indications for angioplasty Angioplasty is not indicated unless the lesion to be dilated is clearly the cause of the patient’s symptoms, and then usually only if these have not responded to medical treatment If a lesion is of equivocal significance (< 50% stenosis) or the symptoms are atypical, a sestamibi test or stress echo may be necessary to demonstrate ischaemia in the territory of the suspect vessel Angioplasty is a very effective treatment for stable angina but has not been proven to improve prognosis when compared with intensive medical treatment It may possibly so when there is three-vessel disease suitable for angioplasty or when the patient has a tight lesion in the left anterior descending artery proximal to the first diagonal branch A lesion in this position that threatens a large area of myocardium Successful angioplasty should always be followed by intensive risk factor modification Treatment of patients with ACS by angioplasty has been shown to improve outcomes, including the risk of death and myocardial infarction (p 157) In busy angioplasty units these patients now provide the majority of the unit’s workload 192 PRACTICA L C A R D I O L O G Y Left main stem stenosis is increasingly being managed with angioplasty and stenting There remains some controversy about this approach There is an incidence of sudden death in patients treated in this way This is quite a different outcome from the gradual return of angina that occurs with restenosis in other vessels In experienced centres the outcomes are as good as those for CABG for left main stenosis The patient who has had bypass surgery and has some patent grafts to the circumflex or LAD is an exception since the vessel is considered ‘protected’ Left main angioplasty is often straightforward for these patients The technique The balloon catheter is introduced using a coronary guiding catheter somewhat different from those used for diagnostic angiography (Fig 5.3) Although diagnostic procedures are usually performed with French gauge catheters, angioplasty guiding catheters are often or French They are designed to provide back-up for the guide wire and balloon catheters—that is, to remain engaged in the coronary ostium as catheters are passed into the artery A fine guide wire is advanced through the guiding catheter and into the coronary and across the lesion (Fig 5.4) A balloon dilatation catheter is advanced along this wire until it crosses the lesion The balloon is dilated with contrast solution to a pressure of up to 18 atmospheres The balloon is kept inflated for about 20 seconds (Fig 5.5) Figure 5.3 A coronary angioplasty guiding catheter This shape is designed for the left main coronary and has the comforting name EBU, or extra back-up Lesion Balloon catheter Guide wire Figure 5.4 A coronary angioplasty balloon has been advanced to the lesion over its guide wire • T H E R E V A S C U L A R I S A T I O N P A T I E N T 193 Since the vessel is completely occluded during the procedure, many patients experience ischaemic chest pain and ST elevation may be visible on the ECG The vessel is injected with contrast and the effectiveness of the dilatation assessed A stent is chosen that is thought to be the correct diameter and length for the artery and the lesion Stents range in size from 2.25 mm diameter to 5.0 mm and in length from mm to a b Figure 5.5 (a) This 62-year-old man presented to the hospital with chest pain His initial ECG showed minor inferior ECG changes Half an hour later his pain became more intense and his ECG showed mm of ST elevation in the inferior leads He was transferred to the catheter laboratory within 20 minutes of the onset of these ECG changes The first picture taken showed a totally occluded right coronary artery (arrow) (b) The balloon being inflated Continues 194 PRACTICA L C A R D I O L O G Y c d Figure 5.5—cont’d (c) Right coronary artery now open after balloon dilatation of the occluded segment A ruptured plaque is visible at the point of occlusion (d) Final result after stent deployment: TIMI flow • T H E R E V A S C U L A R I S A T I O N P A T I E N T 195 about 38 mm The longer the stent, the more difficult it may be to advance through a tortuous or calcified artery to the lesion The stent balloon is placed across the lesion and then inflated The nominal size of the stent will be reached when the balloon is inflated to the standard pressure for that balloon This is shown on a chart that comes with the balloon catheter Dilatation to a higher pressure will result in a larger expanded stent diameter If the result looks unsatisfactory, repeat dilatation (post-dilatation) can be performed with a higher pressure (non-compliant balloon) In some laboratories the lesion and stent expansion are assessed with IVUS (p 137) Further dilatation is performed if the stent struts not seem adequately opposed to the vessel wall Closure devices The femoral artery puncture site can be closed at the end of the procedure using a collagen plug that is inserted into the artery by a sheath or by a stitch also deployed onto the puncture via a sheath This enables the patient to mobilise within an hour or two of the procedure, even when aggressive anticoagulation and anti-platelet treatment have been employed Otherwise, the sheath is withdrawn some hours after the procedure when the ACT has fallen to about 150 seconds Quite prolonged clamping of the site is often required and many patients find this more of an ordeal than the procedure Closure devices are expensive and for that reason are not used for every patient in most hospitals If the procedure has been performed through the radial artery, the artery is compressed with a velcro strap Stable patients who have had an angioplasty performed via the radial artery may sometimes be discharged on the same day; otherwise they are usually kept overnight Complications All the risks associated with coronary angiography apply to the angioplasty procedure Additional possible complications include the following Dissection of the artery during balloon dilatation or from the guiding catheter In most cases stenting will close the dissection flap and lead to a very satisfactory outcome, but a longer stent than would otherwise have been used may be required (Fig 5.2, video clips 20–22) If dissection has been cause by the guide wire during attempts to cross the lesion, dissection and the creation of a false lumen may make it impossible to wire and stent the true lumen (Fig 5.6) Urgent coronary artery bypass grafting may be needed Perforation of the artery This feared complication is most common when attempts are being made to cross a total occlusion with a guide wire Wires designed to cross chronically (more than six months) occluded vessels are very stiff and can perforate the wall of the artery Perforation by a wire may cause only small amounts of bleeding into the pericardium, but if the perforation is not recognised and a balloon is passed over the wire, torrential bleeding into the pericardium may cause cardiac tamponade (p 145) requiring urgent pericardiocentesis The problem may be compounded by the previous administration of IIb/IIIa inhibitors A coronary perforation or tear may be treated with a covered stent This has a layer of gortex between two layers of metal If this rather bulky stent can be passed across the perforation, it will prevent further bleeding No reflow Dilatation of an artery or more often of a degenerated saphenous vein graft can dislodge clot or atheromatous material further down the vessel These fragments can occlude distal arterioles and lead to poor flow into the distal bed and ischaemic symptoms (video clips 24–27) Treatment 196 PRACTICA L C A R D I O L O G Y Figure 5.6 This 40-year-old man presented three days after the onset of ischaemic chest pain The ECG showed inferior T wave changes The right coronary artery was totally occluded and extensively thrombosed Attempts to advance the guide wire led to extensive dissection of the vessel and little blood flow The wire was in a false lumen with vasodilators (nitroglycerine, adenosine or verapamil) may eventually restore flow Various devices have been developed to help prevent this problem, especially in vein graft angioplasties These include occlusion balloons that can be inflated distal to the lesion After dilatation of the lesion a suction device is used to remove material before the balloon is deflated Another approach is to use a protection wire These guide wires have a fine mesh basket attached to them This is opened beyond the lesion before dilatation and stenting are performed It is removed after it has been withdrawn into a fine catheter Side branch occlusion Some of the most difficult angioplasties involve a lesion close to or involving a large (> mm) side branch Dilatation of the main vessel risks shifting plaque into the branch and compromising it Numerous techniques have been developed to deal with this problem In many cases two guide wires are used so that if dilatation of the main vessel narrows or occludes the origin of the branch a balloon can be passed into the branch (Fig 5.7, video clip 23) Simultaneous dilatation of two balloons (kissing balloons) may be necessary to keep both vessels open If, as is usual, the main vessel is stented the side branch needs to be re-wired through the stent struts and dilatation into the side branch performed to open the struts and the proximal part of the branch Other techniques such as stenting the branch first or placing stents into both vessels and dilating them simultaneously can be used Whichever technique is used, there is a higher risk of branch restenosis than for the main vessel The ACT is measured at the end of the case and additional heparin given if the level is less than about 300 seconds • T H E R E V A S C U L A R I S A T I O N P A T I E N T 197 Figure 5.7 Angioplasty of an LAD/first diagonal bifurcation lesion using two wires Stent thrombosis The thrombotic risk associated with the introduction of foreign material into the coronary artery was at first managed with aggressive anticoagulation with heparin and then with warfarin This led to bleeding complications Dual anti-platelet therapy Subacute stent thrombosis is now very uncommon The use of two anti-platelet drugs (aspirin and clopidogrel) in combination has been very effective in preventing stent thrombosis during the peri-procedural period and afterwards Aspirin is a cyclo-oxygenase (COX-2) inhibitor and clopidogrel blocks ADP-dependent platelet aggregation Patients having a non-urgent angioplasty should be pre-loaded with both drugs at least 24 hours before the procedure Clopidogrel should be given as a loading dose of 300–600 mg (four to eight tablets) and then 75 mg a day, and the aspirin dose should be up to 300 mg a day Dual anti-platelet treatment should be continued for at least one month after bare metal stent insertion and single anti-platelet treatment should be continued for ever Patients who receive a DES must continue dual anti-platelet treatment for at least six months, and two years of treatment is now sometimes recommended This is because re-endothelialisation is delayed in these stents and thrombosis remains a risk for at least this period Late stent thrombosis There are increasing (although rare) reports of late thrombosis in DESs (Fig 5.8) These are associated with a high incidence of myocardial infarction and death They are often reported to have occurred after single anti-platelet treatment has been stopped for some reason Patients given DESs should be warned that they must stop anti-platelet treatment only if absolutely necessary (e.g before surgery involving a high risk of bleeding) and for the shortest possible period DESs should be avoided for patients likely to need surgery within six months of the procedure and for those who may not be compliant with their treatment Late stent thrombosis will be an area of intense research over the next few years Since the drug disappears from the stent within a month of implantation, theories as to the cause of late ... symptoms Am Heart J 19 82; 103:156–159 2 Hazinski MF, Nadkarni VM, Hickey RW, et al Major changes in the 20 05 AHA Guidelines for CPR and ECC Circulation 20 05; 1 12: IV206–IV211 (Editorial) 3 Huikuri... Gynecol 20 03; 1 02: 1 326 –1331 23 Elkayam U, Tummala PP, Rao K, et al Maternal and fetal outcome of subsequent pregnancies in women with peripartum cardiomyopathy New Engl J Med 20 01; 7:37 24 Oakley... Engl J Med 20 01; 345:1473–14 82 4 Rubart M, Zipes DP Mechanisms of sudden cardiac death J Clin Investig 20 05; 115 :23 05 23 15 9 • O T H E R P R O B L E M S 371 5 20 05 American