Investigation, workup and patient preparation before PCI

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Chapter 4 Investigation, workup and patient preparation before PCI

IAN R. STARKEY

KEY POINTS

image No matter how urgent the clinical situation, it is essential that certain preliminaries be observed prior to performing a PCI procedure.
image Basic essentials can be summarised under the general headings of:

Oreliminary investigations;

Therapeutic alterations;

Consent; and

Anticipation (and possible prevention) of problems (PTCA).

INTRODUCTION

In 2006, nearly 74,000 PCI procedures were performed in 91 centres in the UK, a rate of just over 1200 per million population (British Cardiovascular Intervention Society [BCIS] annual survey – unpublished data). PCI has now overtaken CABG as the commonest form of myocardial revascularisation procedure performed on patients with obstructive coronary artery disease. It is important to remember that such procedures, while ‘routine’ for some operators and exciting for others, may be frightening, painful and dangerous for the patients on whom they are performed, even though statistically the success rate is high. Before such a procedure begins, much can be done to diminish the patient’s fear and pain, minimise the danger and increase further the likelihood of procedural and clinical success. The essential components of this preparation are:

P preliminary investigations;

T therapeutics;

C consent; and

A anticipation (of possible complications).

There is inevitably some overlap between these elements, all of which require consideration in all patients. The emergency nature of some procedures (e.g. primary PCI for a patient with an acute ST-elevation myocardial infarction) may curtail the time available for preparation of the patient, but should never result in omission of the basic essentials.

PRELIMINARY INVESTIGATIONS

These are needed to allow three questions to be answered:

1. Is percutaneous coronary intervention (PCI) appropriate for this patient?

With few exceptions, PCI should only be considered in a patient with symptoms of coronary artery disease, objective evidence of myocardial ischaemia/infarction and an anatomically suitable lesion(s), as demonstrated by coronary angiography. As a preliminary to such a procedure, therefore, the interventional cardiologist should review the patient’s history and the results of any non-invasive and invasive investigations. While all this information should be available in advance of procedures performed electively, it is now increasingly common that patients, especially those with acute coronary syndromes (ACS: unstable angina or acute myocardial infarction), have combined diagnostic (i.e. coronary angiography) and therapeutic (i.e. PCI) procedures performed. In this situation, it is especially important for the interventional cardiologist to retain a capacity for objective judgement, so that, for instance, a patient who might best be treated surgically does not receive sub-optimal treatment simply because it is ‘convenient’ and it has been scheduled.

2. If PCI is appropriate, is the patient fit for the procedure?

Before arrival in the cardiac catheterisation laboratory, every patient should have a clinical history documented and a physical examination performed (Fig. 4.1). These should be supplemented by some basic investigations, although the number of these will be kept to a minimum in emergency situations (Table 4.1).

image

Figure 4.1 History and examination of patient prior to PCI.

TABLE 4.1 INVESTIGATIONS PRIOR TO PCI

ALL PATIENTS
Full blood count
Blood urea, creatinine and electrolytes
12-lead ECG
Blood group and save

SOME PATIENTS
INR (patients on warfarin)
Chest X-ray (if clinically indicated)
Others (respiratory function tests, plasma glucose, etc. according to clinical indication)

It is of particular importance to discover conditions that might increase the technical difficulty or risk of an invasive cardiac procedure. Some such factors can be corrected but awareness of others may lead to changes in peri-procedural drug therapy (see Therapeutics below), the information provided to the patient (see Consent below) or an ability to predict, and hopefully prevent, possible complications (see Anticipation below).

3. Can anything be done to improve his/her fitness?

This is mostly discussed in the ensuing sections of this chapter. The discovery of some intercurrent medical conditions might appropriately result in the postponement of an elective procedure. Examples would include severe anaemia (especially if this may be related to active or recent bleeding), active or suspected infection, uncontrolled hypertension and possible/definite pregnancy. On rare occasions, the discovery of serious non-cardiac disease (e.g. advanced malignancy) might lead to cancellation of a planned PCI procedure.

THERAPEUTICS (TABLE 4.2)

Anti-anginal drugs

Most patients with symptomatic coronary artery disease are taking regular anti-anginal medication, which can be continued until, and indeed, after the interventional procedure. Treatment with a long-acting nitrate and/or a calcium-channel blocker may actually be of benefit in the prevention of coronary artery spasm during/after the procedure. Although there is no convincing evidence that cholesterol-lowering therapy (e.g. statin drugs) specifically affects the short-term outcome of coronary interventional procedures, such treatment is an important part of the long-term management of patients with coronary artery disease and should, likewise, be continued.

TABLE 4.2 DRUG THERAPY PRIOR TO PCI

DRUG CLASS ACTION REQUIRED
Oral anti-anginal drugs Continue
Cholesterol-lowering therapy Continue
Oral anti-platelet therapy Ensure that aspirin has been taken
ADMINISTER LOADING DOSE OF CLOPIDOGREL (IF NOT ALREADY PRESCRIBED)
Warfarin Discontinue if possible
Measure INR and correct excessive anticoagulation
TAKE APPROPRIATE MEASURES TO AVOID HAEMORRHAGE AT VASCULAR ACCESS SITE
IV Heparin Continue
Measure ACT and consider reduced bolus dose
SC Low molecular-weight heparin Administer last injection >12 hours prior to PCI (if possible)
GP IIb/IIIa receptor antagonists Continue but consider the use of a reduced, weight-adjusted heparin regime
Pre-medication If necessary, use diazepam 5–20 mg orally
Antidiabetic medication See text
Other drug therapy Continue unchanged

Oral anti-platelet therapy

Most patients with coronary artery disease are taking Aspirin, which inhibits the platelet cyclo-oxygenase pathway, thus reducing the formation of thromboxane A2, prostaglandin E2 and prostacyclin. In the unusual circumstance of a patient not taking regular Aspirin presenting for PCI, this drug (300 mg) should be given, preferably at least two hours before the start of the procedure. Aspirin (75–300 mg daily) should be continued long term thereafter.

As the overwhelming majority of PCI procedures now involve the placement of one or more coronary stents, combined anti-platelet therapy, using Aspirin and Clopidogrel (a thienopyridine derivative that inhibits adenosine diphosphate (ADP)-induced platelet aggregation1), has become normal practice even though Clopidogrel is not currently licensed for this indication. Many patients undergoing urgent PCI procedures for the treatment of ACS may already be taking Clopidogrel but patients undergoing elective or emergency procedures should receive a loading dose of Clopidogrel before the procedure. Available evidence suggests that maximal platelet inhibition is not achieved until at least six hours after a loading dose of 300 mg; this time can be reduced to around two hours by administering a loading dose of 600 mg.2

Anticoagulant therapy

Some patients may be anticoagulated with Warfarin, usually for reasons other than the presence of coronary artery disease (e.g. prosthetic heart valve, atrial fibrillation, venous thrombo-embolic disease). It may be impossible or undesirable to discontinue such treatment, but it is imperative that its effect is measured (by international normalised ratio (INR)), preferably before the start of the procedure and certainly prior to the removal of the arterial access sheath. Excessive anticoagulation should be corrected, but even therapeutic anticoagulation increases the risk of haemorrhage, especially at the vascular access site – anticipation of such a problem should lead to the use of appropriate prophylactic measures (see below).

Most patients with acute coronary syndromes are treated with Heparin. Intravenous unfractionated Heparin can be continued until the patient’s arrival in the catheterisation laboratory. Measurement of the activated clotting time (ACT) will then allow the administration of an appropriate bolus of intravenous Heparin, which may not actually be substantially different from that given to a patient not pre-treated with Heparin.3 If a twice-daily regime of subcutaneous low molecular-weight Heparin is being used, the last injection should be given at least 12 hours before any planned coronary interventional procedure.4 At the start of the procedure, an intravenous bolus of unfractionated Heparin can then be given in the usual way. In ‘emergency’ procedures, performed less than 12 hours after the last dose of low molecular-weight Heparin, it is normal practice to use a reduced dose of IV Heparin (<70 U/kg).

Platelet glycoprotein IIb/IIIa receptor antagonists

The results of randomised placebo-controlled clinical trials of several agents of this type demonstrate a clear benefit in patients with acute coronary syndromes, those undergoing percutaneous coronary interventional treatment or both. A detailed discussion of the use of such drug treatment is outwith the scope of this chapter – suffice it to say that it is clear that PCI can be performed safely after/during administration of such agents provided that a reduced, weight-adjusted heparin regime is used, in order to reduce the risk of major bleeding.5

Pre-medication

Despite explanation and reassurance, many patients remain anxious about undergoing PCI. If anxiety is overt and/or the patient expresses a desire for a sedative, a benzodiazepine such as Diazepam 5–20 mg orally may be given 1–1½ hours before the start of the procedure. Benzodiazepines are also effectively absorbed when administered sublingually, but this method conveys no great advantage, as the onset of action is unlikely to be any more rapid. Some patients undergoing PCI will have had many previous invasive procedures, so that femoral arterial access may be difficult and painful. Prior administration of an opiate drug (Pethidine or Morphine), combined with generous quantities of local anaesthetic (Lignocaine) will be much appreciated by such patients.

Diabetes mellitus6

Since patients are usually fasted for several hours before PCI procedures, special precautions may be required to prevent hypoglycaemia in patients with diabetes mellitus. If possible, an elective procedure in a diabetic should be scheduled at the beginning of the list, to avoid the patient having to fast for an unpredictable and excessive length of time.

Treatment with sulphonylureas should be omitted on the morning of the day of the procedure. The administration of significant quantities of glucose-containing IV fluids should be avoided if possible. Insulin treatment is unlikely to be required. Drug treatment can be restarted at the time of the patient’s first meal after the procedure.

Although lactic acidosis associated with treatment with Metformin occurs only rarely, it is more common in diabetics with impaired renal function. There have been a number of reports of cases of Metformin-associated lactic acidosis in patients with acute renal failure precipitated by iodinated contrast material, as is used during diagnostic and therapeutic cardiac procedures. This has led to the manufacturer’s current recommendation that Metformin should be discontinued at the time of, or prior to, any such procedure and withheld for 48 hours after the procedure. Treatment should be re-instituted only after renal function has been re-evaluated and found to be normal. In all but emergency cases, renal function should be checked in all patients taking Metformin before the procedure. As Metformin is contraindicated in the presence of abnormal renal function, such patients should have their drug therapy reviewed, although PCI can be performed provided that special precautions are taken7,8 (see Anticipation below).

Patients controlled with Insulin should receive no subcutaneous Insulin on the day of the procedure. An IV infusion of GKI (e.g. 500 ml 10% glucose with 10 mmol potassium chloride and 15 U Insulin at 100 ml/hour) should be commenced before the procedure and continued until a normal diet and subcutaneous Insulin can be restarted safely. The blood glucose level should be checked at least every two hours using one of the commercially available bedside test strips. Depending on the result, the amount of Insulin may require adjustment (if plasma glucose >11 mmol/l, increase Insulin to 20 U; if <6.5 mmol/l, decrease to 10 U).

Other drug therapy

In general terms, there is no need for other drug therapy to be discontinued or changed. Even long-term steroid therapy is unlikely to need enhancement, although the need for this should be reviewed in the event of a major complication, especially significant myocardial infarction (MI) and/or emergency CABG.

CONSENT9

In an emergency, if consent cannot be obtained, medical treatment may be provided to anyone who needs it, provided that the treatment is limited to what is immediately necessary to save life or avoid significant deterioration in the patient’s health. With this exception, an interventional cardiological procedure should not be performed without the patient giving his/her informed consent. This implies a two-stage process, involving the provision of information to the patient, who then decides voluntarily whether or not to consent to undergo the proposed procedure.

The information that a patient wants or ought to know, before deciding whether to consent to an interventional cardiological procedure, should include:

• Details of the diagnosis and prognosis, including the likely prognosis if the proposed treatment is not carried out.
• Other options for treatment of his/her condition, including the option not to treat.
• The purpose of the proposed procedure and details of exactly what is involved (including the likely duration of the procedure and the hospital stay).
• Details of what he/she might experience during or after the procedure (e.g. ‘will it hurt?’), including a discussion of the risks and the probability of success.
• Advice about whether any part of the proposed procedure is experimental.
• The name of the doctor who will have overall responsibility for the treatment.
• Whether doctors in training will be involved.
• A reminder that a patient can change his/her mind about a decision at any time and has a right to seek a second opinion.

It is important to ensure that this information is provided in such a way that the patient has sufficient time to consider it carefully and ask questions before giving consent. In practical terms, it may well be the case that information is given in stages, sometimes by different people working in different institutions. For instance, a patient may be given information about his/her cardiac condition (and a possible need for an invasive procedure) after coronary angiography performed by a physician/cardiologist working in a district general hospital (DGH). Staff at the Regional Cardiac Centre might then provide further information about the proposed procedure, both before and at the time of the patient’s admission for that procedure. It is important that any information given is both consistent and accurate. Medical staff performing interventional procedures should provide their audited results to colleagues in their referring DGHs.10 It is also important that the facts provided are relevant to the patient’s particular clinical situation. For example, it would be misleading to cite an average risk of death during coronary angioplasty as <1% when talking to a patient (or his/her relatives) about performing coronary angioplasty as treatment for cardiogenic shock following acute myocardial infarction – in this fortunately rare clinical situation, the likelihood of survival is considerably less than 99%!

Provided that the patient agrees, especially in high-risk clinical situations, it may well be appropriate to provide information about the proposed procedure to the next of kin (and/or other relatives/friends). In the worst-case scenario, it will not be the patient who will be asking what went wrong and why!

Ideally the doctor undertaking the procedure should discuss it with the patient and obtain consent, but if this is not practicable, the task can be delegated to another person, provided that he/she is suitably trained and qualified and has sufficient knowledge of the proposed procedure and its risks.

Although in an emergency a patient can indicate their informed consent orally, it is good clinical practice to make a routine of obtaining written consent for a cardiac interventional procedure. Following appropriate discussion, the patient should be asked to give consent for the treatment of any complications that may arise (e.g. emergency CABG). It is also important to ascertain whether there are any procedures to which the patient would object and which, therefore, should not be performed: the consent form should be worded appropriately. Most institutions have special consent forms for Jehovah’s witnesses, whose religious beliefs preclude the transfusion of blood or blood products.

ANTICIPATION

Before and during a cardiac laboratory procedure, it is imperative for the interventional cardiologist to maintain an air of calm and cheerful optimism, as uncertainty will quickly be detected by other members of staff and the patient, with potentially unfortunate consequences. In reality it is important to be thinking at least one step ahead as anticipation of possible problems is a vital step towards preventing them or at least dealing with them swiftly and efficiently if or when they occur. While almost anything can happen to any patient, some are especially vulnerable to particular problems, and appropriate prophylactic measures should be undertaken.

All patients

The ‘easy procedure’ can only be defined in retrospect and one should never assume that an apparently straightforward procedure will necessarily be so. An interventional procedure should only be undertaken by, or under the direct supervision of, a trained operator, with ancillary staff (nurses, technicians and radiographers) who experience a sufficient number of cases in their centre to ensure personal and institutional competence. It is also vital that the procedure is carried out in a fully equipped cardiac catheter laboratory, with an adequate range of equipment and drugs available at all times. This must include full facilities for cardiopulmonary resuscitation, including an intra-aortic balloon pump. There can be no place for a ‘quick angioplasty’ performed by an inexperienced operator in an ill-equipped location.10

Most patients

Although emergency CABG is now required in less than 0.1% of all reported PTCA procedures performed in the UK, the possibility of surgical intervention should be anticipated in all but a very small subgroup of patients in whom a decision is made before the procedure that emergency CABG would be inappropriate. In practical terms this means that coronary interventional procedures should be carried out on patients who have given informed consent for CABG if it should be deemed necessary and have donated a blood sample for blood grouping + formal cross-matching. In other than emergency situations, patients should undergo a three-hour liquid fast and a six-hour solid fast before the procedure. The arrangements for surgical cover for such procedures will vary according to local conditions, but the generally accepted national guideline is that it must be possible to establish cardiopulmonary bypass within 90 minutes of the referral being made to the cardiac surgical service.10

Some patients

It can be anticipated that patients with significant impairment of left ventricular (LV) systolic function may experience considerable haemodynamic deterioration during a cardiac interventional procedure, especially if this is prolonged or complex. If such a procedure is to be performed, systemic circulatory support, most often with intra-aortic balloon pump (IABP) counter-pulsation should be used or at least on standby.

Although no patient is immune from the development of ‘contrast nephropathy’, patients with pre-existing renal dysfunction are especially vulnerable. In such patients, measures that may help prevent the development of this condition7 include:

• Minimising the volume of contrast medium used.
• Avoiding concomitant use of other nephrotoxic drugs (especially non-steroidal anti-inflammatory drugs).
• Ensuring adequate hydration. This usually implies the administration of IV fluid to a fasting patient – as a general rule at 300–500 ml of IV hydration (normal or half-normal saline) should be given before the contrast medium is administered, whilst post-procedure hydration should be adjusted to achieve a diuresis of at least 150 ml/hour.
• The use of low-osmolar non-ionic contrast media, especially iodixanol (Visipaque®).
• N-acetylcysteine (NAC): although this product is used increasingly commonly in this situation, there are considerable uncertainties surrounding its effectiveness. The commonest regimen employed is 600 mg orally twice daily for two days, starting the day before the procedure, although clearly this may be impractical for urgent and (especially) emergency cases.10

A history of ‘allergy’ to contrast media is often unconfirmed on checking. Serious reactions are unusual following arterial administration, but should be anticipated in patients with a confirmed history of anaphylactic reactions during previous procedures. Pre-treatment with Prednisolone 40–60 mg daily, preferably for 3–4 days, may be helpful. In an emergency, hydrocortisone 200 mg IV immediately before the procedure, repeated 4-hourly, is a reasonable alternative. Although Chlorpheniramine is often given in addition, there is no convincing evidence that it is of value.

Finally, as has already been stated, patients taking oral anticoagulant therapy are at increased risk of haemorrhage, especially from the vascular access site. A number of measures may lessen this risk, including the use of small-calibre sheaths, conservative heparin dosing, selective or routine use of arterial closure devices and/or pneumatic compression systems and obtaining arterial access via the radial artery.

REFERENCES

1 Brookes CIO, Sigwart U. Taming platelets in coronary stenting: ticlopidine out, clopidogrel in? Heart. 1999;82:651-653.

2 Longstreth KL, Wertz JR. High-dose clopidogrel loading in percutaneous coronary intervention. Ann Pharmacother. 2005;39:918-922.

3 Blumenthal RS, Wolff MR, Resar JR, et al. Preprocedural anticoagulation does not reduce angioplasty heparin requirements. Am Heart J. 1993;125:1221-1225.

4 FRISC II Investigators. Invasive compared with non-invasive treatment in unstable coronary-artery disease: FRISC II prospective randomised multicentre study. Lancet. 1999;354:708-715.

5 Topol EJ, Byzova TV, Plow EF. Platelet GPIIb-IIIa blockers. Lancet. 1999;353:227-231. Gill GV, Albert KGMM. The care of the diabetic patient during surgery. In: Alberti KGMM, Zimmet P, DeFronzo RA, et al, editors. International textbook of diabetes mellitus. 2nd edn. Chichester: John Wiley; 1997:1243-1253.

6 Ansell G. Complications of intravascular iodinated contrast media. In: Ansell G, Bettman MA, Kaufman JA, et al, editors. Complications in diagnostic imaging and interventional radiology. 3rd edn. Cambridge, MA: Blackwell Science; 1996:245-300.

7 Heupler FA. Guidelines for performing angiography in patients taking Metformin. Cathet Cardiovasc Diag. 1998;43:121-123.

8 General Medical Council. Seeking patients’ consent: the ethical considerations. London: General Medical Council, 1998.

9 Joint working group on coronary angioplasty of the British Cardiac Society and British Cardiovascular Intervention Society. Coronary angioplasty: guidelines for good practice and training. Heart. 2000;83:224-235.

10 Shalansky SJ, Pate GE, Levin A, et al. N-acetylcysteine for prevention of radiocontrast induced nephrotoxicity: the importance of dose and route of administration. Heart. 2005;91:997-999.

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