MANAGEMENT OF ACUTE INFARCTION
MANAGEMENT OF ACUTE INFARCTION
MANAGEMENT OF ACUTE INFARCTION
The aims of management are pain relief, infarct limitation,and the treatment of arrhythmic and mechanical complications.Management is subsequently directed to definingthe relatively small proportion of patients at a greater thannormal risk in the postinfarction period, and to rehabilitationand secondary prevention.
Analgesia and oxygen
Fear and pain exacerbate some of the ill effects of sympathetichyperactivity. Analgesia and sedation is achievedwith opiates, preferably diamorphine (2.5-5.Omg i.v.) ormorphine sulphate (4-8mg i.m.). These drugs combinesedation with an advantageous vasodilatory action, whichimproves haemodynamics. Respiratory depression is rarein the setting of acute infarction. The relief of pain itselfmay help raise blood pressure and reduce the heart rate.Associated nausea is treated using metoclopramide (10 mgi.v.) or prochlorperazine (12.5-25mg i.m.). An inhaledmixture of nitrous oxide and oxygen (Entonox) providespain relief prior to arrival in hospital.
Oxygen by mask is frequently given to patients withacute infarction to counteract the hypoxaemic effectsof pulmonary oedema. However, many patients are nothypoxaemic, and in such cases oxygen delivery to thetissues will not be improved by this treatment.
Acute (3-adrenoreceptor blockade Acute intravenous (3-blockade can be given safely to manyacute infarction patients. Large-scale trials have shown asmall rate of reduction in early deaths caused by reinfarctionand cardiac rupture. An additional effect is a reductionin pain. Acute intravenous -blockade would haveto be given to 200 patients to prevent one death, onereinfarction and one cardiac arrest. Chronic therapy afterinfarction saves two lives for every 100 patients treated for1 year.
Limitation of infarct size
Six hours is the time limit within which it is possible thatmeasures to restore blood supply will salvage ischaemicmuscle. If collateral channels are poor, this time limit maybe considerably less.
Thrombolysis
In approximately 80% of patients a myocardial infarctionis caused by thrombotic occlusion of a vessel, usuallysuperimposed on an atherosclerotic plaque.Despite the first use of thrombolytic agents in myocardialinfarction as early as 1958, their adoption as oneof the mainstays of treatment followed the publication oftwo giant trials using streptokinase. A single injection of1.5 x 106 units i.v. over 1 hour within 12 hours of the firstsymptom reduced mortality by 18%. More than 200000patients have now been randomized in therapeutic trialswith thrombolytic agents.
The most widely used agentsremain streptokinase and the recombinant tissue plasminogenactivator rtPA.Haemorrhagic complications occur, though sufficientlyrarely as not to interfere with the overall beneficial effectof therapy. Patients with clotting disorders, a previoushistory of stroke or peptic ulceration, and those with severehypertension or any injuries are excluded from this treatment.It is important to exclude aortic dissection, as fibrinolytictreatment can prove catastrophic.
Other relativecontraindications are a known hypersensitivity to thedrug, recent streptococcal infection, survivors from cardiacarrest who have had cardiac massage, and those withheart block who may need a temporary pacemaker.Streptokinase should not be administered within 2 yearsof a previous treatment.Benefit from thrombolysis is increased if it is givenwithin 6 hours (and preferably 3 hours) of the first symptom.This has led to newer fibrinolytic agents that can beadministered at the site of the presenting symptoms, byeither the ambulance crew or the GP.
Aspirin and heparin
Aspirin alone reduces mortality by 25%, and with streptokinase gives a combined reduction of 45%. Continuous infusion of heparin after thrombolysis and after coronaryangioplasty is routine in many centres. Patients with largeinfarctions suffer fewer systemic emboli from ventricularclot if treated with heparin.
Bleeding complications andstroke are slightly more common.Heparin treatment is potentially more important afterthe shorter-acting rtPA, when it should be given for 48hours. Warfarin treatment is limited to those in AF, orwhere a large LV thrombus is shown.
Angioplasty and surgery
Early revascularization during acute infarction may bethe revascularization method of choice, but the cost ofproviding a 24-hour service for these complex, labour intensive techniques is considerable. Individual cases willcontinue to be so treated in centres where angioplasty or surgical suites are closely linked to the acute admission wards.
Nitrates and calcium antagonist drugs
Nitrates by intravenous infusion (2-10 mg/h for isosorbide,1-12 mg/h for GTN) are frequently used in the acute phase of infarction, where persistent pain is a problem; their useis associated with a modest reduction in mortality. Theyhave the advantage of causing reduction in preload andafterload, which may relieve left heart failure. Hypotension can be a problem, particularly in patientswho are dependent on a high right heart filling pressureto maintain stroke volume, such as those with right ventricularinfarction.
Cutaneous therapy is best reserved for the less acutestages of infarction, when converting patients from intravenousinfusion to maintenance therapy.
Calcium antagonist drugs are effective in improving ischaemic cardiac pain, but their use has not been associatedwith any improvement in infarction mortality.Calcium antagonists, particularly the rate-slowing agents diltiazem and verapamil, can be used when there are contraindications to b-blockade.
ACE inhibitors Given within a few days of infarction there is an earlybenefit, which has now been proved to persist for manyyears (>4) post MI. These drugs should not be given whilepatients are hypotensive, particularly during the acutestages of myocardial infarction. Benefit from ACE inhibitorsis probably not adequately explained purely bytheir vasodilatory and antihypertensive effects.
HMG-CoA reductaseinhibitors - the statinsMore than 70% of myocardial infarction survivors in theUK have a total cholesterol >5 mmol/L. There is now convincingevidence that the majority will benefit from beingtreated with a statin.
Bed rest, mobilization and rehabilitation
Bed rest during the acute phase of infarction is aimedat minimizing harmful cardiac remodelling processes.However, prolonged bed rest is unnecessary and can causecomplications of its own (such as deep vein thrombosis,pulmonary embolism, deconditioning and bedsores).Prophylactic subcutaneous heparin (12 500 U b.d.) may beindicated if prolonged bed rest is necessary. Mobilizationcan begin within 24 hours in uncomplicated infarction.Patients can generally be discharged on the 10th day,having demonstrated their ability to walk and manage aflight of stairs before returning home. Mobilization should be slowed if there is a return of chest discomfort, a heartrate below 50bpm or above 120 bpm, the return ofischaemic ST elevation on the ECG, or an increase of more than 15mmHg in systolic pressure with gentle ambulation.
Acute myocardial infarction is quite a distressing experience.Patients should be counselled individually and manyof them appreciate a clear explanation of the condition andprognosis in simple layman's terms. Advice on risk factors(e.g. stopping smoking) can be initiated at this stage.
MANAGEMENT OF ACUTE INFARCTION
By: Dr Izharul Hasan
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