Acute myocardial infarction
Myocardial infarction ( MI ) is defined as sudden ischaemic death of myocardial tissue as a result of imbalance between myocardial oxygen supply and demand ( commonly known as heart attack )
Coronary Heart Disease ( CHD ) or Coronary Artery Disease ( CAD ) is the leading cause of morbidity and mortality across the globe The most common form of CHD is myocardial infarction which happens usually due to a thrombotic occlusion of a coronary vessel caused by rupture of a vulnerable lipid laden atherosclerotic coronary plaque Total occlusion causes STEMI and a partial occlusion in the presence of collateral circulation results in NON-STEMI ( more common than STEMI ) or unstable angina Atherosclerosis is the most common cause of CHD Coronary artery becomes occluded by an atherosclerotic plaque -this then leads to the formation of a thrombus MI usually begins in the endocardium and spreads towards the epicardium Adult mammalian heart cannot regenerate – infarcted myocardium heals through formation of scar – this can lead to systolic and diastolic dysfunction and the patient is prone to arrhythmias Eventually the scar tissue forms a fibrotic scar with long term consequences as ventricular remodelling of the remaining myocardium ( e.g development of compensatory hypertrophy or dilatation ) , ventricular failure , arrhythmias and sudden death
CHD is the leading cause of morbidity and mortality throughout the world Global Burden of Disease Study 2017 reported that cardiovascular diseases were responsible for 31.8 % of all deaths worldwide Acute MI ( AMI ) is the leading cause of death among IHDs MI is higher in men in all age-specific groups than women The industrialized world has witnessed a decrease in the incidence of MI partly due to improved health systems and implementation of effective public health systems Low and middle income countries now share the majority of the burden of deaths from AMI Increased life expectancy means more people live with heart disease and assorted comorbid complications In the US a life is lost every second due to AMI In UK CVD is the 2nd most common reason for admission to hospital , 8.4 % of total admissions , specifically with 188,000 people being admitted with AMI / year.
Risk factors -Modifiable risk factors represent over 90 % of the risk of acute MI Risk factors for men and women are generally the same Majority of patients with AMI would have 2 or more established risk factors More the number of risk factors- higher the rate of ischaemic events Risk factors include dyslipidemia , smoking , psychosocial stressors , diabetes mellitus , hypertension , obesity , alcohol consumption , physical inactivity , diet low in fruits and vegetables Non-modifiable risk factors include - being male ( men suffer MI earlier than women ) - h.o atherosclerosis - ageing ( about 80 % of mortality in people aged 65 and over ) - family history ( of AMI in a 1st degree relative doubles the risk ) Cigarette smoking is the most preventative risk factor - results in early STEMI in otherwise healthy individuals - smoking cessation in people with CAD -effect equals that of surgery - smoking works by various multiple and complex mechanisms to increase the risk of AMI for e.g increased LDL cholesterol and low HDL , atherosclerosis Other quoted risk factors include gout ( also incd risk stroke ), periodontal disease , stress , peripheral vascular resistance , elevated homocysteine levels Protective role of natural oestrogen before menopause has been suggested in women - less atherogenic lipid profile and a more healthy fat distribution - but female smokers have a relatively higher CV risk than male smokers.
Other causes of MI -Trauma Vasculitis Drug use ( e.g cocaine ) Coronary artery anomalies Coronary artery emboli Aortic dissection Excess demand on heart for e.g due to hyperthyroidism , anaemia.
Assessment -Take into account CV risk factors , H/o IHD , previous interventions , treatment and presentation which can include.
chest pain which radiates to the neck , jaw or arms ( one or both ) substernal heaviness squeezing or pressure shortness of breath , wheezing , cough fatigue , nausea , sweating , anxiety fainting , light-headedness sleepiness hypertension or hypotension tachycardia arrhythmias unexplained weakness anxiety / fear of death.
All suspected patients with Acute Coronary Syndrome should be in an environment where continuous ECG monitoring and defibrillation is available ie arrange emergency ambulance for an immediate hospital transfer. TIME is the key
note general appearance , assess pulse , bp , JVP , heart sounds and auscultate the chest administer 300 mg Aspirin unless contraindicated do not give IM injections ( can interfere with laboratory tests as creatinine kinase and thrombolysis ) obtain ECG if situation permits but this should not contribute to a delay in hospital transfer.
Acute myocardial infarction ( AMI ) -according to ESC should be used when there is evidence of myocardial injury ( ie elevated cardiac troponin with atleast one value above the 99th percentile upper reference limit ) with necrosis in a clinical setting consistent with myocardial ischaemia.
ST elevation MI -usually due to sudden blockage of a single culprit coronary artery diagnosed on basis of symptoms consistent with myocardial ischaemia ( i.e persistent chest pain ) and signs ( ie 12 lead ECG ) TIME is the CRITICAL factor as nearly half of the potentially salvageable myocardium is lost within 1 hour and 2/3rd are lost within 3 hrs of the blockage Hence the emphasis is on REPERFUSION which can be achieved by - -revascularization ie PCI if this can be achieved within 120 minutes based on angiographic findings ( 2 hrs ) PCI is primary percutaneous coronary intervention which opens the occluded artery OR - thrombolysis.
NSTEMI -due to partial or near-complete occlusion of coronary artery causing myocardial injury / infarction initial ECG may show ischaemic changes as ST depression , T wave changes or transient ST elevation or the ECG may be normal or show non specific changes elevated troponin.
Primary prevention –CVD is an umbrella term which includes ○ coronary artery disease / heart disease ○ cerebrovascular disease ○ peripheral arterial disease ○ rheumatic and congenital heart diseases ○ venous thromboembolism In the UK – CVD is estimated to be the cause of 34 % of all deaths WHO states that 79 % of premature CVD is preventable by risk factor amelioration Primary prevention is to prevent the occurrence of a cardiovascular event by reducing modifiable risk factors through lifestyle changes and drug management NICE reports that CVD affects people older than 50 yrs and modifiable risk factors as smoking , raised BP and cholesterol NICE recommends using risk calculators as QRISK2 to assess CVD risk for primary prevention of CVD in people up to and including 84 yrs.
Exercise -considered beneficial universally recommended by most guidelines as NICE , AHA , ESC any kind of exercise can be beneficial NICE recommends 150 minutes of moderate intensity aerobic activity / week or 75 minutes of vigorous aerobic activity or a mix of moderate vigorous aerobic activity.
Diet -NICE recommends to advice people at high risk of CVD to eat a diet in which total fat intake is 30 % or less of total energy intake , saturated fats are 7 % of less of total energy intake , dietary cholesterol intake < than 300 mg/day and where possible saturated fats are replaced by mono-unsaturated and polyunsaturated fats AHA suggests to use Dietary Approaches to Stop Hypertension ( DASH ) diet -it is low in sugars and saturated fats , high in vegetables , fruits and whole grains ESC suggests to switch from saturated to polyunsaturated fatty acids , increase in fibre , fruit, vegetable and fish as well as abstinence from alcohol and adherence to Mediterranean type diet.
Smoking -advice all people who smoke to stop and provide support , advice & pharmacotherapy smoking doubles the 10 year CVD mortality rate while 30 % of US CVD mortality is attributable to smoking smoking cessation is the single most cost-effective intervention in CVD prevention
Weight-Most guidelines do not recommend specific intervention regarding weight but suggest to maintain a healthy weight NICE recommends to offer overweight people at high risk of CVD /existing CVD-appropriate advice and support to achieve and maintain healthy weight.
Alcohol -remains controversial INTERHEART study indicated a reductions in risk for those with moderate and light alcohol use whereas Holmes et al have shown that a reduced CVD risk with reduction in alcohol intake ESC does not recommend any safe level of alcohol intake and NICE advice moderate intake ( 4 units /day for men and 3 for women )
Lipid lowering agents -Reduction in LDL-C has been shown to reduce CVD mortality and non-fatal MIs Refer to the chart – lipid modification for NICE guidance NICE advices using atorvastatin 20 mg as primary prevention in patients < 85 yrs with a QRISK2 score of > 10 % & notes that patients > 85 may also benefit despite a lack of confirmatory data
Hypertension- independent risk factor for CVD BP reduction is more important than the individual drug used please refer to the chart hypertension for NICE guidance.
Antiplatelets -Aspirin in not licensed for primary prevention of CVD ( CKS ) They ( antiplatelets ) have a role in secondary prevention but it is advised that they be avoided in primary prevention without co-morbidities due to increased risk of bleeding with no evidence of CVD risk reduction.
Post MI care -Discussed here is a summary of the secondary prevention measures for those who had MI as advised by NICE. Secondary prevention is to prevent recurrent events prevent fatality reduce / improve symptoms improve QoL.
ACE inhibitors- titrate to maximum tolerated dose – this would be achieved in most cases before discharge but if that was not possible it should be completed within 4-6 weeks of discharge . monitor U&E/ BP if ACE cannot be tolerated offer an ARB but do not use the two together people who had an MI > 12 months ago -offer a lifelong ACE ( ARB if ACE not tolerated ) and titrate to maximum tolerated or target dose over 4-6 weeks.
Antiplatelets -use of antiplatelets ( by ↓ platelet aggregation ) has reduced the recurrent cardiovascular events after an acute ACS ( risk is greatest in the first months and by 3 months the plaque has usually stabilized , healed and subsequent event rates are the same as for those with stable coronary artery disease ) aspirin indefinitely unless intolerant or they need anticoagulation clopidogrel for those who cannot take aspirin or those who also have other clinical vascular disease and Dual antiplatelet therapy ( DAPT ) is the use of a P2Y12 receptor inhibitor ( clopidogrel , ticagrelor or prasugrel ) + aspirin after percutaneous coronary interventions with drug eluting stents NICE recommends to continue DAPT for up to 12 months after an acute MI unless contraindicated cardiolgists would advice on the duration of DAPT and its a tradeoff between reducing the incidence of future cardiovascular events and causing harm from an ↑ ed risk of bleeding cardiologists may prescribe an oral anticoagulant with an antiplatelet based on individual circumstances / indications
Beta blockers -it is thought that long term ß -blocker post MI reduces mortality and recurrent MI NICE recommends to continue beta blockers indefinitely if reduced LV ejection fraction , otherwise consider continuing for atleast 12 months if beta blockers cannot be used and no pulmonary congestion or reduced LV ejection fraction -consider diltiazem or verapamil.
Statins -recommended indefinitely post MI current guidance recommends use of high intensity statin treatment for e.g atorvastatin 80 mg / day for people with existing CVD ie past or current h/o MI , angina , stroke , TIA or peripheral arterial disease effective in secondary prevention evidence backed by several RCTs.
Aldosterone antagonists -for heart failure with reduced LV ejection fraction monitor renal function and if hyperkalaemia is a problem halve the dose or stop the drug
Cardiac rehabilitation -This involves physical activity ( adapted to the patient ) lifestyle advice ( including information on driving , flying and sex ) stress management health education runs for about 10 -12 weeks with about 2 hrs sessions at a time ( BHF )
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