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Myocardial Infarction |
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Myocardial InfarctionAetiology
Symptoms
Signs
Investigations
Management
Main complications
PathologyInvestigations
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ECG changes Minutes
- Tall pointed T-waves and ST segment elevation. Hours – T-wave inversion. Development of
Q-waves. Days – ST segment returns to baseline. Weeks – T-waves may revert. Q-waves often
persist. ·
Cardiac Enzymes. Necrotic cardiac tissue releases several enzymes. ·
Creatine Kinase (CK). CK-MB is the cardiac specific isoform. It peaks
within 24 hours of an MI and is usually back to normal by 48 hours. ·
Cardiac specific troponins. Troponin T and Troponin I are very highly
specific for cardiac injury. They are released early (2-4 hours) after MI and
can persist for up to 7 days. ·
Aspartate aminotransferase (AST) and Lactate dehydrogenase (LDH). These
non specific enzymes are now rarely used for a diagnosis of MI. LDH peaks at 3-4
days and remains elevated for up to 10 days and thus can be useful in confirming
MI in patients presenting several days after their incidence of chest pain. ·
Giving a diagnosis of MI requires at least two out of a history of
ischaemic type chest pain, ECG changes and altered cardiac enzymes. Complications
·
Commonly occurring complications that may require additional management
include cardiac arrhythmias, cardiac failure and cardiogenic shock, pericarditis,
and thromboembolisation. Reperfusion Injury
Experimentally it has been demonstrated that reperfusion of cardiac
tissue following an ischaemic period can result in increased cell damage and
arrhythmogeneis. The mechanisms behind this have been suggested to be cytotoxic
rises in intracellular calcium, generation of oxygen free radical species and
inhomogeneous extracellular potassium levels across the ischaemic area and
boundaries. The addition of certain pharmacological agents such as Amiloride,
Cariporide or Glutathione to the reperfusiing solution has been demonstrated to
have some cardioprotective effects. Treatment of Myocardial Infarction
-ecg monitor -high flow oxygen -aspirin 300mg -morphine 5-15mg IV at Í1mg/min
if none given before -antiemetic e.g. metoclopramide 5-10mg IV -GTN (o.5mg sublingually for coronary vasodilatation) Consider whether to thrombolysize: Indications
Chest pain consistent with MT within 12hours
AND ST segment elevation
(>1mm in 2 or more contiguous leads)
OR left bundle branch block Contraindications Stroke or active bleeding in last 2 months
Systolic
BP>200mmHg
Proliferative diabetic retinopathy
Pregnancy Relative contraindications Prolonged
or traumatic resuscitation
Recent (>2
weeks) surgery or trauma
Known bleeding diathesis or current use of anticoagulants Following initiation of thrombolysis: o
IV b-antagonist
such as metoprolol 5-10mg should be given particularly if the heart rate is
>100b.p.m. with persistent pain. o
IV nitrates should be given for persistent pain or pulmonary oedema. o
Subsequently Aspirin 150mg daily (if no contraindications) o
b-blocker
(if no contraindications) Patients with clinical evidence of pulmonary oedema or decreased
ejection fraction should be commenced on ACE inhibitors e.g. ramipril 2.5mg/12hr
PO on day 3 after 48hr increase to 5mg/12hr Finally Check lipid fasting profile at 3 months. Review the need for a statin.
Statins may reduce subsequent cardiovascular mortality as much as aspirin and b-blockers. MICrushing chest pain, cold, clammy, sweatingTreatment
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