Myocardial Infarction

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Myocardial Infarction


Aetiology

Symptoms

  • severe chest pain similar in character to exertional angina
    • chest / neck / upper back or arm pain
  • onset is usually sudden,
  • often at rest
  • persists for some hours
  • sweatiness
  • nausea / vomiting
  • dyspnoea
  • extreme distress
  • associated with breathlessness
  • A high proportion (up to 20%) of patients with MI may have no pain
    • more common in diabetics and the elderly

Signs

  • pale,
  • sweaty
  • grey
  • sinus tachycardia
  • fourth heart sound
  • raised JVP
  • sudden death

Investigations

  • ECG
  • cardiac enzymes
  • ?echo
  • CXR
  • Bloods
    • FBC, U&E

Management

  1. reassure patient / bed rest
  2. GTN to relieve symptoms
  3. High-flow 02
  4. ECG
  5. Morphine + anti-emetic (pain relief + some unloading)
  6. 300mg aspirin (preferably soluble)
  7. Consider thrombolysis
  8. Monitor throughout admission
  9. Risk factor management
    • ACE inhibitor
    • statin
    • angioplasty / CABG
  • Beta-blockers reduce mortality
    • atenolol / metoprolol early
    • acebutolol / metoprolol / propranolol / timolol later

Main complications

Pathology

Investigations

·         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.

 

MI

Crushing chest pain, cold, clammy, sweating

Treatment

  • GTN spray
  • 300 mg Aspirin PO
  • Diamorphine
  • Thrombolytic therapy:
  • Steptokinase: can only be used once as antibodies develpo within 4 days
  • Tissue Plasminogen Activator
 

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