Myocardial infarction/acute coronary syndrome Flashcards
What are the three conditions under acute coronary syndrome?
- ST-elevation myocardial infarction (STEMI)
- Non-ST-elevation myocardial infarction (NSTEMI)
- Unstable angina
What is a myocardial infarction (MI)?
MI is defined as the death of cardiac myocytes due to prolonged myocardial ischaemia.
How do you differentiate between unstable angina and NSTEMI?
NSTEMI: occluding thrombus => myocardial necrosis and a rise in serum troponin I & T and creatinine kinase-MB.
Unstable angina: ruptured plaque with non-occlusive thrombus + no rise in troponin
No ST elevation in both
What are the 5 different types of MI?
Type 1: Spontaneous MI with ischaemia (due to primary coronary event i.e. plaque eruption/rupture, fissuring or dissection
Type 2: MI 2nd to ischaemia (due to increased O2 demand or decreased supply i.e. coronary spasm or embolism, anaemia, arrhythmias and hyper/hypotension)
Type 3: MI in sudden cardiac arrest
Type 4a: MI related PCI
Type 4b: MI related to stent thrombosis
Type 5: MI related to CABG
What is the underlying pathophysiology of acute coronary syndromes?
Rupture of the fibrous cap of a coronary artery plaque.
This leads to platelet aggregation and adhesion, localised thrombosis, vasoconstriction & distal thrombus embolisation.
Presence of a rich lipid core and think fibrous cap = increased risk of rupture.
Thrombus formation and vasoconstriction produced by platelet release of serotonin and thromboxane-A2 => myocardial ischaemia due to reduction in coronary blood flow.
What are the risk factors?
Non-modifiable:
Age
Male
Family Hx of ischaemic heart disease (MI in 1st degree relative <55years)
Modifiable: Smoking Hypertension Diabetes Hyperlipidaemia Obesity Sedentary lifestyle Cocaine use
Controversial risk factor:
Stress
Type A personality
Left ventricular hypertrophy
What are the symptoms of acute coronary syndrome (ACS)?
New onset acute central chest pain (at rest or deterioration of angina) lasting >20 mins
Assoc. w/ nausea, sweatiness, dyspnoea, palpitations
Atypical features = indigestion, pleuritic chest pain or dyspnoea
ACS w/o chest pain = silent (mostly seen in elderly & diabetic patients)
Silent MI’s present with syncope, pulmonary oedema, epigastric pain and vomiting
Which investigations are carried out to confirm ACS?
- ECG
- Chest X-ray
- Bloods: FBC, U&E, glucose, cholesterol/lipids, cardiac enzymes
- Cardiac enzymes: Troponin I & T (most sensitive & specific markers of myocardial necrosis)
- Echo
Describe the changes seen in an ECG in the event of an ACS (STEMI / NSTEMI)?
12-lead ECG : ST elevation & T-wave inversion highly suggestive of an ACS, esp assoc. with anginas chest pain.
ECG should be repeated when patient is in pain and monitor continuous ST segment.
STEMI : hyperacute, tall T waves, persistent ST elevation or new left bundle branch block occur within hours (due to complete occlusion of coronary vessel).
T-wave inversion and pathological Q waves follow over hours to days.
NSTEMI/unstable angina : ST depression, T wave inversion, non-specific changes or normal
*In 20% MI, ECG normal initially
Troponin is the most specific and sensitive biochemical marker in ACS.
What are troponins and what is the function of Troponin I, Troponin T and Troponin C?
Troponin are proteins involved in skeletal and cardiac muscle contraction.
Troponin I, T and C are on the thin-acting filament alongside tropomyosin to form the cardiac myofilament.
Troponin T attaches the complex to tropomyosin.
Troponin C binds calcium during excitation-contraction coupling.
Troponin I inhibits the myosin binding site on actin.
*High troponin levels = high mortality risk in ACS
What happens to troponin on myocardial death?
Troponins are released and enter the blood stream within hours of the result.
Which troponins are the most specific to the heart?
Troponin I and T
Which other cardiac conditions result in a raised troponin?
Myocarditis
Pericarditis
Ventricular strain (ie. 2nd to PE)
What are some non-cardiac causes of raised troponin?
Causes that are/have:
- Indirectly related to heart
- No cardiac relation
- Iatrogenically
- Consistently raised troponin
Indirectly related to heart:
Massive PE causing right ventricular strain
No cardiac relation:
Subarachnoid haemorrhage
Burns
Sepsis
Common cause of consistency raised troponin = renal failure
Iatrogenically:
CPR
DC cardioversion
Ablation therapy
Tachyarrhythmias = rise in troponin similar to ACS
Which two main scoring system is used to stratify ACS risk score?
- Thrombolysis in myocardial infarction (TIMI) score
- Global Registry of Acute Coronary Events (GRACE) score
The GRACE score is based on age, heart rate, systolic blood pressure, serum creatinine and the Killip score.
What is the acute management for chest pain and ACS without ST elevation?
M - Morphine 5-10mg IV + metoclopramide 10mg IV
O - Oxygen if SaO2 <90% or breathless, low flow O2
N - Nitrates ; GTN spray or sublingual tablet
A - Aspirin 300mg loading dose then 75mg once daily
T - Tricagrelor or clopidogrel (2nd anti-platelet agent in confirmed ACS)
After acute management of chest pain using MONA in ACS without ST elevation, how do you manage a high risk patient whose troponin is rising, dynamic ST or T wave changes and the patient has either diabetes, CKD, left ventricular ejection fraction <40, early angina post MI, recent PCI, previous CABG or intermediate to high risk GRACE score.
- Anti-thrombin drugs : Fondaparinux, enoxaparin (both = factor Xa inhibitor)
- 2nd anti-platelet agent (if not already added) : ticagrelor (or clopidogrel in lower risk patients)
- IV nitrate if pain continues, titrate to pain and maintain systolic BP >100mmHg
- Oral B-blocker : Bisoprolol 2.5mg OD
- ACE-inhibitor + monitor renal function
- Lipid management : Atorvastatin 80mg OD
- Cardiologist review for angiography urgent if:
Ongoing angina (<120min after presentation) and evolving ST changes, signs of cardiogenic shock or life threatening arrhythmias
Early (<24h) if GRACE score >140 and high risk patient
Within 72h if lower risk patient
When may beta-blockers be contraindicated?
What alternative may be used?
Cardiogenic shock
Heart failure
Asthma/COPD
Heart block
Rate limiting calcium antagonist i.e. verapamil / diltiazem
What is the prognosis for ACS without ST elevation (unstable angine and NSTEMI)?
Which risk factors increase the risk of death?
Risk of death 1-2% ; 15% for refractory angina
Risk stratification (GRACE score) to predict and manage better.
Risk factors:
Hx of unstable angina
ST depression or widespread T-wave inversion
Raised troponin
Age >70yrs
Comorbidity (previous MI, diabetes, poor left ventricle function)
What other interventions may be needed for a high risk NSTEMI patient (GRACE score >140) with
persistent chest pain not responding to medical therapy,
clinical signs of heart failure,
haemodynamically unstable,
cardiogenic shock or
life-threatening arrhythmias (ventricular fib/tachycardia)?
Very high risk = Urgent angiography within 2h
High risk (GRACE score >140) = Coronary angiography ± PCI within 24h
Intermediate risk (GRACE score 109-140) = Angiography within 72h
Patients with multi-vessel disease = consider CABG not PCI
How do you manage a low risk ACS patient without ST elevation after acute management of chest pain?
After acute management of chest pain using MONA in ACS without ST elevation, how do you manage a low risk patient who has No recurrent chest pain No signs of heart failure Normal ECG No rise in troponin
Conservative management
Medical therapy
Outpatient investigations e.g. stress test
What is the underlying pathophysiology of a STEMI?
Rupture of a coronary artery plaque => prolonged occlusion of a coronary artery => myocardial necrosis within 15-30 minutes.
Initially, subendocardial myocardium is affected but with continued ischaemia, the infarct zone extends through to the subepicardial myocardium => producing a transmural Q wave MI.
Which factors increased the risk of death?
Age >65 ; >75 Hx of angina ; hypertension ; diabetes Systolic BP <100mmHg Heart rate >100bpm Killip score II=IV Weight >67kg Anterior MI or LBBB Delay to treatment >4h
What are the typical + atypical signs and symptoms of a STEMI?
- Severe chest pain lasting more than 20mins
Pain does not respond to sublingual GTN & opiate is required for analgesia
Pain may radiate to left arm, neck, jaw.
- In elderly/diabetic patients symptoms are atypical:
Dyspnoea
Fatigue
Pre-syncope / syncope - Autonomic symptoms are common:
Pale & clammy
Marked sweating - Signs:
Pulse thready with sig. hypotension, bradycardia or tachycardia.
