Lab Investigation of Cardiac Disease Flashcards
What are the general biochemical tests in clinical medicine?
- Screening (subclinical conditions)
- Diagnosis (normal vs abnormal values)
- Monitoring (course of disease)
- Clinical management (treatment/ response)
- Prognosis (Risk stratification)
What are the classifications of laboratory tests in cardiac disease?
- Markers of risk factors for development of coronary artery disease
- Genetic analysis for candidate genes of risk factors
- Markers of cardiac tissue damage
- Markers of myocardial function/overload
What are cardiac markers?
They are located in the myocardium, and are released in response to:
- cardiac overload
- cardiac injury.
- cardiac failure
They can be measured in blood samples.
What can biochemical markers of cardiac dysfunction/damage contribute to?
- can rule in/out an acute MI
- can confirm an old MI
- can help to define therapy
- can monitor success of therapy
- diagnosis of heart failure
- risk stratification of death
What are the analytical and clinical characteristics of an ideal cardiac marker?
ANALYTICAL: • Measurable by cost-effective method • Simple to perform • Rapid turnaround time • Sufficient precision & accuracy • Reasonable cost
CLINICAL: • Early detection of disease • Sensitivity vs specificity • Validated decision limits • Selection of therapy • Risk stratification • Prognostic value • Ability to improve patient outcome
Describe the development of an atheromatous plaque.
INITIAL LESION:
- histologically ‘normal’
- macrophage infiltration
- isolated foam cells
FATTY STREAK:
- mainly intracellular lipid accumulation
INTERMEDIATE LESION:
- intracellular lipid accumulation
- small extracellular lipid pools
ATHEROMA:
- intracelullar lipid accumulation
- core of extracelullar lipid
FIBROATHEROMA:
- single or multiple lipid cores
- fibrotic/calcific layers
COMPLICATED LESION:
- surface defect
- haematoma-haemorrhage
- thrombosis
What are the major consequences of coronary thrombosis?
The blockage can lead to ischaemia (restriction of the oxygen supply to the tissue), leading to necrosis (tissue death) and ultimately a myocardial infarction.
List some chronic ishcaemic heart diseases.
- stable angina
- variant angina
- silent myocardial ischaemia
List some acute coronary syndromes.
- unstable angina
- ST-segment elevation MI
- non ST-segment elevation MI
Why is it important to define the type of IHD?
This is because different heart diseases have/need different:
- treatments
- prognosis
- management
What are some causes of chest pain?
- broken rib
- collapsed lung
- nerve infection (shingles)
- “pulled” muscle
- infection
- heart burn (hernia)
- pericarditis
- blood clot in the lungs (PE)
- angina
- myocardial infarction
How would you assess IHD?
- medical history
- risk factors
- presenting signs and symptoms
- ECG
- biomarkers (cardiac troponin, cTn)
- imaging/scans
Describe the prognosis of myocardial injury (i.e. relation between time and damage done).
An irreversible injury typically requires 30 minutes of ischaemia.
There’s a high risk that 80% of cardiac cells die within 3 hours and almost 100% by 6 hours.
Cellular contents leak out through membrane dependent on their size and solubility.
This concentration gradient from inside to outside is important (as a high gradient improves detection of early damage).
Which myocardial cell constituents are released first?
Ions (such as potassium or phosphate) are released first since they are the smallest, followed by metabolites (such as lactate or adenosine), and then finally, we have macromolecules (such as enzymes or proteins).
What are some markers of myocardial damage?
Most are release at the 7-36 hour peak after an MI.
There are heart muscle specific markers such as troponin-T and troponin-I.
Creatine kinase (found in more than 90% of MIs, but less specific as it’s also released from skeletal muscle).
There are heart specific isoforms of creatine phosphokinase (CPK-MB).
Myoglobin is raised early, but is less specific for heart damage.
