HR affect on myocardial oxygen demand
Faster HR shortens diastole reducing coronary filling time
Contractility affect on myocardial oxygen demand
Increased sympathetic tone raises oxygen consumption
Wall stress/afterload affect on myocardial oxygen demand
Higher arterial pressure increases myocardial workload
Preload affect on myocardial oxygen demand
Influences SV and intercardiac pressures
Coronary Perfusion Pressure Definition
Haemodynamic measurement that represents the pressure gradient driving blood flow through the coronary arteries during diastole, when the myocardium is perfused
CPP Equation
Aortic Diastolic Pressure (ADP) - Left ventricular end-diastolic pressure (LVEDP)
Aortic Diastolic pressure
Provides the driving force that pushes blood into the coronary arteries
Left Ventricular End-diastolic Pressure
Represents the back-pressure within the left ventricle that opposes coronary inflow
Primary Indications for ETT
- Screening
- Detection of CAD
- Investigation of exertion chest pain
- Risk stratification in known CAD (functional capacity, arrhythmia provocation)
- Assessment of exercise capacity and functional status
- Evaluation of exertion arrhythmias or exercise-related syncope
- Research
What is absolute contraindication? (definition)
Do not perform an ETT
What is relative contraindication? (definition)
- Weigh risks vs benefits
- Consider alternative testing
Absolute contraindications for ETT
- Unstable angina
- Ongoing MI/ recent MI
- Uncontrolled symptomatic arrhythmias causes haemodynamic compromise
- Severe aortic stenosis with symptoms
- Acute myocarditis or pericarditis
- Acute PE or other ACS
- Aortic dissection
Relative Contraindications for ETT
- Severe uncontrolled HT
- Severe COPD or other conditions limiting exercise
- Orthopaedic or neuromuscular limitations preventing safe exercise
- Left main coronary disease with dynamic symptoms (specialist input)
What is the Bruce Protocol?
- Standard for ETT
- 3 min stages with progressive increases in treadmill speed and incline
What is the modified Bruce Protocol?
- Similar to standard Bruce protocol
- Includes lower-intensity initial stages for elderly or reconditioned pt
What is the bicycle ergometer protocol?
- Done on a bicycle
- Uses incremental wattage increases
What is exercise capacity described in?
Metabolic Equivalent Tasks (MET)
1 MET
Oxygen consumption at rest
~ 3.5 mL o2/Kg/min
Correlation of MET value and ETT
Higher peak METs achieved during ETT correlated with lower mortality risk
Absolute indications for immediate termination of test
- Severe or progressive chest pain with concerning evolving infarction
- Sustained VT or life-threatening arrhythmia
- Signs of poor perfusion
- Drop in SBP with increasing workload or sustained hypotension
- Severe breathlessness, wheeze or pulmonary oedema signs
- Pt requests to stop due to intolerable symptoms
Relative indications to stop test
- Marked ST depression without symptoms
- Extreme hypertension
- Significant bradyarrhythmia/heart block developing during exercise
Post-test monitoring
- Observe until HR and BP near baseline and pt is asymptomatic
- Monitor for delays arrhythmias and ensure recovery ECG available for interpretation
ECG normal response to exercise
- Sinus tachycardia
- PR interval shortens
- Early depolarisation/J-point elevation may appear
- Mild upscoping ST depression can be normal ( horizontal to downscoping ST depression more concerning)
Normal haemodynamic response to exercise
- SBP rises with increasing workload
- DBP usually remains table or falls slightly
