Exercise stress testing(EST) is one of the common investigation modality in the evaluation of CAD.he indication for EST generally fall into two broad categories.
- Diagnostic in patients suspected to have CAD
- Prognostic evaluation in patients with established CAD .9Many times after a coronary angiogram)
Currently there is a major shift in our thinking, patients with classical angina may undergo coronary angiogram directly .This is understandable as the stress test has little to improve diagnostic sensitivity and specificity in patents with clinically obvious CAD.
So , it is now becoming clear , the diagnostic value is increasingly restricted in the evaluation of o atypical chest pain .
What is a strongly positive response ?
- Gross ST segment depression > 2-3mm
- Occurring in stage one
- Fall in blood pressure
- Prolonged angina into recovery
What is the angiographic correlates of strongly positive EST?
- Critical left main disease
- Near total proximal LAD /LCX
- A severely compromised bifurcation lesion
Morphological correlation
- These patients often have eccentric lesions with irregular margins.
- unstable lesions
- Lack collaterals
What is the effect of vigorous excercise on a critical flow limiting lesion ?
The shear stress over the plaque increases with exercise and the transcoronary gradient can reach a theoretical 60-90mmhg .One can imagine the what this stress can do to the unstable lipid core .This is the reason unstable angina is an absolute contraindication to EST.
What does a strongly positive EST imply for the patient ?
- It indicates he needs urgent CAG and most likely an immediate revascularisation.
- Often , these patients have prolonged angina , and mandates admission in a coronary care unit.
- there has been many incidence of ACS in these patients within 24hours of EST.
- Lives have been lost on their way back , as these patients are sent home , as EST is a OP procedure .
Final message
- It need to be realised a strongly positive response to EST could be a clinical equivalent of unstable angina .
- The common response from a physician or cardiologist after witnessing a gross ST depression to EST would be “Had I known this I would have sent him straight into cathlab instead of EST ”
- If only , we give little ear to our patient’s history we can pick the high risk clue in 9 out of 10 cases !
- It can be argued , a strongly positive EST by itself is “A clinical diagnostic failure” , ie failure of the physician to recognise the likely hood of strongly positive EST ie a left main disease.
- These patients should never be sent home immediately after the EST .This is fraught with a risk SCD
- Most of them will require observation in step down unit for 24 hours and if feasible they should be posted for coronary angiogram in the earliest available slot.
Dr.S.Venkatesan MD 