Post #22: Diagnostic testing for Coronary Artery Disease - Part 2

In the previous post (#21), I introduced the concept of pre-test probability (PTP) and when an exercise treadmill test (ETT) should be considered as the initial study instead of an imaging cardiac test.  In addition to PTP, there are other clinical factors that would support NOT doing an ETT and instead performing an imaging stress test, such as inability to walk on a treadmill.  In this post, I will continue the discussion on ETT vs. MPI in both asymptomatic and symptomatic patients.

 Is Stress ECHO an option?

Although stress ECHO can be performed without exercise, traditionally this test is done while walking on a treadmill or using a stationary bicycling.  Dobutamine can be substituted for physical exercise but because of side effects, this chemical stress test is less commonly performed. MPI can be performed with exercise or with chemical stimuli, but many are performed with iv adenosine or regadenoson because physical exercise is impossible. Stress ECHO may be a better choice over MPI if the patient has dyspnea, as ejection fraction is part of the findings.

How to tell if the ETT is interpretable?

In order for an ETT to be interpretable, the test must achieve a target double product: (heart rate X systolic blood pressure).  Some patients may be taking medications (beta blockers or calcium channel blockers) that keep blood pressure or heart rate low (<50) and thus are unable to increase to the target rate with exercise.  Expressing concerns that a double product may be unattainable may result in approval of a stress ECHO or MPI for patients with less than high PTP. Patients with uncontrolled hypertension (systolic BP>180) should not have a stress test until the BP can be controlled.

All patients with chest pain should have a resting ECG regardless of the type of pain. Rarely, some patients with high pretest probability (PTP) and with new abnormal ECG changes may be candidates for immediate angiographic studies.  Others with high pre-test probability can obtain approval for a stress ECHO or MPI.

What ECG findings would render the ETT un-interpretable?

Patients with a low PTP with certain findings on resting ECG may be deemed un-interpretable for an ETT, and thus would still be candidates for a stress ECHO or MPI rather than initial ETT.  These include:

·      Complete LBBB

·      Pre-excitation pattern such as Wolff-Parkinson-White

·      Ventricular paced rhythm

·      Significant arrhythmia (especially ventricular)

·      ST depression (greater than 1 mm)

·      LVH plus repolarization abnormalities

·      T wave inversion in inferior or lateral leads

·      Digitalis treatment

Are there other criteria that would allow an imaging stress test rather than ETT? If any of the following conditions exist, ETT should not be performed.

·      A history of definite CAD (stent, CABG, or prior testing positive for CAD such as cardiac catheterization or CCTA) frequency of imaging discussed in post #24)

·      Coronary Calcium score > 100.

·      Continued chest pain despite a negative ETT in the recent past with suspicion of a false negative ETT.

·      A recent ETT that was equivocal, borderline, or abnormal.

·      Age 40 or greater and known diabetes mellitus

·      True syncope

·      Elevated troponin

·      To assess for CAD before starting a Class IC arrhythmia drug (flecanide or propafenone) and annually while taking the drug.

Lesson #22 Patients with past history of CAD, past revascularization, or a high pre-test probability may have imaging stress tests approved without performing ETT as their initial study. Those with intermediate, low or very low pre-test probability who can physically walk on a treadmill and whose ECG is interpretable for an ETT, should have a non-imaging stress test initially.  As in all cases of prior authorization, the patient’s clinical criteria that supports imaging studies must be clearly communicated to the radiology benefit managers in order to obtain quick approval.

The next two postings will discuss

·      pre-surgical cardiac testing and

·      testing after revascularization.