When to Test Further When an Exercise ECG Is Inconclusive

Marlene Busko

February 06, 2014

BOSTON, MA — A new study has shed light on which low-risk patients who have inconclusive exercise ECG tests might safely avoid additional downstream imaging tests to detect potential CAD[1].

Patients who were most likely to have a positive finding in subsequent imaging tests were those who had "typical angina symptoms despite having a normal ECG during exercise," senior author Dr Ron Blankstein (Brigham and Women's Hospital, Boston, MA) told heartwire .

On the other hand, "patients who have positive ECG changes with rapid recovery—ie, ECG changes that resolve in less than a minute—almost all of those patients, when they underwent further testing, had negative results as well as an excellent prognosis, which suggests that [they] do not require further testing," he noted.

Among patients with an inconclusive exercise ECG test, being female or younger or having a high exercise capacity or a positive ECG with rapid recovery predicted a greater likelihood that a downstream imaging test would not detect CAD.

"These findings may be used to identify patients who are most and least likely to benefit from additional testing," helping to avoid costly, unnecessary tests, Blankstein and colleagues conclude.

The study was published online February 5, 2014 in the Journal of the American College of Cardiology.

Inconclusive Treadmill Test: What Next?

Current AHA and ACC guidelines recommend exercise treadmill tests to detect ischemic heart disease in patients who can exercise and have a normal baseline ECG. "However, to our knowledge, no data exist on the incidence and results of downstream noninvasive testing after [exercise treadmill testing] in patients without known CAD," the group writes.

They studied 3656 consecutive patients who were referred to one center for CAD evaluation in 2009 and 2010. The patients had an average age of 54, and 46% were male.

The patients underwent exercise treadmill tests where the target heart rate was 85% of the maximum predicted heart rate. Most patients (67.7%) had negative test results, and a few (3.7%) had positive results. Less than a third (28.5%) had inconclusive results, which included:

  • Negative ECG, but with submaximal exercise level.

  • Positive ECG, but reduced specificity due to baseline ECG.

  • Positive ECG with ECG changes that resolved within a minute.

  • Typical angina despite no ECG changes.

  • Inappropriate dyspnea despite no ECG changes.

  • Clinically significant rhythm disturbances.

In the six months following the treadmill test, of the 3656 patients, 332 patients (9.1%) underwent noninvasive imaging and 84 patients (2.3%) had angiography. Of those with follow-up tests, 260 patients (62.4%) had had inconclusive treadmill tests.

The noninvasive imaging tests were mainly nuclear stress tests (81.3%), followed by stress echocardiograms (12%), coronary computed tomography angiography (5%), and stress MRI (2%).

Among the 77 patients who had treadmill tests where ECG recovered rapidly and then had a noninvasive imaging test, no patient had a positive imaging test.

On the other hand, seven of the 33 patients (21%) who had typical angina despite no ECG changes had a positive noninvasive imaging test. "Some could consider 21% to be a relatively small number, but I think that many providers, if they knew a patient has a 21% risk of having obstructive coronary disease, may consider further testing," Blankstein said.

During a mean follow-up of 2.7 years, 76 patients experienced a major adverse cardiovascular event, of whom 47 patients died. The annual rate of major adverse cardiovascular events was 0.2% among those with a negative treadmill test, 1.3% among those with an inconclusive treadmill test, and 12.4% among those with a positive treadmill test.

"Vexing Problem"

In an accompanying editorial[2], Drs Albert J Sinusas and Erica S Spatz (Yale University, New Haven, CT) write that "guidelines recommend that most patients being evaluated for ischemic heart disease  undergo exercise ECG, provided they are able to exercise. Yet despite over three decades of data and experience, the test continues to vex interpreting physicians and referring providers alike."

The exercise ECG test has only a sensitivity of 68% and specificity of 77%, far below the test performance of most other cardiovascular imaging modalities, and "all noninvasive imaging tests are inherently subject to delivering false positive and negative results and cannot be used to verify exercise ECG findings," they point out.

"While the study [by Blankstein and colleagues] adds to the literature regarding the performance of specific exercise ECG findings in detecting disease, there continue to be salient questions about our ability to integrate test findings into calculations of disease probability and decisions around next steps," Sinusas and Spatz write. "Given these limitations, the study's impact may be greatest in identifying areas for improvement."

Blankstein has no disclosures. Disclosures for the coauthors are listed in the paper. The editorialists declare that they have no conflicts of interest.

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