Optimizing the Diagnostic Workflow for Stress ECG
Stress tests (ST) are a common and accessible method for diagnosing and examining patients with cardiovascular diseases. Physical stress tests are conducted to diagnose coronary pathology, detect hidden heart rhythm and conduction disorders, determine the level of physical performance (tolerance to physical exertion), and monitor the effectiveness of treatment and rehabilitation measures.
Research protocol
1) On a bicycle ergometer – start with a load of 50 W, and for patients diagnosed with coronary heart disease or reduced physical activity – with 25 W; increase the load by 25 W every 3 minutes;
2) On a treadmill – according to various load protocols that differ in speed and incline of the moving belt. The Bruce protocol is most commonly used – table 25.1-2. In older individuals and patients with heart failure or arterial hypertension, easier protocols should be used (slight increase in load every 1-2 minutes), allowing to extend the physical exertion time to 8-12 minutes. A short warm-up is recommended before performing the stress test.
Doubtful Result
Doubtful result upsloping ST-segment elevation ≥1 mm at 60-80 ms from the J point.
In individuals with ST-segment depression already during resting recording, ST depression measurement on the ECG during stress should be performed relative to the initial ST position, not relative to the PQ segment. However, in individuals with ST-segment elevation during resting recording, the reference point is the PQ segment, not the initial ST displacement.
Right bundle branch block does not affect the interpretation of stress ECG except for leads V1-V3 (ST-segment depression in these leads has no diagnostic value). On the other hand, left bundle branch block, as well as pre-excitation syndrome (preexcitation syndrome), does not allow reliable interpretation of stress test results.
False-Positive Results
Causes of false-positive results relative to coronary angiography
1) False-positive result – myocardial ischemia due to other causes, not caused by coronary artery stenosis – section 2.5, mitral valve prolapse syndrome, anemia, hypothyroidism, treatment with cardiac glycosides, hypokalemia, ST-segment depression on standard ECG of various etiologies;
2) False-negative result – suboptimal physical exertion, stenosis of only one coronary artery, left anterior fascicular block, right ventricular hypertrophy, effect of pharmacological agents (e.g., β-blockers, phenothiazine derivatives).
Often, despite the above criteria for weakly positive and doubtful tests, a novice doctor cannot clearly distinguish these situations. In any case, if there is a non-standard test result, it makes sense to print out as many fragments as possible in various graphical representations of the program.
The test is not informative if the patient has not reached the target (submaximal) heart rate in the absence of diagnostically significant ECG dynamics. In various publications, it is recommended to focus on 75% or 85% of the maximum allowable heart rate for a given age as the submaximal heart rate.
During the stress period, the threshold value is automatically displayed next to the actually achieved heart rate in the program’s working window, so the doctor does not need to calculate anything before conducting the test.
In modern systems, before conducting a stress test, the doctor can manually enter the threshold heart rate value or choose a formula from which it will be calculated from those offered by the program. Other important point that should not be forgotten after the test. If the doctor cannot give a clear answer to most questions (tolerance, presence of ischemia, reaction to stress, and registration of rhythm disturbances), it is worth thinking about the correctness of preparing the patient for stress testing.
Patient preparation
- It is necessary to inform the patient to
1) not eat food or smoke tobacco for 3 hours before performing the test;
2) not perform significant physical exertion for 12 hours before the test.
- If the purpose of the test is to confirm or exclude coronary heart disease, it is necessary, as far as possible, to discontinue medications that may complicate the interpretation of stress test results (especially β-blockers). If the study is performed for risk stratification in patients with coronary heart disease, there is no need to discontinue medications.
- It is necessary to carefully collect the anamnesis, examine the patient, and record a standard ECG to ensure that there are no contraindications for conducting the test.
At Norav Medical, our strategy is shaped by several components, including professional excellency and dedication. Yet, the main of these is patient-centricity. We believe that providing a positive experience for patients is important because it allows patients to feel cared for. And as we see, there are often cases when this experience can influence and optimize the entire ECG diagnostic process.
References
Henzlova, M. J., Cerqueira, M. D., Mahmarian, J. J., & Yao, S. S. (2006). Stress protocols and tracers. Journal of Nuclear Cardiology, 13(6), e80-e90.
Kansal, S., Roitman, D., & Sheffield, L. T. (1976). Stress testing with ST-segment depression at rest. An angiographic correlation. Circulation, 54(4), 636-639.
Qamruddin, S. (2016). False-positive stress echocardiograms: a continuing challenge. Ochsner Journal, 16(3), 277-279.