Exercise ECG With Left Bundle Branch Block
Diane, 62, has had three weeks of exertional breathlessness and fatigue climbing stairs, without chest pain. Her resting ECG shows sinus rhythm at 72 bpm with a left bundle branch block. She takes metoprolol succinate 50 mg daily. She undergoes a Bruce treadmill test and stops at 6:12, achieving 7.0 METs. Heart rate rises from 68 to 118 bpm. Blood pressure is 148/84 at rest and 140/80 at peak. She reports mild breathlessness but no chest pain. The tracing shows 1 mm of downsloping ST depression in V5–V6 and 2 mm of ST elevation in V1.
1. Interpret the test. What do the ECG changes, blood pressure response, and workload mean, and does this count as a positive test?
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This cannot be called a positive test.
- ECG: with LBBB, the ST segment is expected to be discordant to the QRS, so the lateral ST depression and the V1 elevation are consistent with the conduction abnormality itself. Exercise-induced ST changes in LBBB are not reliable markers of ischemia, and the Duke treadmill score was not validated in this population. Sgarbossa criteria apply to acute injury, not to exercise testing.
- Blood pressure: a peak of 140/80 after a rest value of 148/84 means systolic pressure did not rise meaningfully with workload. A failure to rise, or a fall, is an abnormal response and is also a criterion for stopping; the test should have been terminated rather than pushed further.
- Workload: 7 METs is a reasonable functional capacity and makes her a candidate for an exercise-based imaging study.
- Symptoms: breathlessness without chest pain is nonspecific but does not exclude ischemia.
The correct conclusion is that the ECG is nondiagnostic, the blood pressure response is abnormal, and further evaluation is needed.
2. What is the most appropriate next step, and how would you justify it to the referring physician?
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Refer for stress imaging rather than relying on the exercise ECG. Exercise stress echocardiography or exercise myocardial perfusion imaging allows regional wall motion or perfusion to be assessed despite LBBB; if she cannot exercise adequately, pharmacologic stress imaging (e.g., vasodilator perfusion) is appropriate. In a patient with a nondiagnostic ECG, imaging is what adds diagnostic value.
The justification to the physician should state: (1) LBBB makes ST-segment interpretation for ischemia invalid; (2) the systolic blood pressure failed to rise with workload, which is an abnormal response and a reason for concern; (3) she achieved 7 METs, so exercise-based imaging is feasible; (4) her symptoms are new and exertional. Also note that metoprolol blunts her heart-rate response, so 118 bpm does not represent a maximal effort by heart rate alone.
3. What would you document as the reason for stopping and the limitations of this study?
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Document that the test was stopped for an inadequate systolic blood-pressure response (148/84 to 140/80) plus breathlessness, and explicitly record that the ECG was uninterpretable for ischemia because of LBBB. Note the beta-blocker, the peak workload and MET level, the symptom description, and the heart-rate response.
State the limitations plainly: no reliable ST-segment assessment, no valid Duke score, and submaximal effort by heart-rate criteria. Recommend imaging-based stress testing. This documentation protects the patient and communicates clearly to the next clinician; calling it "positive" or "negative" would both be wrong.