Examkin

Question

Difficulty: Very hardDiagnostic Workup and Test Sequencing

A 68-year-old man comes to the clinic for evaluation of a 2-month history of episodic retrosternal chest pressure. The discomfort occurs reliably when he jogs or climbs more than two flights of stairs and resolves within 5 minutes of rest. He has a history of type 2 diabetes mellitus, hypertension, and mild knee osteoarthritis. His medications include metformin, amlodipine, and lisinopril. He is physically active and states that his joint pain does not limit his ability to exercise. Vital signs are within normal limits. Cardiopulmonary examination is unremarkable. A resting 12-lead electrocardiogram demonstrates normal sinus rhythm with a QRS duration of 140 milliseconds, broad notched R waves in leads I, aVL, V5, and V6, and deep S waves with ST-segment elevation in leads V1 and V2. Which of the following is the most appropriate next step in the diagnostic workup of this patient?

  1. A
    Exercise electrocardiography
  2. B
    Exercise echocardiography
  3. C
    Exercise myocardial perfusion imaging
  4. Pharmacologic vasodilator myocardial perfusion imagingAnswer
  5. E
    Coronary angiography

Answer

Pharmacologic vasodilator myocardial perfusion imaging
The correct answer is pharmacologic vasodilator myocardial perfusion imaging. The patient presents with symptoms typical of stable angina and requires diagnostic stress testing to evaluate for coronary artery disease. The baseline electrocardiogram reveals a left bundle branch block (LBBB), characterized by a widened QRS complex, broad lateral R waves, and deep precordial S waves. In the presence of LBBB, standard exercise electrocardiography cannot be interpreted for ischemia due to baseline ST-segment and T-wave abnormalities. Furthermore, an elevated heart rate (via physical exercise or dobutamine) in a patient with LBBB frequently produces an artifactual, false-positive reversible septal perfusion defect on myocardial perfusion imaging, and causes paradoxical septal motion that confounds stress echocardiography. Therefore, even if the patient is physically capable of exercising, the optimal noninvasive test for a patient with LBBB is a pharmacologic stress test using a vasodilator (e.g., adenosine, dipyridamole, regadenoson) coupled with myocardial perfusion imaging. Vasodilators induce coronary hyperemia without significantly increasing the heart rate, thereby circumventing the tachycardic-induced septal artifacts associated with LBBB.

Step-by-Step Solution

1
Analyze the patient's clinical presentation.
The patient has stable exertional chest pain relieved by rest, which is highly suspicious for stable ischemic heart disease (angina pectoris).
Establishing the pre-test probability of coronary artery disease is the fundamental first step in deciding on the need for diagnostic testing.
2
Evaluate the patient's baseline electrocardiogram (ECG).
The ECG findings (QRS > 120 ms, broad R in lateral leads, deep S in right precordial leads) are diagnostic of a left bundle branch block (LBBB).
The baseline ECG determines whether standard exercise stress testing can be interpreted accurately.
3
Determine the optimal stress testing modality based on the patient's exercise capacity and ECG findings.
Although the patient can physically exercise, the presence of a baseline LBBB invalidates standard exercise ECG and severely confounds both exercise echocardiography and exercise myocardial perfusion imaging. Therefore, a pharmacologic vasodilator stress test is required.
In patients with LBBB, increased heart rates during exercise cause delayed septal activation and impaired diastolic filling, leading to false-positive septal perfusion defects on imaging. Vasodilators avoid this tachycardic response.

Key Concept

In patients with suspected stable ischemic heart disease who have a baseline left bundle branch block (LBBB), pharmacologic vasodilator myocardial perfusion imaging is the most appropriate initial diagnostic test, regardless of the patient's physical ability to exercise.
Rate this question

Topics

Diagnostic Workup and Test Sequencing

More questions from this topic