What is the next test for a 55-year-old man with intermittent substernal chest pain, exertional dyspnea, hypercholesterolemia (elevated total cholesterol), and a moderate Atherosclerotic Cardiovascular Disease (ASCVD) risk score?

Pharmacologic Stress Imaging is the Next Test

In this 55-year-old man with exertional chest pain and left bundle branch block (LBBB) on EKG, pharmacologic stress imaging with either nuclear perfusion (SPECT/PET) or stress cardiac MRI is the appropriate next diagnostic test. 1

Why Exercise ECG Testing is Contraindicated

The presence of LBBB on the resting EKG makes standard exercise ECG testing inappropriate for diagnostic purposes, as the ST-segment changes will be uninterpretable regardless of whether ischemia is present. 1 The 2021 ACC/AHA guidelines explicitly list LBBB as a contraindication to exercise ECG for ischemia diagnosis (though it may still assess exercise capacity). 1

Pre-Test Probability Assessment

This patient has:

• Typical exertional substernal chest pain (occurs with exertion and stress)
• Age 55 years, male
• Risk factors: BMI 27 (overweight), total cholesterol 210 mg/dL, ASCVD risk 5.6%

Based on the 2024 ESC guidelines, a 55-year-old man with typical anginal symptoms has a pre-test probability of obstructive CAD around 27%, placing him in the moderate likelihood category (>5%-50%). 1

Recommended Testing Strategy

Primary Options for LBBB Patients:

Pharmacologic stress imaging is mandatory because:

1. Vasodilator stress SPECT (sensitivity 90-91%, specificity 75-84%) 1
2. Vasodilator stress cardiac MRI (sensitivity 67-94%, specificity 61-85%) 1
3. Vasodilator stress PET (sensitivity 81-97%, specificity 74-91%) 1

The 2021 ACC/AHA guidelines specifically note that pharmacologic stress is indicated when LBBB is present, as exercise-induced septal wall motion abnormalities can create false-positive results even with imaging modalities. 1

Why Not CCTA First?

While the 2024 ESC guidelines recommend CCTA as preferred for ruling out obstructive CAD in the moderate pre-test probability range (>5%-50%), 1 the presence of LBBB complicates interpretation. The patient's moderate pre-test probability (approximately 27%) means that:

• An abnormal CCTA would only increase post-test probability to ~40%, requiring sequential functional testing anyway 1
• Functional imaging directly addresses the clinical question of whether his symptoms represent ischemia
• LBBB patients often require functional assessment regardless of anatomical findings 1

Specific Test Selection Algorithm

Choose based on:

1. Vasodilator stress nuclear imaging (SPECT or PET) if:

   • Local expertise available
   • Quantification of ischemic burden needed for revascularization decisions
   • PET preferred if available (superior diagnostic accuracy) 1

2. Vasodilator stress cardiac MRI if:

   • Concern for microvascular dysfunction
   • Need to assess for other myocardial pathology (infiltrative disease, scar)
   • Patient can tolerate MRI environment 1

3. Avoid dobutamine stress as first-line in LBBB due to potential for inducing conduction abnormalities 1

Critical Pitfalls to Avoid

• Never perform exercise ECG alone in patients with LBBB for diagnostic purposes—it provides no useful diagnostic information about ischemia 1
• Exercise stress imaging with LBBB can produce false-positive septal defects due to abnormal septal activation; pharmacologic stress avoids this artifact 1
• Do not assume low ASCVD risk (5.6%) excludes significant CAD—his symptomatic presentation overrides risk score calculations 1

Contraindications to Screen For

Before ordering vasodilator stress testing, ensure patient does not have: 1

• Active bronchospasm or severe COPD (contraindication to adenosine/regadenoson)
• Recent dipyridamole use
• Systolic blood pressure <90 mmHg
• High-grade AV block or severe bradycardia <45 bpm
• Recent caffeine intake (within 12 hours)