Diagnostic Testing in Cardiology

I. Foundational Principles of Diagnostic Testing

The document begins by establishing the "diagnostic cornerstone" of CVD as the "clinical history and physical examination." This initial assessment is critical for ensuring a "focused and appropriate diagnostic evaluation." Subsequent cardiovascular testing serves both "diagnostic and prognostic information," and its application should be judicious, considering:

• Symptoms: The patient's reported symptoms.
• Pretest likelihood of disease: The probability of disease before testing.
• Impact on patient management: Whether test results will change treatment strategies.
• Shared decision-making: Collaboration between clinician and patient.

II. Diagnostic Testing for Atherosclerotic Coronary Artery Disease (CAD)

Diagnostic tests for CAD are broadly categorized into those providing functional evidence (ischemia, blood flow, wall motion abnormalities) and anatomic information (atherosclerotic burden).

A. Functional Studies (Detection of Ischemia and Blood Flow)

These studies reveal the presence, extent, and severity of ischemia.

• Exercise ECG:
• Utility: "Reasonable initial diagnostic test in patients suspected of having CAD." Less accurate than stress testing with imaging.
• Advantages: Provides data on "exercise capacity, blood pressure and heart rate response, and provoked symptoms."
• Limitations: "Not useful when baseline ECG is abnormal (LVH, LBBB, paced rhythm, preexcitation, >1-mm ST-segment depression)."
• Prognostic Value: "Exercise capacity is a powerful predictor of outcomes," with individuals unable to achieve 5 metabolic equivalents (METs) or the first stage of a Bruce protocol having "higher all-cause mortality." Heart rate recovery (drop of <12/min in the first minute post-exercise) is also associated with higher mortality.
• Stress Echocardiography:
• Utility: "Effective diagnostic test option for patients suspected of having CAD." Recommended when baseline ECG is abnormal or specific myocardial area information is needed.
• Advantages: Combines "exercise data acquired along with wall motion images to assess for ischemia," allows evaluation of "valve function and pulmonary pressures," "relatively portable and less costly than nuclear protocols," and "entire study is completed in <1 h."
• Limitations: "Image quality is suboptimal in some patients," "image interpretation is difficult when baseline wall motion abnormalities are present," and diagnostic accuracy decreases with single-vessel disease or delayed image acquisition.
• SPECT Myocardial Perfusion Imaging (MPI) / Nuclear Stress Testing:
• Utility: "Effective diagnostic test option for patients suspected of having CAD." Recommended with abnormal baseline ECG or need for specific myocardial area information.
• Advantages: Gating and attenuation correction improve specificity. Late reperfusion imaging can assess myocardial viability with thallium.
• Limitations: "Attenuation artifacts can be caused by breast tissue or diaphragm interference." LBBB may cause false-positive septal abnormalities. Involves "Radiation exposure."
• Viability Testing: Regions with fixed defects can be infarct or hibernating myocardium; viability assessment (e.g., thallium or dobutamine echo) helps differentiate.
• Cardiac PET/CT:
• Utility: "Provides best perfusion images in patients with perfusion, function, and viability."
• Advantages: "Study duration is shorter and radiation dose is lower than SPECT stress only," "absolute myocardial blood flow can be measured," and "can be combined with CAC scoring."
• Limitations: "Not widely available," "more expensive than SPECT," and involves "Radiation exposure."
• Cardiac Magnetic Resonance (CMR) Imaging:
• Utility: Assesses "wall motion abnormalities during dobutamine infusion" and "perfusion abnormalities during adenosine infusion." Identifies "anomalous coronary artery origin."
• Advantages: "Provides excellent spatial resolution," "accurate test for myocardial ischemia or viability," and provides data on "infarction and viability using gadolinium contrast."
• Limitations: "Some patients experience claustrophobia," "may be contraindicated in patients with an older pacemaker, ICD, or other implanted device," certain gadolinium agents are contraindicated in CKD, "sinus rhythm and a slower heart rate are needed for improved image quality," and "limited availability and expertise."

B. Anatomic Information (Atherosclerotic Burden)

These studies visualize the coronary arteries.

• Coronary Angiography (Invasive):
• Utility: "Provides anatomic diagnosis of the presence and severity of CAD."
• Advantages: Allows "evaluation of coronary anatomy with functional assessment of coronary stenosis (FFR, IFR)" and "Percutaneous revascularization can be performed after diagnostic study."
• Limitations: "Invasive," with risks associated with "vascular access and radiocontrast exposure (kidney dysfunction, allergy, bleeding)," and "Radiation exposure."
• FFR/IFR: "Measures the hemodynamic significance of a lesion and helps determine the need for intervention."
• Coronary CT Angiography (CTA):
• Utility: "Useful for patients with intermediate risk for CAD, particularly in patients aged <65 y." Also used for "acute chest pain in the emergency department" in select cases.
• Advantages: "Identifies anomalous coronary arteries," and "coronary artery vessel lumen and atherosclerotic lesions can be visualized in detail."
• Limitations: Requires high-resolution CT, "does not provide detailed images of distal vessel anatomy," "Catheterization will be needed if intervention is planned," and involves "Radiation and radiocontrast exposure."
• PROMISE trial: Showed low composite cardiovascular event rates and similar outcomes at 2 years for initial CTA vs. functional testing in intermediate pretest probability patients.
• Coronary Artery Calcium (CAC) Scoring:
• Utility: "May inform preventive treatment decisions for patients with intermediate or borderline 10-y risk for cardiovascular events."
• Advantages: "CAC scores are predictive of cardiovascular risk in selected patients."
• Limitations: "Does not provide data on coronary luminal narrowing," and involves "Radiation exposure."
• Interpretation: Scores categorized as 0 (no disease), 1-99 (mild), 100-400 (moderate), >400 (severe). Absence of CAC is associated with low cardiovascular event risk.

C. Cardiac Stress Testing General Considerations:

• Pretest Probability: Stress testing is most effective in patients with an "intermediate pretest probability of CAD (10% to 90%)."
• Exercise Preference: "Stress testing to evaluate for CAD should always be performed with exercise unless exercise is contraindicated or the patient is unable."
• Medication Management: Cardiac medications may be withheld before testing to achieve adequate h...