Cardiology

Diagnostic Tests

Initial Tests 

I) Electrocardiogram (ECG):  

Best initial test for chest pain (look for ST changes, arrhythmias). 

• ECG in Different CAD Presentations: 

A) Stable Angina 

• • Normal at rest 

• • May show: 
    
    • Non-specific ST-T changes 
    • LVH, prior MI evidence (Q waves) 
    • Exercise Stress Testing is used to detect ischemia 

B) Unstable Angina (UA) / NSTEMI 

• • ST-segment depression  

• • T-wave inversion 
  • No ST elevation 
    
    • Cardiac enzymes (CK-MB, troponins) help differentiate UA (normal CK-MB, troponins) from NSTEMI (elevated troponin) 

C) ST-Elevation Myocardial Infarction (STEMI) 

• • Persistent ST-segment elevation in two or more contiguous leads 

• • Q waves (develop later) = transmural infarction 

• • Indicates complete coronary artery occlusion → emergent reperfusion needed 

Localizing MI with EKG 

II) Cardiac enzymes (Troponins, CK-MB): 

Cardiac enzymes (biomarkers) are primarily used to diagnose myocardial infarction (MI). When a patient presents with acute chest pain, the goal is to determine if myocardial injury has occurred — which is when cardiac enzymes become essential. 

Are gold standard for myocardial infarction evaluation after initial EKG. 

Key Cardiac Biomarkers 

A) Troponins (I & T) 

Are gold standard for detecting myocardial injury. Highly sensitive and specific for cardiac muscle necrosis. Elevated in NSTEMI and STEMI, but not in unstable angina. 

Serial measurements (typically at 0, 3, and 6 hours) help confirm rising or falling levels → key to diagnosis of acute MI. 

B) CK-MB 

Less specific than troponin; elevated in skeletal muscle injury. 

Preferred to detect reinfarction (second MI within days), as it returns to baseline quicker than troponin. 

C) Myoglobin 

Very early marker; rises before troponin. 

Not specific for cardiac tissue → mostly used to rule out MI early due to its rapid normalization. 

II) Stress Testing: 

Stress testing, in stable patients, identify who may benefit from further testing or revascularization. The types of stress testing are exercise stress testing (EST), stress echocardiography, and nuclear stress test. 

A) Exercise stress test is best for patients with normal resting ECG, low to intermediate   pretest probability, and ability to exercise. 

B) Stress Echocardiography combines exercise or pharmacologic stress with   echocardiography. It detects new wall motion abnormalities during stress (suggesting   ischemia), using dobutamine (increases HR and contractility). Stress echo is useful for patients unable to exercise or those with abnormal baseline ECG. 

C) Nuclear Stress Test (Myocardial Perfusion Imaging) uses radioactive tracers (e.g., technetium-99m, thallium-201) to assess blood flow at rest and stress. Perfusion defects suggest ischemia or infarction. Pharmacologic agents used are: adenosine, regadenoson, dipyridamole (vasodilators). It is useful in baseline ECG abnormalities (e.g., LBBB, LVH) or inability to exercise 

III) Coronary angiography:  

Provides definitive diagnostic evaluation for CAD. Also called cardiac catheterization, coronary angiography is an invasive diagnostic procedure used to visualize the coronary arteries, evaluate the degree of stenosis, and guide management of suspected or known CAD, when diagnosis is unclear after noninvasive testing (equivocal stress test) or when urgent revascularization is needed. 

Therapeutically, it provides Percutaneous Coronary Intervention (PCI) (eg, stenting), Ballon Angioplasty, and assessment for Coronary Artery Bypass Grafting (CABG). 

Additional Testing

• • Complete blood count (CBC)  

• • Comprehensive metabolic panel (CMP) 
  • Lipid panel 

• • Chest X-ray (to rule out alternative causes of chest pain) 

• • ABG if hypoxic 

• • BNP (if heart failure suspected) 

• • Type and crossmatch (in case of cath/blood loss) 

• • Coagulation panel (before anticoagulation or surgery) 

• • Urine drug screen (if young or unclear etiology)