7.1 Diagnostic Cardiac Catheterization & Coronary Angiography Interpretation

Clinical Indications for Cardiac Catheterization

Diagnostic cardiac catheterization is the definitive invasive gold standard for evaluating coronary artery disease (CAD), valvular heart disease, myocardial disorders, pulmonary hypertension, and congenital heart defects. It is broadly categorized into Right Heart Catheterization (RHC) and Left Heart Catheterization (LHC).

Right Heart Catheterization (RHC)

• Access Routes: Central venous access via the Right Internal Jugular, Subclavian, or Femoral vein.
• Diagnostic Scope: Measures Right Atrial, Right Ventricular, Pulmonary Artery, and PAOP pressures; quantifies Cardiac Output/Index via thermodilution or Fick principle; calculates Pulmonary Vascular Resistance (PVR); and assesses left-to-right intracardiac shunts via oxygen saturation runs.
• Primary Indications: Unexplained pulmonary hypertension, heart failure evaluation for mechanical circulatory support or cardiac transplantation, severe valvular heart disease, and cardiogenic shock management.

Left Heart Catheterization (LHC)

• Access Routes: Percutaneous arterial access via the Radial Artery (transradial approach, preferred) or Femoral Artery (transfemoral approach).
• Diagnostic Scope: Evaluates epicardial coronary artery anatomy via selective contrast injection (Coronary Angiography); measures Left Ventricular Systolic and End-Diastolic Pressures (LVEDP); measures aortic valve pressure gradients; and performs Left Ventriculography to calculate Left Ventricular Ejection Fraction (LVEF) and identify regional wall motion abnormalities (akinesis, hypokinesis, dyskinesis).
• Primary Indications: Acute Coronary Syndromes (emergent for STEMI, urgent for high-risk NSTEMI/UA), stable angina refractory to medical therapy, positive non-invasive stress testing, and preoperative evaluation prior to major cardiac surgery.

Coronary Anatomy and Angiographic Lesion Interpretation

Accurate interpretation of coronary angiograms requires familiarity with epicardial coronary anatomy and standard nomenclature.

Primary Coronary Architecture

• Left Main Coronary Artery (LMCA): Arises from the left aortic sinus of Valsalva and bifurcates into the LAD and LCx. Clinical Significance: Provides blood supply to over 75% of the left ventricular myocardium. Stenosis ≥ 50% is considered critical, carrying high mortality and indicating Coronary Artery Bypass Graft (CABG) surgery.
• Left Anterior Descending (LAD): Courses down the anterior interventricular groove, giving off Septal perforator branches (supplying the anterior 2/3 of the interventricular septum and bundle branches) and Diagonal branches (D₁, D₂) (supplying the anterior free wall of the LV).
• Left Circumflex (LCx): Courses along the left atrioventricular groove, giving off Obtuse Marginal branches (OM₁, OM₂) supplying the posterolateral LV wall.
• Right Coronary Artery (RCA): Arises from the right aortic sinus, supplying the RV free wall, SA node (60%), and AV node (90%). Gives off Acute Marginal branches and branches into the Posterior Descending Artery (PDA) and Posterolateral Branch (PLB) in right-dominant circulation.
• Coronary Dominance: Determined by which vessel gives rise to the PDA. Approximately 85% of individuals are Right-Dominant (PDA arises from RCA), 10% are Left-Dominant (PDA arises from LCx), and 5% are Co-Dominant (PDA supplied by both RCA and LCx).

Angiographic Stenosis Grading and TIMI Flow

• Diameter Stenosis Grading: Expressed as percentage narrowing of vessel lumen diameter compared to adjacent normal reference segments:

  • Mild: <40% stenosis.
  • Intermediate: 40% to 69% stenosis (requires physiological testing).
  • Severe / Obstructive: ≥ 70% stenosis (or ≥ 50% for LMCA).
  • Critical: ≥ 90% stenosis.
  • Total Occlusion: 100% stenosis.

• Thrombolysis in Myocardial Infarction (TIMI) Flow Grade Classification:

  • TIMI Grade 0 (No Perfusion): Complete absence of any anterograde contrast flow beyond the point of obstruction.
  • TIMI Grade 1 (Penetration without Perfusion): Contrast passes beyond the occlusion site but fails to opacify the distal coronary vessel bed.
  • TIMI Grade 2 (Partial Perfusion): Contrast opacifies the distal vessel bed, but rate of entry and clearance is distinctly slower than in adjacent normal non-involved arteries.
  • TIMI Grade 3 (Complete Normal Perfusion): Contrast fills and clears the distal coronary vessel bed briskly and completely at normal velocity.

Physiological Lesion Assessment and Intravascular Imaging

Anatomical luminal stenosis seen on 2D angiography does not always correlate with functional ischemia. Invasive physiological and intravascular imaging modalities provide essential diagnostic clarification.

Fractional Flow Reserve (FFR) and Instantaneous Wave-Free Ratio (iFR)

• Fractional Flow Reserve (FFR): Evaluates the functional hemodynamic impact of intermediate coronary stenosis. A sensor-tipped pressure wire is advanced distal to the lesion. Maximal hyperemic microvascular vasodilation is induced by intravenous adenosine infusion (140 mcg/kg/min). FFR is calculated as the ratio of mean distal coronary pressure (Pd) to mean aortic pressure (Pₐ) during peak hyperemia: $FFR = \frac{P_d}{P_a}$
  • Ischemic Threshold: An FFR ≤ 0.80 indicates functional ischemia, justifying revascularization (PCI). An FFR > 0.80 indicates non-ischemic stenosis, safe for medical therapy.
• Instantaneous Wave-Free Ratio (iFR): Measures the Pd/Pₐ ratio strictly during a specific resting diastolic window (the "wave-free period") when microvascular resistance is naturally minimal and constant. It eliminates the need for adenosine administration.
  • Ischemic Threshold: An iFR ≤ 0.89 indicates significant functional ischemia requiring revascularization.

Intravascular Ultrasound (IVUS) vs. Optical Coherence Tomography (OCT)

Pre- and Post-Catheterization Nursing Management

Comprehensive nursing care minimizes procedural complications and ensures early detection of vascular adverse events.

Pre-Procedure Nursing Assessment and Care

1. Renal Function Screening: Review baseline Serum Creatinine and eGFR. Patients with chronic kidney disease (eGFR < 60 mL/min/1.73 m²) or diabetes are at high risk for Contrast-Induced Acute Kidney Injury (CI-AKI).
   • Hydration Protocol: Administer IV 0.9% Normal Saline at 1.0 - 1.5 mL/kg/h for 6 to 12 hours pre-procedure and 6 to 12 hours post-procedure.
2. Contrast Allergy Premedication: In patients with documented prior severe iodinated contrast reactions, administer prophylactic corticosteroids (e.g., Oral Prednisone 50 mg at 13, 7, and 1 hour pre-procedure) and IV H1-blocker (Diphenhydramine 50 mg).
3. Medication Management: Hold oral anticoagulants (Warfarin, DOACs) and Metformin per institutional protocol (Metformin held on day of procedure and 48 hours post to prevent lactic acidosis if CI-AKI develops).
4. NPO Status and Peripheral Pulses: Maintain NPO status for 4-6 hours. Mark baseline distal peripheral pulses (Radial, Brachial, Dorsalis Pedis, Posterior Tibial).

Post-Procedure Access Site Care and Monitoring

• Transradial Access Care:

  • Compression with a dedicated radial hemostatic band (e.g., TR Band). Maintain patent hemostasis (applying minimal pressure necessary to prevent bleeding while maintaining radial artery blood flow).
  • Perform hourly neurovascular checks of the ipsilateral hand (warmth, color, capillary refill, sensation, motor function).
  • Deflate TR band gradually per protocol (removing 2-3 mL of air every 15-30 minutes). Monitor for radial artery occlusion (painless loss of pulse) or hematoma.

• Transfemoral Access Care:

  • Maintain strict bedrest with the affected extremity kept straight (HOB elevated ≤ 30^°). Bedrest duration is 2 to 6 hours depending on whether a vascular closure device (e.g., Angio-Seal, Perclose) or manual compression was utilized.
  • Frequent vital sign and access site assessments (every 15 min × 1 hour, every 30 min × 1 hour, hourly thereafter).
  • Detecting Retroperitoneal Hematoma: A life-threatening complication caused by arterial puncture above the inguinal ligament (above the inferior epigastric artery). Symptoms include flank or back pain, sudden unexplained hypotension, tachycardia, abdominal distension, and dropping hemoglobin without obvious external bleeding. Immediate Actions: Notify operator, order STAT CT scan of abdomen/pelvis, hold manual pressure if access site is involved, administer fluid boluses and blood products.