Diagnostic Testing

Algorithms

Source MK_SAP, UpTo Date

Note:

• PreTest probability is dependent on a number of risk factors:
• Age, Gender, type of chest discomfort, other RF's.

• Source: Gibbons RJ, Abrams J, Chatterjee K, et al. ACC/AHA 2002 guideline update

Imaging Techniques

• Exercise ECG is recommended for patient with suspected CAD. (preferred b/c gives functional information)
• Exercise patients to get HR up to >85% of predicted maximum.

Pharmacological Stress

• Pharmacologic agents can be used to induce perfusion abnormalities.
• Lexiscan (Regadenoson)
  • Vasodilator (like Adenosine)
    • Less S/E than adenosine (less chest discomfort, less bronchial constriction)
  • Nuclear SPECT, but lexiscan refers to the pharmacologic agent used detect perfusion abnormalities.
  • Similar to adenosine without the side-effects of adenosine.

Contrast Induced Nephropathy

• Radiation Exposure: Nuclear Spect >> CT Angio (high resolution)
• Iodine-based contrast agents: AKI (2%)
  • Risk Factors:
    • Contrast load
    • Pre-existing CKD
    • DMII
    • Dehydration / Volume depleted
  • Reduce risk:
    • ***Hydration (before + after procedure)*** - Most proven way to reduce risk.
    • Low osmolar contrast
    • Protocols to reduce contrast load (avoid ventriculogram etc..)
    • Pre-treatment with NAC (N-acetyl cysteine) aka mucomyst.
      • Controversial: Small study of significant lowering of kidney injury, but very small study.
      • Another publication: reviewed multiple studies --> neutral effect.
      • Often used (i.e. in Duke) because risk is small feels like doing something.  Also often used if cannot give fluids (i.e. CHF)
• Cholesterol emboli is another way to cause AKI in patients with endovascular catheter manipulation. (uncommon)
  • Classically: see pt after cath with modeled skin in legs or purple toes.
  • Associated with urine and peripheral eosinophilia.
  • Supportive therapy, improves over time.

Exercise EKG

• Stress imaging is best done for patients with intermediate pre-test probability to reclassify patients to a low risk or high risk post-test probability.
• Exercise patient until HR is >85% of predicted maximum (220-patientAge)
• Two strongest determinants of myocardial oxygen demand are HR and BP called Rate-Pressure product.
  • In setting of exercise, both are elevated --> increased myocardial oxygen demand, which may provoke abnormalities.
• Exercise also gives you information on exercise tolerance etc...
• B-Blockers and non-dihydropuridine CCB can prevent reaching target HR.  Need to hold for 1-2 days prior to test.
  • Sometimes exercised on medications to see if they improved on meds.
• Worse outcomes:
  • Poor exercise capacity (best prognosis with good capacity, even if has CAD than those with poor capacity)
  • Propagation of angina
  • Hypotension during exercise
  • Chronotropic incompetence (rate does not rise)
  • Ischemia at low work loads
• If cannot get to target heart rate: called "ideterminate" or "submaximal" study.

• Not indicated for:
  • If cannot exercise (deconditioning etc.) or has baseline ECG changes--> pharmacologic therapy is indicated.
  • If abnormal baseline EKG (abnormalities limiting analysis of ST segment and risk of false positives- need different modality)
    • LBBB
    • LVH
    • Paced rhythm
    • WPW Syndrome
• Contraindicated in: (Safety)
  • Recent MI in <1mo (or active ischemia)
  • Uncontrolled arrhythmia (i.e. VTach, AFib w/ rapid rate, AV block)
  • Symptomatic severe AS
  • Acute decompensated HF
  • Acute PE
  • Acute aortic dissection
  • Acute systemic illness
• Duke Treadmill Score
  • Duke - group that started CVD database with longest cohorts of pts with CAD
  • Duke Score = Exercise time - 5 x (ST Dev in MM) - 4 x Angina (0, 1, 2)
    • Angina 0 - none
    • Angina 1 - angina but continued exercising
    • Angina 2 - angina caused them to stop exercising
    • Low risk > +5 (5yr survival 97%)
  • Three things used to make a score to prognosticate future risk of CAD events:
    • 1. Degree of ST segment depression
    • 2. Presence/absence of exercise induced angina
    • 3. Exercise duration.
  • Classifies as:
    • Low, Intermediate, High risk groups.
• NOTES:
  • Women have high rate of false positives (estrogen postulated to have digoxin like effect)

Stress Echocardiogram

• Generally lesion has to be more than 70% stenosed in diameter to decreased blood flow during exercise. (minimal detected with stress tests).
  • 90% stenosis to induce ischemia at rest.
• The more significant the lesion and the more lesions (i.e. multi-vessel CAD) --> the better sensitivity.
• However, poor sensitivity in single-vessel or mild disease.
• Prognostic Factors:
  • Exercise Testing:
    • Exercise Duration
    • ST segment changes
    • BP responce during exercise
    • Degree of symptoms.
  • Imaging
    • Amount of LV effected (by WMA or perfusion abnormalities), i.e. multiple areas of ischemia = bad.
    • Resting LVEF
    • Decrease in LV EF during exercise (i.e. dilated, poor LV function).

MIBI

• Using radioactive tracer to check perfusion
• Stress modalities:
  • Exercise
  • Persantine (contraindicated in asthma)
  • Dobutamine
• High-Risk Findings:
  • Large area of ischemia (esp anterior wall)
  • Multiple territory defects (multi-vessel CAD)
  • LV dilation with stress

Viability

• Stress echo and nuclear perfusion imaging studies can look at myocardial viability.
• Viability study finds areas of the heart that have abnormal function, but may still be viable due to chronic ischemia.
  • Suggests that function in that area will improve if reperfusion established.
  • However, new data shows that viability is not associated with better outcomes with revascularization compared to no revascularization... but may be some improvement in wall motion.  Hard to transfer to overall survival benefit.
    • Results of the post-hoc analysis of the STICH trial: Post-revascularization, was viability associated with better outcome?  NO it was not, no mortality difference at 5 years.
    • Never been a randomized trial. (as of 2014)

• 
• 1st row: stress, 2nd row: rest.  Bright areas show areas of normal perfusion.  Top row indicates decreased stress perfusion 4-11 o'clock that refills at rest.  

Nuclear Tracers

• Radioisotopes used for nuclear perfusion imaging tests
• Thallium
  • In myocardium breast tissue and obesity can lead to false positive imaging artifacts due to high photon scatter.
  • Faster washout
  • Can be used for viability
• Technecium (more common now)
  • Newer isotope, less scatter and attenuation, better image quality. 
  • However test may take more time because adequate washout needed between sessions.
    • Sometimes need a two-day study.
  • Only used for perfusion (not viability)

Vasodilator Agents

• Adenosine

  • No caffeine 24hrs prior. (controversial)

    • Methylxanthines are adenosine antagonists, concern still there.

• Dipyridamole

• Regadenoson (aka Lexi)

  • Better safety profile.

  • Comparable diagnostic features as adenosine, with less side-effects.

  • Often given same caffeine restriction as adenosine.

Conventional Angiography

• Mason Stones (pediatric cardiology) accidentally injected coronary artery when trying to inject the aortic valve with contrast.
  • He injected RCA and got a picture of it.
  • Patient went into asystole, he asked the patient to cough, and has rosc. Found this was safe. 
  • Previously angiography was attempted with dogs, and they all died. Did not attempt in humans. 
  • Another person invented the catheter for it, but didn't get a patent  wanted it to be readily available. 
  • Arthur M Vineberg - Vineberg procedure - move LIMA to coronaries. 
  • Rene Favaloro - developed saphenous vein graft.
  • Andreas Gruntzig - first percutaneous angioplasty (1979)
• Visually assessing lesions for stenosis.
• Techniques:
  • Visual Assessment.
  • Endovascular ultrasound
  • Fractional Flow Reserve (FFR) [≤80 = PCI, >80 = optimal med therapy)
  • iFR

CAC (Coronary Artery Calcification Score)

• Associated with high likelihood of CAD and high future CV events.
• However everyone develops calcium in vessels, so age-based cutoffs exist.
• Low specificity, high false positive rate.
• ACC and AHA DO NOT recommend as a screening tool.
  • May be appropriate with intermediate risk (10-20% Framingham score), if prompts more intensive risk factor modifation.

Coronary CT

• Must have HR < 60bpm
• Contrast load