Diagnostic Testing

    .

    Coronary Artery Disease

    Algorithms

    Source MK_SAP, UpTo Date

    ChronicAnginaDiagnosis.png

     

    Note:

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

    PreTestPobability.png

    • 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.

     

    Test Indications Advantages Limitations
    FUNCTIONAL
    Exercise ECG Initial test for pts with suspected CAD

    Data on:

    - Exercise capacity, BP, HR, 

      and provoked symptoms

    Not useful when baseline ECG is

    abnormal (LVH, LBBB, paced rhythm

    WPW, >1mm ST depressions).

    Stress

    Echocardiography

    When baseline ECG is abnormal

    or when localization of lesion needed

    - Exercise data

    - Wall motion abnormalities

      (exercise induced ischemia)

     

    - Valve function, pulmonary pressures

    - Portable, lower cost than nuclear

    - <1h study

     

    - Cheaper than nuclear

    - Image quality poor insome pts

    (can improve with microbubble

    transpulmonary contrast)

     

    - Difficult to interpret if has baseline

     WMA (hard to see changes in 

     exercise)

     

    - Accuracy drops with single-vessel

      disease or delayed stress image

      acquisition. 

    Nuclear SPECT

    perfusion

    - When baseline ECG abnormal

    or when localization needed.

    - With LBBB, conduction delay in

     septum may cause false-positive

     abnormality (can improve with

     vasodilator stress)

    - Technetium has less attenuation and

      superior images to thallium.

    - Thallium used for rest and technetium

      for stress images (shorter test)

    - If improved penetration is needed

      can use technetium for rest and stress

      but need adequate washout between

      injections (longer test)

    - Attenuation artifacts by breast tissue

      or diaphragm interference.

     

    - Radiation exposure (more than

      regular CT), but less than coronary

      angiogram

    PET/CT

    - Best perfusion images in larger

      patients

    - Data on myocardial perfusion and

      function.

    - Study duration is shorter and radiation

      dose is lower than conventional 

      nuclear perfusion imaging.

    - Absolute myocardial blood flow can 

      be measured

    - Can be combined with CAC scoring

    - Not widely available

    - More expensive than other imaging

    - ONLY used with pharmacologic 

      stress (no exercise protocol)

    - Radiation exposure (less)

    ANATOMICAL

    Coronary

    Angiography

    - Definitive diagnosis of CAD and 

      severity

    - Revascularization can be performed

      right after diagnosis

    - Invasive

    - Risk of vascular access and radio

      contrast exposure (kidney injury,

      allergy, etc..)

    - Radiation exposure

    CAC Testing

    Coronary Artery

    Calcium Testing

    (think of it as

    hsCRP)

    - Screening test (Asymptomatic pts

      at intermediate CAD risk)

    - Predictive of CV events in future.

    - No data on coronary narrowing.

    - Radiation exposure

    Coronary CT

    aka CT angio

    (Some ED docs

    use to quickly

    check for CAD)

    - Identifies/characterizes

      coronary artery disease

      non-invasively

    - Useful for some pts with

      intermediate CAD risk.

    - Coronary vessel lumen and 

      atherosclerotic lesions can be 

      visualized in detail.

    - Requires high-res (64 slice) CT

    - Poor imaging of distal vessel 

      anatomy

    - Pts with prev severe disease or

      prev stent, hard to see through these

    - Need inhalation breath hold, gated 

    (less effective afib), needs B-blockade

    for low HR.

    - Cath still needed for intervention

    - Radiation and dye exposure

      (like in coronary angiography)

    CMR Imaging

    Cardiac MRI

    - Gadolinium-enhanced images

      identify viable and infarcted

      myocardium

    - Identifies anomalous coronaries.

    - More accurate test of myocardial

      viability

    - Claustrophobia in some pts.

    - May be contraindicated in pts with

      pacemaker, ICD, or other implanted

    - Gadolinium contraindicated in renal

      failure

    - Sinus rhythm and slower HR needed

    - Limited availability and expertise

    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.
    Test Indications Advantages Limitations

    Dobutamine

    Echocardiography

     

    (B1 agonist causes

    higher oxygen demand

    increasing HR and LV

    contractility)

     

    - Pts who cannot exercise

    - When need to localize the area

      of myocardium at risk.

    - Images acquired continuously

      Can stop test if ischemia found

    - Dobutamine contraindicated in:

      Severe Baseline Hypertension

      Arrhythmias

     

    - B-blockers must be withheld before

      the test

    Dobutamine

    Nuclear Perfusion

     

    (Dobutamine induces

     changes in myocardial

     oxygen demand - perfusion

     abnormalities are

     uncovered in territories)

    - Pts who cannot exercise

    - When need to localize the area

      of myocardium at risk

    - Diagnostic accuracy equivalent

      to echo

     

    - Preferred when echo image quailty

      is suboptimal.

    - Dobutamine contraindicated in:

      Severe Baseline Hypertension

      Arrhythmias

     

    - B-blockers must be withheld before

      the test

     

    - Radiation Exposure

    Vasodilator Nuclear

    Perfusion

    (Adenosine, Dipyridamole,

    Regadenoson aka Lexi)

    - Recommended in pts who 

      cannot exercise and have 

      contraindications to dobutamine

     

    - With LBBB, a conduction delay

      in the septum can cause false-

      positive abnormality.

      This can be improved with

      vasodilator stress.

    - Late reperfusion imaging allows

      evaluation of myocardial viability

    - Contraindicated in:

      Bronchospastic airway disease

      Theophylline use

     

    - Caffeine must be withheld 24hrs

      before the test.

     

    - Adenosine is contraindicated in

      Sick sinus syndrome and

      High Degree AV Block

     

    - Adenosine or dipyridamole may

      cause chest pain, dyspnea,

      or flushing.

    PET/CT (see above)      

     

    Complications

    • Vascular Access (i.e. angiogram)
      • Vascular access complications (femoral artery).
      • AV fistula (often small, often just observe)
        • On Px: Look for swelling/tenderness, vascular bruits.
      • Pseudoaneurisms
        • On Px: Look for swelling/tenderness, bruits.
        • If >1cm in size, can inject thrombin into narrow neck to occlude pseudoaneurism by IR to shrink it.
        • OR Ultrasound guided compression, but much more painful.
      • Retroperitoneal bleed
        • Due to vessel trauma, bleeding.
        • Pt describes flank/abdo discomfort, hemodynamic instability.
        • Most self-terminating, rare require vascular surgery. (discontinue anticoagulation!)
        • Diagnose with non-contrast abdo CT.

    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.

     

    Stress Imaging

    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)

     

    • NuclearExample.png
    • 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.

    Comparison

    • Diagnostic Test

      in dx of CAD

      Sensitivity Specificity Number of Pts

      Number of Studies

      (meta-analysis)

      Exercise ECG 68% 77% 24,074 132
      Nuclear SPECT perfusion 88% 77% 628 8
      Stress Echocardiography 76% 88% 1174 10
      PET Stress 91% 82% 206 3

     

    Visualizing Coronary Anatomy

    • Modalities for visualizing coronary anatomy:
      • Conventional Angiography
      • CT Angiography
        • Preferred if suspicious of: Aortic dissection, PE.  (Called "triple rule-out")
          • However to rule out all three need a high contrast load and high radiation dose.
      • CMR (Cardiac MRI Imaging)
    • Ongoing studies: Unclear if functional studies or anatomical studies are better as initial test.

     

    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
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