Table of contents
- 1. Coronary Artery Disease
- 1.1. Algorithms
- 1.2. Imaging Techniques
- 1.3. Pharmacological Stress
- 2. Complications
- 3. Stress Imaging
- 3.1. Exercise EKG
- 3.2. Stress Echocardiogram
- 3.3. MIBI
- 3.4. Viability
- 3.5. Nuclear Tracers
- 3.6. Vasodilator Agents
- 4. Comparison
- 5. Visualizing Coronary Anatomy
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Coronary Artery Disease
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.
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.
- Vasodilator (like 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)
- Risk Factors:
- 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).
- Exercise Testing:
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
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Adenosine
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No caffeine 24hrs prior. (controversial)
-
Methylxanthines are adenosine antagonists, concern still there.
-
-
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Dipyridamole
-
Regadenoson (aka Lexi)
-
Better safety profile.
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Comparable diagnostic features as adenosine, with less side-effects.
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Often given same caffeine restriction as adenosine.
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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.
- Preferred if suspicious of: Aortic dissection, PE. (Called "triple rule-out")
- 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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