Resting echocardiography

• LV and RV size and function:
  • LV ejection fraction (LVEF) = (LVEDV – LVESV) / LVEDV where LVEDV and LVESV are measured in apical 4 or apical 2 chamber view and calculated by biplane method of disks (modified Simpson’s rule).
  • Regional wall motion (akinesia, dyskinesia, hypokinesia) in coronary distribution may indicate underlying ischemia, infarction, stunning as well as conduction disease, infiltrative disease, Takotsubo’s, or myocarditis.
  • Diastolic dysfunction assessed by (1) measuring mitral inflow indices during early and late ventricular filling and (2) tissue Doppler at myocardium adjacent to mitral annulus during early diastole. Graded as normal, impaired relaxation, pseudonormal, restrictive, and indeterminate.
  • Strain imaging measures myocardial deformation in systole and diastole. Impairments in longitudinal (long-axis) strain patterns are associated with coronary disease, valvular disease and other cardiomyopathy (amyloid, sarcoid, HoCM). Values less than -18% (more negative) are normal, -16 to -18% are borderline, and greater than -16% is impaired.
  • TAPSE (tricuspid annular plane systolic excursion) in M Mode is a measure of RV longitudinal function as a surrogate for RV global function.
• Hemodynamic measurements:
  • Right atrial pressure (RAP) (normal <8mmHg) is estimated by IVC diameter and collapse.
  • Right ventricular systolic pressure (RVSP) (normal <35mmHg) as estimation of pulmonary artery systolic pressure (PASP): measured by regurgitant tricuspid jet with the estimated RAP from the IVC measurement.
  • Left atrial pressure (LAP): see diastolic dysfunction above.
  • LV outflow tract velocity time integral (LVOT VTI) represents stroke volume and is calculated by measuring the LVOT diameter, flow across the outflow tract, and time.
• Valve measurements:
  • Can assess severity of regurgitation or stenosis (mild, moderate or severe).
  • Can assess valve morphology (e.g. bicuspid/unicuspid aortic valve, prolapsing mitral or tricuspid valve).
  • Can identify leaflet vegetations and masses.
• Additional assessments:
  • LV contrast increases sensitivity for LV thrombus and improves resolution in patients with emphysema, chest wall deformities, and obesity. Contrast is used in patients when visualization of 2 or more wall segments is not possible or when there is need to assess for LV thrombus. Contrast is consistent of very small inert microspheres that are small enough to move through capillaries and which enhance ultrasound. They do not have any effect on the kidneys. Contrast is used with caution in those with very large shunts and in pregnant women.
  • Bubble study is when agitated normal saline is injected to assess for intracardiac shunt (e.g. PFO or ASD) or intrapulmonary shunt (e.g. hepatopulmonary syndrome).

Principles of Noninvasive Evaluation for Ischemic Heart Disease

• Stress testing is used:
  • In people with suspected CAD for diagnosis and risk stratification.
  • In people with known CAD (1) to determine if medical therapy is adequate (2) to assess the location and degree of ischemia for revascularization, and (3) when there is a change in clinical status.
• Noninvasive evaluation for obstructive CAD is only useful when the pre-test probability for disease is intermediate (pre-test probability anywhere from 10-75%).
• Contraindications to stress testing can be seen in the table below:

• Stress testing can be categorized along two dimensions:
  • First, there is the “stressor,” which is used to induce increased myocardial stress. Stressors include exercise (treadmill and bike), coronary vasodilators (adenosine, dypridamole, and regadenoson), and inotropes (dobutamine).
  • Second, there is the “detector,” which is used to assess for problems with perfusion.
    • Detectors include EKG, echocardiography, radionuclide imaging (SPECT), PET, and MRI.
    • Generally, imaging (TTE, SPECT or PET perfusion imaging) is added to EKG for (1) patients requiring pharmacologic stress or (2) for those with abnormal EKGs or (3) for patients with known CAD to increase sensitivity and to localize the exact territory of ischemia.
• Coronary CTA is not a stress test and gives structural information only (no functional information) and may have increased sensitivity in women and younger patients. It also may be used in the emergency room setting or those with equivocal tests and lower intermediate pretest probability. CTA is very good at identifying coronary anomalies.

Exercise Stress

• Clinical use:
  • Paired with EKG to detect response to stress.
  • The most common and physiologic type of stress test for diagnosis and risk stratification for patients with known or suspected CAD in patients who have normal EKG.
  • Exercise capacity, ischemic threshold, inducible arrhythmias or pre-excitation, and chronotropic competence (ability to augment HR or BP with exercise) also assessed.
• Progressive increases in workload based on an escalating workload protocol (Bruce is most common) will increase myocardial O2 demand and unmask ischemia. An adequate test will have peak HR of ≥85% predicted maximum heart rate (220-age).
• Hold BB and CCB (48 hours before) unless the goal of study is to assess effectiveness of medical therapy. Do not discontinue other antihypertensives.

Pharmacologic Stress 

• Clinical use:
  • Paired with imaging (TTE, SPECT or PET) to detect response to stress.
  • Patients who are unable to exercise adequately for exercise treadmill testing.
  • Patients who need stress imaging because EKG will not be an accurate detector (LBBB, V-pacing, V-pre-excitation, ≥1mm ST-T changes at rest, LVH, prior revascularization, or taking digoxin).
  • Patients who need imaging to localize ischemia or assess viability.
• Pharmacologic stress agents:
• Coronary vasodilators: adenosine and regadenoson are A2A agonists, dipyridamole blocks reuptake of endogenous adenosine.
  • Response of normal coronaries is 4x vasodilation but decreased vasodilatory reserve in obstructive CAD will cause relative perfusion defect.
  • Multivessel disease can result in balanced ischemia and cause false negatives.
• Contraindications: bronchospasm, hypotension, sick sinus syndrome, high degree AV block.
• Paired only with SPECT or PET imaging, not echocardiography.
  • Avoid caffeine or theophylline use 12 and 48 hours prior to test, respectively.
  • Hold Viagra (24 hours before), Cialis (72 hours before), Nitrates (48 hours before), CCB (48 hours before).
• Inotropes/chronotropes: dobutamine is a β1 and β2 agonist that mimics the effect of exercise.
  • Low dose used in evaluation of myocardial viability and aortic stenosis severity.
  • High dose used in evaluation of CAD.
  • Contraindications: arrhythmia, significant hypertension, LVOT obstruction.
  • Typically paired with echocardiography but can also be paired with SPECT or PET.
  • Hold BB and CCB (48 hours before) unless the goal of study is to assess effectiveness of medical therapy. Do not hold other antihypertensives.

EKG Detector

• Clinical use: paired with exercise stress (treadmill or recumbent bicycle).
• A positive test is ≥1 mm horizontal or down-sloping ST depression in contiguous leads either during exercise or in recovery.
• Chest pain, ventricular arrhythmias, and hypotension with exercise may also suggest presence of CAD.
• Duke treadmill score incorporates exercise duration, ST segment deviation and angina into validated prognostic score:

• False positives: more common in women and patients with baseline ST-T wave abnormalities.
• Discrepant findings between EKG and imaging (if performed) typically require cardiology to review and determine next steps.

Echocardiography Detector

• Clinical use: paired with exercise (recumbent bicycle) or dobutamine stressor.
  • Diagnosis and risk stratification of known or suspected CAD who have uninterpretable ECG or unable to exercise (necessitating pharmacologic stress).
  • Preferred in women of child bearing age and younger individuals to avoid unnecessary radiation.
  • Assess severity of valvular disease, congenital heart disease or pulmonary hypertension.
• Measure regional wall motion, global LV function and wall thickening with stress as an indication of viability (poorer Se/Sp than other viability studies below).
• Limitations:
  • Time delay between exercise and image acquisition for treadmill testing (but not for bicycle or dobutamine where imaging is done during exercise or infusion of stressor).
  • Exercise-induced hypertension can cause false positives.
  • Exercise-induced tachypnea can limit acoustic windows.

Radionuclide Imaging Detector

• Clinical use: paired with vasodilator stressor.
  • Patients with intermediate pretest probability for CAD who require pharmacologic stress (therefore cannot exercise), who have baseline ECG abnormalities (therefore require imaging), and/or have extensive wall motion abnormalities at rest.
  • Assess viability or localize ischemia in patients with known CAD or prior re-vascularization.
• After tracer injection, rest and stress images are detected by SPECT or PET imaging.
• SPECT tracers:
  • Technetium (Tc99m, including sestamibi, tebroxime, tetrofosmin) are most commonly used for perfusion study.
  • Thallium (T1-201) more widely used for viability.
• PET tracers:
  • Rubidium-82 is used for perfusion studies.
  • FDG used to identify hibernating (viable) myocardium.

• Cardiovascular MRI (CMR) can also be used to assess for viability through the use of late gadolinium enhancement techniques.

Coronary CTA

• Clinical use:
  • Acute chest pain with low probability of disease (ER setting).
  • Suspect coronary anomaly.
  • Assess bypass graft patency or if there is a question about graft anatomy.
  • Indeterminate result from functional testing or continued symptoms despite normal stress test.
• Contraindications: contrast allergy, eGFR <30, extensive calcification (will obscure images).
• Patient requirements:
  • Cooperate and hold breath 5-10 seconds.
  • Give beta blocker to achieve HR <60.
• Measures structural (not functional) information only. Coronary stenosis is classified using CAD-RADS score.
  • High negative predictive value for obstructive CAD.
  • Detect nonobstructive coronary plaque, which carries prognostic significance.

When Should my Patient Have Invasive Angiography (LHC)? 

References:

Askew JW, Chareonthaitawee P, Arruda-Olson AM. Selecting the optimal cardiac stress test. UpToDate. Accessed: September 16, 2020

Curfman G, Hillis LD. A New look at cardiac exercise testing. N Engl J Med 2003;348:775-776.

Hillis G, Bloomfield P. Basic transthoracic echocardiography. BMJ 2005;330:1432-1436.

Douglas, Pamela S., et al. "Outcomes of anatomical versus functional testing for coronary artery disease." New England Journal of Me8952dicine 372.14 (2015): 1291-1300.

Fihn SD, Gardin JM, Abrams J, Berra K, Blankenship JC, Dallas AP, Douglas PS, Foody JM, Gerber TC, Hinderliter AL, King SB. 2012 ACCF/AHA/ACP/AATS/PCNA/SCAI/STS guideline for the diagnosis and management of patients with stable ischemic heart disease: executive summary: a report of the American College of Cardiology Foundation/American Heart Association task force on practice guidelines, and the American College of Physicians, American Association for Thoracic Surgery, Preventive Cardiovascular Nurses Association, Society for Cardiovascular Angiography and Interventions, and Society of Thoracic Surgeons. Journal of the American College of Cardiology. 2012 Dec 18;60(24):2564-603.

Lee TH, Boucher CA. Noninvasive tests in patients with stable coronary artery disease. New England Journal of Medicine. 2001 Jun 14;344(24):1840-5.

Pellikka PA, Arruda-Olson A, Chaudhry FA, Chen MH, Marshall JE, Porter TR, Sawada SG. Guidelines for Performance, Interpretation, and Application of Stress Echocardiography in Ischemic Heart Disease: From the American Society of Echocardiography. Journal of the American Society of Echocardiography. 2020 Jan 1;33(1):1-41.