Unlike most other circulatory beds in the body, coronary circulation allows maximum O2 extraction from the blood when the body is
at rest
How does a stress test work?
A healthy coronary circulation can vasodilate up to 5 times above baseline level to accomodate myocardial oxygen demand. When it is limited, there is an imbalance of supply and demand of O2.
Which lab tests have shown promising results in predicting cardiovascular events?
C-reactive protein, interleukin-6 and monocyte-macrophage colony stimulating factor are markers.
Injury or insult to the vascular endothelium is a precursos for the process of
Atherogenesis to begin.
Treadmill exercise test
Assesses ischemia, functional capacity, prognosis
What are the limitations of the treadmill exercise test
Sensitivity is lower. Poor specificity with women, resting ecg st-t abnormalities
Exercise myocardial perfusion imaging
Reproducible results. Improved sensitivity and specificity higher, diagnostic accuracy.
Limitations of the exercise myocardial perfusion imaging
Increased cost. Requires longer testing times. Modest radiation exposure, artifacts from soft tissue (breast) or obese patients attenuate signal, decrease specificity.
Cardiac MRI
High resolution of cardiac structure, function and morphology. No radiation exposure. Stress perfusion MRI an option. Can be used with most cardiac stents.
Limitations of Cardiac MRI
Claustrophobic patients. patients with implantable AICDs.
Exercise radionuclide angiography
Well validated to identify patients with severe disease. Risk stratification after MI. Good images with obese or COPD patients. Accurate information about EF.
Limitations of exercise radionuclide angiography
Limited availablity and high expense. Uses Bicycle, not treadmill exercise. Innacurate when heart rate is irregular. Reduced specificity with women, abnormal resting left ventricular function.
Exercise echocardiography
Less test time, lower cost than nuclear imaging. Assesses multiple parameters; global and regional ventricular cuntion, chamber size, wall thickness, valve function. Used with resting ECG abnormalities. LBBB. Detects reversible ischemia (wall motion abnor
Limitations of exercise echocardiography
Images limited with obesity or obstructive lung disease. Does not detect non blood flow limiting blockages. Reduced accuracy with resting wall motion abnormalities (prior MI, paced rhythm, certain cardiac surgeries)
Pharmacologic stress with adenosine (Adenosine stress tes)
Accurate assessments in patients unable to complete exercise protocol. Usefull assessment in patients with claudicatin or MS limitations. Side effects rapidly reversible by ending infusion or giving aminophylline.
Limitations of adenosine stress test
Can't assess functional capacity. Contraindicated with hypotension, SSS, high grade heart black, hyperactive airways. Chest pain during test is not indicative of CAD.
Dobutamine Echocardiography
Improves CAD assessments in patients unable to exercise. Side effects rapidly reversible by terminating infusion or administering beta blocker. Perfusion defects represent true MI.
Limitations of dobuatamine Echocardiography
Can't assess functional capacity. Contraindicated with recent MI (<1/week), unstable angina, high grade heart block, BBB, severe aortic stenosis, hypertrophic cardiomyopathy, Supraventricular dysrhythmias, large aneurysm, severe pulmonary HTN, Beta blocke
Cardiac catheterization is indicated if ecg findings and biomarkers indicate
an Acute MI
Which lab test result can be used in men older than 50 years and women older than 60 yrs to determine if statin therapy is indicated?
CRP
Which non invasive office test is acceptable for intermediate risk individuals to detemrine their risk for subclinicial CV disease?
Ankle brachial index.
The standard first line test for CAD is the
Stress test.
What does chronotropic mean?
rate related
What does inotropic mean?
related to the strength of the myocardial contraction
The ECG response to normal hearts is maintenance of an isoelectric
ST segment
A positive test result for CAD is
A horizontal or downsloping ST segment of 1 mm measure 80 msec after the J point
How do you calculate maximum heartrate?
(220-age)
A second important predictor of more advanced CAD is exercise induced
Hypotension (a fall of at least 20 points during exericse)
Which drugs interfere with the exercise test?
Beta blockers, digoxin, CCH, other anti-hypertensives
During a stress test, which parts of the heart are more difficult to detect?
Ischemia of the posterior or lateral aspects of the left ventricle.
Some pertinent contraindications of a stress test?
Acute MI, SVT, Sustained Ventricular arrhythmias, high grade heart block, severe HTN, Acute venous thromboembolic disease, myocarditis, endocarditis, symptomatic CHF.
Indications for coupling of nuclear or US imaging to standard stress tests
1. LVH with ST segment or T wave abnormalities
2. Baseline ST and T wave abnormalities at rest
3. Recent MI
4. Clinical use of digoxin
5. Wolff Parkinson White syndrome
6. BBB
7. Ventricular pacemaker