Dr. Rose's Peripheral Brain--DIAGNOSIS OF CORONARY ARTERY DISEASE

DIAGNOSIS OF CORONARY ARTERY DISEASE

Factors which favor a dx of panic disorder over myocardial ischemia:

Many different autonomic sx

Major depressive sx

Agoraphobic behavior

Response to Organic Nitrates

Relief of chest pain or other suspicious symptoms is traditionally thought to predict high likelihood of myocardial ischemia as a cause, however,
- In a prospective study of 459 pts presenting with chest pain to an emergency department, all of whom received nitroglycerin 0.4mg SL, symptom relief (50% or more reduction in pain within 5min of receiving the NTG) had sensitivity and specificity of only 35% and 59% for an ultimate diagnosis of myocardial ischemia, respectively (Ann. Int. Med. 139:1036, 2003--JW)
- In a prospective study of 664 pts presenting to an emergency department with chest pain and who were treated with sublingual nitroglycerin, there were no significant differences between those eventually diagnosed with cardiac-related chest pain and those not in recorded response of numerical pain scores to NTG (Ann. Emerg. Med. 45:581, 2005--abst)

Exercise Stress Testing

Sensitivity/Specificities (source: 2002 ACC/AHA preoperative evaluation guidelines)

For single vessel CAD: 68%/77%

For multivessel CAD: 81%/66%

For 3-vessel or left main disease: 86%/53%

ST DEPRESSIONS in stress test: upgoing are least ominous, flat are intermediate, and downgoing are most ominous (for future MI)

Functional exerise capacity was the MOST POWERFUL predictor of mortality (> evidence of ischemia) results in 2y f/u study of 3400 adults who underwent thallium ETT (JACC 30:641, 1997-JW)

Exercise-induced LBBB during ETT was strongly associated with a combined endpointed that included all-cause mortality, CABG, PTCA, nonfatal MI, or documented symptomatic tachyarrhythmia in one prospective trial comparing 70 such pts w/70 matched controls (JAMA 279:153, 1998--abst)

Adding right precordial leads (V3R, V4R, and V5R) to standard ETT increases sensitivity with no change in specificity (NEJM 340:340, 1999--JW)

Exaggerated BP responses with exercise is ass'd with sig. higher risk of developing HTN in the following years (Circ. 99:1831, 1999--JW)

Non-exercise Stress Testing

When pt cannot exercise, pharmacologic stress can be used:

By increasing myocardial oxygen demand (pacing or IV dobutamine)
- Dobutamine relatively contraindicated in patients with serious arrhythmias or severe hypertension or hypotension.
By inducing hyperemic responses with vasodilators (e.g. IV dipyridamole (Persantine) or adenosine)
- Dipyridamole relatively contraindicated in pts with significant bronchospasm, critical carotid disease, or a condition that prevents their being withdrawn from theophylline preparations
- In combination with myocardial perfusion scanning, this it the test of choice in pts with Left Bundle Branch Block--The tachycardia induced by exercise and dobutamine can result in false-positive findings suggestive of septal ischemia (sens/spec of ex-thallium scans with LBBB 78%/33%; vasodilator scans in such pts ass'd with sens/spec of 98%/84%, per 2002 ACC/AHA preoperative evaluation guidelines)

Adding imaging modalities to Exercise Stress Testing to increase sensitivity

Myocardial perfusion scintigraphy w/single-photon emission computed tomography ("Exercise SPECT")
- Although often known as "Stress Thallium," Technicium-99 (both sestamibi and tetrogosmin) is also used as an imaging agent, in addition to thallium-201
- The radioisotope is injected about 1min prior to stopping exercise. Images obtained shortly afterward and then another injection is made & images taken sev. hours later (or the next day)
- Is most appropriate for use in diagnosing CAD in situations where the baseline risk of CAD is intermediate; for low-baseline-risk pts, ETT is probably better; for high-risk pts, going straight to cath may be more appropriate
- If stress/resting myocardial perfusion scan is normal but stress ECG is "intermediate" risk according to the "Duke" score, there is very little 5y risk of myocardial death (1%) or MI (2.2%) in a prospective study of 4649 pts (Circ. 100:2140, 1999--JW/abst)
Stress echocardiography
- In a prospective study of 4,000 pts with known or suspected CAD AND a normal exercise ECG stress test, pts with ischemia vs. no ischemia stress echo had sig. higher incidence of major cardiac events (J. Am. Coll. Cardiol. 53:1981, 2009-JW)
A meta-analysis of 44 studies involving > 5800 pts comparing these two techniques, using coronary angiography as a gold standard, found that stress echo had sensitivity of 85% and specificity of 77% while exercise SPECT had sensitivity of 87% and specificity of 64% (diff in spec. was sig.). Plain exercise stress test had sensitivity of 52% and specificity of 71% (JAMA 280:913, 1998)

Positron Emission Tomography ("PET") of the heart for diagnosis of CAD

Myocardial perfusion imaging with conventional techniques may produce false-positive findings of a fixed perfusion defect in areas of myocardium that are still viable but functioning poorly because of chronic ischemia. Such areas of "hibernating" myocardium may respond well to revascularization procedures
PET scanning is more sensitive than SPECT and dobutamine stress echocardiography at detecting hibernating myocardium, and better than SPECT at predicting recovery of regional myocardial function after revascularization procedures (Circulation. 2003;108:1404-18; Nuclear Medicine Communications 2002;23:323-30)

Coronary Angiography

Rarely necessary to make Dx of angina (can do clinically & with EKG) or determine extent of CAD (can do with ETT)

Good to identify lesions amenable to PTCA/CABG in

Pts w/angina refractory to medical Tx

Pts at high risk for MI despite med. tx (e.g. LV dysfn)

MR Angiography

Associated with sensitivity of 77% and specificity of 71% in one meta-analysis of 9 trials comparing MRA to conventional coronary angiography (J Am Coll Cardiol. 42:1867-78, 2003)

CT of Coronary Arteries

aka Coronary electron beam computed tomography (EBCT)

Measures calcium deposits in arterial walls, generating a "Calcium Score"

Techniques are advancing rapidly so results from more than a few years back need to be evaluated with caution.

One study looked at 1173 asymptomatic pts who were referred by MD's or by self for coronary EBCT, and followed them for avg. of 19 mos to correlate EBCT findings with clinical outcome (Circulation. 1996;93:1951)

Calcium scores were sig. higher in those who eventually had MI, PTCA, CABG, sudden death, or ischemic stroke
Depending on threshold of calcium score used, was able to predict such events with either:
Sensitivity 89%; neg. pred. value 99.8%, pos. pred. value 5.5%
Sensitivity 50%, neg. pred. value 99.2%, pos. pred. value 14%

In another study comparing electron beam CT vs. angiography in 125 pts, EBCT yielded satisfactory imaging in only 75% of arteries; in those arteries that were adequately seen on EBCT, it had 92% sensitivity and 94% specificity for high-grade stenosis (NEJM 339:1964, 1998--JW)

In another study, 1,196 pts < 45yo w/o known CAD but with CAD risk factors underwent EBCT; presence of detectable coronary calcifications did not predict coronary events over a mean f/u period of 41mos (Circ. 99:2633, 1999--JW)

There's significant inter-scan variability in Ca scores in pts undergoing consecutive EBCT studies (Am. J. Roentgenol. 174:803, 2000--JW)

Another study found sig. correlation between calcium scores on EBCT and incidence of cardiac death or nonfatal MI over 32mo f/u, BUT only 22% of events occurred in pts with "severely abnormal" calcium scores; thus, majority of events occurred in pts with mild or moderate Ca scores (Circ. 101:850, 2000--JW)

In a study comparing 16-slice CT angiography of the coronary arteries with standard coronary angiography in 187 pts with suspected CAD, CT angiography had sensitivity of 89% and specificity of of 65% (for detection of > 50% stenosis on standard angiography) (JAMA 296:403, 2006--JW)

CT for evaluating left main coronary artery patency after stenting

In a study in 70 pts s/p left main coronary aftery stenting who underwent multislice CT and coronary angiography, sensitivity of CT for restenosis was 100% but positive predictive value was only 67% (Circ. 114:645, 2006--JW)

CT coronary angiography

Use of high-resolution multislice spiral CT modalities with high #'s of especially thin detector rows (e.g. 16)
Had sensitivity of 96% and specificity of 95% for stenoses/occlusions of bypass grafts compared with standard angiography in one study (J. Am. Coll. Cardiol. 44:1224, 2004--abst)
In a study in 133 pts undergoing both conventional angiography and multi-slice CT with a 16-detector-row scanner, CT, for detection of > 50% stenosis, had sensitivity of 95% and specificity of 98% (JAMA 293:2471, 2005--abst)
In a study in 187 pts undergoing nonemergent coronary angiography, all of whom had 16-row multidetector CT of the coronaries first, the latter had sensitivity of 89% and specificity of 65% for > 50% stenosis, and sensitivity of 94% and specificity of 51% for > 70% stenosis.