Rest and treadmill exercise first-pass radionuclide ventriculography: validation of left ventricular ejection fraction measurements

BACKGROUND

To assess the accuracy of rest and treadmill exercise first-pass radionuclide ventriculographic measurements of left ventricular ejection fraction (LVEF), 40 patients underwent treadmill exercise first-pass and bicycle exercise equilibrium radionuclide ventriculography. To determine the frequency of technically adequate treadmill exercise first-pass studies, an additional 128 consecutive patients undergoing treadmill exercise first-pass procedures during stress 99mTc-labeled sestamibi myocardial perfusion studies were assessed.

METHODS AND RESULTS

The treadmill exercise first-pass procedure used a multicrystal camera and an 241Am point source to allow for correction of patient motion. Excellent correlations were observed between resting first-pass and resting equilibrium LVEF (r = 0.91; standard error of the estimate = 5.6). A high correlation was also observed between treadmill exercise first-pass and bicycle equilibrium exercise LVEF measurements (r = 0.85, standard error of the estimate = 7.6). Treadmill first-pass LVEF systematically underestimated the bicycle equilibrium LVEF. Intraobserver agreement for rest and exercise first-pass LVEF was high (r values of 0.98 and 0.94, respectively). Of the 168 consecutive treadmill exercise first-pass studies evaluated for technical adequacy, 21 (12.5%) were deemed technically inadequate, with most of the sources of error being avoidable. The frequency of technically adequate studies was as high (87%) in high levels of exercise (Bruce stages 3 and 4) as in lower levels (88%). The findings of this study validate the first-pass treadmill exercise LVEF measurement.

CONCLUSION

This procedure now provides the option for combining the information of peak treadmill exercise LVEF with measurements of exercise myocardial perfusion from the same injection of radioactivity.

"Upward creep" of the heart: a frequent source of false-positive reversible defects during thallium-201 stress-redistribution SPECT

A new cause of artifactual 201Tl defects on single photon emission computed tomography (SPECT) termed "upward creep" of the heart is described. In 102 consecutive patients undergoing 201Tl SPECT, 30 (29%) demonstrated upward creep defined by an upward movement of the heart of greater than or equal to 2 pixels during acquisition. In 45 consecutive patients with a less than 5% likelihood of coronary artery disease, 17 (38%) had upward creep. Of these nine had reversible 201Tl defects localized to the inferior and basal inferoseptal walls, while none of the 28 without upward creep had defects. The 17 low likelihood patients with upward creep had longer exercise duration and higher peak heart rate than those without upward creep. In five additional low likelihood patients with upward creep in whom imaging was immediately repeated, the upward creep pattern disappeared on the repeated images. After we changed our test protocol to begin imaging 15 min postexercise, only five (14%) of 36 low likelihood patients tested demonstrated upward creep. Upward creep is probably related to a transient increase in mean total lung volume early following exhaustive exercise, resulting in a mean lower position of the diaphragm (and thus the heart) at the beginning of imaging. The frequency of this source of false-positive 201Tl studies can be reduced by delaying SPECT acquisition until 15 min postexercise.

Patient motion in thallium-201 myocardial SPECT imaging. An easily identified frequent source of artifactual defect

Because Tl-201 SPECT requires that patients remain in an awkward position for a prolonged time, patient motion is a potentially serious source of artifactual defects on tomographic reconstructions. Thus, a simple method was developed for detection and correction of motion from SPECT images using a Co-57 point source placed on the lower anterior chest, an area remaining in the camera's field of view throughout imaging. In the absence of motion, this point source inscribes a straight line on planar summation of the 32 projections over 180 degrees. Movement is detected by deviation from this line. The number of pixels of motion is used to shift images so that the resultant images of the point source are linear. The method of motion detection and correction was tested in 48 consecutive patients undergoing Tl-201 SPECT. The corrected and uncorrected images were reconstructed and long and short axis tomographic cuts were quantitatively analyzed using circumferential profiles of maximal counts with comparison to the lower limits of normal. Motion was detected in eight of 48 patients (17%). The amount of motion was 2 pixels in three patients and 1 pixel in five patients. Quantitative defect extent was less after correction in seven of eight patients, with a mean decrease of 71% in patients with 2 pixel motion and 44% in patients with 1 pixel motion. This corresponded with a definite reduction in the size of the tomographic defect by visual analysis, and closer resemblance to quantitatively analyzed planar images performed either before or after tomography in the same patient.(ABSTRACT TRUNCATED AT 250 WORDS)

Mental stress and the induction of silent myocardial ischemia in patients with coronary artery disease

To assess the causal relation between acute mental stress and myocardial ischemia, we evaluated cardiac function in selected patients during a series of mental tasks (arithmetic, the Stroop color--word task, simulated public speaking, and reading) and compared the responses with those induced by exercise. Thirty-nine patients with coronary artery disease and 12 controls were studied by radionuclide ventriculography. Of the patients with coronary artery disease, 23 (59 percent) had wall-motion abnormalities during periods of mental stress and 14 (36 percent) had a fall in ejection fraction of more than 5 percentage points. Ischemia induced by mental stress was symptomatically "silent" in 19 of the 23 patients with wall-motion abnormalities (83 percent) and occurred at lower heart rates than exercise-induced ischemia (P less than 0.05). In contrast, we observed comparable elevations in arterial pressure during ischemia induced by mental stress and ischemia induced by exercise. A personally relevant, emotionally arousing speaking task induced more frequent and greater regional wall-motion abnormalities than did less specific cognitive tasks causing mental stress (P less than 0.05). The magnitude of cardiac dysfunction induced by the speaking task was similar to that induced by exercise. Personally relevant mental stress may be an important precipitant of myocardial ischemia--often silent--in patients with coronary artery disease. Further examination of the pathophysiologic mechanisms responsible for myocardial ischemia induced by mental stress could have important implications for the treatment of transient myocardial ischemia.

Thallium-201 stress-redistribution myocardial rotational tomography: development of criteria for visual interpretation

Despite high sensitivity and specificity for overall detection of coronary artery disease (CAD), planar stress-redistribution thallium-201 (Tl-201) scintigraphy remains suboptimal in localizing disease, because of overlap of myocardial segments. Single photon emission computerized tomography (SPECT), by providing three-dimensional representation of myocardial Tl-201, offers promise for improved localization of CAD. In 50 consecutive patients (22 normal and 28 with CAD), who underwent SPECT stress-redistribution Tl-201 imaging, we systemically developed visual interpretive criteria for perfusion abnormality on SPECT. For overall detection of disease, the best criterion for abnormality was greater than or equal to 8 sectors of moderately decreased Tl-201 uptake. With this criterion, the true positive and true negative rates for overall detection of disease were 96% and 91%, respectively. The best criterion for significant defect in the anterior or posterior coronary circulation was greater than or equal to 3 sectors of moderately decreased Tl-201 uptake. With this criterion, the true positive and true negative rates for anterior circulation disease were 71% and 100%, respectively. With respect to posterior circulation disease, the true positive and true negative rates were 100% and 50%, respectively. Regarding identification of dual circulation disease, the true positive and true negative rates were 71% and 82%, respectively.