A reappraisal of exercise electrocardiographic indexes of the severity of ischemic heart disease: angiographic and scintigraphic correlates

Prevalence of Coronary Microvascular Dysfunction Among Patients With Chest Pain and Nonobstructive Coronary Artery Disease

OBJECTIVES

This study assessed the prevalence of coronary microvascular abnormalities in patients presenting with chest pain and nonobstructive coronary artery disease (CAD).

BACKGROUND

Coronary microvascular abnormalities mediate ischemia and can lead to an increased risk of cardiovascular events.

METHODS

Using an intracoronary Doppler guidewire, endothelial-dependent microvascular function was examined by evaluating changes in coronary blood flow in response to acetylcholine, whereas endothelial-independent microvascular function was examined by evaluating changes in coronary flow velocity reserve in response to intracoronary adenosine. Patients were divided into 4 groups depending on whether they had a normal (+) or abnormal (-) coronary blood flow (CBF) in response to acetylcholine (Ach) and a normal (+) or abnormal (-) coronary flow velocity reserve (CFR) in response to adenosine (Adn): CBFAch+, CFRAdn+ (n = 520); CBFAch-, CFRAdn+ (n = 478); CBFAch+, CFRAdn- (n = 173); and CBFAch-, CFRAdn- (n = 268).

RESULTS

Two-thirds of all patients had some sort of microvascular dysfunction. Women were more prevalent in each group (56% to 82%). Diabetes was uncommon in all groups (7% to 12%), whereas hypertension and hyperlipidemia were relatively more prevalent in each group, although rates for most conventional cardiovascular risk factors did not differ significantly between groups. There were no significant differences in the findings of noninvasive functional testing between groups. In a multivariable analysis, age was the only variable that independently predicted abnormal microvascular function.

CONCLUSIONS

Patients with chest pain and nonobstructive CAD have a high prevalence of coronary microvascular abnormalities. These abnormalities correlate poorly with conventional cardiovascular risk factors and are dissociated from the findings of noninvasive functional testing.

Computing ischemic regions in the heart with the bidomain model--first steps towards validation

We investigate whether it is possible to use the bidomain model and body surface potential maps (BSPMs) to compute the size and position of ischemic regions in the human heart. This leads to a severely ill posed inverse problem for a potential equation. We do not use the classical inverse problems of electrocardiography, in which the unknown sources are the epicardial potential distribution or the activation sequence. Instead we employ the bidomain theory to obtain a model that also enables identification of ischemic regions transmurally. This approach makes it possible to distinguish between subendocardial and transmural cases, only using the BSPM data. The main focus is on testing a previously published algorithm on clinical data, and the results are compared with images taken with perfusion scintigraphy. For the four patients involved in this study, the two modalities produce results that are rather similar: The relative differences between the center of mass and the size of the ischemic regions, suggested by the two modalities, are 10.8% ± 4.4% and 7.1% ± 4.6%, respectively. We also present some simulations which indicate that the methodology is robust with respect to uncertainties in important model parameters. However, in contrast to what has been observed in investigations only involving synthetic data, inequality constraints are needed to obtain sound results.

Predictors of an ischemic electrocardiographic response in patients with exercise-induced myocardial ischemia

BACKGROUND

The determinants of an ischemic electrocardiographic (ECG) response in patients with exercise-induced ischemia on single-photon emission computed tomography (SPECT) remain poorly defined. Specifically, it is unknown whether the occurrence of an ischemic ECG response is related to the extent and/or severity of SPECT ischemia.

METHODS AND RESULTS

Among 3,294 patients who underwent exercise SPECT using a rest thallium-201/exercise Tc-99m sestamibi protocol, 699 (21%) patients had myocardial ischemia defined as summed difference score (SDS) ≥2. The extent of SPECT ischemia was further defined as the total number of segments with difference score ≥1, and severity of ischemia as the largest difference score among all segments. Patients with ischemic ECG changes (n = 315) were significantly older and had a significantly greater prevalence of hyperlipidemia. SDS (7.4 ± 2.2 vs 4.7 ± 1.9, P < .0001), extent (4.2 ± 2.6 vs 2.9 ± 1.7, P < .0001), and severity (2.8 ± 0.9 vs 2.3 ± 0.8, P < .0001) of SPECT ischemia were greater among patients with ischemic ECG changes. In multivariate analysis, age and SDS (which is a composite of the extent and severity of ischemia) were associated with ischemic ECG. When analyzed in a separate model which did not include SDS, both severity of SPECT ischemia (OR 1.42, CI 1.13-1.79) and extent of SPECT ischemia (OR 1.21, CI 1.10-1.33) were independently associated with ischemic ECG.

CONCLUSIONS

Among patients with exercise-induced myocardial ischemia by SPECT, age and SDS were associated with ischemic ECG changes. When analyzed separately, the severity and extent of SPECT ischemia were both independent predictors of ischemic ECG changes.

Interrelation of ST-segment depression during bicycle ergometry and extent of myocardial ischaemia by myocardial perfusion SPECT

PURPOSE

The aim of this study was to compare ST-segment depression (STD) during bicycle ergometry and extent of myocardial ischaemia assessed by myocardial perfusion SPECT (MPS) in a large patient cohort.

METHODS

Consecutive patients (n = 955) referred for MPS with bicycle ergometry and interpretable stress ECG were evaluated with respect to ECG and MPS findings of ischaemia. The maximal STD was recorded and exercise ECG was considered ischaemic if STD was horizontal or downsloping (>or=1 mm). MPS was interpreted using a 20-segment model with a scale of 0 to 4. A summed stress (SSS), summed rest (SRS) and summed difference score (SDS = SSS-SRS, e.g. extent of ischaemia) were derived. Ischaemia was defined as an SDS >or= 2.

RESULTS

An exercise-induced STD was present in 215 patients (22%) and myocardial ischaemia on MPS was present in 366 patients (38%). The extent of ST-segment depression and the number of ECG leads with significant STD were each strongly and significantly associated with increasing severity of ischaemia and the number of coronary territories involved (p < 0.01 for all correlations).

CONCLUSION

These data demonstrate a strong correlation between the extent of STD, number of ischaemic leads and severity of myocardial ischaemia as assessed by MPS during bicycle ergometry.

Incremental prognostic value of the exercise electrocardiogram in the initial assessment of patients with suspected angina: cohort study

OBJECTIVE

To determine whether resting and exercise electrocardiograms (ECGs) provide prognostic value that is incremental to that obtained from the clinical history in ambulatory patients with suspected angina attending chest pain clinics.

DESIGN

Multicentre cohort study.

SETTING

Rapid access chest pain clinics of six hospitals in England.

PARTICIPANTS

8176 consecutive patients with suspected angina and no previous diagnosis of coronary artery disease, all of whom had a resting ECG recorded. 4848 patients with a summary exercise ECG result recorded (positive, negative, equivocal for ischaemia) comprised the summary ECG subset of whom 1422 with more detailed exercise ECG data recorded comprised the detailed ECG subset.

MAIN OUTCOME MEASURE

Composite of death due to coronary heart disease or non-fatal acute coronary syndrome during median follow-up of 2.46 years.

RESULTS

Receiver operating characteristics curves for the basic clinical assessment model alone and with the results of resting ECGs were superimposed with little difference in the C statistic. With the exercise ECGs the C statistic in the summary ECG subset increased from 0.70 (95% confidence interval 0.68 to 0.73) to 0.74 (0.71 to 0.76) and in the detailed ECG subset from 0.74 (0.70 to 0.79) to 0.78 (0.74 to 0.82). However, risk stratified cumulative probabilities of the primary end point at one year and six years for all three prognostic indices (clinical assessment only; clinical assessment plus resting ECG; clinical assessment plus resting ECG plus exercise ECG) showed only small differences at all time points and at all levels of risk.

CONCLUSION

In ambulatory patients with suspected angina, basic clinical assessment encompasses nearly all the prognostic value of resting ECGs and most of the prognostic value of exercise ECGs. The limited incremental value of these widely applied tests emphasises the need for more effective methods of risk stratification in this group of patients.

Effects of exogenous metabolic substrate modulation on exercise-induced myocardial ischemia

BACKGROUND

The aim of the study is to compare the impact of intravenous glucose versus lipid versus saline on exercise-induced myocardial ischemia in patients with stable angina.

METHODS

Twelve men with coronary artery disease and positive exercise tests performed a symptom-limited, modified Bruce electrocardiogram (ECG) exercise test at 3 sessions, 3 weeks apart. They randomly received, in double-blind design, at each session equal intravenous volumes of 10% glucose/insulin or Intralipid plus heparin or saline. We assessed the effects on (1) ischemic threshold (heart rate x systolic pressure at 1-mm ST-segment depression [STD]) and (2) maximum ST-depression (Max STD) corresponding to the highest heart rate x systolic pressure common to the 3 tests.

RESULTS

During glucose infusion, glycemia increased from 5.7 +/- 0.4 to 9.4 +/- 3.0 mmol/L but did not change during lipid or saline infusion. During lipid infusion, free fatty acids increased from 0.32 +/- 0.19 to 1.44 +/- 0.46 mmol/L but decreased during glucose infusion from 0.39 +/- 0.21 to 0.04 +/- 0.03 mmol/L and did not change during saline. Exercise times were 10.0 +/- 3.4, 9.8 +/- 3.4, and 10.3 +/- 3.5 minutes, during glucose, lipid, and saline infusions, respectively. Ischemic thresholds (x 10(-3)) were 16.5 +/- 2.8, 16.8 +/- 2.7, and 16.6 +/- 2.6, respectively. MaxSTD was 2.5 +/- 1.4, 2.5 +/- 1.0, and 2.5 +/- 1.0 mm, respectively.

CONCLUSION

Neither glucose-insulin nor lipid infusion modified exercise ischemic parameters compared with saline control, suggesting that marked and acute changes in exogenous energy substrate are unlikely to affect exercise-induced myocardial ischemia.

Receiver operating characteristic (ROC) curves and the definition of threshold levels to diagnose coronary artery disease on electrocardiographic stress testing. Part II: the use of ROC curves in the choice of electrocardiographic stress test markers of ischaemia

A common problem in diagnostic medicine, when performing a diagnostic test, is to obtain an accurate discrimination between 'normal' cases and cases with disease, owing to the overlapping distributions of these populations. In clinical practice, it is exceedingly rare that a chosen cut point will achieve perfect discrimination between normal cases and those with disease, and one has to select the best compromise between sensitivity and specificity by comparing the diagnostic performance of different tests or diagnostic criteria available. Receiver operating characteristic (or receiver operator characteristic, ROC) curves allow systematic and intuitively appealing descriptions of the diagnostic performance of a test and a comparison of the performance of different tests or diagnostic criteria. This review will analyse the basic principles underlying ROC curves and their specific application to the choice of optimal parameters on exercise electrocardiographic stress testing. Part II will be devoted to the comparative analysis of various parameters derived from exercise stress testing for the diagnosis of underlying coronary artery disease.

The Quebec Heart Institute: 50 years of excellence in cardiology

The Quebec Heart Institute was established in 1957 at the Laval Hospital in Sainte-Foy, Quebec. Since then, clinical and research activities have made this Institute one of the largest tertiary care cardiology centres in Canada. With its vast catchment area of more than 3,000,000 people, the Institute has developed a strong collaboration with referral physicians centred on clinical, teaching and research interests. The Institute pioneered several aspects of cardiac surgery, invasive cardiology, echocardiography, basic research and, more recently, a network of researchers and clinicians working in the field of 'metabolic cardiology'. The first 50 years of the Quebec Heart Institute are depicted in this overview, which will also introduce this special supplement to The Canadian Journal of Cardiology.

Diagnostic impact of SPECT image display on assessment of obstructive coronary artery disease

BACKGROUND

Diagnostic assessment of myocardial perfusion impacts the management of patients with suspected coronary artery disease (CAD). Although various image displays are available for single photon emission computed tomography (SPECT) interpretation, the effects of display differences on SPECT interpretation remain undetermined.

METHODS AND RESULTS

We studied 183 patients undergoing SPECT, including 131 consecutive patients referred for angiography and 52 at low CAD risk. Studies were visually interpreted by use of color and gray images, with readers blinded to the results of the other display. In accordance with established criteria, a summed stress score (SSS) of 4 or greater was considered abnormal. The prevalence of abnormal SPECT findings was higher with gray images than with color images (54% vs 48%, P < .001) based on a uniform criterion (SSS > or =4). However, color images yielded equivalent sensitivity (79% vs 82%, P = .7) and improved specificity for global (50% vs 33%, P = .02) and vessel-specific CAD involving the right coronary artery (P < .01) and left anterior descending artery (P < .05). When the criterion for gray images was adjusted upward (SSS > or =5) to reflect increased mean defect severity (SSS of 5.1 vs 4.4, P = .01), gray and color images provided equivalent sensitivity and specificity for global and vessel-specific CAD.

CONCLUSIONS

SPECT interpretation can vary according to image display as a result of differences in perfusion defect severity. Adjustment of abnormality criteria for gray images to reflect minor increases in defect severity provides equivalent diagnostic performance of gray and color displays for CAD assessment.

Correlation between R wave amplitude, exercise ischemic electrocardiographic indices and thallium-201 imaging defects in patients with known coronary artery disease

We investigated the relation between R wave amplitude (RWA) and ST depression as well as the presence and extent of reversible ischemia in thallium-201 scanning in patients with known coronary artery disease (CAD) and found that RWA both at rest and during exercise testing (ET) correlates with the magnitude of ST depression in the same leads. Greater ST changes appear on leads with highest RWA. Thus lead selection strongly influences interpretation of ECG ischemic changes during ET in patients with CAD. An electrocardiographic result negative for ischemia in patients with low RWA should prompt the alternative use of echocardiography and scintigraphy.

Anatomic distribution of myocardial ischemia as a determinant of exercise-induced ST-segment depression

Cardiac single-photon emission computed tomographic correlates of ST depression were examined in 129 subjects who had inducible ST depression of > or =0.1 mV and reversible perfusion defects. Patients were separated on the basis of single-photon emission computed tomographic defect distribution into a group with anatomically contiguous ischemia (anterior or posterior/inferior defects, n = 68) and a group with anatomically opposed ischemia (anterior and posterior/inferior defects, n = 61). ST depression in the contiguous ischemia group correlated with defect size (r = 0.40, p = 0.001) and severity (r = 0.38, p = 0.002); multivariate regression demonstrated each to be independent determinants of ST-depression magnitude (r = 0.51, p <0.001). In the opposed ischemia group, ST depression did not significantly correlate with defect extent or severity. After adjusting for differences in perfusion indexes, ST depression was paradoxically greater in the contiguous than in the opposed group (2.82 +/- 1.15 vs 2.44 +/- 1.15 mm, p <0.001). In conclusion, these findings demonstrate that the anatomic distribution of ischemia can alter the relation between ST depression and functional indexes of ischemia and may confound the accuracy of assessments of coronary artery disease based on ST-depression magnitude alone.

Quantitative relation of ST-segment depression during exercise to the magnitude of myocardial ischemia as assessed by single-photon emission computed tomographic myocardial perfusion imaging

The mechanism of ST-segment depression during exercise electrocardiographic treadmill testing (ETT) is unknown. The relatively good correlation between the results of ETT and myocardial perfusion imaging suggests that ST-segment depression may be related to the magnitude of ischemia. Previous studies that investigated this relation have produced conflicting results. We evaluated 1,006 patients who underwent symptom-limited ETT and technetium-99m single-photon emission computed tomographic myocardial perfusion imaging at rest and during stress at a single institution. The magnitude, extent, and duration of ST-segment depression were each strongly associated with the magnitude of myocardial ischemia (p <0.001 for all). The magnitude, extent, and duration of ST-segment depression were highly correlated with each other and had similar relations to the magnitude of ischemia. After adjustment for significant clinical and ETT parameters, these relations remained highly significant. The location of myocardial ischemia was unrelated to ST-segment depression. This large study found that ST-segment depression during ETT is strongly associated with the magnitude of ischemia. These data support a causative role for the magnitude of ischemia in the generation of ST-segment depression.

Prolonged ST segment depression after stress testing: does it really identify more severe disease?

BACKGROUND

It is generally perceived that the persistence of ST segment depression for more than 5 min after treadmill exercise testing (ETT) signifies a strongly positive test and predicts more severe ischemia and coronary artery disease.

AIM

The aim of this study was to determine if prolonged ST segment changes (>5 min) after ETT identifies patients with more severe ischemia and thus severe coronary artery disease.

METHODS

Twenty five patients (19 males, mean age 58+/-10 years) with >1 mm ST segment depression and recovery time <or=5 min (group 1) and 25 patients (20 males, mean age 62+/-10 years) with >1 mm ST segment depression and recovery time >5 min (group 2) undergoing ETT and single photon emission computed tomography were prospectively enrolled. Summed stress and difference scores, stress and reversible extent % of perfusion abnormalities, and lung heart ratio was calculated.

RESULTS

There was no significant difference in the mean summed stress score (9+/-9 versus 13+/-10, P=0.13), summed difference score (4+/-3 versus 6+/-5, P=0.13), stress extent % (14+/-16 versus 19+/-13, P=0.13), extent of reversibility % (7+/-9 versus 7+/-7, P=0.93), or lung heart ratio (0.48+/-0.07 versus 0.46+/-0.07, P=0.50) between the two groups. There was no significant difference in the incidence of severe ischemia (summed difference score >13) in the 2 groups (24% versus 40%, P=0.36).

CONCLUSION

We conclude that utilizing the commonly used cutoff for prolonged ST segment depression: >5 min in recovery, does not identify patients with more severe ischemia or coronary artery disease and, therefore, at increased risk. Thus, it appears unnecessary to give special consideration to these patients by way of prolonged monitoring in recovery, or a more aggressive non-invasive ischemia imaging approach after the ETT.

[Angiographic correlates of the high-risk criteria for conventional exercise testing and the Duke treadmill score]

OBJECTIVE

To compare the sensitivity, the specificity, the positive and negative predictive value and the predictive accuracy of the Duke Treadmill Score, the Spanish Society of Cardiology (SEC) and American College of Cardiology/American Heart Association (ACC/AHA) high-risk criteria for exercise testing in the detection of left main disease, three vessel disease and two vessel disease involving the proximal left anterior descending artery.

PATIENTS AND METHOD

A cohort of 199 patients (age 75 years) consecutively admitted to hospital for unstable angina was studied. All patients underwent an exercise stress test and coronariography.

RESULTS

The SEC high-risk Criteria showed a sensitivity of 69.2% and a specificity of 49.0%. The ACC/AHA high-risk Criteria demonstrated a sensitivity of 98.1% and a specificity of 23.8% and the Duke Treadmill Score presented a sensitivity of 30.8% and a specificity of 90.5%. In patients with moderate risk in the Duke Treadmill Score we found a sensitivity of 62.9% and a specificity of 39.8% for the SEC high-risk criteria, while the ACC/AHA high-risk Criteria presented a sensitivity of 100.0% and a specificity of 5.8%.

CONCLUSIONS

The ACC/AHA high-risk Criteria showed a higher sensitivity while the Duke Treadmill Score presented a higher specificity for the detection of left main disease, three vessel disease and two vessel disease involving the proximal left anterior descending artery. The ACC/AHA and SEC high-risk Criteria were found to be very useful in the group of patients with moderate risk in the Duke Treadmill Score.

Myocardial perfusion imaging findings and the role of adenosine in the warm-up angina phenomenon

OBJECTIVES

This study examined the roles of myocardial perfusion and adenosine in warm-up angina.

BACKGROUND

In warm-up angina, neither the role of an adenosine-mediated mechanism, as is found in experimental ischemic preconditioning, nor of increased myocardial perfusion is well defined.

METHODS

In substudy A, a single-photon emission computed tomography (SPECT)-thallium-201 exercise test was performed by 12 subjects with ischemic heart disease on three occasions one week apart. The third test was preceded by a warm-up test. The extent of the thallium deficit and its intensity on the third test were compared with the baseline tests controlling for the heart rate-systolic blood pressure product (RPP) at thallium injection. In substudy B, 12 similar subjects did two successive exercise tests at two separate sessions and received the adenosine antagonist, aminophylline (intravenous 5 mg/kg bolus and 0.9 mg/kg/h infusion) at one session, and equivalent saline at the other session. Change in ischemic threshold (RPP at 1 mm ST segment depression) and in maximum ST depression adjusted for RPP were analyzed.

RESULTS

In substudy A, despite a significant attenuation of electrocardiogram indexes of myocardial ischemia between the baseline and third (warmed-up) tests, the thallium extent deficits (20.8 +/- 15.1% and 16.8 +/- 12.4%) and intensity deficits (41.2 +/- 12.6% and 39.3 +/- 12.6%) did not differ significantly. In substudy B, the increase in ischemic threshold on re-exercise was unaffected by aminophylline. Adjusted maximum ST depression even decreased to a greater extent on re-exercise with aminophylline (by 51 +/- 21%) than with saline (by 32 +/- 19%) (p = 0.012).

CONCLUSIONS

While warm-up angina is associated with a significant attenuation of exercise electrocardiogram indexes of ischemia, it is unaccompanied by significant changes in SPECT perfusion and does not appear to be mediated by an adenosine-dependent mechanism since it is not blocked by aminophylline. Thus, its mechanism, which appears distinct from experimental ischemic preconditioning, remains unidentified.

Peak systolic blood pressure in exercise testing is associated with scintigraphic severity of myocardial ischemia in patients with exercise-induced ST-segment depression

Some electrocardiographic variables, including the degree of maximal ST-segment depression (STD), may not necessarily indicate the severity of exercise-induced myocardial ischemia. The present study examined whether maximal STD correlates with the severity and extent of exercise-induced myocardial ischemia, as assessed by thallium-201 (201Tl) imaging, and which parameter of exercise testing reflects scintigraphic severity and extent in 270 patients who had a 1 mm or greater horizontal or down-sloping STD on exercise 201Tl imaging. The scintigraphic severity and extent of exercise-induced ischemia was assessed and correlated with maximal STD, number of positive leads, workload, peak heart rate, peak systolic blood pressure (SBP), rate-pressure product, chest pain and the Duke treadmill score. Most of the scintigraphic markers of the severity and extent of ischemia had significant but weak correlation with all of those parameters. Multivariate analysis demonstrated that peak SBP and the Duke treadmill score (chest pain in only simple variables model) correlated independently with scintigraphic severity and extent of ischemia. Furthermore, most of the patients with a peak SBP of 200 mmHg or more had milder and less extensive ischemia. In patients with exercise-induced STD, the scintigraphic severity and extent of ischemia may be estimated by peak SBP and the Duke treadmill score.

Relation between the electrocardiographic stress test and degree and location of myocardial ischemia

Factors that influence frequency and location of stress-induced electrocardiographic (ECG) ST depression and the development of chest pain are incompletely understood. We studied 331 patients with ischemic myocardial nuclear defects in response to routine clinical treadmill testing with simultaneous ECG recording. Nuclear defects were analyzed for location and extent of myocardium involved. Exercise-induced ischemic ST changes were demonstrated in 59% of patients (196 of 331). Subjects with stress-induced ECG changes and/or chest pain had more extensive nuclear perfusion defects. Diabetic patients were significantly less likely to experience chest pain (24%) versus nondiabetics (41%) during testing (p = 0.04). Larger perfusion defects were associated with greater magnitude, lead distribution, and incidence of ECG changes. The number of ECG lead zones (anterior, lateral, and inferior) responding positively were related to both magnitude of ST depression and severity of ischemia, but not to location of ischemic defects. Regardless of location of ischemia, ST depression occurred with similar frequency. Thus, exercise-induced ECG ST depression remains a valuable indicator of the severity of myocardial ischemia. Greater ST depression involving multiple leads usually signified extensive myocardial ischemia, but provided no information regarding its location. Anginal-type chest pain induced by exercise testing also denoted more extensive ischemia.

123I-MIBG myocardial scintigraphy in diabetic patients: relationship with 201Tl uptake and cardiac autonomic function

PURPOSE

To investigate the influence of diabetic myocardial damage (suspected myocardial damage; SMD) diagnosed by 201Tl-SPECT and diabetic cardiac autonomic neuropathy (AN) on myocardial MIBG uptake in patients with non-insulin-dependent diabetes mellitus (NIDDM).

SUBJECTS AND METHODS

Eighty-seven diabetic patients divided into four subgroups: 23 with SMD (+) AN (+); 19 with SMD (+) AN (-); 27 with SMD (-) AN (+); 18 with SMD (-) AN (-), and 10 controls were studied. Both planar and SPECT images were taken at 30 minutes (early) and 3 hours (delayed) after 123I-MIBG injection. The heart to mediastinum uptake ratio (H/M) and washout ratio of 123I-MIBG (WR) were obtained from both planar images. On SPECT images, the total uptake score (TUS) was obtained by the 5 point score method by dividing the myocardium into 20 segments on visual analysis. Similarly, the difference between the 201Tl image and the 123I-MIBG image in TUS was taken as the difference in the total uptake score (delta TUS) representing cardiac sympathetic denervation without SMD.

RESULTS

On both early and delayed planar images, the mean H/M value in the subgroups of diabetic patients was significantly lower in the SMD (+) AN (+) group than in the control group, but among those subgroups, there was statistically significant difference between the SMD (+) AN (+) and SMD (-) AN (-) groups only on the delayed images. Regarding the WR value, there was no statistically significant difference among subjects. On SPECT image analysis, the diabetic subgroup with AN or SMD had statistically significant lower values for TUS than those of the control group. Among diabetics, there was a statistically significant differences between SMD [+] AN [+] and SMD [-] AN [-] on both early and delayed images. Similarly, the SMD [+] AN [-] group also had significantly lower values than those of SMD [-] AN [-] on early images. Regarding delta TUS, there was a statistically significant differences between AN [+] subgroups and controls. Similarly, the mean value for delta TUS was much higher in AN [+] subgroups than in AN [-] subgroups with or without SMD in diabetes mellitus.

CONCLUSION

123I-MIBG myocardial uptake is affected by both SMD and cardiac autonomic neuropathy. Based on the finding that delta TUS was much higher in AN [+] subgroups and there was no statistically significant difference between SMD [+] AN [+] and SMD [-] AN [+] subgroups, a decrease in myocardial 123I-MIBG uptake might progress independently of SMD.

Prevalence of coronary blood flow reserve abnormalities among patients with nonobstructive coronary artery disease and chest pain

OBJECTIVE

To determine the prevalence of abnormalities in endothelium-dependent and endothelium-independent coronary flow reserve among patients with non-obstructive coronary artery disease and chest pain.

MATERIAL AND METHODS

We studied endothelium-dependent (after infusion of 10(-6) M to 10(-4) M of acetylcholine) and endothelium-independent (after administration of 18 to 36 micrograms of adenosine) coronary flow reserve among patients with nonobstructive coronary artery disease and chest pain who were undergoing assessment at Mayo Clinic Rochester. Coronary blood flow was derived from coronary artery diameter assessed by quantitative angiography and Doppler flow velocities.

RESULTS

The cohort consisted of 203 patients (158 female and 45 male patients), who ranged in age from 17 to 78 years (mean, 51). Most patients (92%) had at least one risk factor for atherosclerosis; a substantial proportion had undergone extensive cardiac and noncardiac evaluation. Whereas 41.5% of the patients had normal coronary flow reserve, 58.5% had an abnormal response: 11.3% an impaired response to adenosine (flow velocity ratio of 2.5 or less), 29.2% an impaired response to acetylcholine (flow reserve ratio of 1.5 or less), and 18% a combined abnormality. No correlation (r2 = 0.03) was noted between endothelium-dependent and endothelium-independent flow reserve.

CONCLUSION

Most study patients with chest pain and nonobstructive coronary artery disease undergoing coronary vasomotor evaluation had risk factors for coronary artery disease and diverse abnormalities in endothelium-dependent or endothelium-independent coronary flow reserve (or both). These findings underscore the need for a comprehensive assessment.

Attenuation of myocardial ischemia with repeated exercise in subjects with chronic stable angina: relation to myocardial contractility, intensity of exercise and the adenosine triphosphate-sensitive potassium channel

OBJECTIVES

This study characterized the attenuation of myocardial ischemia observed with re-exercise to determine whether: 1) a differing exercise intensity modifies this attenuation; 2) it could be explained by contractile down-regulation or stunning; 3) it is mediated by activation of ATP-sensitive potassium channels (K+-ATP).

BACKGROUND

Subjects with ischemic heart disease (IHD) frequently note less angina with re-exercise after a brief rest. Potential mechanisms of this 'warm-up' phenomenon have been little explored.

METHODS

IHD subjects with a positive exercise test were studied. Groups I and II (12 subjects each) underwent 2 successive Naughton protocol exercise echocardiography tests (with 1 min instead of 2 min stages for Group II). Group D (10 subjects) had type II diabetes, were on > or =10 mg daily of the K+-ATP blocker, glibenclamide, and underwent the group I exercise protocol. The ischemic threshold or rate-pressure product at 1 mm ST segment depression, ST depression corresponding to the peak rate-pressure product of the first exercise (maximum ST depression equivalent), and left ventricular wall motion indexes before and immediately after each exercise were analyzed.

RESULTS

Exercise-induced myocardial ischemia with re-exercise was similarly attenuated in groups I, II, and D. The ischemic threshold was raised by nearly 20% with re-exercise (p=0.001, p=0.02, and p=0.02, respectively) and the maximum ST depression equivalent was nearly halved on re-exercise (p=0.005, p=0.006, and p=0.001, respectively). Exercise-induced wall motion dysfunction was attenuated with re-exercise. In group I, wall motion returned to the initial baseline score prior to exercise 2, whereas in the more intense protocol of group II, wall motion dysfunction persisted prior to exercise 2.

CONCLUSIONS

Thus, the attenuation of myocardial ischemia observed with re-exercise appears to be independent of the intensity of the exercise protocol and is not explained by down-regulation of myocardial contractility induced by the initial ischemic stimulus. Since results were similar in diabetic subjects on robust doses of glibenclamide, this phenomenon does not appear to be mediated by K+-ATP activation.