Left ventricular dilatation and pulmonary thallium uptake after single-photon emission computer tomography using thallium-201 during adenosine-induced coronary hyperemia

Transient ischaemic dilation and post-stress wall motion abnormality increase risk in patients with less than moderate ischaemia: analysis of the REFINE SPECT registry

AIMS

Ischaemia on single-photon emission computed tomography (SPECT) myocardial perfusion imaging (MPI) is strongly associated with cardiovascular risk. Transient ischaemic dilation (TID) and post-stress wall motion abnormalities (WMA) are non-perfusion markers of ischaemia with incremental prognostic utility. Using a large, multicentre SPECT MPI registry, we assessed the degree to which these features increased the risk of major adverse cardiovascular events (MACE) in patients with less than moderate ischaemia.

METHODS AND RESULTS

Ischaemia was quantified with total perfusion deficit using semiautomated software and classified as: none (<1%), minimal (1 to <5%), mild (5 to <10%), moderate (10 to <15%), and severe (≥15%). Univariable and multivariable Cox proportional hazard analyses were used to assess associations between high-risk imaging features and MACE. We included 16 578 patients, mean age 64.2 and median follow-up 4.7 years. During follow-up, 1842 patients experienced at least one event. Patients with mild ischaemia and TID were more likely to experience MACE compared with patients without TID [adjusted hazard ratio (HR) 1.42, P = 0.023], with outcomes not significantly different from patients with moderate ischaemia without other high-risk features (unadjusted HR 1.15, P = 0.556). There were similar findings in patients with post-stress WMA. However, in multivariable analysis of patients with mild ischaemia, TID (adjusted HR 1.50, P = 0.037), but not WMA, was independently associated with increased MACE.

CONCLUSION

In patients with mild ischaemia, TID or post-stress WMA identify groups of patients with outcomes similar to patients with moderate ischaemia. Whether these combinations identify patients who may derive benefit from revascularization deserves further investigation.

Coronary microvascular dysfunction: An important interpretation on the clinical significance of transient ischemic dilation of the left ventricle on myocardial perfusion imaging

PURPOSE

To further investigate the clinical significance of transient ischemic dilation (TID) on myocardial perfusion imaging (MPI) by analyzing the effect of anisodamine hydrobromide (a drug that can effectively ameliorate microcirculation) on the patients with isolated TID and the findings of previous literatures.

METHODS

Total 107 patients with isolated TID (TID value≥1.11) were randomly divided into group A (n = 36; intravenous administration of anisodamine hydrobromide), group N (n = 36; intravenous administration of isosorbide dinitrate), and group C (n = 35; intravenous administration of normal saline). MPI and treadmill exercise test (TET) were performed again after 14-day course of intervention. Pre- and post-intervention frequencies of symptom were recorded.

RESULTS

In group A, after intervention of anisodamine hydrobromide, the summed stress score (SSS) and TID value on MPI significantly decreased than those before intervention (P < 0.001), the durations of exercise (DEs) and metabolic equivalents (METs) in TET notably ascended (P < 0.001), as well as the symptom remarkably improved. In group N and group C, there were no significant differences in SSS, TID value, DEs, METs, and frequencies of symptom between pre- and post-intervention (P > 0.05). No significant improvement of symptoms in group N before and after treatment.

CONCLUSIONS

TID with perfusion defect may usually predict a possibility of severe and extensive coronary artery disease (CAD). An isolated TID should be considered as a likelihood of coronary microvascular dysfunction (CMD). TET and coronary CT angiography (cCTA) are extremely helpful for the antidiastole on CAD and CMD. The administration of anisodamine hydrobromide might be an optional treatment for the patients with isolated TID.

Upper reference limits of transient ischemic dilation ratio for different protocols on new-generation cadmium zinc telluride cameras: A report from REFINE SPECT registry

BACKGROUND

Upper reference limits for transient ischemic dilation (TID) have not been rigorously established for cadmium-zinc-telluride (CZT) camera systems. We aimed to derive TID limits for common myocardial perfusion imaging protocols utilizing a large, multicenter registry (REFINE SPECT).

METHODS

One thousand six hundred and seventy-two patients with low likelihood of coronary artery disease with normal perfusion findings were identified. Images were processed with Quantitative Perfusion SPECT software (Cedars-Sinai Medical Center, Los Angeles, CA). Non-attenuation-corrected, camera-, radiotracer-, and stress protocol-specific TID limits in supine position were derived from 97.5th percentile and mean + 2 standard deviations (SD). Reference limits were compared for different solid-state cameras (D-SPECT vs. Discovery), radiotracers (technetium-99m-sestamibi vs. tetrofosmin), different types of stress (exercise vs. four different vasodilator-based protocols), and different vasodilator-based protocols.

RESULTS

TID measurements did not follow Gaussian distribution in six out of eight subgroups. TID limits ranged from 1.18 to 1.52 (97.5th percentile) and 1.18 to 1.39 (mean + 2SD). No difference was noted between D-SPECT and Discovery cameras (P = 0.71) while differences between exercise and vasodilator-based protocols (adenosine, regadenoson, or regadenoson-walk) were noted (all P < 0.05).

CONCLUSIONS

We used a multicenter registry to establish camera-, radiotracer-, and protocol-specific upper reference limits of TID for supine position on CZT camera systems. Reference limits did not differ between D-SPECT and Discovery camera.

Diagnostic and prognostic significance of transient ischemic dilation (TID) in myocardial perfusion imaging: A systematic review and meta-analysis

BACKGROUND

Transient ischemic dilatation (TID) of the left ventricle is a potential marker of high risk obstructive coronary artery disease on stress myocardial perfusion imaging (MPI). There is, however, interstudy variation in the diagnostic performance of TID for identification of severe and extensive coronary disease anatomy, and varied prognostic implications in the published literature.

METHODS

We searched MEDLINE, EMBASE, and COCHRANE databases for studies where TID was compared with invasive or CT coronary angiography for evaluation of coronary artery stenosis. Two reviewers independently evaluated and abstracted data from each study. A bivariate random effects model was used to derive pooled sensitivities and specificities, in order to account for correlation between TID in MPI and anatomic disease severity.

RESULTS

A total of 525 articles were reviewed, of which 51 met inclusion criteria. Thirty-one studies contributed to the analysis, representing a total of 2037 patients in the diagnostic meta-analysis and 9003 patients in the review of prognosis. The ratio above which TID was deemed present ranged from 1.13 to 1.38. Pooled sensitivity was 44% (95% CI 30%-60%) and specificity was 88% (95% CI 83%-92%) for the detection of extensive or severe anatomic coronary artery disease. Analysis of outcome data demonstrated increased cardiac event rates in patients with TID and an abnormal MPI. In otherwise normal perfusion, TID is an indicator of poor prognosis in patients with diabetes and/or a history of coronary disease.

CONCLUSIONS

Among patients undergoing MPI, the presence of TID is specific for the detection of extensive or severe coronary artery disease.

Computer derived transient ischemic dilation ratio for identifying extensive coronary artery disease using a CZT camera and imaging in the upright position

BACKGROUND

Transient ischemic dilation (TID) of the left ventricle (LV) has not been validated as a marker of extensive coronary artery disease (CAD) for studies using a cadmium-zinc-telluride (CZT) camera with upright imaging.

METHODS

TID ratios were obtained from upright stress and rest images on a CZT camera. Separate cut-off values were determined for exercise and for regadenoson stress. The cutoffs were then applied to 28 patients with extensive CAD and 101 patients without extensive CAD.

RESULTS

With treadmill exercise, an upright TID ratio ≥1.16 provided a positive predictive value of 50% and a negative predictive value of 85.4% for the identification of extensive CAD. In the regadenoson group, an upright TID ratio of 1.29 provided a positive predictive value of 20% and a negative predictive value of 75.9%. Although not an independent predictor of extensive CAD in all subjects, in subjects with a normal upright LVEF, it provided a predictive value by receiver operating characteristics comparable to the SSS.

CONCLUSIONS

Increased upright TID measurements on a CZT camera are associated with extensive CAD. The upright TID measurements can serve in an adjunctive role to SSS, and may be most effective in patients with a normal upright exercise LVEF.

Transient Ischemic Dilation Ratio in Regadenoson, Single Isotope Gated Single-photon Emission Computed Tomography Myocardial Perfusion Imaging

Single isotope 99mTc single-photon emission computed tomography-myocardial perfusion imaging (SPECT-MPI) is the most commonly used protocol for nuclear stress testing. Transient ischemic dilation of the left ventricle (TID) has been considered a specific marker of severe coronary artery disease (CAD). Recent publications have questioned the clinical utility of TID, specifically with regadenoson as a stressor and 4DM-SPECT software for TID analysis. These findings have not been demonstrated using other imaging packages. The goal of our study was to establish the TID threshold in the identification of Multi-vessel CAD using Quantitative Perfusion SPECT (QPS) software. Included in this study are 190 patients that had undergone regadenoson-stress, same day, single-isotope 99mTc MPI and had a coronary angiography within a designated 3-month period. QPS (Cedars-Sinai, LA, CA) automated image analysis software was used to calculate TID ratios which were compared across different CAD categories. Coronary angiograms were reviewed to identify both obstructive and nonobstructive CAD. The mean TID for patients with nonobstructive CAD (n = 91) was 1.02 ± 0.11, and the threshold for TID was 1.24. A receiver operating characteristic curve showed that TID had a poor discriminatory capacity to identify MVD (area under the curve 0.58) with a sensitivity of 3% and a specificity of 97%. In our study with regadenoson MPI in a predominantly African-American population, TID was found to be a poor predictor of MVD using QPS software. The reason is unclear but possibly related to the significant decline in the prevalence of severe CAD in the area where our study took place.

Apparent left ventricular cavity dilatation during PET/CT in hypertrophic cardiomyopathy: Clinical predictors and potential mechanisms

BACKGROUND

Apparent left ventricular cavity dilatation (LVCD) in patients with hypertrophic cardiomyopathy (HCM) is an incompletely understood phenomenon. We aimed at investigating its clinical predictors and potential mechanisms.

METHODS

Sixty one HCM patients underwent N-13-ammonia PET for visual evaluation of LVCD, transient ischemic dilatation (TID) index, myocardial blood flow (MBF), coronary flow reserve (CFR), and regional myocardial perfusion (rMP). TID index was also derived at 2-4 and 15-20 minutes.

RESULTS

Visual LVCD and quantitative TID (>1.13 abnormal) agreement were excellent (k 0.91; P < .0001). LVCD-positive (n = 32) patients had greater LV thickness (2.26 ± 0.59 vs 1.92 ± 0.41 cm; P = .005), but lower stress MBF (1.66 ± 0.42 vs 2.07 ± 0.46 mL/minute/g; P < .0001), and CFR (1.90 ± 0.46 vs 2.46 ± 0.69; P < .0001) than LVCD-negative (n = 29) patients. Abnormal rMP was present in 31/32 LVCD-positive but only 12/29 (P < .0001) LVCD-negative. TID index was higher at 2-4 (1.30 ± 0.13) than at 15-20 minutes (1.27 ± 0.12; P = .001) in LVCD-positive, whereas it was the same (1.04 ± 0.07 vs 1.04 ± 0.07; P = .9) in LVCD-negative. In multivariate analysis, global peak MBF, abnormal rMP, and LV thickness were the best predictors of LVCD.

CONCLUSION

Apparent LVCD is a common finding in HCM, intimately related to abnormal myocardial perfusion, globally impaired vasodilator flow reserve, and degree of hypertrophy. In addition to regional and/or diffuse subendocardial ischemia, some degree of true LV chamber dilatation may also contribute to the occurrence of apparent LVCD in HCM.

Prognostic value of transient ischemic dilation with regadenoson myocardial perfusion imaging

BACKGROUND

Transient ischemic dilation (TID) of the left ventricle seen on myocardial perfusion imaging (MPI) is sometimes used as a marker of severe coronary artery disease. The prognostic value of TID obtained using regadenoson, a selective adenosine A2A receptor agonist, as a stress agent for MPI has not been studied.

METHODS

TID ratio was measured using an automated software program on consecutive patients with normal and abnormal perfusion pattern on regadenoson MPI at a single institution. An abnormal TID was defined as greater than 1.33. The primary outcome was a composite of cardiac death, non-fatal myocardial infarction (MI), and late coronary revascularization (CR, >90 days after MPI).

RESULTS

The study population consisted of 887 patients (62 ± 12 years, 66% male, 48% diabetes, 46% prior CR, 75% with abnormal perfusion pattern, left ventricular ejection fraction-LVEF 55 ± 6%). An abnormal TID was present in 51 (6%) patients. Baseline characteristics were not different based on the presence or absence of TID. Early CR (≤90 days) was performed in 11 (22%) patients with vs 92 (11%) patients without TID (P = .04). During a mean follow-up of 29 ± 19 months, the primary outcome occurred in 271 (31%) patients (22% cardiac death, 6% MI, 9% late CR). TID was associated with increased risk of the primary outcome (log-rank P = .017), an association largely driven by late CR. In a Cox proportional model adjusted for multiple variables including perfusion defect size (PDS) and LVEF, the hazard ratio for TID was 1.92 (95% CI 1.20-3.08, P = .007). In the subset of patients with normal perfusion pattern, there was no association between TID and outcomes.

CONCLUSIONS

TID on regadenoson MPI carries important prognostic information that is independent from PDS and LVEF, but this association is restricted to patients with abnormal perfusion on imaging.

The prognostic value of non-perfusion variables obtained during vasodilator stress myocardial perfusion imaging

Myocardial perfusion imaging (MPI) is an established diagnostic test that provides useful prognostic data in patients with known or suspected coronary artery disease. In more than half of the patients referred for stress testing, vasodilator stress is used in lieu of exercise. Unlike exercise, vasodilator stress does not provide information on exercise and functional capacity, heart rate recovery, and chronotropy, and ECG changes are less frequent. These non-perfusion data provide important prognostic and patient management information. Further, event rates in patients undergoing vasodilator MPI are higher than in those undergoing exercise MPI and even in those with normal images probably due to higher pretest risk. However, there are a number of non-perfusion variables that are obtained during vasodilator stress testing, which have prognostic relevance but their use has not been well emphasized. The purpose of this review is to summarize the prognostic values of these non-perfusion data obtained during vasodilator MPI.

Correlation between transient ischemic dilatation (TID) and coronary artery disease in Saudi male patients

OBJECTIVE

A high transient ischemic dilatation ratio (TID) for the left ventricle (LV) from a gated myocardial perfusion imaging (G-MPI) study is widely believed to be associated with significant coronary artery disease (CAD). We have investigated the relationship between TID and CAD for our male Saudi Arabian patient population.

METHODS

In this retrospective study, all male Saudi Arabian patients who underwent a two-day G-MPI study using Tc99m MIBI during the year 2011 having a TID ⩾ 1.20 were included. Quantitative perfusion and gated parameters were obtained using Cedar Sinai's AutoQuant software version 3.0, 2003, Means of summed stress scores, summed rest scores and summed difference scores (SSS, SRS, SDS, respectively), stress and rest ejection fraction (EF) were calculated. Visual interpretation was performed to classify the perfusion as normal, fixed, mixed (fixed and reversible defects), single reversible or multiple reversible defects. Coronary angiograms were assessed as normal with no CAD, single vessel, two-vessel or three-vessel disease. Correlations between the TID and other parameters were studied using analysis of variance (ANOVA) with IBM-SPSS version 20.

RESULTS

A total of 52 male patients had a high TID of ⩾1.20 (mean 1.30 ± 0.13). Ten patients had a SSS of 0-3 and 16 were classified as normal by visual assessment. Stress EF (mean 50.4 ± 12%) was lower than the rest EF (mean 56.6 ± 12.8%) with the difference being statistically significant (Students paired t-test, p = 0.001). Angiography results were available in 44 patients, 3 having a normal angiogram, 24 having three vessel disease, 7 having two vessel disease and 10 having one vessel disease. Five patients with normal perfusion and SSS = 0-3 had CAD as seen on a coronary angiography. CAD on coronary angiography showed a significant correlation with perfusion abnormalities as assessed by visual interpretation (p = 0.002). TID showed a significantly correlation with both perfusion abnormalities (p = 0.009), as assessed by visual interpretation, and with Summed difference scores, SDS (p = 0.000).

CONCLUSION

A high TID on G-MPI was a very sensitive indicator of significant CAD. In patients with normal perfusion and high TID further workup is warranted.

Diagnosing CAD: additional markers from myocardial perfusion SPECT

Over the past decades, stress/rest myocardial perfusion SPECT (MPS) has been utilized as a standard modality for the diagnosis, risk stratification and prognostic assessment of coronary artery disease (CAD). In addition to the perfusion information, MPS can also provide functional information of the left ventricle, including volume, ejection fraction, wall motion and dyssynchrony. This article introduces the incremental value of these non-perfusion parameters as markers and prognosticators of CAD.

Comparative assessment of rest and post-stress left ventricular volumes and left ventricular ejection fraction on gated myocardial perfusion imaging (MPI) and echocardiography in patients with transient ischaemic dilation on adenosine MPI: myocardial stunning or subendocardial hypoperfusion?

BACKGROUND

Transient ischaemic dilation (TID) on myocardial perfusion imaging (MPI) is an important finding, conveying a high risk of subsequent cardiac events. However, the mechanism leading to TID on MPI is not well elucidated. This study aimed to determine if TID is due to true LV cavity dilation and ventricular stunning, or is due to relative subendocardial hypoperfusion.

METHODS

31 patients undergoing single-day Tc-99m adenosine sestamibi MPI were recruited. All had routine ECG-gated single-day rest-stress adenosine MPI, with transthoracic echocardiograms (echo) acquired concurrently at rest, and both immediately, and 2 hours, post-stress. Echocardiography was performed using a Vivid-7 (GE). LV volumes and LVEF were quantified blinded to MPI results, using biplane Simpson method on echo, and quantitatively (including TID) with QGS(®), on MPI.

RESULTS

Patients were divided into quartiles for TID, with the top quartile considered TID positive [TID+ 9/31 (TID ratio 1.3 ± 0.09)], and TID negative [TID- 22/31 (TID ratio 1.01 ± 0.04)]. There was good correlation between resting echo and MPI physical measurements (LVEDV r(2) = 0.79, LVESV r(2) = 0.9, and LVEF r(2) = 0.75). On MPI, a significant drop in LVEF was observed between rest and early stress in the TID+ group (56.6% vs 46.5%, P < .002), as well as an increase in both LVESV (62 vs 79 mls, P < .0001) and LVEDV (113 vs 131 mls, P < .0001). However, no statistically significant change in LVEF, LVESV or LVEDV was identified on concurrent echo imaging (LVEF 57% vs 56%, P < .66; LVESV 48 vs 54 mls, P < .26; LVEDV 87 vs 97 mls, P < .299). No significant change in LVEF or ventricular volumes was noted in the TID- group by either echo or MPI.

CONCLUSION

Transient dilation of the left ventricle on adenosine MPI is not related to chamber enlargement and myocardial stunning, but is more likely a function of subendocardial hypoperfusion and impaired coronary flow reserve.

Assessment of transient ischemic dilation (TID) ratio in gated SPECT myocardial perfusion imaging (MPI) using regadenoson, a new agent for pharmacologic stress testing

BACKGROUND

Abnormal values of the transient ischemic dilation (TID) ratio are associated with severe and extensive coronary artery disease (CAD). The objective of this study was to determine the relationship between TID, determined from stress and rest ventricular volumes during regadenoson gated single-photon emission computed tomography myocardial perfusion imaging (MPI) dual isotope studies, and the extent of CAD found during coronary angiography.

METHODS

195 patients who underwent dual isotope MPI with regadenoson and cardiac angiography between March 2009 and February 2010 were analyzed. TID was calculated using commercially available software, Emory Cardiac Toolbox. Mean TID values were compared across disease types. A threshold for abnormal TID was determined by adding two standard deviations (SDs) to the mean TID of the "non-obstructive CAD" subgroup.

RESULTS

In the 195-patient group analyzed, the mean TID ratio for non-obstructive CAD (n = 104) was found to be 1.09 with a SD of 0.15. In a subgroup of patients whose angiogram was within 3 months of MPI (n = 155), the mean TIDs for non-obstructive disease (n = 81), single-vessel disease (n = 35), and multi-vessel disease (n = 39) were 1.09, 1.15, and 1.19 with SDs of 0.16, 0.19, and 0.26, respectively. Those with an abnormal TID had a crude and adjusted odds ratio of 3.4 for multi-vessel disease which was statistically significant. History of diabetes was not found to be a significant confounder, effect modifier, or mediator of the relationship between the TID and the vessel disease.

CONCLUSION

The mean TID ratio in patients with multi-vessel disease was 1.19. The threshold for an abnormal TID was 1.39 with specificity of 95% and sensitivity of 15% for determining multi-vessel CAD status. We conclude that the level of TID in gated SPECT MPI using regadenoson is associated with the degree of CAD on angiography.

Influence of attenuation correction on transient left ventricular dilation in dual isotope myocardial perfusion imaging in patients with known or suspected coronary artery disease

The aim of this study was to assess the effect of attenuation correction (AC) on left ventricular (LV) volumes and LV transient ischemic dilatation (TID) during dual-isotope single-photon emission computer tomographic (SPECT) myocardial perfusion imaging (MPI). Ninety-six patients (mean age 58 ± 11 years, 15% women, 38 patients completed exercise and 58 dipyridamole pharmacologic stress tests) assessed for known or suspected coronary artery disease underwent dual-isotope thallium-201 rest and technetium-99m sestamibi stress SPECT MPI with computed tomography-based AC. The TID ratio was calculated separately for non-AC and AC SPECT MPI studies as the ratio of the LV endocardial volume at stress divided by LV endocardial volume at rest. The mean and range of the gated LV ejection fraction during exercise and pharmacologic stress was 54 ± 12% (29% to 80%) and 58 ± 12% (27% to 80%), respectively. In the exercise stress group, the same mean LV endocardial volumes in non-AC and AC stress (76.4 ± 30 and 76.5 ± 28) and rest (66.3 ± 26 and 66.4 ± 24) studies were found (p = 0.90). There was no statistical difference between the mean exercise TID ratio in non-AC and AC studies (1.27 vs 1.31, respectively, p = 0.10). The same mean LV endocardial volumes in non-AC and AC in pharmacologic stress (79.9 ± 42 and 80 ± 41) and rest (71.4 ± 41 and 72.3 ± 37), respectively, were found (p = 0.50). There was no statistical difference between the mean dipyridamole TID ratio in non-AC and AC studies (1.20 vs 1.17, respectively, p = 0.10). In conclusion, LV volumes and TID indexes obtained on SPECT MPI with exercise or pharmacologic stress using dipyridamole are not affected by AC.

Transient ischemic dilation for coronary artery disease in quantitative analysis of same-day sestamibi myocardial perfusion SPECT

BACKGROUND

Transient ischemic dilation (TID) of the left ventricle in myocardial perfusion SPECT (MPS) has been shown to be a clinically useful marker of severe coronary artery disease (CAD). However, TID has not been evaluated for 99mTc-sestamibi rest/stress protocols (Mibi-Mibi). We aimed to develop normal limits and evaluate diagnostic power of TID ratio for Mibi-Mibi scans.

METHODS

TID ratios were automatically derived from static rest/stress MPS (TID) and gated rest/stress MPS from the end-diastolic phase (TID(ed)) in 547 patients who underwent Mibi-Mibi scans [215 patients with correlating coronary angiography and 332 patients with low likelihood (LLk) of CAD]. Scans were classified as severe (≥ 70% stenosis in proximal left anterior descending (pLAD) artery or left main (LM), or ≥ 90% in ≥ 2 vessels), mild to moderate (≥ 90% stenosis in 1 vessel or ≥ 70%-90% in ≥ 1 vessel except pLAD or LM), and normal (<70% stenosis or LLk group). Another classification based on the angiographic Duke prognostic CAD index (DI) was also applied: DI ≥ 50, 30 ≤ DI < 50 and DI < 30 or LLk group.

RESULTS

The upper normal limits were 1.19 for TID and 1.23 for TID(ed) as established in 259 LLk patients. Both ratios increased with disease severity (P < .0001). Incidence of abnormal TID increased from 2% in normal patients to >36% in patients with severe CAD. Similarly, when DI was used to classify disease severity, the average ratios showed significant increasing trend with DI increase (P < .003); incidence of abnormal TID also increased with increasing DI. The incidence of abnormal TID in the group with high perfusion scores significantly increased compared to the group with low perfusion scores (stress total perfusion deficit, TPD < 3%) (P < .0001). The sensitivity for detecting severe CAD improved for TID when added to mild to moderate perfusion abnormality (3% ≤ TPD < 10%): 71% vs 64%, P < .05; and trended to improve for TID(ed)/TID(es): 69% vs 64%, P = .08, while the accuracy remained consistent if abnormal TID was considered as a marker in addition to stress TPD. Similar results were obtained when DI was used for the definition of severe CAD (sensitivity: 76% vs 66%, P < .05 when TID was combined with stress TPD).

CONCLUSION

TID ratios obtained from gated or ungated Mibi-Mibi MPS and are useful markers of severe CAD.

Transient ischemic dilation ratio in 82Rb PET myocardial perfusion imaging: normal values and significance as a diagnostic and prognostic marker

In myocardial perfusion SPECT, transient ischemic dilation ratio (TID) is a well-established marker of severe ischemia and adverse outcome. However, its role in the setting of (82)Rb PET is less well defined.

METHODS

We analyzed 265 subjects who underwent clinical rest-dipyridamole (82)Rb PET/CT. Sixty-two subjects without a prior history of cardiac disease and with a normal myocardial perfusion study had either a low or a very low pretest likelihood of coronary artery disease or negative CT angiography. These subjects were used to establish a reference range of TID. In the remaining 203 patients with an intermediate or high pretest likelihood, subgroups with normal and abnormal TID were established and compared with respect to clinical variables, perfusion defect scores, left ventricular function, and absolute myocardial flow reserve. Follow-up was obtained for 969 ± 328 d to determine mortality by review of the social security death index.

RESULTS

In the reference group, TID ratio was 0.98 ± 0.06. Accordingly, a threshold for abnormal TID was set at greater than 1.13 (0.98 + 2.5 SDs). In the study group, 19 of 203 patients (9%) had an elevated TID ratio. Significant differences between subgroups with normal and abnormal TID ratio were observed for ejection fraction reserve (5.0 ± 6.4 vs. 1.8 ± 7.9; P < 0.05), difference between end-systolic volume (ESV) at rest and stress (ΔESV[stress-rest]; 1.8 ± 7.4 vs. 12.3 ± 13.0 mL; P < 0.0001), difference between end-diastolic volume (EDV) at rest and stress (ΔEDV[stress-rest]; 10.8 ± 11.5 vs. 23.8 ± 14.6 mL; P < 0.0001), summed rest score (1.8 ± 3.8 vs. 3.8 ± 7.6; P < 0.05), summed stress score (3.0 ± 5.4 vs. 7.5 ± 9.8; P < 0.002), summed difference score (1.3 ± 2.6 vs. 3.7 ± 5.3; P < 0.02), and global myocardial flow reserve (2.1 ± 0.8 vs. 1.7 ± 0.6; P < 0.02). Additionally, TID-positive patients had a significantly lower overall survival probability (P < 0.05). In a subgroup analysis of patients without regional perfusion abnormalities, TID-positive patients' overall survival probability was significantly smaller (P < 0.03), and TID was an independent predictor (exponentiation of the B coefficients [Exp(b)] = 6.22; P < 0.009) together with an ejection fraction below 45% (Exp[b] = 6.16; P < 0.002).

CONCLUSION

The present study suggests a reference range of TID for (82)Rb PET myocardial perfusion imaging that is in the range of previously established values for SPECT. Abnormal TID in (82)Rb PET is associated with more extensive left ventricular dysfunction, ischemic compromise, and reduced global flow reserve. Preliminary outcome analysis suggests that TID-positive subjects have a lower overall survival probability.

Predictive and prognostic values of transient ischemic dilatation of left ventricular cavity for coronary artery disease and impact of various managements on clinical outcome using technetium-99m sestamibi gated myocardial perfusion imaging

BACKGROUND

Transient ischemic dilatation (TID) of LV cavity during stress gated myocardial perfusion imaging (GMPI) is known as a predictor of severe CAD and signifies worse prognosis.

OBJECTIVES

To assess predictive and prognostic value of TID of LV cavity using GMPI and clinical outcome in patients treated conservatively or with revascularization.

METHODS

189 patients out of 2689 were recruited (M:F 127/62, mean age 56 ± 9 years) whose same-day stress GMPI revealed TID ratio (> 1.22) with no (sum stress score, SSS < 2) or reversible perfusion defects (sum difference score, SDS > 2). Coronary angiography (CA) was performed within 3 months in 125/189 cases who were followed for mean period of 18 ± 4 months for fatal or non-fatal MI.

RESULTS

CA was positive in 121/125 patients with TID for significant CAD (LAD = 11, multi vessel disease = 110 patients, positive predictive value 95%) and negative for obstructive disease in 4/125 (false-positive cases). 41/121 underwent revascularization within 2 months of CA (Intervention group), and remaining 80/121 were managed conservatively (Non-Intervention group). Overall event rate was 20% (4/16%: fatal/non-fatal MIs). Kaplan-Meier survival curves revealed event-free survival in Intervention and Non-Intervention groups for fatal MI 98/96% (P = 0.758), and for non-fatal MI, it was 97/58%, respectively (P = 0.042).

CONCLUSION

We conclude that TID is a reliable predictor of multi vessel CAD and is associated with high incidence of non-fatal MIs than fatal MIs. Revascularization (PCI/CABG) rather than medical treatment should be considered in patients with TID for better clinical outcome.

The significance of transient ischemic dilation in the setting of otherwise normal SPECT radionuclide myocardial perfusion images

BACKGROUND

Transient ischemic dilation (TID) in the setting of an abnormal SPECT radionuclide myocardial perfusion imaging (MPI) study is considered a marker of severe and extensive coronary artery disease (CAD). However, the clinical significance of TID and its association with CAD in patients with an otherwise normal MPI study is unclear.

METHODS

From a database of patients who underwent MPI over a 9-year period, 96 without known cardiac history who had normal image perfusion patterns, and who underwent coronary angiography within 6 months, were identified. TID quantitative values were derived. To adjust for varying stress and image protocols, a TID index based on published threshold values was derived for each patient, with >1 considered as TID. We examined the relationship of TID to the presence/extent of CAD, and to a CAD prognostic index. TID was also correlated with patient survival. To address referral bias, survival in a separate cohort of 3,691 patients with a normal perfusion MPI who did not undergo angiography in the 6-month interval was correlated with the presence and severity of TID.

RESULTS

For 28 (29.2%) patients with normal MPI perfusion patterns but with TID, there was no increased incidence of CAD, multivessel or left main disease, or a higher prognostic index compared with no TID. In addition, there was no increased mortality associated with TID in both the angiography cohort and in the patients who did not undergo immediate angiography.

CONCLUSIONS

TID in patients with an otherwise normal SPECT MPI study does not increase the likelihood of CAD, its extent or severity, and is not associated with worsened patient survival.

Clinical predictors of stress-induced transient left ventricular dilatation in patients with nonsignificant coronary disease

Left ventricular transient dilatation (TD) during stress myocardial perfusion imaging has been associated with extensive and severe coronary artery disease (CAD). The authors investigated the clinical predictors of TD in patients with nonsignificant CAD. The authors retrospectively studied 134 consecutive patients with exercise (n=59) or dipyridamole (n=75) stress-induced TD who had undergone coronary angiography within 6 months of the test. Significant CAD was defined as diameter stenosis ≥70% in at least one major coronary artery, and significant left main disease as >50% diameter stenosis. Angiographically-significant CAD was found in 126 patients (94%), and nonsignificant CAD in the remaining 8 patients (6%). No differences in gender, history of smoking, hyperlipidemia, family history of CAD, body mass index, and left ventricular ejection fraction were found between patients with significant and nonsignificant CAD. All 8 nonsignificant CAD patients had a history of either hypertension (7/8) or electrocardiographic criteria for left ventricular hypertrophy (1/8), compared with 58% of the hypertensive patients in the significant CAD group (P=.02). Nonsignificant CAD patients were also characterized by lack of diabetes mellitus (P=.05) or prior myocardial infarction (P=.05). Hypertension seems to be an important clinical predictor of TD in patients with nonsignificant CAD.

Prospective evaluation of the impact of diabetes and left ventricular hypertrophy on the relationship between ischemia and transient ischemic dilation of the left ventricle on single-day adenosine Tc-99m myocardial perfusion imaging

BACKGROUND

Diabetes and left ventricular hypertrophy (LVH) can cause coronary flow reserve abnormalities in the absence of coronary artery disease (CAD). We sought to evaluate the impact of LVH and diabetes on the relationship between ischemia, severe CAD, and transient ischemic dilation (TID) on adenosine myocardial perfusion imaging (MPI).

METHODS AND RESULTS

We prospectively recruited 157 patients referred for routine single-day adenosine technetium 99m MPI. LVH was assessed by use of transthoracic echocardiography. A ratio of 1.19 or greater on MPI defined TID in men and 1.31 or greater in women. Summed difference scores were determined by use of a 17-segment 5-point scoring system. TID was present in 22 of 157 patients (14%), diabetes in 54 of 157 (34%), and LVH in 42 of 157 (27%). By multivariate logistic regression, LVH, ischemia (summed difference score >2), and diabetes were independently predictive of TID. The incidence of TID was stratified by the presence or absence of diabetes and/or LVH in those with ischemia on MPI (8/8 [100%] vs 0/11 [0%], P < .002) or severe CAD on angiography (5/7 [71%] vs 0/8 [0%], P < .01). All those with TID (22/22 [100%]) had either diabetes or LVH (or both).

CONCLUSION

Although this study confirms the association between TID and both ischemia and severe CAD, all patients with TID had diabetes, LVH, or frequently, both, suggesting that the pathophysiology of these disease processes may play an integral role in the manifestation of TID on adenosine MPI.

Important parameters in the detection of left main trunk disease using stress myocardial perfusion imaging

OBJECTIVES

We sought noninvasively to diagnose left main trunk (LMT) disease using myocardial perfusion imaging (MPI).

METHODS

Five hundred and eight patients with suspected coronary artery disease (CAD) underwent both stress MPI and coronary angiography. The extent and severity of perfusion abnormalities were assessed using a 20-segment model. In addition, perfusion defects in both left anterior descending and left circumflex arterial territories were defined as a left main (LM) pattern defect, and those in 3-coronary arterial territories as a 3-vessel pattern defect.

RESULTS

In 42 patients with LMT disease, a summed stress score (19.4 ± 10.0 vs. 13.5 ± 10.0; p < 0.0001) and a summed rest score (12.1 ± 9.7 vs. 7.0 ± 7.8; p = 0.002) were greater than in 466 patients without LMT disease, while a summed difference score was similar (7.3 ± 7.7 vs. 6.5 ± 6.1; p = NS). The prevalence of an LM-pattern defect was low in both groups (12% vs. 8%; p = NS). However, a 3-vessel pattern defect (33% vs. 7%; p < 0.0001), lung uptake of radiotracers (38% vs. 11%; p < 0.0001), and transient ischemic dilation (31% vs. 13%; p = 0.003) were more frequently observed in patients with LMT disease than in those without. Logistic regression analysis showed that a 3-vessel pattern defect (OR=3.5, 95% CI = 1.4-8.8; p = 0.007), lung uptake of radiotracers (OR = 2.5, 95% CI = 1.1-5.7; p = 0.03), and previous myocardial infarction (MI) (OR = 2.4, 95% CI = 1.0-5.7; p = 0.05) were the most important parameters to detect LMT disease. After excluding 163 patients with previous MI, a repeat analysis revealed that lung uptake of radiotracers (OR = 8.2, 95% CI = 2.3-29.2; p = 0.001) and an LM-pattern defect (OR = 6.3, 95% CI = 1.4-27.2; p < 0.02) were independent predictors for LMT disease.

CONCLUSION

In the identification of LMT disease, lung uptake of radiotracers was a single best parameter, which was independent of the presence or absence of previous MI.

Transient ischemic dilation ratio (TID) correlates with HbA(1c) in patients with diabetes type 2 with proven myocardial ischemia according to exercise myocardial SPECT

OBJECTIVE

Abnormal values of the transient ischemic dilation ratio (TID) according to an exercise myocardial SPECT are linked to severe coronary artery disease. The authors investigated the relationship between TID and the levels of VCAM, ICAM, E-selectin, microalbuminuria, intima-media thickness and HbA(1c) of diabetic subjects.

METHODS

We observed 38 subjects with diabetes type 2 (10 women, 28 men), of average age 56.08 +/- 8.24 years, with no past history of cardiovascular disease. All subjects were examined using an exercise myocardial SPECT. Transient ischemic dilation, summed stress score (SSS), summed rest score (SRS) and stress total severity score (STSS) were determined to quantify myocardial ischemia.

RESULTS

The average IMT value was 1.05 +/- 0.31 mm. The TID value was 1.02 +/- 0.154, VCAM 795.24 +/- 163.25 mg/l, ICAM 516.55 +/- 164.07, E-selectin 63.82 +/- 38.89, HbA(1c) 7.09 +/- 1.68%, microalbuminuria 68.01 +/- 55.21 mg/l. When ascertaining the relation of TID to the other factors we used Pearson's correlation at the level of significance p < 0.05. We proved a statistically significant correlation between the value of TID and glycosylated hemoglobin HbA(1c) (p = 0.035); the other factors did not show any significant correlation.

CONCLUSION

Diabetes and its long- term unsatisfactory compensation can be one of the factors which affect left ventricular transient ischemic dilation.

Role of angiographic coronary artery collaterals in transient ischemic left ventricular cavity dilatation during stress echocardiography

BACKGROUND

The role of coronary artery collaterals in transient ischemic left ventricular (LV) dilatation (TID) during stress echocardiography is not well defined.

HYPOTHESIS

Transient ischemic LV dilatation is a marker for extensive and severe coronary artery disease and represents patients without good collaterals.

METHODS

We evaluated 212 consecutive patients (57 +/- 16 years, 70% male) who had coronary angiography and stress echocardiography within a 3-month period. This cohort of patients was divided into three groups based on type of collaterals: Group A: no collaterals; Group B: collaterals supplied by vessels without flow-limiting stenosis (good collaterals); Group C: collaterals supplied by vessels with flow-limiting stenosis (bad/jeopardized collaterals). In all patients, angiographic jeopardy score (AJS), ejection fraction (EF), and wall motion score index (WMSI) at rest and during stress were evaluated. Transient ischemic LV dilatation was defined as transient increase in the end-systolic dimensions from rest to peak stress.

RESULTS

Transient ischemic LV dilatation was present in 42 (20%) patients. Patients with TID had a lower EF, higher AJS, greater number of ischemic segments, and higher peak WMSI. Patients with TID in Group A (no collaterals) and Group C (jeopardized collaterals) had a greater percentage of multivessel disease than those in Group B (good collaterals). Presence of Group A or Group C collaterals was a predictor of TID even after controlling for multivessel disease, rest and peak WMSI, and left anterior descending artery disease.

CONCLUSIONS

Transient ischemic LV dilatation on stress echocardiography is a marker for extensive and severe coronary artery disease and represents patients with angiographically absent collaterals or those with jeopardized coronary collaterals.

Relationship of transient ischemic dilation in dipyridamole myocardial perfusion imaging and stress-induced changes of functional parameters evaluated by Tl-201 gated SPECT

BACKGROUND

This study assessed whether transient ischemic dilation (TID) of the left ventricle is related to ischemic stunning, manifested by stress-induced decrease of left ventricular ejection fraction (LVEF) and worsening of wall motion, by use of dipyridamole-stress and redistribution thallium 201 gated single photon emission computed tomography (SPECT).

METHODS AND RESULTS

Ninety-two consecutive patients undergoing dipyridamole Tl-201 gated SPECT were included. Patients with a TID ratio in the highest quartile were defined as having TID. In patients with TID, end-diastolic volume (EDV) and end-systolic volume (ESV) were both significantly greater on dipyridamole-stress images than on redistribution images (P < .001). The degree of enlargement was much greater for ESV than EDV. In patients without TID, EDV and ESV were both decreased after stress (P < .001). Patients with TID had a lower mean LVEF on dipyridamole-stress images than on redistribution images (P < .001). Patients without TID had a higher mean LVEF on dipyridamole-stress images than on redistribution images (P < .001). Patients with TID had a significant worsening of global wall motion on dipyridamole-stress images than on redistribution images (P < .001), but patients without TID did not.

CONCLUSION

TID was significantly correlated with ischemic stunning, and the enlargement of ESV was an important factor resulting in TID.

Prediction of Cardiac Events in Patients With Transient Left Ventricle Dilation on Stress Myocardial Perfusion SPECT Images

BACKGROUND

The purpose of this study was to investigate cardiac events in patients with transient left ventricle (LV) dilation on stress myocardial perfusion single-photon emission computed tomography images (MPI).

METHODS AND RESULTS

Consecutive patients (n=53, 31 males, mean age 71 years) with transient LV dilation on thallium-201 stress MPI (treadmill: 21, pharmacologic: 32) were followed for 17 months. Follow-up time was censored at the occurrence of cardiac death, congestive heart failure, acute coronary syndrome, or revascularization. Images were scored and then the summed stress score (SSS), summed rest score, and summed difference score were calculated. Cardiac death occurred in 3 patients, hospitalization occurred in 8 patients, and revascularization occurred in 20 patients. The combined cardiac event rate was 59% (76% for exercise stress vs 47% for pharmacologic stress, p=0.034). Cox regression analysis demonstrated that a combination of higher SSS and slow washout rate was the best predictor of cardiac events (hazard ratio =3.3, p=0.029).

CONCLUSIONS

A high cardiac event rate is associated with transient LV dilation on thallium-201 stress MPI. The event rate is particularly high for exercise stress MPI. Furthermore, a combination of the SSS and thallium-201 slow washout is the best predictor of cardiac events in patients with transient LV dilation.

Transient Left Ventricular Dilatation in the Absence of Epicardial Disease on Angiography

A 58-year-old woman with a previous anterior myocardial infarction, recurrent chest pain, transient adenosine-induced left ventricular dilatation but no apparent epicardial disease on angiography is presented. Transient ischemic dilatation during myocardial perfusion imaging, and the reported causes of transient left ventricular dilatation in the absence of epicardial disease, are discussed.

Transient ischemic dilation ratio of the left ventricle is a significant predictor of future cardiac events in patients with otherwise normal myocardial perfusion SPECT

OBJECTIVES

This study evaluated the prognostic value of transient ischemic dilation (TID) of the left ventricle (LV) in patients with normal stress myocardial perfusion single photon emission computed tomography (MPS).

BACKGROUND

The prognostic value of TID in patients with an otherwise normal MPS has not been defined.

METHODS

We identified 1,560 patients who had normal stress MPS (436 vasodilator and 1,124 exercise stress), and no rest LV enlargement (Population 1) and followed up for 2.30 +/- 0.67 years for hard events (HE) (cardiac death or myocardial infarction) and soft events (SE) (revascularization). Prediction of first HE or SE (total events [TE]) was evaluated by multivariable Cox analysis, which was also applied to a broader group of 2,037 patients (including patients with minimal defects (Population 2).

RESULTS

In Population 1, there were 13 HE, 36 SE, and 42 TE. Patients in the highest TID quartile (TID > or =1.21) had a higher TE rate than others, regardless of stress type. By multivariable analysis, highest TID quartile was predictive of TE (p = 0.008). Other independent predictors of TE were age, typical angina, and diabetes. In Population 2, TID was also predictive of TE.

CONCLUSIONS

An entirely normal stress MPS study does not always imply an excellent prognosis. In patients with otherwise normal MPS, TID is an independent and incremental prognostic marker of TE even after significant clinical variables--age, typical angina, and diabetes--are accounted for. When TID is present, caution in making low-risk prognostic statements may be warranted, especially in patients with typical angina, the elderly, and diabetics. Our findings also appear to apply to the broader population of "normal" MPS, which included patients with minimal perfusion defects.

Electrocardiogram-gated single-photon emission computed tomography versus cardiac magnetic resonance imaging for the assessment of left ventricular volumes and ejection fraction: a meta-analysis

OBJECTIVES

The purpose of this study was to evaluate the accuracy of electrocardiogram (ECG)-gated single-photon emission computed tomography (SPECT) for assessment of left ventricular (LV) end-diastolic volume (EDV), end-systolic volume (ESV) and ejection fraction (EF) compared with the gold standard of cardiac magnetic resonance imaging (MRI).

BACKGROUND

Several comparisons of ECG-gated SPECT with cardiac MRI have been performed for evaluation of LV volumes and EF, but each has considered few subjects, thus leaving uncertainty about the frequency of discrepancies between the two methods.

METHODS

We performed a meta-analysis of data on 164 subjects from nine studies comparing ECG-gated SPECT versus cardiac MRI. Data were pooled in correlation and regression analyses relating ECG-gated SPECT and cardiac MRI measurements. The frequency of discrepancies of at least 30 ml in EDV, 20 ml in ESV and 5% or 10% in EF and concordance for EF < or =40% versus >40% were determined.

RESULTS

There was an overall excellent correlation between ECG-gated SPECT and cardiac MRI for EDV (r = 0.89), ESV (r = 0.92) and EF (r = 0.87). However, rates of discrepancies for individual subjects were considerable (37% [95% confidence interval [CI], 26% to 50%] for at least 30 ml in EDV; 35% [95% CI, 23% to 49%] for at least 20 ml in ESV; 52% [95% CI, 37% to 63%] for at least 5% in EF; and 23% [95% CI, 11% to 42%] for at least 10% in EF). The misclassification rate for the 40% EF cutoff was 11%.

CONCLUSIONS

Electrocardiogram-gated SPECT measurements of EDV, ESV and EF show high correlation with cardiac MRI measurements, but substantial errors may occur in individual patients. Electrocardiogram-gated SPECT offers useful functional information, but cardiac MRI should be used when accurate measurement is required.

Assessment of transient left ventricular dilatation on rest and exercise on Tc-99m tetrofosmin myocardial SPECT

In myocardial perfusion imaging, multiple-vessel involvement of coronary artery disease (CAD) sometimes makes diagnosis difficult. Transient left ventricular (LV) dilatation on Tl-201 myocardial SPECT is a useful finding that enables the clinician to identify patients with multiple-vessel disease. The aim of this study was to confirm the utility of measuring transient LV dilatation for the detection of multiple-vessel CAD in exercise Tc-99m tetrofosmin myocardial SPECT. The participants were 55 CAD patients and 20 controls who underwent Tc-99m tetrofosmin myocardial SPECT exercise and resting imaging. During exercise, 370 MBq (10 mCi) Tc-99m tetrofosmin was injected. Exercise images were obtained 30 minutes after injection. At 210 minutes after injection, 740 MBq (20 mCi) Tc-99m tetrofosmin was administered intravenously. The rest SPECT images were acquired 30 minutes later. Thirty-six radii at every 10 degrees were generated from the center of short-axis images. An area surrounded by 36 maximal points of the myocardial Tc-99m tetrofosmin counts on each radius was calculated for exercise and rest images. The area surrounded by the 36 maximal points in the same slice of the exercise and rest images was assigned the variables A (Ex) and A(R), respectively. The transient dilatation index (TDI) of the left ventricle was calculated using the formula mean A (Ex)/A(R) in the apical, middle, and basal myocardial short-axis images. In the controls, the TDI was 0.970 +/- 0.021. In patients with CAD, the TDIs of one-vessel disease, two-vessel disease, and three-vessel disease were 1.034 +/- 0.032, 1.093 +/- 0.046, and 1.131 +/- 0.076, respectively. The TDIs were significantly greater in patients who had more occluded coronary arteries (P < 0.01). If the mean + 2SD of the TDI (1.012) in controls were assumed to be the normal upper limit, the sensitivity, specificity, and accuracy of this method in detecting two-vessel or three-vessel disease would be 91.4%, 76.9%, and 84%, respectively. The TDI is a useful index for evaluating subendocardial ischemia non-invasively and detecting multiple-vessel disease clinically.

Postexercise left ventricular function: a comparative assessment by different noninvasive imaging modalities

The variety of noninvasive imaging modalities now available permits assessment of different aspects of left ventricular function in the postexercise state. Some of these modalities, such as first-pass radionuclide ventriculography, permit a nearly instantaneous assessment of left ventricular function in the early postexercise state. These modalities indicate that most exercise-induced left ventricular wall motion abnormalities resolve quickly after exercise. Resting wall motion abnormalities may also improve in the postexercise period; this response indicates the presence of hibernating myocardium capable of improving in response to myocardial revascularization procedures. On the other hand, all imaging techniques indicate that a certain percentage of exercise-induced wall motion abnormalities may persist into the postexercise period, and this finding signifies that severe coronary disease subtends the region of persisting wall motion abnormality. Further, if there is increased left ventricular size after exercise, both extensive and severe coronary disease are present. A conceptual framework for unifying these disparate findings is provided. These results underscore the importance of postexercise imaging in enhancing clinical assessment and imply that there are important technical considerations to contemplate when performing certain tests such as postexercise echocardiography.

Comparison of methods for quantification of transient ischaemic dilation in myocardial perfusion SPET

The purpose of this study was to compare six methods of measuring the left ventricular (LV) transient ischaemic dilation (TID) ratio during stress-rest myocardial perfusion single-photon emission tomography (SPET). The TID ratio was defined as the mean LV short-axis area at stress divided by the mean LV area of similar slices at rest. The centre of the LV wall was defined as either the maximum, mean or median of the radial short-axis count profiles. The area within the endocardial wall was also calculated for each definition of the LV wall centre. We identified 50 consecutive patients undergoing dipyridamole technetium-99m-tetrofosmin SPET imaging and angiography. Continuous receiver operating characteristic (CROC) analysis showed no significant difference between the six methods in terms of identifying severe coronary artery disease (P >0.47). Algorithms using the mean or the median value in the profile were significantly more robust than those using the maximum (P <0.0005). TID measured by all the algorithms is an indicator of severe coronary disease (P < 0.05). The algorithms compared provide a repeatable, quantitative and specific measure of the TID ratio.

Pharmacological stress testing

Pharmacological stress in conjunction with radionuclide myocardial perfusion imaging has become a widely used noninvasive method of assessing patients with known or suspected coronary artery disease. In the United States, over one third of perfusion imaging studies are performed with pharmacological stress. Pharmacological stress agents fall into two categories: coronary vasodilating agents such as dipyridamole and adenosine, and cardiac positive inotropic agents such as dobutamine and arbutamine. For both, in the presence of coronary artery disease (CAD), perfusion image abnormalities result from heterogeneity of coronary blood flow reserve. Vasodilating agents work directly on the coronary vessels to increase blood flow, whereas inotropic agents work indirectly by increasing myocardial work load, which then leads to an increase in coronary blood flow. Both classes of agents have high accuracies for diagnosing coronary artery disease, and they have excellent safety records with acceptably low occurrences of side effects. For dipyridamole planar thallium imaging, pooled analysis yields a sensitivity of 85% and a specificity of 87% for diagnosis of coronary disease, but there is a large variation in reported values depending on various factors, such as the extent of postcatheterization referral bias, the type of imaging (planar versus single photon emission computed tomography [SPECT]), the types of patients being studied (single versus multivessel disease, men versus women), and the imaging agent used (thallium versus one of the technetium-based agents). Diagnostic accuracies for adenosine are similar to those of dipyridamole, with reported overall sensitivities ranging from 83% to 97%, and specificities ranging from 38% to 94%. For dobutamine, pooled analyses yield a sensitivity of 82% and a specificity of 75%. There is some concern that dobutamine may interfere with uptake of technetium-99m sestamibi, lowering the sensitivity for detection of disease, and thus the vasdodilating agents are generally preferred. Pharmacological stress testing has high clinical use for risk stratifying patients with known or suspected CAD, in patients after myocardial infarction, and in patients needing noncardiac surgery. Vasodilating agents are particularly advantageous in assessing post-myocardial infarction patients, allowing testing as soon as 2 days after the event. Like patients undergoing exercise stress testing, patients with normal perfusion images by pharmacological stress have a <1% annual incidence of cardiac events. The likelihood of an event increases with the extent and severity of perfusion abnormalities. However, it is important to consider clinical variables when using perfusion imaging for risk stratification, particularly in the presurgery patients. As with exercise testing, adjunct markers such as ST segment depression during testing, lung uptake of radiotracer (if thallium is used), and ventricular cavity dilatation add additional prognostic information to that available from the perfusion images alone. The aim of current research is to find better agents that are easier to use and that have fewer side effects. MRE-0470 is an experimental vasodilating agent that is more receptor selective than adenosine and promises a lower incidence of hypotension. Arbutamine more closely simulates exercise than dobutamine, and it can be administered by a closed-loop computerized delivery device. Work is also underway to look at novel uses of pharmacological stress agents, such as acquiring gated SPECT images during dobutamine infusion to enhance detection of myocardial viability. With increasing use of noninvasive testing in elderly patients and in patients with comorbidities that preclude adequate exercise, pharmacological stress testing has become an indispensable tool for radionuclide myocardial perfusion imaging studies. A good understanding of pharmacological stress testing is essential for performing high-quality nuclear cardiology