Intrinsic dual-energy processing of myocardial perfusion images

We have developed a software-based method for processing dual-energy 201TI SPECT emission projection data with the goal of calculating a spatially dependent index of the local impact of gamma-ray attenuation. We refer to this method as intrinsic dual-energy processing (IDEP).

METHODS

IDEP exploits the differential attenuation of lower energy emissions (69-83 keV) and higher energy emissions (167 keV) resulting from the decay of 201TI to characterize the relative degree of low-energy gamma-ray attenuation throughout the myocardium. In particular, IDEP can be used to estimate the relative probability that a low-energy gamma-ray emitted from a particular region of the myocardium is detected during the acquisition of SPECT projection data. Studies on phantoms and healthy human volunteers were performed to determine whether the IDEP method yielded detection probability images with systematic structure visible above the noise of these images and whether the systematic structure in the detection probability images could be rationalized physically. In patient studies, the relative regional detection probabilities were applied qualitatively to determine the likely effects of attenuation on the distribution of mapped photon emissions.

RESULTS

Measurements of the detection probability in uniform phantoms showed excellent agreement with those obtained from computer simulations for both 180 degrees and 360 degrees acquisitions. Additional simulations with digital phantoms showed good correlation between IDEP-estimated detection probabilities and calculated detection probabilities. In patient studies, the IDEP-derived detection probability maps showed qualitative agreement with known nonuniform attenuation characteristics of the human thorax. When IDEP data were integrated with the findings on the emission scan, the correlation with coronary anatomy (known in 6 patients and hypothesized on the basis of clinical and electrocardiographic parameters in 5 patients) was improved compared with evaluating the mapped emission image alone.

CONCLUSION

The IDEP method has the potential to characterize the attenuation properties of an object without use of a separate transmission scan. Coupled with the emission data, it may aid coronary diagnosis.

Ventricular contraction abnormalities in dilated cardiomyopathy: effect of biventricular pacing to correct interventricular dyssynchrony

OBJECTIVE

To measure ventricular contractile synchrony in patients with dilated cardiomyopathy (DCM) and to evaluate the effects of biventricular pacing on contractile synchrony and ejection fraction.

BACKGROUND

Dilated cardiomyopathy is characterized by abnormal ventricular activation and contraction. Biventricular pacing may promote a more coordinated ventricular contraction pattern in these patients. We hypothesized that biventricular pacing would improve synchrony of right ventricular and left ventricular (RV/LV) contraction, resulting in improved ventricular ejection fraction.

METHODS

Thirteen patients with DCM and intraventricular conduction delay underwent multiple gated equilibrium blood pool scintigraphy. Phase image analysis was applied to the scintigraphic data and mean phase angles computed for the RV and LV. Phase measures of interventricular (RV/LV) synchrony were computed in sinus rhythm and during atrial sensed biventricular pacing (BiV).

RESULTS

The degree of interventricular dyssynchrony present in normal sinus rhythm correlated with LV ejection fraction (r = -0.69, p < 0.01). During BiV, interventricular contractile synchrony improved overall from 27.5 +/- 23.1 degrees to 14.1 +/- 13 degrees (p = 0.01). The degree of interventricular dyssynchrony present in sinus rhythm correlated with the magnitude of improvement in synchrony during BiV (r = 0.83, p < 0.001). Left ventricular ejection fraction increased in all thirteen patients during BiV, from 17.2 +/- 7.9% to 22.5 +/- 8.3% (p < 0.0001) and correlated significantly with improvement in RV/LV synchrony during BiV (r = 0.86, p < 0.001).

CONCLUSIONS

Dilated cardiomyopathy with intraventricular conduction delay is associated with significant interventricular dyssynchrony. Improvements in interventricular synchrony during biventricular pacing correlate with acute improvements in LV ejection fraction.

Long-term estrogen replacement therapy is associated with improved exercise capacity in postmenopausal women without known coronary artery disease

BACKGROUND

Short-term estrogen administration improves vasodilation and has been shown to improve exercise capacity. However, it is unknown whether long-term estrogen replacement therapy is associated with improved exercise capacity in postmenopausal women without known coronary artery disease.

METHODS AND RESULTS

We studied 248 postmenopausal women without known coronary artery disease (mean age 63.5 years); 158 (64%) were current or past hormone replacement therapy (HRT) users and 108 (44%) were current users of HRT. Attributes potentially affecting exercise capacity and cardiac risk factors were carefully measured. These included duration of estrogen replacement therapy, all variables in the Framingham risk index, physical activity level, body mass index, waist-to-hip ratio, presence of osteoporosis, and family history of heart disease. We measured maximal oxygen uptake (MVO (2)) and anaerobic threshold as objective markers of exercise capacity. The relation between exercise capacity and use of HRT was analyzed with the use of logistic regression, controlling for confounding variables. We found that fitness, as measured by MVO (2) and anaerobic threshold, was significantly greater in women who had used HRT currently or in the past compared with women who had never used HRT. This difference in fitness was not confounded by age or physical activity level.

CONCLUSIONS

Estrogen replacement therapy is associated with increased exercise capacity as measured by MVO (2) and anaerobic threshold in postmenopausal women without coronary artery disease. This finding is consistent with the beneficial effect of short-term estrogen administration on improved endothelium-dependent and endothelium-independent vasodilation.

Effects of the repeated administration of adenosine and heparin on myocardial perfusion in patients with chronic stable angina pectoris

The mechanism by which ischemia stimulates angiogenesis is unknown. Adenosine is released during myocardial ischemia and may be a mediator of this process. Experimental data suggest that heparin may enhance this effect. The purpose of this open-labeled, placebo-controlled trial was to determine whether repeated intravenous administration of adenosine and heparin could mimic physiologic angiogenesis and reduce the amount of exercise-induced myocardial ischemia in patients with coronary artery disease. Subjects with chronic stable angina refractory to conventional medical therapy and not suitable for revascularization received either adenosine (140 microg/kg/min for 6 minutes) and heparin (10,000 U bolus), (n = 14), or placebo, (n = 7) daily for 10 days. All patients underwent baseline and follow-up exercise testing with thallium-201 single-photon emission computed tomography myocardial perfusion imaging. A semiquantitative assessment of the extent and severity of the perfusion abnormalities was calculated by 2 blinded investigators. There was no significant change in exercise duration or in the peak heart rate systolic blood pressure product associated with adenosine and heparin compared with placebo treatment. There was, however, a 9% reduction in the extent (60.6 +/- 4.0 vs 54.9 +/- 4.1, p = 0.03) and a 14% improvement in severity (41.5 +/- 3.2 vs 35.7 +/- 2.9, p = 0.01) of the myocardial perfusion abnormalities seen in patients who received adenosine and heparin compared with placebo. Thus, in this pilot study, repeated administration of adenosine and heparin reduced the amount of exercise-induced ischemia in patients with chronic stable angina refractory to conventional treatment.

Is there any advantage to the acquisition of 24-hour thallium images, in the presence of persistent perfusion defects at 4 h after reinjection?

We determined the incidence of delayed 24-h reversibility post thallium-201 reinjection and imaging at 4 h, as well as the prognostic and significance of such delayed reversibility. We studied 46 consecutive patients with persistent thallium-201 perfusion or incompletely reversible single-photon emission tomography (SPET) perfusion defects acquired within 10 min after reinjection performed 4 h after stress. In 38 of 46 patients (82%) 24-h images showed no further reversibility beyond the post-reinjection 4-h study (group A). Eight of 46 patients (17%) demonstrated reversibility on 24-h imaging (group B). Of these eight, three patients showed no improvement compared with the post-stress images, with a mean perfusion score of the abnormal segments of 1. 25+/-0.50 on the 4-h images, and of 3.00 on the 24-h images, where normal is 4. Four patients presented with nine mixed regions. Four of these regions showed an improvement in the mean perfusion score of 2.50+/-0.58 on 4- and 24-h images. Two of them, with moderate/severe defects, demonstrated complete reversibility at 4-h post-reinjection imaging. In addition, five other regions presented no improvement at 4-h imaging, but showed an improvement in the mean perfusion score from 0.80+/-0.84 at 4-h to 3.30+/-0.89 at 24-h imaging. Two of these regions in one patient showed a severe perfusion score of 0 at 4 h, and complete reversibility at 24 hours, with a mean score improvement of 4. Another patient had three severe perfusion defects; two of them redistributed partially at 4 h and completely at 24 h. The remaining segment with a perfusion score of 0 at 4 h, presented complete reversibility with a score of 4 at 24 h. Two (4%) patients revealed significant reversibility at 24 h in a region that was severely underperfused after post-reinjection imaging at 4 h. Among group B patients, 75% (6/8) had recent acute ischemic syndrome, compared with only 13% (5/38) in group A (P = 0. 001). Among 11 patients with unstable angina, six (55%) had evidence of delayed 24-h reversibility, compared with 2 of 35 (6%) patients without clinically acute ischemia (P = 0.001). On follow-up, there were seven (17%) cardiac deaths among the 38 group A patients but three (38%) among the eight group B patients (P = 0.3). These findings suggest that although the presence of delayed 24-h 201Tl, post-reinjection reversibility is infrequent, it has potential clinical importance. Thus, delayed 24-h imaging should be considered in the context of unstable angina or other acute coronary syndromes.

Potential added value of three-dimensional reconstruction and display of single photon emission computed tomographic gated blood pool images

BACKGROUND

Single photon emission computed tomographic (SPECT) acquisition provides potential advantages for blood pool imaging. However, the method has been little applied.

METHODS

An improved method of three-dimensional (3-D) reconstruction and display of SPECT equilibrium blood pool scintigrams and related phase data was developed. Dynamic slices and volume-rendered dynamic 3-D images were displayed. Images were viewed from each of 34 solid angles referenced to a sphere surrounding the reconstruction field. Each image pixel was "painted" with intensity-coded regional amplitude and color-coded for its phase angle. The method was applied to evaluate the cardiac anatomy, regional contraction, and related conduction sequence at rest in 17 patients. Twelve had normal left ventricular function including 7 patients with minimal septal preexcitation. Five patients had abnormal left ventricular function, including 2 with left bundle branch block.

RESULTS

Slices contained all of the functional information, but necessary data integration was time-consuming and evaluation of chamber size and anatomy was difficult. Three-dimensional projection images condensed and integrated the data, presenting new vantage points on anatomy, contraction, and conduction not otherwise available in the clinically limited angulations of planar images. This provided excellent visual separation of cardiac chambers with full and increased visualization of right and left ventricular wall motion in all segments compared with the conventional projections acquired clinically (p < 0.05). Atria and great vessels were well separated with evident size and function. Phase-angle progression paralleled the electrocardiogram, permitting bypass pathway localization and the direct noninvasive localization of posteroseptal pathways.

CONCLUSIONS

The 3-D method permits greater access to and utilization of SPECT blood pool image data. It suggests specific advantages for clinical use.

Fast acquisition of myocardial SPECT images with Tc-99m sestamibi for the diagnosis of coronary artery disease

BACKGROUND

Shortening the acquisition time for myocardial single-photon emission computed tomographic (SPECT) imaging increases patient comfort and laboratory throughput. The purpose of this study was to compare the diagnostic accuracy for coronary artery disease detection of myocardial SPECT images acquired in 5 to 10 minutes versus 25 minutes using Tc-99m methoxyisobutylisonitrile (Tc-99m sestamibi) and a single-head gamma camera.

METHODS AND RESULTS

Forty-one subjects had a standard 1-day rest/stress Tc-99m sestamibi myocardial SPECT study. Two sets of rest and stress images were acquired on the same day for each subject. One set of images was acquired with a 5- to 10-minute fast acquisition protocol; the second set of images was acquired with a 25-minute standard protocol. The accuracies of the fast and standard protocols for identifying individuals with and without coronary artery disease were equivalent. Accuracy was 76% for the fast protocol and 73% for the standard protocol in individuals with at least one coronary stenosis > or = 70%. The accuracies of the two protocols for identifying individual coronary arteries with stenoses > or = 70% also were equivalent. Accuracy was 77% for the fast protocol and 74% for the standard protocol.

CONCLUSIONS

SPECT myocardial images may be acquired in as little as 5 to 10 minutes using Tc-99m sestamibi and a 1-day rest/stress protocol. Accuracy is equivalent to that attained in studies with longer imaging times.

Strategies for extraction of quantitative data from volumetric dynamic cardiac positron emission tomography data

The ability of positron emission tomography (PET) to serve as a useful myocardial perfusion indicator is well established. We describe a methodology for obtaining reliable quantitative kinetic parameters from dynamic cardiac PET data. Reconstructed images of the myocardium are subdivided into three-dimensional volumes of interest which are used to obtain quantitative measures of myocardial perfusion over physiologically meaningful anatomical regions. The quantitation technique rigorously models the uncertainty of estimated parameters while compensating for effects such as patient motion and partial volumes to arrive at model parameters with well-established confidence intervals.

Comparison of adenosine to dipyridamole in degree of coronary hyperemic response in heart transplant recipients

Transplant coronary vasculopathy is associated with endothelial dysfunction. Microvascular function, assessed as coronary flow reserve, has been reported to be normal. We used intracoronary ultrasound technology to simultaneously assess conductance and resistance vessel function in response to standard dosages of the vasodilators adenosine and dipyridamole. Coronary hemodynamic changes were assessed in 11 heart transplant recipients, at a mean duration of 784 +/- 516 days after transplantation, using a 3.2Fr or 4.3Fr, 30-MHz ultrasound imaging catheter over a 0.014-inch Doppler guidewire. Measures of coronary average peak flow velocity (APV) and coronary cross-sectional area (CSA) were used to calculate volumetric flow during intravenous infusions of adenosine (140 micrograms/kg/min over 4 minutes) and dipyridamole (140 micrograms/kg/min over 4 minutes). Flow reserve was assessed as a ratio of maximal pharmacologically induced flow to steady baseline flow before infusion. Increase in APV (261.9% vs 194.6%, p = 0.005), lumenal CSA (+11.8% vs +4.2%, p = 0.01), peak volumetric blood flow (515.8 vs 317.2 ml/min, p = 0.007), and coronary flow reserve (2.93 +/- 0.74 vs 1.99 +/- 0.53, p < 0.001) were higher with adenosine than dipyridamole. Both agents caused similar decreases in systemic blood pressure and little change in heart rate. Adenosine appears to be a more potent coronary vasodilator than dipyridamole in denervated human transplant subjects. Adenosine has a vasodilator effect at the epicardial and microvascular levels, resulting in an overall increase in volumetric flow. Flow reserve in response to both endothelium-independent agents is decreased in comparison with previously established values, but the attenuation is greater with dipyridamole.

Diagnostic utility of tomographic myocardial perfusion imaging with technetium 99m furifosmin (Q12) compared with thallium 201: results of a phase III multicenter trial

BACKGROUND

Based on physical properties, 99mTc-labeled perfusion agents offer several advantages over 201Tl for myocardial perfusion imaging. The results of in vivo and experimental studies, along with preliminary experience in human subjects, have shown 99mTc-labeled furifosmin to be a promising new perfusion tracer. The purpose of this study was to evaluate the safety of a new myocardial perfusion agent, 99mTc-labeled furifosmin (Q12), and determine the concordance of furifosmin perfusion scintigraphy to 201Tl imaging. In addition, we sought to determine the normalcy rate of myocardial scintigraphy with furifosmin.

METHODS AND RESULTS

One hundred fifty patients constituted the study group in this multicenter trial. Patients underwent exercise testing with furifosmin injected at peak exercise, and tomographic imaging was begun 15 to 30 minutes afterward. After a separate injection, resting images were obtained 3 to 4 hours later. Thallium scintigraphy was performed within 2 weeks of the furifosmin scans, after a similar exercise workload. Patients with a low likelihood of coronary artery disease (n = 39) also underwent furifosmin imaging. All images were processed and displayed in uniform manner and interpreted by a panel of readers. No adverse effects or clinically important laboratory alterations were related to furifosmin imaging. Image quality was slightly better with furifosmin than with thallium. The overall concordance between the perfusion studies was 86% (kappa value = 0.669). The normalcy rate for furifosmin scintigraphy was 100%.

CONCLUSIONS

99mTc-labeled furifosmin is a promising new 99mTc-labeled myocardial perfusion agent, providing diagnostic results similar to those obtained with 201Tl.

Stress imaging. Current clinical options for the diagnosis, localization, and evaluation of coronary artery disease

As technology advances, new methods evolve. In this article, the methods of stress testing and related imaging in coronary disease are addressed, and dynamic and pharmacologic stress, direct and indirect methods, are defined and evaluated. The stress imaging methods related to the modalities of scintigraphy and ultrasound are reviewed and their advantages and disadvantages assessed in view of scientific and economic factors.

Acute and chronic effects of transient myocardial ischemia on sympathetic nerve activity, density, and norepinephrine content

OBJECTIVES

The sympathetic nervous system has profound influences on myocardial function, particularly during ischemia. There is controversy, however, as to whether myocardial ischemia results in damage to myocardial sympathetic nerves coursing through the ischemic territory. To further evaluate these issues, we assessed the acute and chronic effects of transient myocardial ischemia on sympathetic nerve function and morphology.

METHODS

A total of 20 dogs were studied. For acute studies (n = 9), we performed serial dynamic imaging of I-123 metaiodobenzylguanidine (MIBG) washout during coronary occlusion and reperfusion, and assessed residual myocardial perfusion with thallium-201. For chronic studies (n = 11), we assessed sympathetic innervation and perfusion 11 days following a transient intracoronary balloon occlusion. Imaging results were correlated with electrocardiographic responses, histology, and tissue norepinephrine (NE).

RESULTS

In the acute studies, regional MIBG washout increased more than 2-fold in the ischemic territory compared to the control region during coronary occlusion (14.2 +/- 2.3 vs. 5.9 +/- 1.2%, P < 0.01). Tissue NE was reduced in the ischemic territory compared to the non-ischemic territory (335 +/- 162 vs. 751 +/- 190 ng/g, P < 0.01). Myocardial perfusion was normal. In the chronic studies, 9/11 dogs showed ischemic ECG changes during balloon occlusion, and developed ventricular arrhythmias. On follow-up imaging, 5/11 dogs showed reduced MIBG uptake relative to thallium, in viable myocardium overlying necrotic subendocardium, reduced NE (226 +/- 77 vs. 733 +/- 82 ng/g in control regions, P < 0.01), decreased nerve density, and a larger extent of denervation than scar (25.5 +/- 3.7 vs. 8.2 +/- 2.7%, P < 0.02). Six of 11 dogs showed normal innervation patterns.

CONCLUSIONS

These studies suggest that the sympathetic nerves are acutely affected in regions of myocardial ischemia as detected by enhanced regional washout of MIBG. In addition, chronic sympathetic nerve denervation can occur in the absence of transmural myocardial necrosis; however, the occurrence of transient ischemia does not predict the development of chronic denervation. The severity of ischemia, as evidenced by the extent of the related necrosis, does appear to predict chronic denervation. The severity of ischemia, as evidenced by the extent of the related necrosis, does appear to predict chronic denervation. The mechanisms leading to chronic denervation of sympathetic nerves in the absence of transmural infarction remain to be defined.

Variability of normal coronary anatomy: implications for the interpretation of thallium-SPECT myocardial perfusion images in single-vessel disease

Standard criteria for assigning perfusion defects to a specific vascular territory often result in mistaken identification of the affected coronary artery due to the normal variability of coronary anatomy. A retrospective study was performed to determine the frequency of this type of error and to identify the most common perfusion patterns associated with specific coronary lesions.

METHODS

Records were reviewed of all patients with single-vessel coronary artery disease (CAD) who had exercise or dipyridamole thallium SPECT myocardial perfusion studies since 1987. Patients with coronary artery bypass grafts and an interval between the two studies greater than 6 wk or interval change in medical status were excluded. Ninety-three studies were available for review. The size, severity and location of all perfusion defects were noted by three observers who had no knowledge of the angiographic data. Significant CAD was defined as luminal diameter stenosis greater than 50%.

RESULTS

The diseased vessel was correctly identified in 85% of positive studies. Thallium SPECT, however, mistakenly predicted additional vessel involvement in 29% of those studies. Another 15% correctly predicted single-vessel disease but identified the wrong artery. Using standard criteria, thallium SPECT correctly predicted the arteriogram findings in only 56% of studies. Most of these findings could be correlated with variations in individual coronary anatomy.

CONCLUSION

The accurate localization of coronary stenoses by thallium SPECT imaging requires close correlation with arteriography owing to the significant variability in normal coronary anatomy.

Segmental analysis of resting echocardiographic function and stress scintigraphic perfusion: implications for myocardial viability

In 73 patients with coronary artery disease, we performed segmental analysis of resting two-dimensional echocardiography and stress thallium-201 single photon emission computed tomographic scintigraphy with 24-hour delayed imaging to test the hypotheses that (1) combined analysis of stress thallium-201 scintigraphy (with 24-hour redistribution) and echocardiography provides an evaluation of the viability of most myocardial segments; and (2) the severity of the scintigraphic perfusion abnormality in a given segment is equivalent to the severity of its echocardiographically determined functional impairment. Scintigraphy showed 14% of the 1168 segments analyzed to have fixed severe defects. Echocardiography showed 11% of the 1070 segments analyzed to be akinetic or dyskinetic. However, with combined analysis, only 62 (5%) segments showed no evidence of viability by either imaging technique. We conclude that in this group of patients, 95% of segments have evidence of viability by one of these two conventional imaging techniques.

A consideration of current clinical options for stress imaging in the diagnosis and evaluation of coronary artery disease

The evolution of technology and our health care system, tinctured by advocacy groups for specific imaging modalities, has produced controversy, relating to the optimal stress imaging method for coronary disease evaluation. Stress perfusion scintigraphy and stress echocardiography advocates seem to make claims that each nullify the other. This extensive, in-depth review of the subject presents facts as well as opinion and experience in an effort to assess the full portrait of the issue for consideration by advocates as well as those many yet undecided. The issue is an evolving one, affected strongly by the reader's own experience. The presentation is not meant to be the final word. Rather, it seeks to present a basis for understanding and progress in both fields.

Does myocardial perfusion scintigraphy demonstrate clinical usefulness in patients with markedly positive exercise tests? An assessment of the method in a high-risk subset

To evaluate the clinical utility of perfusion scintigraphy in patients with markedly positive exercise ECGs, we studied 94 consecutive patients with markedly positive exercise ECGs; 74 of them were also studied with scintigraphy. Patients undergoing scintigraphy had an intermediate pretest likelihood of coronary disease and were divided into two groups: those with reversible defects involving one complete area or aspects of multiple vascular areas (group 1, 38 patients), and those with normal scintigrams and reversible defects in a limited aspect of one vascular area, isolated fixed defects, or both (group 2, 36 patients). Among all demographic and exercise variables, only a hypotensive or blunted blood pressure response and scintigraphic lung uptake or cavitary dilation, although insensitive, were more frequent in group 1 (all p < 0.05). All 36 patients in group 1 and 14 of 18 in group 2 who underwent coronary angiography had significant coronary lesions; 31 in group 1 but only seven in group 2 had multivessel disease (p < 0.05). Subsequently 32 patients in group 1 had revascularization compared with only two patients in group 2. Only one cardiac event was noted among 34 patients in group 2 who were followed for a mean of 38 months while they were being treated medically. However, four of nine patients in group 1 initially treated medically required late revascularization because of clinical progression of disease, and one patient died (p < 0.05). Compared with patients having scintigraphy, patients not imaged had a higher pretest likelihood of coronary disease, a higher incidence of angina, unstable angina, and induced angina, with a lower exercise time and time to ST depression (p < 0.05). All underwent angiography, and 16 had multivessel disease. Not all patients with markedly positive exercise ECGs were at similarly high coronary risk. Some with high-risk coronary anatomy were identified without the use of scintigraphy. In others, where diagnosis and prognosis were less clear, scintigraphy aided in the diagnosis and accurately identified a low-risk subgroup as did no other parameter.

Myocardial perfusion scintigraphy in left bundle branch block: a perspective on the issue from image analysis in a clinical context

Among selected study populations, myocardial perfusion scintigraphy (MPS) in patients with left bundle branch block (LBBB) has been reported to show a low specificity for the diagnosis of coronary disease. However, the stress electrocardiogram (ECG) is nondiagnostic in this setting. To place this method in its appropriate clinical context, we evaluated MPS in all 69 consecutive patients with LBBB studied with scintigraphy for clinical reasons during a 4-year period. Among 32 patients who underwent coronary angiography for clinical indications, per patient sensitivity, 96%; per vessel sensitivity, 84%, 50%, and 100% for left anterior descending (LAD), left circumflex (LCX), and right coronary artery (RCA) involvement, respectively; and per vessel specificity, 95% and 68% for LCX and RCA disease, respectively, were not significantly different from those previously published for the method in patients without LBBB. Although per patient specificity, 38%, and specificity, 39%, for LAD disease were low, the predictive value of a positive test remained relatively high (83%) owing to the small number of patients selected for angiography, in part based on scintigraphic findings, with normal coronary anatomy. In addition to a possible specific pathophysiologic cause related to LBBB, apparent perfusion abnormalities in the LAD distribution may relate to generic conditions that can make scintigraphic interpretation ambiguous, often in the anterior distribution, regardless of the clinical setting. Additionally, the apparent lack of scintigraphic specificity in the LAD distribution could relate in part to a selection bias toward catheterization of patients with induced scintigraphic abnormalities, especially in the LAD distribution.(ABSTRACT TRUNCATED AT 250 WORDS)

Basal interventricular septal thallium-201 defects: real or artifact?

Misinterpretation of reversible defects at the base of the interventricular septum is perhaps among the greatest single causes of false positive TI-201 myocardial perfusion images. This is a report of a patient with angiographically documented ischemia at the base of the septum and corresponding reversible defects as seen using TI-201 imaging. Illustrated are two different forms of malalignment artifact that duplicate this patient's findings in a patient with normal perfusion.

A quantitative assessment of patient motion and its effect on myocardial perfusion SPECT images

Patient motion during image acquisition is a frequent cause of SPECT perfusion image artifacts. We sought to determine the relationship between patient motion and the resultant image artifact. The effect of patient motion on 201Tl SPECT scintigrams was assessed with computer simulation to create 66 new image sets with artifactual vertical, horizontal and combined patient motion introduced over a broad range in six normal studies. Visual analysis of regional radioactivity in these simulated images, as well as quantitative analysis of the resultant polar coordinate display was performed. The presence and extent of "motion" artifacts varied with the number and location of the projection images affected, as well as the extent of their displacement. Although the extent of the defect varied with the frames affected, they were not necessarily more extensive when related to vertical displacement in the center of the orbit. The location of induced defects varied with direction of displacement and the location of frames affected. Vertical and horizontal motion created additive defects. Defect size grew with incremental vertical displacement but subsequently decreased with yet increasing displacement. Both the irregular, "lumpy" distribution of radioactivity, often with opposing "defects", as well as curvilinear extraventricular radioactivity, were visual clues suggesting SPECT defects related to motion artifact. A clinical case review revealed that approximately 25% of studies demonstrate such motion during acquisition but only 5% contribute to visible image deterioration. While detection is important, postacquisition attempts to correct such artifacts are incomplete and optimally, they must be prevented.

Diagnostic and prognostic value of ambulatory electrocardiographic monitoring

To evaluate the diagnostic and prognostic value of continuous ambulatory ECG (AECG) monitoring, we studied 124 patients with chest pain syndromes by stress myocardial perfusion scintigraphy (MPS) and AECG. MPS was classified as normal or with fixed or reversible defects involving one or more than one vascular territory. Positive AECGs were divided into those with mild (< or = 1.5 mm), moderate (1.5 to 2.5 mm), and severe (> or = 2.5 mm) ST segment displacement. Among 61 patients with a negative AECG, 93% had limited ischemia or normal scintigraphic studies. All 24 patients with moderately or severely positive AECGs had reversible defects on MPS. Among those with severely positive AECGs, nine (75%) had multivessel scintigraphic ischemia. Severe ST segment depression on AECG was highly related to multivessel perfusion defects and to a large amount of myocardium in jeopardy. A negative AECG generally indicated limited or absent ischemia and thus a more benign prognosis. Induced symptoms and the daily ischemic burden were not related to the severity of induced AECG or MPS abnormalities. AECG may provide independent information as to the severity and related risk of ischemia.

Scintigraphic assessment of MIBG uptake in globally denervated human and canine hearts--implications for clinical studies

To further characterize the behavior of metaiodobenzylguanidine (MIBG) in the myocardium and to test the hypothesis that the denervated heart would show normal early uptake on MIBG due to non-neuronal localization, we examined the early and late distribution of 123I-labeled MIBG in normal and globally denervated canine and human hearts. Canine hearts were denervated by intravenous injections of 6-hydroxydopamine, while patients were studied a mean of 4.3 mo following cardiac transplantation. Results in denervated hearts were compared to normal controls. Normal hearts showed prominent MIBG uptake on initial 5-min and 3-hr delayed images. Globally denervated canine hearts showed prominent uptake on initial images and absence of localization on delayed images, indicating complete washout of non-neuronally bound radionuclide. The transplanted human hearts showed no localization of MIBG on either early or delayed images. These results suggest that the non-neuronal uptake mechanism (uptake 2) is not significant in human myocardium. This finding has significant implications for interpreting the myocardial behavior of MIBG in various pathologic situations such as dilated cardiomyopathy.

Usefulness of adenosine in augmenting ventricular preexcitation for noninvasive localization of accessory pathways

Adenosine was administered to test the hypothesis that it would maximize preexcitation and facilitate noninvasive localization of accessory pathways in 22 patients with suspected accessory pathway-mediated tachycardias. Twelve-lead electrocardiograms and 2-dimensional echocardiograms were recorded at baseline and during adenosine-augmented ventricular preexcitation to localize the accessory pathway. Phase analysis was performed on digitized 4-chamber and short-axis views using a first harmonic Fourier transformation. At baseline, 15 patients had manifest preexcitation. In 14 of these patients (93.3%), preexcitation became more prominent after adenosine. Four patients without preexcitation at baseline clearly had it after adenosine. In patients who had preexcitation in response to adenosine, the electrocardiogram correctly identified the accessory pathway locations in 18 of 19 patients at a regional level and was incorrect in 1 of 19 patients. Echocardiographic phase analysis correctly identified the accessory pathway location in all 17 patients, who had technically adequate studies, at a regional level. In conclusion, administration of adenosine accentuates preexcitation, allowing for more accurate electrocardiographic and echocardiographic accessory pathway localization.

The applications of adenosine in noninvasive cardiac imaging

In this paper the cardiac actions of adenosine, as well as its therapeutic and diagnostic applications are reviewed. Adenosine has been demonstrated to be useful in the assessment of coronary artery disease in conjunction with perfusion SPECT scintigraphy, PET imaging and two-dimensional echocardiography. The reported sensitivities and specificities of adenosine in these settings are high and similar to those of imaging after exercise or dipyridamole induced coronary hyperemia. Minor side effects are commonly associated with adenosine infusion, however they are transient, generally well tolerated, and rarely require test termination or the administration of aminophylline. Adenosine has proven very useful in the noninvasive diagnosis of Wolff-Parkinson-White syndrome and in the localization of the ventricular insertion of the accessory pathway. As a provocative test, adenosine 12.0 mg rapid bolus has a sensitivity and specificity of 100% for identifying anterograde atrioventricular accessory pathway conduction. The use of adenosine is particularly well suited to the technique of echocardiographic phase analysis and cine-loop inspection as image acquisition is rapid and may be obtained on-line. Although the only approved therapeutic use of adenosine is in the emergency treatment of paroxysmal supraventricular tachycardia, several other clinical applications are suggested by the agents specific cardiovascular and electrophysiologic properties. These include 1. post-thrombolytic therapy to reduce reperfusion injury, 2. as an afterload reduction agent in malignant hypertension and congestive heart failure, 3. to produce controlled hypotension intraoperatively during vascular procedures, and 4. to terminate catecholamine and exercise mediated ventricular tachycardia. Furthermore, the technique of adenosine echocardiographic phase analysis offers the potential for precise subsegmental localization of accessory pathways which has never been achieved by any noninvasive technique, and adenosine augmentation of preexcitation obviates the need for invasive cardiac pacing. Future applications of adenosine scintigraphic and echocardiographic methods will undoubtedly involve newer imaging modalities, such as multiplanar transesophageal and magnetic resonance imaging, which may improve our current abilities to localize accessory pathways and noninvasively diagnose coronary artery disease.

Two-dimensional echocardiographic phase analysis. Its potential for noninvasive localization of accessory pathways in patients with Wolff-Parkinson-White syndrome

BACKGROUND

In patients with the preexcitation syndrome who are undergoing transcatheter or surgical ablation, accurate localization of accessory pathways is critical. Because preexcitation is known to alter ventricular activation sequence and result in focal areas with presystolic contraction, we investigated whether phase analysis applied to two-dimensional echocardiographic cine loops objectively identifies these focal areas and can be used to localize ventricular insertion sites of accessory pathways.

METHODS AND RESULTS

We prospectively obtained phase images in 17 patients (11 males; age range, 11-35 years) during minimal preexcitation in normal sinus rhythm and during maximal preexcitation induced by right atrial pacing. A group of 11 normal subjects (six men; age range, 26-37 years) served as controls. Pathway locations predicted from phase imaging were compared with those predicted from routine 12-lead ECGs, from visual inspection of cine loop images, and from catheter-mounted electrode endocardial mapping. Cross-sectional views in a digital cine loop format were mathematically transformed using a first harmonic Fourier algorithm to obtain the corresponding phase images. Phase angle histograms were derived in eight wall segments. Mean and earliest phase angles were derived by computer analysis to quantitate contraction sequence. We found that during right atrial pacing, phase angles in focal areas markedly deviated from normal--mean phase angles from 33 degrees to 164 degrees, and earliest phase angles from 50 degrees to 180 degrees. Accessory pathways could be precisely localized in 53% of the patients by 12-lead ECG, in 59% by visual inspection of cine loop images, in 82% by phase imaging, and in 94% by a combination of the three methods.

CONCLUSIONS

Our results suggest that phase imaging, especially when used in combination with cine loop and 12-lead ECG, can be used to localize ventricular insertion sites of accessory pathways and may be clinically useful as a noninvasive adjunct to endocardial mapping in patients with Wolff-Parkinson-White syndrome.

Comparison of the findings on preoperative dipyridamole perfusion scintigraphy and intraoperative transesophageal echocardiography: implications regarding the identification of myocardium at ischemic risk

The evidence of myocardium at potential ischemic risk on preoperative dipyridamole perfusion scintigraphy was compared with that of manifest ischemia on intraoperative transesophageal echocardiography in 26 patients at high risk of a coronary event undergoing noncardiac surgery. The clinical outcome was also assessed. Induced intraoperative wall motion abnormalities were more common in patients and myocardial segments with, than in those without, a preoperative reversible perfusion defect (both p less than 0.05). Conversely, a preoperative reversible perfusion defect was more common in patients and segments with, than in those without, a new intraoperative wall motion abnormality (both p less than 0.05). Six patients, five with a reversible scintigraphic defect but only three with a new wall motion abnormality, had a hard perioperative ischemic event. Events occurred more often among patients with, than in those without, a reversible perioperative scintigraphic defect (5 [33%] of 15 vs. 1 [9%] of 11) but this difference did not reach significance (p = 0.14), probably owing to the sample size. Intraoperative wall motion abnormalities were all reversible and did not differentiate between risk groups; these findings were possibly influenced by treatment. These preliminary data support the known relation between reversible scintigraphic defects and perioperative events and identify another manifestation of ischemic risk in the relation between reversible scintigraphic defects and induced intraoperative wall motion abnormalities. The value of intraoperative echocardiography in identifying ischemia and guiding therapy in patients with a reversible scintigraphic abnormality should be further assessed.

Dipyridamole perfusion scintigraphy

Dipyridamole is one of several agents that may be infused intravenously to nonivasively evaluate coronary perfusion without dynamic exercise. Among such agents it is the most investigated, and it is associated with the greatest clinical experience. Its mechanism of action utilizes intrinsic adenosine and does not require the induction of ischemia. Rather, the method tests the coronary flow reserve by dilating the precapillary and arteriolar capillary beds. Vessels with a limited coronary flow reserve demonstrate reduced responsiveness with relative flow reduction and a resultant defect on perfusion scintigraphy. Side effects are common and generally benign, but deaths have been reported and they generally relate to severe hypotension, prolonged dense ischemia and resultant infarction, or bronchospasm. Severe complications are rare and can be avoided by the prompt administration of aminophylline, the dipyridample antedote. Diagnostic accuracy for the identification of coronary disease appears similar to that for exercise perfusion scintigraphy. It should be applied to patients with known or suspected coronary disease who require coronary evaluation, but who cannot exercise adequately for diagnostic or prognostic purposes. In such patients, the method is useful for the preoperative assessment of risk at peripheral vascular and other major noncardiac surgery. It may be of value as well in the assessment of the otherwise uncomplicated patient postinfarction. Not yet established is its application to the patient with unstable angina or in the acute setting, after coronary reperfusion. Similarly, its comparison with direct adenosine infusion or with pharmacological agents whose mechanism rests entirely on ischemia induction, as does dobutamine, has until now been limited. Unlike its use with perfusion scintigraphy, the application of dipyridamole with echocardiography and other functional ischemic indicators is totally dependent on the induction of ischemia. This is likely less frequent than the induction of nonischemic perfusion heterogeneity. The agent is now commonly available and will make a significant beneficial impact on patient evaluation and management.

Phase image triangulation of accessory pathways in patients undergoing catheter ablation of posteroseptal pathways

The outcome of posteroseptal accessory pathway ablation by direct current (DC) shocks delivered just outside the os of the coronary sinus was studied in 21 patients. Electrocardiographic and electrophysiological parameters as well as phase image patterns of equilibrium multiple-gated blood-pool scintigrams were studied to determine their usefulness in predicting the success of ablation. A second free-wall pathway was documented by electrophysiological or surgical findings in six patients, and the value of phase images in detecting this second pathway was studied as well. Ablation was successful in 57%. The cumulative mean energy of DC shocks amounted to 524 +/- 170 joules and was not predictive of ablation outcome, neither was the mean ventriculoatrial (VA) conduction time. The predictive value of the 12-lead maximally preexcited electrocardiogram was poor in the 15 patients with a single posteroseptal bypass tract. A new method to triangulate the site of the earliest phase angle on the atrioventricular (AV) valve plane successfully localized the bypass pathway in 14 of those patients. No specific phase pattern predicted successful ablation except for a symmetrical, concentric peripheral phase progression found to be predictive of ablation success in the four patients who showed this pattern. Phase analysis was able to localize the second, nonposteroseptal pathway in four of six patients. This study showed that a concentric peripheral phase progression in the gated blood-pool scintigrams is predictive for ablation success in patients with posteroseptal pathways. A free-wall localization of the earliest phase angle is suggestive of a second bypass tract in this area.

Scintigraphic assessment of sympathetic innervation after transmural versus nontransmural myocardial infarction

To evaluate the feasibility of detecting denervated myocardium in the infarcted canine heart, the distribution of sympathetic nerve endings using I-123 metaiodobenzylguanidine (MIBG) was compared with the distribution of perfusion using thallium-201, with the aid of color-coded computer functional map in 16 dogs. Twelve dogs underwent myocardial infarction by injection of vinyl latex into the left anterior descending coronary artery (transmural myocardial infarction, n = 6), or ligation of the left anterior descending coronary artery (nontransmural myocardial infarction, n = 6). Four dogs served as sham-operated controls. Image patterns were compared with tissue norepinephrine content and with histofluorescence microscopic findings in biopsy specimens. Hearts with transmural infarction showed zones of absent MIBG and thallium, indicating scar. Adjacent and distal regions showed reduced MIBG but normal thallium uptake, indicating viable but denervated myocardium. Denervation distal to infarction was confirmed by reduced norepinephrine content and absence of nerve fluorescence. Nontransmural myocardial infarction showed zones of wall thinning with decreased thallium uptake and a greater reduction or absence of MIBG localized to the region of the infarct, with minimal extension of denervation beyond the infarct. Norepinephrine content was significantly reduced in the infarct zone, and nerve fluorescence was absent. These findings suggest that 1) MIBG imaging can detect viable and perfused but denervated myocardium after infarction; and 2) as opposed to the distal denervation produced by transmural infarction, nontransmural infarction may lead to regional ischemic damage of sympathetic nerves, but may spare subepicardial nerve trunks that course through the region of infarction to provide a source of innervation to distal areas of myocardium.

Relative importance of activation sequence compared to atrioventricular synchrony in left ventricular function

This study evaluated the relative hemodynamic importance of a normal left ventricular (LV) activation sequence compared to atrioventricular (AV) synchrony with respect to systolic and diastolic function. Twelve patients with intact AV conduction and AV sequential pacemakers underwent radionuclide studies at rest and Doppler echocardiographic studies at rest and during submaximal exercise, comparing atrial demand pacing (AAI) to sequential AV sensing pacing (DDD) and ventricular demand pacing (VVI). Studies at rest were performed at a constant heart rate between pacing modes, and the exercise study was performed at a constant heart rate and work load. Cardiac output was higher during AAI than during both DDD and VVI (6.2 +/- 1 vs 5.6 +/- 1 and 5.3 +/- 1 liters/min, p less than 0.05). LV ejection fraction was likewise higher during AAI (55 +/- 12 vs 49 +/- 11 vs 51 +/- 13, p less than 0.05). VVI with or without AV synchrony was associated with a paradoxical septal motion pattern, resulting in a 25% impairment of regional septal ejection fraction. In addition, LV contraction duration was more homogenous during AAI. Peak filling rate during AAI and VVI was higher than during DDD (2.86 +/- 1 and 2.95 +/- 1 vs 2.25 +/- 1 end-diastolic volume/s; p less than 0.05). During VVI, the time to peak filling was significantly shorter than during both AAI and DDD (165 +/- 34 vs 239 +/- 99 and 224 +/- 99 ms; p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Dipyridamole perfusion scintigraphy: the experience with its application in one hundred seventy patients with known or suspected unstable angina

We evaluated the safety, accuracy, and potential clinical utility of intravenous dipyridamole perfusion scintigraphy with thallium-201 in 170 patients, 78 with suspected and 92 with known unstable angina. All had coronary angiography. Noncardiac side effects (26%), induced chest discomfort (44%), and ST segment changes (12%) were similar in the two groups. No significant arrhythmias occurred. Two patients had prolonged chest pain, both with extensive reversible image abnormalities and associated creatinine kinase-MB release. Both had elective bypass surgery. Twenty-eight patients had normal coronary arteries, and 35 had single-vessel disease. Scintigraphic per patient sensitivity and specificity were 91% and 79% with a per vessel sensitivity of 74% and a per vessel specificity of 78% without between-group differences. During a brief follow-up period, 62 patients with image abnormalities had coronary revascularization, and there were seven deaths without intergroup differences. In a similar patient group that did not have angiography, scintigraphic defects were less frequent and less extensive, revascularization was not performed, and subsequent deaths occurred less often. Dipyridamole perfusion scintigraphy is an accurate alternative to exercise testing in the evaluation of patients with unstable angina pectoris. Although not without risk, the method appears relatively safe and should be considered as a guide to diagnosis, and probably to prognosis and management.

Benefits of physiologic atrioventricular synchronization for pacing with an exercise rate response

Although the loss of atrioventricular (AV) synchronization may diminish resting cardiac output, previous studies have not shown any impact on exercise capacity as long as an exercise rate response is present. To test the impact of suboptimal atrial activation during treadmill exercise, 12 patients with normal sinoatrial node function and dual chamber pacemakers were evaluated in pacemaker modes with normal AV intervals allowing maximal atrial contribution to ventricular filling and with the shortest programmable nonphysiologic AV delay. During a double-blinded randomized crossover protocol, exercise performance was improved with physiologic AV filling in comparison with nonphysiologic AV filling: (1) mean increase in exercise time was 16 +/- 16% (mean +/- standard deviation) (p less than 0.05); (2) time to anaerobic threshold was increased by 23 +/- 28% (p less than 0.05); and (3) the level of perceived exertion during comparable stages of exercise was decreased. In 3 patients, exercise time was greater by greater than 35% in the physiologic AV filling mode. Resting echo-Doppler parameters of left atrial and ventricular function did not predict benefit from AV synchronization during exercise. During exercise with rate-responsive pacing an appropriate AV relation is beneficial, and in a subset of patients this benefit may be striking.

Imaging of the heart using metaiodobenzylguanidine

Catecholamines have profound influences on cardiac function. Mechanisms relating abnormalities in sympathetic innervation to myocardial dysfunction are poorly understood, however. Recent studies have demonstrated the feasibility of noninvasively imaging the sympathetic nerves of the heart using radiolabeled MIBG. This article examines some of the experimental evidence to support the neuronal localization of MIBG. In addition, the early clinical experience is reviewed.

Comparison of transesophageal echocardiographic and scintigraphic estimates of left ventricular end-diastolic volume index and ejection fraction in patients following coronary artery bypass grafting

Transesophageal echocardiography (TEE) has become a commonly used monitor of left ventricular (LV) function and filling during cardiac surgery. Its use is based on the assumption that changes in LV short-axis ID reflect changes in LV volume. To study the ability of TEE to estimate LV volume and ejection immediately following CABG, 10 patients were studied using blood pool scintigraphy, TEE, and thermodilution cardiac output (CO). A single TEE short-axis cross-sectional image of the LV at the midpapillary muscle level was used for area analysis. Between 1 and 5 h postoperatively, simultaneous data sets (scintigraphy, TEE, and CO) were obtained three to five times in each patient. End-diastolic (EDa) and end-systolic (ESa) areas were measured by light pen. Ejection fraction area (EFa) was calculated (EFa = (EDa - ESa)/EDa). When EFa was compared with EF by scintigraphy, correlation was good (r = 0.82 SEE = 0.07). EDa was taken as an indicator of LV volume and compared with LVEDVI which was derived from EF by scintigraphy and CO. Correlation between EDa and LVEDVI was fair (r = 0.74 SEE = 3.75). The authors conclude that immediately following CABG, a single cross-sectional TEE image provides a reasonable estimate of EF but not LVEDVI.

Oblique reformatting of multislice magnetic resonance images for improved visualization of coronary arteries

A technique for reformatting multislice magnetic resonance images into arbitrary oblique planes has been developed and implemented on a Toshiba MRT-35 (formerly Diasonics MT/S) imaging system (South San Francisco, CA). This method is designed to allow the user to easily define a new plane by marking with a cursor features of interest on two or three different image levels. These features are combined in the resulting oblique image. The reformatted image can have arbitrary angulation and is created with a pixel dimension equivalent to the original data set. Resolution ranges from the original in-plane resolution to the slice thickness, depending on angulation. An improvement in signal-to-noise ratio results from the effective averaging performed by interpolation. This method is optimally used to correct for small variations in alignment, such as the positioning of the intervertebral disks. It can also be used to generate reformatted images at many different angles from a single multislice data set. This method has been applied to the particular problem of improving the presentation of coronary arteries on a conventional set of multislice spin-echo cardiac images by increasing the visible length of individual coronary segments.

Epicardial and endocardial localized 31P magnetic resonance spectroscopy: evidence for metabolic heterogeneity during regional ischemia

Previous studies have noted that myocardial blood flow and high energy phosphates are heterogeneous across the myocardial wall during ischemia. In order to determine whether differences in metabolites between the subendocardium and subepicardium could be detected using 31P magnetic resonance spectroscopy, the Fourier series window (FSW) experiment was implemented on a porcine model of graded regional ischemia. FSW experiments using a planar phantom showed a 46% improvement in localization to the subendocardium compared to a one-pulse experiment. Animal studies of graded ischemia demonstrated a gradient in the phosphocreatine to inorganic phosphate ratio in the myocardium that paralleled the gradient in blood flow. These studies demonstrate the ability of spatially localized 31P magnetic resonance spectroscopy to detect regional changes in myocardial high energy phosphates localized to the subepicardium and subendocardium.