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Biomedical subjects

M W Dae

Publications and source records attributed to M W Dae.

At least 37 records · Page 2Linked to original sources
PubMed1994

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.

Aged↗
PubMed1993

Daily physical activity levels in congestive heart failure.

To determine the level of daily physical activity routinely performed by patients with congestive heart failure (CHF) and the ability of clinical and laboratory assessments of function to predict peak daily activity levels, 45 patients with CHF were evaluated in the laboratory and during 2 days of usual activity. Subjects performed symptom-limited treadmill exercise tests with respiratory gas analysis and wore a Vitalog activity monitor with continuous measurement of heart rate and body motion. Mean maximal oxygen uptake for this sample was 16.8 ml/kg/min. Peak daily physical activity involved walking on a flat surface (44%), or general activities (housework/yardwork, 42%). Most subjects were asymptomatic (49%) during daily physical activity, 22% noted dyspnea, 16% fatigue and 13% sore muscles/joints. Perceived intensity of peak daily physical activity (mean = 4.19, SD = 2.21) was similar to perceived exertion (mean = 3.73, SD = 1.37) reported at ventilatory threshold measured during treadmill exercise testing. Subjects may control their peak daily physical activity to minimize symptoms experienced. It was further observed that current methods of assessing functional capacity in these patients were inadequate for estimating the peak level of daily activity. In conclusion, daily physical activity levels are low in patients with congestive heart failure and a gap exists between exercise capacity and actual performance of daily physical activity.

Aged↗
PubMed1993

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)

Adult↗
PubMed1993

Assessment of perfused left ventricular mass in normal, ischemic, and reperfused myocardium by means of single-photon emission computed tomography of technetium-99m isonitrile.

To test the hypothesis that single-photon emission tomography of technetium (Tc) 99m hexakis 2-methoxyisobutyl isonitrile (Tc-MIBI) can accurately measure perfused left ventricular (LV) mass in nonischemic, ischemic, and reperfused myocardium, we acquired Tc-MIBI tomographic images in canines with normally perfused hearts (n = 33) after occlusion of the left anterior descending coronary artery (n = 15), after reperfusion (n = 13), and with subsequent second injection of Tc-MIBI (15 to 18 mCi; n = 12). In all ischemic studies the initial dose of Tc-MIBI (5 to 6 mCi) was injected after coronary artery occlusion but before reflow. Scintigraphic perfused LV mass was calculated from the total voxels demonstrating Tc-MIBI uptake x voxel volume (cm3) x specific gravity of myocardium (1.05 gm/cm3). After being imaged the animals were killed, the left ventricle was weighed, and the risk area was determined by dual perfusion with phthalocyanine blue dye and triphenyltetrazolium chloride (TTC). Perfused LV mass was defined as total LV mass minus the risk area mass. There was good correlation between scintigraphic and morphologic determinations of perfused left ventricular mass in nonischemic hearts (Tc-MIBI left ventricular distribution = 0.84 x left ventricular weight + .20.4, n = 33, r = 0.93, p = 0.0001) and ischemic hearts (Tc-MIBI left ventricular distribution = 0.51 x left ventricular weight + 37.9, n = 15, r = 0.83, p = 0.0001). In animals imaged both before and after reperfusion, scintigraphic determinations of the nonischemic region correlated closely (after-reflow Tc-MIBI distribution = 1.07 x before-reflow Tc-MIBI distribution--8.0, n = 13, r = 0.88, p = 0.0001), indicating that Tc-MIBI does not significantly redistribute into the ischemic zone after reperfusion. After injection of the second dose of Tc-MIBI in acutely reperfused canines, there was good correlation between the distribution mass of Tc-MIBI and the mass of viable myocardium by TTC staining (Tc-MIBI distribution = 0.61 x viable LV mass + 34.2, n = 12, r = 0.77, p = 0.0001). Furthermore, the apparent redistribution of myocardial Tc-MIBI from before and after second injection images correlated with the degree of myocardial salvage by histochemical staining (r = 0.72, p = 0.0082). In conclusion, single-photon emission computed tomography of Tc-MIBI can measure perfused LV mass accurately in both ischemic and nonischemic canine preparations.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1993

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.

Aged↗
PubMed1993

Comparison of T1-enhancing and magnetic susceptibility magnetic resonance contrast agents for demarcation of the jeopardy area in experimental myocardial infarction.

RATIONALE AND OBJECTIVES: This study compared the areas demarcated by a T1-enhancing agent, Gd-DTPA-BMA, and a magnetic susceptibility agent, Dy-DTPA-BMA, with 201thallium autoradiography (indicator of perfusion) and postmortem histochemical staining with triphenyltetrazolium chloride (TTC)(indicator of infarction). METHODS: Thirteen rats were subjected to coronary artery occlusion for 3 to 4 hours before acquisition of four sets of electrocardiogram-gated spin-echo magnetic resonance (MR) images: T1-weighted images before and after 0.2 mmol/kg Gd-DTPA-BMA; and T2-weighted images before and after 0.3 mmol/kg Dy-DTPA-BMA. After MR imaging, intravenous 201thallium delineated the area of decreased myocardial perfusion. At autopsy, TTC staining delineated the area of myocardial infarction. RESULTS: A myocardial region in the distribution of the occluded artery was delinated as a hyperintense area ("hot-spot") by Dy-DTPA-BMA and as a hypointense area ("cold-spot") by Gd-DTPA-BMA. The hyperintense area demarcated by Dy-DTPA-BMA (51 +/- 3% of the area of the midequitorial slice of the left ventricle) showed a closer relationship to the area of decreased myocardial perfusion (jeopardized area) (46 +/- 3%), determined by 201thallium autoradiography, than the area of myocardial infarction (36 +/- 4%), determined by histochemical staining. However, the hypointense area demarcated by Gd-DTPA-BMA (29 +/- 2%) did not relate as closely to the area of decreased myocardial perfusion (slope = 0.54) or the area of myocardial infarction (r = 0.46). CONCLUSIONS: The abnormal myocardial area delineated by the magnetic susceptibility agent showed a closer relationship to the area of deficient myocardial perfusion (jeopardy area) after coronary occlusion than that defined by T1-enhancing contrast media.

Animals↗
PubMed1993

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.

Artifacts↗
PubMed1992

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.

Adult↗
PubMed1992

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.

3-Iodobenzylguanidine↗
PubMed1991

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)

Arrhythmia, Sinus↗
PubMed1991

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.

Adult↗
PubMed1991

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.

Coronary Disease↗
PubMed1991

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.

3-Iodobenzylguanidine↗
PubMed1991

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.

Coronary Disease↗
PubMed1991

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.

Adolescent↗