Impact of imaging protocol on left ventricular ejection fraction using gated-SPECT myocardial perfusion imaging.

BACKGROUND: There are limited data on the impact of the imaging protocol (single-day stress-rest, SD, vs. dual-day, DD) on the change in left ventricular (LV) ejection fraction (EF) (post-stress-rest) in relation to ischemia and on outcome. METHODS: Using propensity score matching procedure, 490 of 1121 patients with known CAD, undergoing a SD or a DD in a multicenter study, were evaluated. Stress and rest gated-SPECT myocardial perfusion imaging was used to quantify LV perfusion, EF, and volumes. Outcome was assessed at an average follow-up time of 3.2 years. RESULTS: Post-stress LVEF in SD and DD were comparable across all degrees of ischemia. The change in LVEF in patients with severe ischemia was, however, higher in the DD protocol, independent of the extent of CAD. At follow-up, 240 patients (49.0%) required coronary revascularization (CR) and 52 patients (10.6%) had hard events. The ischemic burden was independently associated with CR and hard-events; the post-stress LVEF was associated with CR but the change in EF was not predictive of either CR or hard events. CONCLUSIONS: In patients with severe ischemia, underestimation of post-stress myocardial stunning could be observed with the SD protocol. Post-stress LVEF and the extent ischemia, but not the change in EF, are predictive of CR and hard events.

EACVI survey on radiation exposure in interventional echocardiography.

AIMS: The European Association of Cardiovascular Imaging (EACVI) Scientific Initiatives Committee performed a global survey on radiation exposure in interventional echocardiography. The survey aimed to collect data on local practices for radioprotection in interventional echocardiography and to assess the awareness of echocardiography operators about radiation-related risks. METHODS AND RESULTS: A total of 258 interventional echocardiographers from 52 different countries (48% European) responded to the survey. One hundred twenty-two (47%) participants were women. Two-thirds (76%) of interventional echocardiographers worked in tertiary care/university hospitals. Interventional echocardiography was the main clinical activity for 34% of the survey participants. The median time spent in the cath-lab for the echocardiographic monitoring of structural heart procedures was 10 (5-20) hours/month. Despite this, only 28% of interventional echocardiographers received periodic training and certification in radioprotection and 72% of them did not know their annual radiation dose. The main adopted personal protection devices were lead aprons and thyroid collars (95% and 92% of use, respectively). Dedicated architectural protective shielding was not available for 33% of interventional echocardiographers. Nearly two-thirds of responders thought that the radiation exposure of interventional echocardiographers was higher than that of interventional cardiologists and 72% claimed for an improvement in the radioprotection measures. CONCLUSION: Radioprotection measures for interventional echocardiographers are widely variable across centres. Radioprotection devices are often underused by interventional echocardiographers, portending an increased radiation-related risk. International scientific societies working in the field should collaborate to endorse radioprotection training, promote reliable radiation dose assessment, and support the adoption of radioprotection shielding dedicated to interventional echocardiographers.

Congenital Segmental Absence of Tracheal Rings in a Kitten.

Congenital anomalies of the trachea are rare in cats. This article reports segmental absence of tracheal cartilage rings in a kitten. An 8-month-old female kitten was presented with a history of weight loss and respiratory distress for 2 months. Radiographs of the thorax demonstrated a large air-filled sac suggestive of pneumomediastinum. No cartilaginous structures were evident radiographically over the caudal portion of the trachea. At necropsy examination, approximately 2 cm from the carina, a 3 cm segment of the trachea lacked cartilaginous rings. The clinical and morphological features of this lesion were similar to those described in human and canine cases of congenital segmental absence of tracheal rings.

Residual coronary reserve identifies segmental viability in patients with wall motion abnormalities.

OBJECTIVES: The aim of this study was to determine whether the presence of residual coronary reserve can in itself identify viable segments. BACKGROUND: Experimental data suggest that despite hypoperfusion at rest, viable myocardium may exhibit persistence of coronary reserve. Preliminary observations in patients show that in basally dyssynergic areas, a residual vasodilator capability is present despite hypoperfusion at rest and that a flow-mediated increase in regional wall motion identifies residual viability. METHODS: Fourteen patients with evidence of previous myocardial infarction, infarct-related single-vessel coronary artery disease and impaired regional ventricular function at rest underwent positron emission viability imaging by fluorine-18 deoxyglucose. In addition, blood flow at rest and vasodilator capability were regionally evaluated in all patients by means of nitrogen-13 ammonia. RESULTS: Of a total of 252 segments, 133 were dyssynergic at rest. Of these 133 segments, 60 (group 1) showed normal metabolic activity and only mild reduction in myocardial blood flow. The other 73 segments showed a marked reduction in flow; of these, 25 (group 2, viable) had persistent metabolic activity, whereas 48 (group 3, necrotic) did not. Despite similar levels of hypoperfusion at rest, group 2 segments showed a preserved coronary reserve that was virtually absent in necrotic segments (2.6 +/- 1.3 vs. 1.3 +/- 0.5, p < 0.01). This value was similar to that observed in viable group 1 segments (2.5 +/- 1.6, p = NS). CONCLUSIONS: In addition to characterizing myocardium at risk, imaging of coronary flow at baseline and after dipyridamole by positron emission tomography provides helpful information on myocardial viability that may integrate the "static" viability information obtained with the baseline flow/metabolic approach.

Homogeneously reduced versus regionally impaired myocardial blood flow in hypertensive patients: two different patterns of myocardial perfusion associated with degree of hypertrophy.

OBJECTIVES: The aim of this study was to quantitatively measure regional and global myocardial blood flow and coronary reserve in hypertensive patients without coronary artery disease and to assess the correlation with left ventricular mass. BACKGROUND: The effect of left ventricular hypertrophy on regional vasodilating coronary capability in arterial hypertension is controversial, and no quantitative method has been applied to assess a possible correlation. METHODS: Positron emission tomography was performed in 50 untreated hypertensive patients and 13 normotensive subjects. Blood flow at baseline and after dipyridamole was globally and regionally measured by using nitrogen-13 ammonia; coronary reserve and resistance were calculated. Left ventricular mass was assessed by two-dimensional echocardiography. RESULTS: In hypertensive patients, flow at baseline was similar to that of normotensive subjects (p = 0.21), but values were reduced after pharmacologic vasodilation (p < 0.05). This impairment of maximal coronary flow was not correlated with left ventricular mass (p = 0.13). Among hypertensive patients, we identified a group with a homogeneous distribution of perfusion and a group with a heterogeneous flow pattern. Flow was globally reduced in the former group, but it was abnormal only at the site of perfusion defects in the latter. Patients with regional defects showed the highest likelihood of having an increased left ventricular mass. CONCLUSIONS: In arterial hypertension, left ventricular mass is not correlated with global myocardial blood flow. Nevertheless, patients with ventricular hypertrophy are likely to show a heterogeneous flow pattern with regional defects and almost normal blood flow in nonaffected regions. In hypertensive patients with a homogeneous perfusion pattern during stress, myocardial blood flow frequently shows a diffuse reduction.

Myocardial and forearm blood flow reserve in mild-moderate essential hypertensive patients.

BACKGROUND: Structural readaptation of systemic resistance-sized arterioles in response to an elevated blood pressure reduces the forearm vasodilator reserve in patients with essential hypertension. The development of a similar process at the coronary microvascular level has frequently been hypothesized, but little information about coronary remodeling during the uncomplicated stage of hypertension has been obtained, and the relationship with concomitant changes in forearm blood flow reserve is not known. OBJECTIVE: To assess the minimal myocardial resistance and its relationship with the minimal forearm resistance in a group of male patients with mild-to-moderate uncomplicated hypertension and carefully matched controls. MATERIAL AND METHODS: The minimal myocardial resistance (Rmin(myocardia), the mean arterial pressure: hyperemic myocardial flow ratio after administration of 0.84 mg/kg dipyridamole, measured by using positron emission tomography and [3N]-ammonia), minimal forearm vascular resistance (Rmin(forearm), a hemodynamic index of arteriolar structure derived from the mean blood pressure and maximal postischemic forearm blood flow by venous plethysmography), echocardiographic cardiac mass and wall thickness were measured in 25 male patients with mild-to-moderate uncomplicated essential hypertension, most of whom had previously been treated, and in seven sex- and age-matched normotensive controls. RESULTS: Rmin(myocardial) (and hyperemia: baseline myocardial flow ratios) did not differ significantly between the two groups, whereas Rmin(forearm) was significantly higher in hypertensives. There was no significant intra-individual correlation between the two parameters. The left ventricular mass index was greater in patients and was related previously to Rmin(forearm) but not to Rmin(myocardial) for the overall sample. In a subgroup analysis, Rmin(forearm) values were 2SD above control values in nine patients and within the normal range in the remaining 16. The myocardial reserve was very similar in the two subgroups. CONCLUSIONS: The myocardial vasodilator reserve appeared to be preserved in these mild-to-moderate uncomplicated hypertensive patients, whereas the forearm vasodilator capacity was reduced, suggesting that the hypertensive readaptation process was not distributed homogeneously over the two vascular beds.

Thallium-201 reverse redistribution at reinjection imaging correlated with coronary lesion, wall motion abnormality and tissue viability.

UNLABELLED: Previous studies based on standard stress-redistribution 201TI scintigraphy provided conflicting results about the clinical significance 201Tl reverse redistribution. Recent observations indicate that the majority of these defects normalize following reinjection reflecting viable myocardium. METHODS: In this study, the meaning of reverse redistribution occurring at reinjection imaging, its relation to standard 4-hr redistribution, coronary lesion, abnormal wall motion and tissue viability were assessed. A region with normal activity in the stress image was considered as having reverse redistribution if 201Tl activity at reinjection imaging was definitely abnormal with a decrease in relative tracer uptake >15% of the peak. From a series of 270 patients, 29 showed reverse redistribution. Of these 29 patients, 27 had evidence of previous myocardial infarction. Coronary lesions were detected in all but 1 patient. Average ejection fraction was 0.38 +/- 0.11. RESULTS: On a segmental basis, 50/377 regions showed the pattern of reverse redistribution. A significant coronary lesion (> or = 50%) was found in 78% of these regions; occlusion rate was 50%, and collateral circulation was found in 35% of occluded vessels. Hypokinesis or akinesis was present in 72% of segments. Tissue viability, defined as an uptake >55% of the peak, was found in 44% of these segments. The 50 segments showing reverse redistribution were divided into two groups according to an abnormal uptake also at 4-hr redistribution (group 1, 25 segments) or appearing only following reinjection (group 2,25 segments). Despite segments of group 1 showing a higher degree of coronary stenosis (80 +/- 32 versus 59 +/- 43%, p < 0.01), a similar rate of coronary occlusion, ventricular dysfunction and maintained viability was found in the two groups. CONCLUSION: Reverse redistribution in chronic coronary artery disease is frequently associated with significant coronary lesion, collateral-dependent dysfunctioning myocardium and preserved tissue viability. The occurrence of reverse redistribution following reinjection expands the indication for viability imaging to all patients with known coronary artery disease and regional wall motion abnormalities who undergo diagnostic and prognostic 201TI scintigraphy.

Reverse redistribution in resting thallium-201 myocardial scintigraphy in chronic coronary artery disease: an index of myocardial viability.

UNLABELLED: The aim of this study was to evaluate whether segments with reverse redistribution on rest-redistribution 201Tl scintigraphy represent viable tissue or scar. METHODS: Nineteen patients (17 men, 2 women; mean age 53 +/- 8 yr) with coronary artery disease underwent rest-redistribution 201Tl study before coronary revascularization. Regional 201Tl uptake was analyzed quantitatively. Regional left ventricular wall motion was assessed before and after coronary revascularization using two-dimensional echocardiography and a three-point scale (1 = normal, 2 = hypokinetic, 3 = akinetic/dyskinetic). Two patterns of reverse redistribution were identified: pattern with normal 201Tl uptake in rest and abnormal in redistribution images and pattern with abnormal 201Tl uptake in rest and a significant decrease in redistribution images. RESULTS: Of the 247 segments analyzed, 85 were classified as normal, 37 as reversible defects, 83 as fixed defects and 42 as reverse redistribution (19 RR-A, 23 RR-B). Segments with RR-A differed from those with RR-B in wall motion score (1.4 +/- 0.7 versus 2.0 +/- 1.0). Electrocardiographic Q-waves were present in 26% of segments with RR-A and in 57% of segments with pattern B. After revascularization, all dyssynergic segments with pattern A showed improved wall motion, while only 40% of segments with pattern B and abnormal wall motion had such improvement. CONCLUSION: Our results suggest that dyssynergic segments with pattern A should be considered viable, while more caution should be used in classifying those with pattern B.

Comparison of combination of dipyridamole and dobutamine during echocardiography with thallium scintigraphy with thallium scintigraphy to improve viability detection.

The aim of this study was to investigate the relation between radioisotopic and echocardiographic markers of myocardial viability and their correlation with functional recovery after coronary revascularization. Myocardial viability can be detected by techniques exploring various aspects of cell physiology: thallium-201 scintigraphy and dobutamine and dipyridamole echocardiography focus on cell membrane integrity, beta-1 and adrenoceptor, and A2-adenosine receptor-mediated inotropic response, respectively. Fifty-seven patients (mean age 60+/-8 years) with previous myocardial infarction (>3 months), angiographically assessed coronary artery disease, and resting regional dysfunction underwent rest-redistribution 201-thallium scintigraphy and low-dose pharmacologic stress echo with dobutamine (up to 10 microg/kg/min), very low dose regimen of dipyridamole (0.28 mg/kg over 4 minutes), and combined dipyridamole-dobutamine. Criteria for viability in a 13-segment model for both techniques were percent peak activity in redistribution images >55% for thallium-201 and a decrease in wall motion score >1 grade (1 [normal] to 4 [dyskinetic]) for stress echo. Thirty patients underwent coronary revascularization (bypass surgery in 8, angioplasty in 22) and were followed up at 4 weeks from intervention with a resting echocardiogram. The rate of agreement between thallium-201 and stress echo was 63% for dipyridamole, 66% for dobutamine, and 74% for combined dipyridamole-dobutamine (p <0.05 vs dipyridamole and dobutamine). In the 30 patients who underwent revascularization, a regional resting dyssynergy was observed in 225 segments, assuming that postrevascularization functional recovery (which occurred in 126 segments) was the gold standard; combined dipyridamole-dobutamine showed a higher sensitivity (90% confidence interval [CI] 85% to 95%) than thallium-201, dobutamine, or dipyridamole (87%, CI 81% to 92%; 82%, CI 76% to 89%; and 82%, CI 76% to 89%, respectively). Specificity was lower for viability recognition with thallium-201 (61%, CI 51% to 71%) than with dobutamine (93%, CI 88% to 98%), dipyridamole (95%, CI 91% to 99%), and combined dipyridamole-dobutamine (92%; CI 87% to 97%). Combined adrenergic and adenosinergic stimulation recruits an inotropic reserve in a significant proportion of segments with preserved thallium uptake that were nonresponders after either dipyridamole or dobutamine. When functional recovery after successful revascularization is considered as the postoperative gold standard, thallium has a higher sensitivity than dipyridamole or dobutamine; this sensitivity gap is filled with combined dipyridamole-dobutamine. The specificity of all forms of pharmacologic stress echo is better than thallium-201.

Value of rest thallium-201/technetium-99m sestamibi scans and dobutamine echocardiography for detecting myocardial viability.

The relation between radioisotopic and echocardiographic markers of myocardial viability and postrevascularization recovery of function is still to be defined. To this purpose, 14 patients (11 men, 3 women, aged 35 to 64 years, mean 54 +/- 7) with ventricular dysfunction were studied by a multiparametric approach. Each patient underwent, on separate days, rest thallium-201 and technetium-99m sestamibi scintigraphy, dobutamine echocardiography and coronary angiography. Coronary angiography was analyzed by a quantitative approach. Thallium uptake at rest was quantified from planar early (10-minute) and delayed (16-hour) thallium-201 images and expressed as a percentage of maximal activity in each projection using a 13-segment model. Sestamibi uptake was expressed in the same way. Dobutamine (up to 10 micrograms/kg/min) echocardiography was analyzed using a score index ranging from 1 (normokinesia) to 4 (dyskinesia) and a similar segmental model. Before revascularization 50 segments were grouped as normal (coronary stenosis < 50% and normal function, group 1); of the remaining 132 segments with > 50% coronary stenosis, 57 had normal wall motion (group 2) and 75 showed regional dyssynergies (group 3). Early and delayed thallium-201 regional percent activities did not differ in group 1 and in group 2 but were significantly less in group 3 segments. Sestamibi percent activity was more in group 1 and significantly reduced both in group 2 and 3 segments. Segments with improved wall motion after dobutamine had more early, delayed thallium-201 and sestamibi percent activities than unresponsive segments. Postrevascularization echocardiography was performed in all patients. Delayed thallium-201 scans and dobutamine echocardiography showed good sensitivity and specificity in detecting viable myocardium. (ABSTRACT TRUNCATED AT 250 WORDS)

Does the myocardium become "stunned" after episodes of angina at rest, angina on effort, and coronary angioplasty?

To assess whether myocardial stunning occurs after brief periods of ischemia, global and regional ventricular function assessed by radionuclide angiography was studied in 52 patients. Patients were divided into 3 groups according to the type of ischemic episodes. Group 1 consisted of 15 patients studied before, during and after episodes of angina at rest. Seventeen patients studied immediately before and after coronary angioplasty constituted group 2. Group 3 consisted of 20 patients with stable angina studied before, during and after exercise-induced ischemia. Medical therapy was discontinued 48 hours before the study in all patients except those undergoing coronary angioplasty who were receiving diltiazem 180 mg/day. No difference in baseline ejection fraction was found between groups, whereas peak filling rate was statistically lower in group 3 patients. Evidence of left ventricular dysfunction during ischemia was seen in patients in groups 1 and 3, whereas transient ischemia was documented by ST-segment displacement and/or typical chest pain during balloon inflation in group 2. Persistence of systolic or diastolic dysfunction was not observed in any of the 3 groups in the recovery phase after ischemia. In conclusion, transient ischemia caused either by a primary reduction in oxygen supply (angina at rest, coronary angioplasty) or by an increase in oxygen demand (angina on effort) did not reproduce the phenomenon of systolic and diastolic stunning observed in animal experiments, although in all patients the ischemia was of sufficient duration and severity to induce marked ventricular dysfunction. The search for stunned myocardium should be extended to other different clinical models characterized by prolonged ischemia such as unstable angina or myocardial infarction.

Ischemia on effort is not a determinant of stunned myocardium in man: a radioisotopic study based on quantitative evaluation of ventricular dynamics.

To assess whether myocardial stunning occurs following brief episodes of effort ischemia, ventricular function was assessed by radionuclide angiography in 29 patients with coronary artery disease. No patient had evidence of previous myocardial infarction. Patients were divided into two groups according to presence of single (14 patients, Group 1) or multi-vessel (15 patients, Group 2) coronary artery disease. Equilibrium radionuclide angiocardiography was performed in the left anterior oblique projection by a small field-of-view gamma-camera. Acquisition were performed at baseline, at peak exercise, then again at 1 and 5 minutes of the recovery phase. For each acquisition, ejection fraction, peak filling rate and wall motion index were measured and compared. No difference in baseline and stress measurements was found between Group 1 and Group 2, except for the wall motion index that was more impaired during ischemia in patients of Group 2. Global and regional indexes of ventricular function did not show significant differences also in the two recovery periods when compared to the relative baseline values. Transient ischemia caused by an increase of oxygen demand did not reproduce the phenomenon of systolic and diastolic stunning observed in animal experiments, although in all patients the ischemia was of sufficient duration and severity to induce transient ventricular dysfunction.

Non-invasive assessment of residual viability in post-myocardial infarction patients. Role of nuclear techniques.

The failure of non-imaging techniques in identifying viable segments has favoured the clinical application of nuclear imaging. The main pathways that support radionuclide imaging are cell membrane integrity, persistence of intermediary metabolism and demonstration of a residual coronary reserve. Thallium-201 reinjection or rest protocols allow the identification of viable myocardium in most of patients with wall motion abnormalities and appear to be the most diffuse, low-cost and available method to detect viable myocardium. More complex approaches use positron emission tomography and matched flow/metabolic information. Flow/metabolic 'mismatch' usually identifies most of hypoperfused regions that show post-operative improvement of regional wall motion. The last promising approach is represented by the demonstration of a maintained regional coronary reserve in dyssynergic areas. Technetium-99m-microspheres (or Teboroxime in the future) can be successfully used for this purpose. The clinical application of radionuclides appears to be one of the principal imaging tools able to identify residual viability.

Different tracers and stressors in patients with coronary artery disease: how to standardize clinical questions and nuclear cardiology answers.

The recent introduction of new tracers and stressors has increased the number of combinations of techniques that can be used for the diagnostic and prognostic stratification of patients with coronary artery disease. However, these new techniques still need to be standardized for clinical use. Thallium-201 scintigraphy is at present the most common method to assess transient ischemia and viability in patients. Dynamic exercise and dipyridamole show similar incidence of major cardiac complications and their use can be considered sufficiently safe. Further experimental and multicenter clinical studies are needed for 99mTc-Sestamibi and 99mTc-Teboroxime and for new stressors such as adenosine and dobutamine.

[Global change in the regulation of regional coronary flow in patients with single vessel coronary disease evidenced by positron emission tomography]. / Alterazione globale nella regolazione del flusso coronarico regionale in pazienti con coronaropatia monovascolare evidenziata mediante tomografia ad emissione di positroni.

AIM OF THE STUDY: Aim of this study is to investigate whether, in patients with coronary artery disease (CAD), regional myocardial blood flow (rMBF) regulation is affected with further mechanisms besides the effects of epicardial coronary stenosis. MATERIAL AND METHODS: RMBF and coronary reserve are measured in 13 normal subjects and in 36 patients with effort angina and isolated (> or = 50% diameter narrowing) left anterior descending (LAD, 27 patients) or left circumflex (LCX, 9 patients) coronary artery stenosis. Measurements are obtained both at baseline and following dipyridamole (0.56 mg/kg in 4 minutes) using positron emission tomography and N13-ammonia. RESULTS: At rest, patients with CAD show similar rMBF values in the stenotic and remote areas (0.71 +/- 0.19 vs 0.77 +/- 0.22 ml/min/gr, respectively, ns); both values are significantly (p < 0.01) reduced with respect to mean rMBF observed in the normal subjects (1.07 +/- 0.21 ml/min/gr). Following dipyridamole, patients with CAD show lower rMBF values in stenotic than in control regions (1.25 +/- 0.54 vs 1.73 +/- 0.80 ml/min/gr, p < 0.01); however, both these values are significantly reduced when compared with mean rMBF in the normal subjects (3.76 +/- 0.88 ml/min/gr, p < 0.01). To evaluate whether reduction in resting myocardial perfusion indicates maximal vasodilatation, patients with CAD are divided into 2 groups: Group 1 with homogeneous baseline perfusion (0.73 +/- 0.2 vs 0.75 +/- 0.24 ml/min/gr, in stenotic and remote areas, respectively, ns), and Group 2 with baseline perfusion defect in the stenotic related territory (0.62 +/- 0.14 vs 0.84 +/- 0.17 ml/min/gr, p < 0.01). Coronary reserve (dipyridamole flow/baseline flow) is similar in the 2 Groups (1.74 +/- 0.66 vs 1.93 +/- 0.45, ns). CONCLUSIONS: These data suggest that, in patients with CAD, other factors beyond hydraulic effects of epicardial coronary stenosis, could modulate rMBF regulation; in fact: 1) myocardium perfused by angiographically normal coronary artery shows reduced values of both resting rMBF and coronary reserve; 2) myocardium supplied by stenotic vessel maintains a residual vasodilating capability despite a reduced baseline perfusion.

Regional concordance and discordance between rest thallium 201 and sestamibi imaging for assessing tissue viability: comparison with postrevascularization functional recovery.

BACKGROUND: Whether the combined analysis of rest 201Tl and sestamibi uptake provides additional information regarding myocardial viability in patients with coronary artery disease is still to be investigated. METHODS AND RESULTS: To this aim we studied 22 patients with previous myocardial infarction and regional ventricular dysfunction by quantitative rest sestamibi and 201Tl scintigraphy. All patients underwent revascularization, and echocardiography was repeated 11 +/- 2 weeks later. Concordant results were obtained in 80 of 105 dyssynergic segments. Fifty-one segments showed normal and 29 abnormal activity. Follow-up echocardiography showed increased wall motion contractility in 76% of segments with maintained 201Tl and sestamibi uptake and in only 17% of segments characterized by subthreshold activities. Twenty-five segments, or 24%, showed sestamibi/201Tl mismatch. Eleven of 12 segments with normal sestamibi/abnormal 201Tl activity did not improve after revascularization, whereas 11 of 13 segments with abnormal sestamibi but normal 201Tl showed postoperative improvement of regional wall motion. CONCLUSIONS: In patients with previous myocardial infarction, sestamibi and 201Tl showed concordant results in most segments. However, in segments with mismatch a maintained sestamibi uptake was a poor indicator of tissue viability, whereas significant 201Tl uptake reflected tissue viability in most segments.

Myocardial viability: nuclear medicine versus stress echocardiography.

The failure of nonimaging techniques in the identification of myocardial viability has promoted the clinical application of radioisotopic and echocardiographic methods. Unfortunately, none of these techniques provides, per se, a 100% predictive accuracy and only few studies have been based on the postoperative improvement in regional wall motion, the absolute "gold standard" for myocardial viability. The recent thallium-201 protocols (reinjection, late redistribution, rest studies) have provided nuclear cardiology with a cell membrane integrity image able to unmask viable myocardium in more than 85% of viable segments. Sestamibi has been introduced as a nonrecirculating flow tracer able to detect transient ischemia as well as thallium-201. Its main limit, a high sensitivity to intermediate reductions in coronary blood flow, determines a high incidence of false positive studies. Positron emission tomography allows the evaluation of regional myocardial blood flow and metabolism. The marker of viable myocardium is the mismatch between reduced blood flow and normal or increased uptake of 18-F fluorodeoxyglucose. This technique allows the detection of viable tissue in most segments showing improved postoperative function. In our experience, applying a multiparametric approach, rest thallium-201 scan, rest sestamibi, dobutamine, and dipyridamole echocardiography showed a sensitivity and a specificity of 86%, 75%, 82%, 75% and 92%, 84%, 92%, and 89%, respectively, in the detection of residual viability. The main advantages of thallium-201 are reproducibility and standardization; those of stress echo are low cost and availability. In patients with severely depressed ventricular function, positron emission tomography retains a primary role when compared to thallium-201 and stress echocardiography.

Imaging of myocardial viability: a head-to-head comparison among nuclear, echocardiographic, and angiographic techniques.

The relationship between radioisotopic, echocardiographic, and angiographic markers of myocardial viability is still to be defined. To this purpose, 14 patients with previous myocardial infarction were studied using a multiparametric approach. Each patient underwent, on separate days, rest thallium 201 and technetium 99m Sestamibi planar scintigraphy, dobutamine/dipyridamole stress echocardiography, and coronary angiography; 11 of these patients underwent also dipyridamole echocardiographic testing. Thallium 201 and Sestamibi uptakes at rest were expressed as percentage of maximal activity in each projection using a 13 segment model. Dobutamine and dipyridamole stress echocardiography were analyzed using a score index ranging from 1 (normokinesis) to 4 (dyskinesis) and a similar segmentation. Coronary angiography was analyzed by quantitative approach. In all patients, follow-up echocardiography was performed following coronary revascularization. Before revascularization, 75 segments showed regional dyssynergies. Thallium 201 showed the highest sensitivity and specificity in the preoperative identification of viability, whereas Sestamibi was affected by a significant number of false-negative studies. Among echocardiographic techniques, dobutamine was slightly superior to dipyridamole in the detection of viable segments. The degree of coronary stenosis failed to predict the recovery of function following by-pass graft or angioplasty in almost all segments; however, in case of occlusion, most viable segments were perfused by adequately collateralized coronary arteries.