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D Georgiadis

Publications and source records attributed to D Georgiadis.

99 records · Page 6Linked to original sources
PubMed1994

Differentiation between gaseous and formed embolic materials in vivo. Application in prosthetic heart valve patients.

BACKGROUND AND PURPOSE: Doppler emboli detection is an established technique, but the nature of the underlying embolic material remains unclear. The intensity and spectral distribution of emboli signals could help to distinguish between signals arising from formed and gaseous emboli. We undertook this study to develop and evaluate a differentiation algorithm based on the spectral characteristics of emboli signals. Subsequently the algorithm was applied to patients with mechanical prosthetic cardiac valves. METHODS: Emboli signals detected in patients with carotid disease, acute stroke, and atrial fibrillation were used as formed emboli data, and signals detected in patients undergoing cardiac catheterization studies were used as gaseous emboli data. For each embolus signal, the maximal amplitude, the sum of amplitudes, and the spectral intensity distribution were calculated. Two hundred emboli signals from each category were used to develop a differentiation algorithm, which was subsequently evaluated on 501 additional solid and 995 gaseous emboli signals. The same algorithm was used to analyze 5958 emboli signals detected in 60 patients with mechanical prosthetic valves. RESULTS: The best results were obtained with an algorithm based on both the maximal amplitude and the sum of amplitudes (sensitivity, 99%; specificity, 96.5%). On subsequent evaluation, the sensitivity and specificity of the algorithm were 99.6% and 89.8%, respectively. Of the 5958 emboli signals detected in prosthetic valve patients, 92.4% were classified as gaseous. CONCLUSIONS: Differentiation between gaseous and formed emboli signals, as detected by transcranial Doppler in vivo, is feasible by means of spectral analysis. Application of the differentiation algorithm in prosthetic valve patients suggests that the embolic material in these patients is gaseous. The possibility of distinguishing between different formed embolic materials with this technique remains to be evaluated.

Adult↗
PubMed1994

Ultrasound detection of cerebral emboli in patients with prosthetic heart valves.

This study was undertaken in 64 patients, 50 with mechanical and 14 with porcine prosthetic valves, to evaluate the incidence of intracranial emboli and their distribution in the basal cerebral arteries. The patients were studied using transcranial Doppler (EME TC2-64B, Uberlingen, Germany), with a monitoring time of two minutes over each of the internal carotid arteries, middle and anterior cerebral arteries, vertebral arteries and the basilar artery. Sixty-three of the 64 patients were stabilized on warfarin at the time of the study. The incidence of emboli signals was significantly higher in patients with mechanical compared to porcine cardiac valves (88% versus 14%, p < 0.01). The number of emboli signals was significantly higher in the anterior compared with the posterior circulation, with a median of eight signals in the internal carotid arteries (95% confidence interval 5-15), 2.5 in the vertebral arteries (95% confidence interval 1-5.5)(p < 0.03). It was also significantly higher in those patients who had undergone double (aortic and mitral) as opposed to those who had undergone single aortic valve replacement: 18 versus two signals per minute (confidence intervals 5-30.5 versus 0.5-3.5) (p < 0.01). It is concluded that subclinical emboli signals are readily detectable using transcranial Doppler and are common in patients with prosthetic heart valves. Their number depends on both the type and the number of the prosthesis, while their distribution in the basal cerebral arteries is consistent with their cardiac source.

Adult↗
PubMed1993

Transhemispheric passage of microemboli in patients with unilateral internal carotid artery occlusion.

BACKGROUND AND PURPOSE: Ischemic episodes distal to an internal carotid artery occlusion are common. We undertook this study to look for evidence of transhemispheric passage of embolic material in this patient category as a mechanism for embolic events. METHODS: Seven symptomatic patients with unilateral internal carotid artery occlusion and contralateral stenosis were examined by transcranial Doppler ultrasonography with 2-MHz probe (average monitoring time, 2.5 hours per patient). Both middle cerebral arteries and (if present) the reverse-flow anterior cerebral artery ipsilateral to the occluded internal carotid were monitored. Three patients were reexamined 1 month after carotid endarterectomy. RESULTS: Embolic signals were detected in the middle cerebral artery ipsilateral to the stenosed internal carotid artery in all seven patients and in the opposite middle cerebral artery in four patients. In these four patients, a reverse-flow anterior cerebral artery was observed in which embolic signals were detected. No embolic signals were detected after surgery in any of the three patients who underwent carotid endarterectomy. CONCLUSIONS: Transhemispheric passage of embolic material occurs in patients with unilateral internal carotid artery occlusion and contralateral stenosis. Endarterectomy of the stenosed internal carotid artery may eliminate the detected embolic signals in both hemispheres. Transcranial Doppler ultrasonography could be used as a diagnostic tool to identify the embolic source in patients with unilateral carotid occlusion.

Aged↗
PubMed1993

Quantification of ultrasound emboli signals in patients with cardiac and carotid disease.

BACKGROUND AND PURPOSE: The use of Doppler ultrasound to detect arterial emboli has major implications for the classification and treatment of stroke. Experimental studies indicate that embolic materials produce different ultrasound signals, depending on their acoustic properties. To examine the possibility of characterizing emboli of different sources in the clinical setting, we compared the emboli signals of patients with cardiac embolic sources with those of patients with signals of carotid embolic sources. METHODS: Transcranial Doppler monitoring (30 minutes per patient) of the middle cerebral arteries was performed in 80 patients with prosthetic cardiac valves and 20 patients with internal carotid artery stenosis. The signal power of emboli was calculated in relation to the background Doppler signal. RESULTS: In patients who were embolizing from prosthetic heart valves, the frequency of embolus signals was greater than in patients with carotid stenosis who were embolizing (mean +/- SEM: 58.2 +/- 11 versus 8.2 +/- 3 signals per hour; P < .0001, two-sample t test), and total signal power and duration also were higher (power, 2231 +/- 63 versus 455 +/- 109 power units; duration, 55.9 +/- 0.8 versus 29.9 +/- 1.4 milliseconds; both P < .001). The majority of emboli signals were seen during cardiac systole, especially in patients with carotid stenosis (89% in the first half of the cardiac cycle versus 72% in prosthetic valve patients). In 19 patients with prosthetic valves, embolus signals were also recorded from the anterior cerebral artery; the signal count was not significantly different from the middle cerebral artery (43.2 +/- 12.5 versus 64.3 +/- 16 per hour), but anterior cerebral artery signals were of higher power (3306 +/- 148 versus 2441 +/- 109 power units, P < .001). CONCLUSIONS: There is promise of being able to distinguish emboli on the basis of power measurements. Emboli of different sources (eg, carotid and cardiac) appear to have different ultrasonic characteristics, which are likely to be based on composition and size.

Aged↗
PubMedDate not supplied

Future challenges facing the development of specific active-site-directed synthetic inhibitors of MMPs.

Despite a deep knowledge on the 3D-structure of several catalytic domains of MMPs, the development of highly specific synthetic active-site-directed inhibitors of MMPs, able to differentiate the different members of this protease family, remains a strong challenge. Due to the flexible nature of MMP active-site, the development of specific MMP inhibitors will need to combine sophisticated theoretical and experimental approaches to decipher in each MMP the specific structural and dynamic features that can be exploited to obtain the desired selectivity.

Amino Acid Sequence↗
PubMedDate not supplied

Venous microemboli in patients with artificial heart valves.

BACKGROUND: Detection of microemboli signals (MES) in patients with artificial heart valves has been extensively described, but the underlying material remains unclear. We assumed that the detection of MES in the jugular vein of patients with prosthetic valves would clearly argue for gaseous embolic material, since formed emboli are unable to cross through the capillaries. METHODS AND RESULTS: Twenty-five patients with artificial heart valves, 15 patients with asymptomatic carotid artery disease, and 25 normal controls were examined. Monitoring was performed simultaneously over the dominant jugular vein and the ipsilateral middle cerebral artery for 30 min per subject, using 2-MHz transducers of a color duplex scanner for the jugular vein and a pulsed-wave Doppler for the middle cerebral artery. Data were harvested in an eight-channel digital recorder and MES counts evaluated by two separate observers. MES prevalence in the middle cerebral artery was 100, 13 and 0% in patients with artificial heart valves, asymptomatic carotid artery disease, and normal controls, respectively. No MES were detected in the jugular veins of patients with carotid artery disease or in normal controls, while their prevalence was 68% in patients with artificial heart valves. The interobserver agreement was satisfactory. CONCLUSION: Our results suggest that the embolic material of at least a part of MES in patients with artificial heart valves is gaseous.

Cerebral Arteries↗