Mehdi Namdar

Validation of a new cardiac image fusion software for three-dimensional integration of myocardial perfusion SPECT and stand-alone 64-slice CT angiography

PurposeCombining the functional information of SPECT myocardial perfusion imaging (SPECT-MPI) and the morphological information of coronary CT angiography (CTA) may allow easier evaluation of the spatial relationship between coronary stenoses and perfusion defects. The aim of the present study was the validation of a novel software solution for three-dimensional (3D) image fusion of SPECT-MPI and CTA.MethodsSPECT-MPI with adenosine stress/rest 99mTc-tetrofosmin was fused with 64-slice CTA in 15 consecutive patients with a single perfusion defect and a single significant coronary artery stenosis (≥50% diameter stenosis). 3D fused SPECT/CT images were analysed by two independent observers with regard to superposition of the stenosed vessel onto the myocardial perfusion defect. Interobserver variability was assessed by recording the X, Y, Z coordinates for the origin of the stenosed coronary artery and the centre of the perfusion defect and measuring the distance between the two landmarks.ResultsSPECT-MPI revealed a fixed defect in seven patients, a reversible defect in five patients and a mixed defect in three patients and CTA documented a significant stenosis in the respective subtending coronary artery. 3D fused SPECT/CT images showed a match of coronary lesion and perfusion defect in each patient and the fusion process took less than 15xa0min. Interobserver variability was excellent for landmark detection (ru2009=u20091.00 and ru2009=u20090.99, pu2009<u20090.0001) and very good for the 3D distance between the two landmarks (ru2009=u20090.94, pu2009<u20090.001).Conclusion3D SPECT/CT image fusion is feasible, reproducible and allows correct superposition of SPECT segments onto cardiac CT anatomy.

Diagnostic accuracy of myocardial perfusion imaging with single photon emission computed tomography and positron emission tomography: a comparison with coronary angiography

Objective The aim of this study was to compare the diagnostic accuracy of myocardial perfusion imaging (MPI) by positron emission tomography (PET) with the diagnostic accuracy of MPI by single photon emission computed tomography (SPECT) in two comparable patient cohorts, using coronary angiography (CA) as the standard of reference. Methods A “SPECT-group” of 80 patients (15 female, 65 male; mean age 60xa0±xa09xa0years) and a “PET-group” of 70 patients (14 female, 56 male; mean age 57xa0±xa010xa0years) underwent a one day stress/rest examination either with attenuation-corrected 13N-ammonia PET or attenuation-corrected 201TlCl SPECT or 99mTc-hexakis-methoxy-isobutyl-isonitril (MIBI) SPECT. PET and SPECT results were semiquantitatively graded using a 6-segment heart model. All patients underwent CA, and stenoses were graded as a diameter reduction ≥50%. Results Coronary findings between both groups did not significantly differ at CA. For the SPECT-group overall sensitivity and specificity for localisation of stenoses was 77% and 84%. Respective values for the PET-group were 97% and 84%. The specificity of MPI by SPECT in the detection of ischemia was 74% and 91% for MPI by PET. The diagnostic accuracy of MPI improves when the individual coronary dominance and previous coronary revascularisations are taken into account. Conclusion MPI by 13N-ammonia PET is more sensitive in the detection and localisation of coronary stenoses, and more specific in the detection of ischemia than MPI by 201TlCl/99mMIBI SPECT.

Electrophysiological findings in patients with isolated left ventricular non-compaction.

AIMSnPatients with isolated left ventricular non-compaction (IVNC) are at high risk for developing ventricular tachyarrhythmias. However, no analysis of invasive electrophysiological (EP) findings in these patients has yet been performed.nnnMETHODS AND RESULTSnWe performed a retrospective analysis of EP findings in 24 patients with IVNC. Ventricular tachyarrhythmias were inducible in nine patients; of these, two patients had sustained monomorphic ventricular tachycardia (VT) and two patients had ventricular fibrillation. No specific electrocardiographic or echocardiographic finding was predictive of VT inducibility. Three of the 9 patients with inducible VT experienced ventricular tachyarrhythmias during the follow-up of 61.4+/-50 months, whereas no tachyarrhythmias or sudden deaths were noted in 12 patients without inducible VT during the follow-up of 30+/-19 months (3 patients in the latter group were lost to follow-up). Supraventricular tachyarrhythmias were inducible in seven patients.nnnCONCLUSIONnOur present study provides the first comprehensive analysis of EP findings in patients with IVNC. Ventricular and supraventricular arrhythmias can readily be induced in these patients, whereas the inducibility of a sustained monomorphic VT is relatively low. Further studies including long-term follow-up are required to investigate the role of EP testing for arrhythmic risk stratification in these patients.

Electrocardiographic changes in early recognition of Fabry disease

Background Fabry disease (FD) is an inherited X-chromosomal lysosomal storage disease resulting in intracellular storage of globotriaosylceramide. Cardiac involvement is most frequently manifested as left ventricular hypertrophy (LVH). However, patients with FD may also have various conduction abnormalities before LVH develops. The present study was designed to analyse early conduction abnormalities on baseline ECG of patients with FD and to investigate their diagnostic value. Methods and results Baseline electrocardiographic (ECG) and echocardiographic measurements of patients with FD (n=30) were compared with those of heart rate and age-matched healthy individuals (n=50). The PQ-interval (131±18 vs 155±20u2005ms, p<0.000001) and the QRS width (83±11 vs 90±9u2005ms, p<0.05) were significantly shorter and repolarisation dispersion was more pronounced in patients with FD (QTc dispersion: 66±32 vs 40±24u2005ms, p<0.001, Tpeak−Tend dispersion: 56±20 vs 37±16u2005ms, p<0.0005). Moreover, P-wave duration was significantly shorter (74±16 vs 105±14u2005ms, p<0.000001) in FD and accounted predominantly for the shortening of the PQ-interval. P-wave duration showed a 92% sensitivity and 80% specificity for the diagnosis of FD. Conclusions P-wave duration, PQ-interval and QRS width are shorter and repolarisation dispersion more pronounced in patients with FD compared with heart rate and age-matched controls. The significant shortening of the PQ-interval in FD occurs because of a marked shortening of the P-wave duration, which in itself demonstrated a high sensitivity and specificity for early detection and treatment of this disease.

Caffeine Impairs Myocardial Blood Flow Response to Physical Exercise in Patients with Coronary Artery Disease as well as in Age-Matched Controls

Background Caffeine is one of the most widely consumed pharmacologically active substances. Its acute effect on myocardial blood flow is widely unknown. Our aim was to assess the acute effect of caffeine in a dose corresponding to two cups of coffee on myocardial blood flow (MBF) in coronary artery disease (CAD). Methodology/Principal Findings MBF was measured with 15O-labelled H2O and Positron Emission Tomography (PET) at rest and after supine bicycle exercise in controls (nu200a=u200a15, mean age 58±13 years) and in CAD patients (nu200a=u200a15, mean age 61±9 years). In the latter, regional MBF was assessed in segments subtended by stenotic and remote coronary arteries. All measurements were repeated fifty minutes after oral caffeine ingestion (200 mg). Myocardial perfusion reserve (MPR) was calculated as ratio of MBF during bicycle stress divided by MBF at rest. Resting MBF was not affected by caffeine in both groups. Exercise-induced MBF response decreased significantly after caffeine in controls (2.26±0.56 vs. 2.02±0.56, P<0.005), remote (2.40±0.70 vs. 1.78±0.46, P<0.001) and in stenotic segments (1.90±0.41 vs. 1.38±0.30, P<0.001). Caffeine decreased MPR significantly by 14% in controls (P<0.05 vs. baseline). In CAD patients MPR decreased by 18% (P<0.05 vs. baseline) in remote and by 25% in stenotic segments (P<0.01 vs. baseline). Conclusions We conclude that caffeine impairs exercise-induced hyperaemic MBF response in patients with CAD to a greater degree than age-matched controls.

Prognostic value of revascularising viable myocardium in elderly patients with stable coronary artery disease and left ventricular dysfunction: a PET/CT study

Sparse information is available on the role of cardiac viability imaging in elderly patients. We aimed at evaluating the prognostic value of FDG-PET/CT in elderly patients with stable coronary artery disease (CAD) and reduced left ventricular ejection fraction (rLVEF) before revascularisation. Elderly patients (>u200965xa0years old, mean 74u2009±u20097xa0years old) with CAD and rLVEF were followed after cardiac FDG-PET/CT and stratified according to presence/absence of viable myocardium and subsequent revascularisation. Fatal events of any cause as well as hospitalisations related to acute cardiac conditions were reported as clinical end-points. Predictors of fatal events in patients with viable myocardium (>u20091 myocardium segment/20) were analysed. A total of 89 patients were followed (64 viable myocardia; 37 and 27 patients with and without subsequent revascularisation, respectively). The change in LVEF during follow-up (2.1u2009±u20091.6xa0years) was 3.8u2009±u20096.6% (Pu2009=u20090.013) and −u20090.75u2009±u20092.6% (Pu2009=u20090.170) in patients with and without revascularisation, respectively. Log-rank (Pu2009=u20090.037) and multivariate analysis (Wald: 6.305, Pu2009=u20090.012) showed viable myocardium to be significantly associated with fatal events if not revascularised. Elderly patients with viable myocardium might potentially benefit from revascularisation procedures as improved left ventricular ejection fraction and survival were observed in our retrospective study as compared to patients in whom a revascularisation procedure was denied. Viable myocardium as detected by cardiac FDG PET/CT was associated with better clinical outcomes in elderly patients when revascularised.

Recovery mismatch between myocardial blood flow and cardiac workload after physical exercise: a positron emission tomography study

AIMSnWe studied the interrelation between oxygen consumption and myocardial blood flow (MBF) during recovery. MBF is directly dependent on oxygen consumption. The latter is linearly related to the heart rate-blood pressure product (RPP, bpm × mmHg), an index reflecting external cardiac work. In the immediate post-exercise period, cardiac output decreases considerably. This is expected to be paralleled by a rapid fall in oxygen demand, rendering ischaemia unlikely. Thus, the phenomenon of ST-segment depression during recovery remains unexplained.nnnMETHODS AND RESULTSn(15)O-labelled water and positron emission tomography were used to measure MBF in 14 young healthy volunteers (mean age 27 ± 3 years) during the following study conditions: (i) at rest, (ii) during a steady submaximal supine bicycle exercise stress within the scanner, and (iii) during recovery immediately after cessation of exercise. During recovery, RPP decreased by 43% (18 768 ± 1337 vs. 11 652 ± 3224, P < 0.001). In contrast, the associated decrease in MBF (2.52 ± 0.52 vs. 1.93 ± 0.50 mL/min/g, P < 0.001) and perfusion reserve (2.68 ± 0.51 vs. 2.03 ± 0.42, P < 0.001) was significantly less pronounced (-24%, P < 0.01), indicating a relative delay in MBF recovery compared with cardiac work load.nnnCONCLUSIONnThe mismatch between a rapid decrease in cardiac workload but preserved hyperaemic response early after cessation of physical exercise suggests an uncoupling of cardiac work and MBF during recovery.

Natural history of aortic stenosis

Background: Management of patients with aortic stenosis is challenging since only few data exists indicating the rate of progression and the correlation to relevant determinants. We investigated whether analysis of the long-term progression, etiology and vascular risk factors could help to define optimal control intervals. Methods: We included 77 patients (age 51.1 ± 14.3 years) in one referral centre with an echocardiographyproven aortic stenosis (mean gradient >12 mm Hg) and a long-term follow-up of three echocardiographic examinations. Missing clinical data were supplemented by a questionnaire to the general practitioner. Two retrospective examination time intervals were defined as a second interval of <2 years (1.3 ± 0.4) and a first interval of >2 years (6.0 ± 2.4) dating back to the initial examination (maximum of 10.6 years prior to the last examination). Results: During 6.0 ± 2.4 years, the mean pressure gradient increased from 24.2 ± 13.6 to 38.1 ± 20.4 mm Hg (p <0.0001); respectively 2.1 ± 3.0 mm Hg/year in the first time period and 4.2 ± 8.2 mm Hg/year in the second time period (p = 0.049), for the entire population. According to severity, patients with mild or moderate aortic stenosis showed an increase from 2.0 ± 2.7 to 4.0 ± 6.6 mm Hg/year (p = 0.04) or from 2.2 ± 3.2 to 3.5 ± 10.9 mm Hg/year respectively (p = 0.66). The group with severe aortic stenosis had an increase of 9.6 ± 12.0 mm Hg/year (group too small for statistical analysis). During the total examination period, left ventricular mass index increased from 149 ± 60 g/m2 to 168 ± 63 g/m2 (p <0.0001), which corresponds to an increase of 3.2 to 7.8 g/m2 per annum (p = 0.52), and the relative wall thickness increased from 40.0 ± 8.5 to 43.0 ± 9.8% (p = 0.002). Ejection fraction remained stable and we found no correlation between etiology, vascular risk factors and progression of the disease. Conclusions: Progression of the mean pressure gradient in patients with aortic stenosis went from 2 mm Hg/year for mild stenosis, to 4 mm Hg/year for moderate stenosis. We found no correlation to conventional vascular risk factors. In patients with mild aortic stenosis and preserved left ventricular ejection fraction, echocardiographic follow-up every 3 to 5 years, until a mean transvalvular pressure gradient of 30 mm Hg is reached, might be a safe and cost-effective follow-up strategy. In patients with more severe aortic stenosis, follow-up has to be more frequent.

Erratum: Tetrahydrobiopterin restores impaired coronary microvascular dysfunction in hypercholesterolaemia (European Journal of Nuclear Medicine and Molecular Imaging (2005) 32 (84-91) DOI: 10.1007/s00259-004-1621-y)

PURPOSEnTetrahydrobiopterin (BH4) is an essential co-factor for the synthesis of nitric oxide (NO), and BH4 deficiency may cause impaired NO synthase (NOS) activity. We studied whether BH4 deficiency contributes to the coronary microcirculatory dysfunction observed in patients with hypercholesterolaemia.nnnMETHODSnMyocardial blood flow (MBF; ml min(-1) g(-1)) was measured at rest, during adenosine-induced (140 microg kg(-1) min(-1) over 7 min) hyperaemia (mainly non-endothelium dependent) and immediately after supine bicycle exercise (endothelium-dependent) stress in ten healthy volunteers and in nine hypercholesterolaemic subjects using 15O-labelled water and positron emission tomography. Measurements were repeated 60 min later, after intravenous infusion of BH4 (10 mg kg(-1) body weight over 30 min). Adenosine-induced hyperaemic MBF is considered to represent (near) maximal flow. Flow reserve utilisation was calculated as the ratio of exercise-induced to adenosine-induced hyperaemic MBF and expressed as percent to indicate how much of the maximal (adenosine-induced) hyperaemia can be achieved by bicycle stress.nnnRESULTSnBH4 increased exercise-induced hyperaemia in controls (2.96+/-0.58 vs 3.41+/-0.73 ml min(-1) g(-1), p<0.05) and hypercholesterolaemic subjects (2.47+/-0.78 vs 2.70+/-0.72 ml min(-1) g(-1), p<0.01) but had no influence on MBF at rest or during adenosine-induced hyperaemia in controls (4.52+/-1.10 vs 4.85+/-0.45 ml min(-1) g(-1), p=NS) or hypercholesterolaemic subjects (4.86+/-1.18 vs 4.53+/-0.93 ml min(-1) g(-1), p=NS). Flow reserve utilisation remained unchanged in controls (70+/-17% vs 71+/-19%, p=NS) but increased significantly in hypercholesterolaemic subjects (53+/-15% vs 66+/-14%, p<0.05).nnnCONCLUSIONnBH4 restores flow reserve utilisation of the coronary microcirculation in hypercholesterolaemic subjects, suggesting that BH4 deficiency may contribute to coronary microcirculatory dysfunction in hypercholesterolaemia.