Pierre Peronneau

Inhomogeneity of cellular refractoriness in human atrium: factor of arrhythmia?

Spatial inhomogeneity of refractory periods, as measured during clinical electrophysiological studies, is a known predisposing factor of arrhythmia. We studied elective refractory periods (ERP) and action potential duration (ADP90) on isolated human atrium. Twelve samples of right atrium obtained during cardiac surgery from patients with (n = 6) and without (n = 6) atrial fibrillation (AF) were studied by microelectrode technique. For each preparation, ERP were measured at basic cycle lengths (BCL) of 1,600, 1,200, 800, and 400 msec in five different cells located around (0.8 mm) the stimulating electrode. Dispersion of ERP was significantly greater in the AF group (96.7 ± 9 versus 70.9 ± 9 msec, p = 0.01). In the non‐AF group, we observed a positive linear correlation between (1) ERP and BCL (f = 0.86) (2) ADP90 and BCL (r̄= 0.93). On the contrary, in the AF group this correlation was absent between ERP and BCL (r̄= 0.28), poor between ADP90 and BCL (r̄= 0.62). These results suggest that nonhomogeneous recovery of excitability (dispersion and poor adaptation) may be an important factor of arrhythmia. This inhomogeneity is present at the cellular level as well as in the entire heart.

Transcatheter Radiofrequency Ablation of Atrial Tissue Using a Suction Catheter

Closed chest ablative technique that avoid barotrauma would be attractive for ablation at thin walled cardiac structures, such as the atrial free wall or coronary sinus. Transcatheter radiofrequency (RF) currents produce tissue necrosis the size of which is dependent on the contact between the tissue and the electrode. In order to assess the effects of transvenous RF ablation of atrial free wall using a suction electrode catheter, we delivered in ten dogs, one single unmodulated RF pulse 1.2 MHz, in a unipolar mode, through the distal electrode of a lumen catheter (USCI 8F) (USCI, Billerica, MA, USA) located in the right appendage. During the pulse an 80 KPa vacuum depression was applied to the lumen of the catheter. Each pulse had a 10 seconds duration and the mean delivered power was 4.3 ± 1.4 W. Aortic pressure and electrocardiogram were monitored during the procedure. A right airial electrophysiological study was performed at the ablated site, at control, after suction application and after RF pulse delivery. The animals were sacrificed after 14 or 21 days. Atrial pacing threshold values decreased after suction application in comparison to control values after the pulse (0.42 ± 0.06 vs 0.60 ± 0.23 mA, P < 0.05) but increased after the pulse delivery (2.60 ± 1.85 mA, P < 0.01). In contrast, the atrial effective refractory period did not significantly change after suction, nor after RF pulse delivery. Aortic pressure remained unchanged throughout the procedure. Complex arrhythmias were not observed during or after RF pulse delivery. One dog died suddenly at the first day after ablation, but this death was most probably unrelated to RF ablation. Anatomic lesions had a length of 8.8 ± 3.3 mm, a width of 4.6 ± 2.5 mm and a depth of 3.6 ± 1.1 mm. They were transmural in nine of the ten dogs but without atrial wall perforation in any case. Lesions suggesting tissue volatilization were present in four dogs. These results demonstrate that low energy RF currents delivered with a suction electrode catheter can produce transmural necrosis of free wall, without risk of perforation. Such ablative technique would be of interest for ablation of right sided accessory pathways or atrial ectopic foci. Further experimental data are required in order to define the optimal energy level required to avoid tissue volatilization.

Limitations of ultrasound imaging and image restoration

The definition of medical ultrasound images is strongly limited by the need for low examination frequencies which is imposed by the high attenuation of acoustic waves in tissues. The filtering effect of imaging systems is described and quantified for echography, transmission tomography and reflection tomography. Improvement of image definition is demonstrated to be the result of a numerical restoration of the received echoes implemented, in the present case, by a simplified Kalman filter. The improvement in definition obtained is emphasized on simulated data and tissue images. The comparison between the results obtained from the three techniques shows that: if only echography provides a real-time acquisition of signals, tomographic methods lead to faster processing associated with a better signal-to-noise ratio on the reconstructed images, and reflection tomography offers the best definition.

Segmentation, modelling and reconstruction of arterial bifurcations in digital angiography

The paper presents a method to model an arterial bifurcation from a pair of X-ray angiographic images. It is the initial step of a reconstruction process aiming at detecting and quantifying abnormal sites located on bifurcations. The method proposed consists of two steps. First, each image is independently segmented to extract the vessels in the images. The algorithm uses dynamic programming first to find the bifurcation centrelines from the original images, and secondly to extract vessel edges from the morphological gradient images, under a constraint of parallelism with the previously detected centrelines. Then, a three-dimensional bifurcation model is built by adapting cylinders around the three-dimensional bifurcation centrelines. These cylinders are obtained as a stack of binary orientable ellipses fitted to the projection densities in the corresponding cross-sections. Results obtained on simulated data, phantom and femoral bifurcations are displayed.

Influence of pulsatility on the development of intracardiac jets : an in vitro laser doppler study

So far, it has been hypothesized that numerical data obtained in steady flow conditions apply to pulsatile flows. In order to study the modifications of the velocity fields due to pulsatility, jets were produced by 8 orifices (with a diameter D of 4.4 to 11.3 mm) included in a chamber of 50 mm. The velocity was measured using laser Doppler anemometry with a pulsatile flow (pf) and compared to the values obtained in steady (sf): at maximum velocity, the longitudinal velocity profile is qualitatively similar to this observed in steady flow: it is made of a plateau followed by an hyperbolic velocity decay in the turbulent area. The length of the core (Lpf) is strongly related to D (Lpf = 3.72 D + 5.49, r = .99) and the velocity decay depends on the ratio between the distance x from the orifice and D (V/Vo = 2.83D/x + 3.46, r = .85, where V is the velocity at x and Vo the initial velocity). During the acceleration and the deceleration, the laminar core is disturbed by turbulences. The comparison of pf data with sf data demonstrated similar diameters at the origin of the jets (Dpf = 0.96 Dsf + .12, r = .99), but significant (p less than .0001) differences both for L and V/Vo: Lpf = .91Lsf + 6.58, r = .97, V/Vopf = .63 V/Vosf + .34, r = .76. Thus, pulsatility modifies velocity fields and the results obtained in steady flow conditions do not apply to pulsatile jets.

Effects of Physical Parameters of Fulguration on Electrophysiological and Anatomical Properties of Canine Myocardium

In order lo determine the respective roles of catheter (Ct) physical properties and of energy levels in myocardial effects of fulguration, we delivered an electrical shock between the tip electrode of a Ct placed at the apex of the right ventricle and a large cutaneous cathodal electrode in 12 dogs. Two energy levels were used: Group A = 25 J (n = 6) and group B = 100 J (n = 6), and three Cts were studied. These Cts had different resistances (R) and active surface electrodes (S): Ct 1 (R = 0.3 ω S=12 mm2), Ct 2 (H = 0.3 ω, S = 2 mm2, Ct 3 (R = 2 ω S = 13 mm2). Complex ventricular arrhythmias were observed in 5/6 cases at 100J but only in 1/6 case at 25J and were independent of the Ct type. Following the shock, the effective ventricular refractory period (S1 S1= 300 msec) increased significantly only at 100J(11%, p = 0.03). Anatomical lesions were wider (10.6 vs. 5.2 mm, p < 0.05) and deeper (100 vs. 55%, p < 0.05) in the 100 J group. In contrast, there was no significant difference in the electrophysiological and anatomical changes between the three Cts. In conclusion, (1) arrhythmogenic adverse effects of ventricular Ct fulguration are related to the delivered energy; (2) on the contrary, they seem only slightly dependent on Ct physical properties at these energy levels; (3) a 2 J/kg shock is not only effective but also seems to be safe.

Heterogeneity in migration of smooth muscle cells from normal and injured rat thoracic aorta in primary culture.

OBJECTIVEnAside from proliferation, migration of smooth muscle cells is an essential component of the arterial sclerotic reaction. The aim of this study was to define a model to study migration.nnnMETHODSnPrimary cultures of smooth muscle cells were derived from normal or injured rat thoracic aorta. An image analysis system was used to track cells migrating out of the explants and measure the displacement of their centre of gravity.nnnRESULTSnMigration speeds for smooth muscle cells randomly sampled from the normal whole media were very heterogeneous. The media were therefore separated into three vertical segments. Cells from the middle third migrated faster than those from the upper and lower thirds, regardless of whether they originated from the anterior and posterior parts of the segment (P = 0.001). Heparin (10 micrograms.ml-1) only inhibited smooth muscle cell migration from the middle segment (P < 0.001). Migration of smooth muscle cells from explants of aorta 3 and 14 d after injury was also studied using a balloon catheter. Three days after injury, cell velocity varied widely among the segments of the same media. In contrast, 14 d after injury cells from neointimal explants migrated homogeneously and at a slower rate than those obtained from normal media.nnnCONCLUSIONSnThese experiments show migratory variations among smooth muscle cells depending upon their position in the normal aorta and their state of activation after arterial injury. This variability must be taken into account when planning experiments to study smooth muscle cell migration.

Simulation sur calculateur analogique du fonctionnement mecanique du systeme cardiovasculaire

Linteret general des modeles pour lanalyse et la comprehension de systemes complexes multiparametriques et multiboucles apparait remarquable dans le domaine de la biologie. Lapport de la methode est particulierement evident pour la physiologie du systeme cardio-circulatoire, au niveau duquel se trouvent intriques des phenomenes hydrauliques et de regulation. Le travail a ete deliberement limite a letude de linfluence des facteurs mecaniques du systeme cardio-vasoulaire dans le but essentiel de degager le role de ces facteurs dans la regulation de lensemble. Pour cela, un modele mathematique a constantes localisees a ete defini et sa resolution effectuee sur calculateur analogique. Une preoccupation constante a ete la confrontation a des resultats experimentaux, soit pour lidentification des parametres soit pour lestimation du degre de conformite.

Animal evaluation of the prototype omnicath atherectomy catheter

A prototype directional atherectomy catheter (OmnicathTM) was evaluated in four Yucatan microswines. Atherectomy was performed on iliac or aortic target lesions. After control angiography, the animals were sacrificed and the target arteries were examined histologically. Atherectomy resulted in arterial ruptures in three cases, and the track of the blade was measured to be of an average depth of 0.38 mm. Maneuverability was satisfactory but aspiration was not efficient. Precise localization of the atherectomy window was difficult. We conclude that modification of the catheter seems mandatory before use in humans.

Segmentation And Modelisation For Reconstruction Of Arterial Bifurcations In Digital Angiography

This paper presents a sequence of processings applied in parallel on two stereoscopic projections of angiographic images, in order to detect vascular pathologies site on bifurcations. Following directing centerlines of the bifurcation detection via a peaktracking algorithm, vascular boundaries are searched via dynamic programmation on the image of the morphological gradient. The two segmented original images are then matched in order to build a 3D bifurcation model made of generalised cylinders. Ultimately, this model will be deformed to minimize an energy function using an optimization method. Preminilary steps of projection processing are displayed on images of real bifurcations.