[The role of Holter monitoring and electrophysiological studies in the evaluation of ventricular anti-arrhythmia agents]. / Le rôle du Holter et des explorations électrophysiologiques dans l'évaluation des antiarythmiques ventriculaires.

The roles of Holter monitoring and electrophysiological studies (EPS) in the evaluation of antiarrhythmic drugs for ventricular arrhythmias are to record their effects on ventricular extrasystoles (VES) and ventricular tachycardia (VT), and to search for undesirable rhythmological effects. The usual protocol is to perform baseline studies and then repeat them after a certain period of treatment using a number of modalities, comparison with placebo, control group, in acute or oral administration. Holter monitoring is an economical non-invasive method which carries no risk. Spontaneous arrhythmias of sufficient frequency to be recorded during the monitoring period can be studied. When applied to VES, it provides quantitative rather than qualitative information despite classifications such as Lown's. The results should be analysed taking spontaneous variations of the arrhythmia into consideration. Holter monitoring may also reveal proarrhythmic drug effects (bradycardia, torsades de pointe). However, there are no absolute criteria of efficacy except total suppression of VES, unexplainable by spontaneous variability. Holter antiarrhythmic studies require stable VES which creates a bias in the evaluation of results due to the special selection of patients. Electrophysiological studies are costly, invasive and uncomfortable but they are the only way of assessing paroxysmal VT apart from clinical follow-up. This method is only applicable to inducible VT, which is the commonest form. The investigating protocols are specific and reproducible: a tachycardia which is non-inducible does not recur in 90% of cases, which enables prediction of the antiarrhythmic effect.(ABSTRACT TRUNCATED AT 250 WORDS)

[Demonstration of muscular activity in the human aorta. Effects of trinitrin]. / Mise en évidence d'une activité musculaire au niveau de l'aorte humaine. Effet de la trinitrine.

The human thoracic aorta is usually considered to be a purely elastic vessel. Transoesophageal echo-cardiography (TEE) provides a new approach to study the mechanical properties of the descending aorta. The aim of the study was to evaluate the reproducibility and accuracy of M mode recordings of the human descending thoracic aorta and to appreciate the changes produced by an infusion of glyceryl trinitrate (GTN). The reproducibility of M mode recordings was studied in vitro on plexiglass tubes of different calibre, and also in vivo, the inter and intra-observer error was estimated to 0.6% in vitro and 1% in vivo. The accuracy of the method was evaluated in vitro by comparing the measured values (MV) with the actual diameters of the plexiglass tubes (T): MV = 1.012T + 0.9; r = 0.99; SE = 0.8 mm. The systolic and diastolic diameters of the descending thoracic aorta were measured in 8 healthy volunteers by TEE, before and during continuous intravenous infusion of GTN at a rate of 0.9 mg/hr and then 1.35 mg/hr after a 10 minutes interval. Systolic and diastolic blood pressures were recorded automatically every minute. The results showed a very significant increase in the systolic (from 20.3 +/- 0.7 to 20.9 +/- 1.3 and 22.1 +/- 2.2 mm) and diastolic diameters of the aorta (from 18.3 +/- 0.7 to 19.1 +/- 1.4 and 20.1 +/- 2.4 mm) despite a fall in systolic blood pressure (from 121.3 +/- 7.7 to 114.5 +/- 6.6 and 108.4 +/- 5.4 mmHg). This study shows that TEE is a reliable and reproducible method of measuring the diameter of the human descending thoracic aorta.(ABSTRACT TRUNCATED AT 250 WORDS)

[Doppler echocardiographic evaluation of left ventricular wall stress in aortic stenosis]. / Evaluation en échocardiographie doppler des contraintes pariétales du ventricule gauche dans le rétrécissement aortique.

The measurement of wall stress allows study of morphological adaptation of the left ventricle, especially in conditions associated with symmetric hypertrophy (hypertension, aortic stenosis). The calculation is performed in hypertensive heart disease but not in aortic stenosis because of the ventriculo-aortic pressure gradient. In a preliminary study, the authors validated the peak systolic left ventricular pressure calculated by adding the systolic brachial artery pressure to the maximal transvalvular pressure gradient by comparing the value with that obtained by catheterization in 21 patients with aortic stenosis. The second phase of the study was to measure meridian and circumferential wall stress prospectively in 35 patients with aortic stenosis (29 symptomatic, 6 asymptomatic) and to compare the results with those observed in 21 normal subjects. In the latter group, the values were 151 +/- 22 and 311 +/- 37 10(3) dynes/cm2 respectively, whereas in asymptomatic aortic stenosis the stresses were 136 +/- 28 and 303 +/- 41 10(3) dynes/cm2 respectively (NS) and in symptomatic aortic stenosis 210 +/- 55 and 437 +/- 94 10(3) dynes/cm2 respectively (p < 0.0001). None of the cases of asymptomatic aortic stenosis had raised wall stress values whereas only 6 symptomatic aortic stenosis patients had normal wall stress. The values of wall stress obtained using the method proposed were comparable to those reported by other authors with invasive investigations. Non-invasive measurement of wall stress by Doppler echocardiography may be proposed as a method of evaluation of left ventricular adaptation, especially in severe stenosis and in patients with a patent geometric abnormality (abnormal dilatation or even an inadequately hypertrophied wall).

[Atrial flutter with 1/1 nodo-ventricular conduction with amiodarone. From physiopathology to diagnosis]. / Flutter atrial à conduction nodo-ventriculaire 1/1 sous amiodarone. De la physiopathologie au dépistage.

Atrial flutter with 1/1 nodo-ventricular conduction is a classical complication of Vaughan-Williams's Class I antiarrhythmic drugs. The increase of the flutter cycle and weak action of the antiarrhythmic on the atrioventricular node leads to 1/1 conduction of atrial depolarisation to the ventricles. In view of their marked action on the atrioventricular node, this type of pro-arrhythmic effect is very unexpected with Class III antiarrhythmics. The authors report 7 cases of 1/1 atrial flutter with oral amiodarone observed between 1994 and 2001. The patients were 6 men and 1 woman with an average age of 58 +/- 14 years. Four of them had underlying cardiac disease; none were hyperthyroid. The initial arrhythmia was 2/1 atrial flutter (n = 4), 1/1 atrial flutter (n = 2) and atrial fibrillation (n = 1). Treatment was preventive with doses of 400 mg/day associated with carvedilol in one patient and 200 mg/day in another. The other five patients all received loading doses of 9200 +/- 2400 mg over 10 +/- 4 days. The symptoms were palpitations (n = 2) associated in one patient with hypotension, one syncope, one near syncope and one cardiogenic shock. The ventricular cycle of the 1/1 flutter was 287 +/- 33 ms. The QRS duration was 136 +/- 35 ms with ventricular tachycardia-like appearances in 3 cases. An adrenergic trigger factor was noted in 5 patients. One patient required emergency cardioversion. The authors discuss the physiopathology of 1/1 flutter and theoretical diagnostic methods are proposed. In conclusion, amiodarone does not always prevent the occurrence of 1/1 nodo-ventricular conduction in atrial flutter.

Antireflection structured surfaces for the infrared spectral region.

Antireflection structured (ARS) surfaces on GaAs substrates for application with normally incident, randomly polarized, 10.6-microm-wavelength radiation are designed and analyzed. Both one-dimensional (1-D) and two-dimensional (2-D) multilevel profiles are examined with special attention given to multilevel approximations of 1-D triangular and 2-D pyramidal profiles. The 1-D profiles are designed by using second-order effective medium theory (EMT), as we have found zeroth-order EMT to be insufficient when ARS surfaces are designed for use with optically dense materials, e.g., most materials used in the infrared spectral region. We analyze both 1-D and 2-D profiles by using rigorous coupled-wave analysis and find that the more levels the profile contains, the better the ARS surface's response to bias angles, wavelength detunings, and errors in etch depth. Although both 1-D and 2-D profiles can efficiently suppress reflections for unpolarized light, 2-D gratings are advantageous when randomly polarized light is of interest.

Analysis of antireflection-structured surfaces with continuous one-dimensional surface profiles.

A novel thoretical treatment of antireflection-structured surfaces possessing general one-dimensional continuous profiles is presented. Closed-form solutions for the field reflection coefficients of these antireflection-structured surfaces are obtained through the use of effective medium theory and tapered transmission-line theory. Two specific surface profiles (sinusoidal and triangular) are analyzed in detail. Both the sinusoidal and triangular profiles are found to exhibit low reflectances over a broad range of angles and wavelengths. Results obtained with effective medium theory and transmission-line theory are compared with results obtained through the application of rigorous coupled-wave analysis.

Multiwavelength operation with thin diffractive elements.

It is generally accepted that diffractive elements designed for multiwavelength operation require deep surface-relief profiles. We show, however, that thin diffractive elements can be designed to operate with more than one wavelength. A novel, to our knowledge, optimization technique is introduced for this purpose. The maximum phase delay is limited to only a few multiples of 2pi, and the element can implement different functions for different wavelengths. Examples with fan-out gratings are discussed.