The influence of different electrode configurations on the inhibitory effect of subthreshold high-frequency stimuli.

Subthreshold stimuli trains may inhibit the response to a subsequent suprathreshold stimulus; the inhibitory effect decreases or even disappears when the subthreshold stimuli are delivered apart from the suprathreshold stimulus. The purpose of this study is to analyse, in atrial epicardium, the influence of different electrode configurations upon the inhibitory effect of subthreshold stimuli trains delivered at a short distance from the explored zone. In 18 anaesthetized dogs, the basal atrial effective refractory period was determined using an epicardial unipolar cathodal electrode. A second determination was performed when a subthreshold stimuli train (1 ms cathodal pulses, 800 Hz, and intensity 10% less than the diastolic threshold of the train) was delivered prior to the extrastimulus through: (a) 8 electrodes equidistant (4.5 mm) from the central test electrode (Group 1, n = 5); (b) a 1 mm wide ring electrode, 2.5 mm from the central test electrode (Group 2, n = 7); and (c) a 3.5 mm wide ring electrode, 2.5 mm from the central test electrode (Group 3, n = 6). A third determination was performed in all experiments delivering both the subthreshold stimuli train and the extrastimulus through the same central test electrode. Atrial effective refractory period did not vary significantly with respect to the basal values in Group 1 (141 +/- 22 vs 142 +/- 25 ms; ns) though it increased in Group 2 (168 +/- 27 vs 142 +/- 18 ms; P < 0.01) and in Group 3 (160 +/- 20 vs 133 +/- 25 ms; P < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Doppler assessment of left ventricular diastolic function in marathon runners.

The possible alteration in diastolic function as a result of physiological left ventricular hypertrophy was evaluated in 28 male marathon runners (mean age 38.6 +/- 5.7 years) using Doppler echocardiography. The subjects were divided into two groups according to the intensity of training and chronometered running times: Group I (n = 14), 80-100 km weekly and marathon times under 3 hours; and Group II (n = 14), 30-50 km weekly and marathon times between 3 hours 15 min. and 3 hours 45 min. A control group (n = 14) of similarly aged sedentary individuals free of cardiovascular disease was used for comparisons. The following parameters were analyzed: (a) left ventricular mass and left ventricular mass index by means of M mode two-dimensional guided echocardiography; (b) peak velocities of E and A waves, E/A peak velocities ratio, E/A velocity-time integrals ratio, E wave/total diastolic flow velocity-time integrals and A wave/total diastolic flow velocity-time integrals (last one also called atrial filling fraction) that, together with E wave deceleration time, were obtained from pulsed Doppler recordings of transmitral flow; (c) isovolumic relaxation time measured from a continuous Doppler recording of aortic ejection flow. Left ventricular mass index was significantly greater in both groups of marathon runners with respect to controls (group I: 121.1 +/- 15.5 vs 81.8 +/- 11.1 g/m2, p < 0.01; group II: 106.5 +/- 21.1 vs 81.8 +/- 11.1 g/m2, p < 0.01), but there were no significant differences in any of the diastolic function parameters analyzed (Anova and Scheffe tests).(ABSTRACT TRUNCATED AT 250 WORDS)

[Left ventricular outflow obstruction due to accessory mitral tissue]. / Obstrucción a la eyección ventricular izquierda causada por tejido mitral accesorio.

An asymptomatic 31-year-old woman was studied because she presented a systolic ejection cardiac murmur. The echocardiogram showed a mobile, sac-like mass attached to the ventricular surface of the anterior mitral leaflet and its chordae tendineae and papillary muscle. This structure moved to the left ventricular outflow tract during every systole occupying the subaortic area. Conventional and color-coded Doppler examination revealed left ventricular outflow obstruction caused by the accessory mitral valve tissue that produced a high-velocity turbulent flow pattern in the subaortic area where the sac-like structure approximated to the outflow tract walls.

Radiofrequency versus pharmacologic modification of the atrioventricular node.

Although transcatheter radiofrequency modification of the atrioventricular (AV) node has been proposed as curative treatment in AV nodal reentry tachycardias, its role for the control of the ventricular rate in atrial tachyarrhythmias remains unclear. The aim of this study was to analyze the acute effect of radiofrequency current on AV nodal conduction and refractoriness, and to compare it with the effects of two antiarrhythmic drugs such as amiodarone (class III) and flecainide (class I). Twenty-one dogs were studied: (1) radiofrequency group (5 W for less than 45 seconds; 2 to 12 discharges; seven dogs); (2) amiodarone group (5 mg/kg intravenously; seven dogs); and (3) flecainide group (2 mg/kg intravenously; seven dogs). The following parameters were measured under basal conditions and after each procedure: AH interval, AV nodal functional refractory period, Wenckebach cycle length, minimum R-R interval during atrial fibrillation, and fitting of AV nodal function curve to a hyperbolic equation using its linear transformation. The AV nodal effective refractory period could not be calculated in any dog in the basal study because it was shorter than the atrial functional refractory period.(ABSTRACT TRUNCATED AT 250 WORDS)

Atrioventricular electrotonic interaction in complete atrioventricular block: an experimental model using radiofrequency energy in the rabbit heart.

UNLABELLED: Provided the conditions for electrotonic transmission exist, an automatic focus surrounded by a block zone may be externally modulated. The atrioventricular (AV) electrotonic interaction was studied in 16 perfused rabbit hearts with supra-Hisian complete AV block induced using low radiofrequency energy doses (2.5 watts; 10 seconds). In nine experiments the sinus node was preserved (group I), whereas in seven it was removed maintaining an AV nodal rhythm (group II). The V-V (ventricular cycle length) and V-A (coupling of the intervening atrial beat) in both groups, and also the A-A (atrial cycle length) and A-V (coupling of the intervening ventricular beat) intervals in group II, were measured beat by beat after current delivery. The phase response curves V-V versus V-A, and A-A versus A-V showed AV interaction in five experiments from group I, and in four from group II, as follows: (1) accelerating phase response curve, characterized by a pacemaker acceleration (V-V or A-A abbreviation) at a critical V-A or A-V coupling interval; maximum acceleration could be progressively (phase response curve without rapid cross-over) or briskly (phase response curve with rapid crossover) reached; from this point onwards acceleration decreased with a further increase in V-A or A-V coupling interval (acceleration slope). (2) Biphasic phase response curve, characterized by initial delaying and late accelerating phases. Maximum acceleration and the acceleration slope were both smaller in accelerating phase response curves without rapid cross-over. On reverting complete block in two experiments, a progressive increase in maximum acceleration and acceleration slope was observed. CONCLUSIONS: (1) AV interaction in complete AV block can be manifested as accelerating or biphasic phase response curves; (2) transition from electrotonic interaction to conduction seems to be a continuum.

[Left ventricular pseudoaneurysm. The dynamics and flow patterns analyzed by Doppler echocardiography]. / Seudoaneurisma ventricular izquierdo. Dinámica y patrones de flujo analizados mediante ecocardiografía-Doppler.

A patient with antecedents of ischemic cardiopathy is presented. Echocardiographic exploration revealed the presence of an accessory cavity in connection with the left ventricle behind the basal segment of the posterior left ventricular wall, the characteristics of which were compatible with a ventricular pseudoaneurysm. The Doppler study (both conventional and color coded) allowed us to determine the multiphasic characteristics of the flow between both cavities, and its relation with the variations of volume of the same, as well as with the transmitral and aortic flows. The filling of the pseudoaneurysm was observed to begin before initiation of the ejection through the aorta. Initiation of emptying towards the left ventricular cavity took place in the late systole, and there was a new flow inversion towards the pseudoaneurysm in the early diastole coinciding with the rapid ventricular filling, and therefore before producing the atrial contraction.

[Aneurysm of the interatrial septum associated with Lutembacher's syndrome. Echocardiographic and Doppler study]. / Aneurisma de septo interauricular asociado a síndrome de Lutembacher. Estudio ecocardiográfico y con técnica Doppler.

The case of a patient with suspected atrial septal defect is presented. Echocardiographic-Doppler study confirms the defect associated with mitral stenosis (Lutembacher syndrome) and shows an atrial septal aneurysm through which the shunt is revealed.

[Obstruction of transmitral flow caused by a free-floating thrombus in the left atrium]. / Obstrucción al flujo transmitral causada por un trombo flotante libre en la aurícula izquierda.

We present a patient diagnosed of rheumatic mitral valve disease. Echography revealed a free-floating left atrial thrombus. A sporadic obstruction of transmitral flow was detected using the Doppler technique. The frequency and severity of the obstruction was analyzed.