[Evaluation of ventricular synchronization by fourier phase analysis in a radionuclide ventriculography]. / Evaluación de la sincronización ventricular por análisis de fase de Fourier en una ventriculografía radioisotópica.

INTRODUCTION: Radionuclide ventriculography (RNV) evaluates segmental and global ventricular contractility and also detects conduction abnormalities. OBJECTIVE: To assess the temporal parameters of ventricular synchronization in the normal heart by a third harmonic (3H) Fourier phase analysis in a RNV and introduce this technique in our center. MATERIAL AND METHODS: Thirty normal subjects (19 men and 11 women) were included. An equilibrium RNV was performed in 35 degree left anterior oblique projection with 10 degree caudal tilt. The onset (T0); mean time (T(m)); total contraction time (T(t)); final time (T(f)) and propagation time (T(p)) for right (RV) and left ventricle (LV); as well as total propagation time (T(TP)); interventricular time (T(RV-LV)) and septum-lateral wall conduction time (T(S-LW)) were measured on the 3H Fourier histogram of the time-activity curve. RESULTS: Right ventricle contraction started 5 ms before that of the left ventricle (T(0RV) = 66 +/- 38 ms; T(OLV) = 71 +/- 30 ms), with a longer total contraction time (T(tVD) = 67 +/- 28 ms vs T(tVI) = 64 +/- 38 ms). Total propagation time (T(TP)) was 69 +/- 37 ms and the interventricular time (T(RV-LV)) was 2 +/- 25 ms. Contraction progressed from septum to lateral wall, with a septum-lateral wall conduction time (T(S-LW)) of 4 +/- 22 ms. CONCLUSION: Simultaneous contraction of right and left ventricles can be quantified by RNV phase analysis, providing a useful tool for ventricular resynchronization assessment in multisite pacing.

Evaluación de la sincronización ventricular por análisis de fase de Fourier en una ventriculografía radioisotópica / Evaluation of ventricular synchronization by Fourier phase analysis in a radionuclide ventriculography

Introducción: La ventriculografía radioisotópica (VRI) permite la evaluación de la contractilidad global y segmentaria, así como la detección de trastornos de conducción. Objetivo: Se realizó el análisis de fase del tercer armónico de Fourier en una VRI con el propósito de evaluar los parámetros temporales de la sincronización ventricular en el corazón normal e introducir esta técnica en nuestro centro. Material y Métodos: Se incluyeron 30 individuos normales (19 hombres y 11 mujeres). A todos se les realizó una VRI en equilibrio en proyección oblicua anterior izquierda de 35 grados con 10 grados de angulación caudal. En el histograma del tercer armónico de Fourier de la curva actividad-tiempo se midieron: el tiempo de inicio (T0); el tiempo medio (Tm); el tiempo total (Tt); el tiempo final (Tf) y el tiempo de propagación (Tp) para cada ventrículo; así como el tiempo total de propagación (TTP); el tiempo de conducción interventricular (TVD-VI) y el tiempo de conducción septum-pared lateral (TS-PL).Resultados: El ventrículo derecho comienza a contraerse 5 ms antes que el izquierdo (T0VD = 66 ñ 38 ms; T0VI = 71 ñ 30 ms), con un tiempo de contracción total ligeramente mayor (TtVD = 67 ñ 28 ms vs TtVI = 64 ñ 38 ms). El tiempo total de propagación (TTP) fue de 69 ñ 37 ms y el tiempo interventricular (TVD-VI) fue 2 ñ 25 ms. La contracción progresó de septum a pared lateral, con un tiempo septum-pared lateral (TS-PL) de 4 ñ 22 ms. Conclusión: A través del análisis de fase en una ventriculografía radioisotópica puede cuantificarse la contracción simultánea de ambos ventrículos, lo que proporciona un instrumento que pudiera resultar de utilidad para la evaluación de la resincronización ventricular en la estimulación multisitio (AU)

[The usefulness of electrophysiology in a patient undergoing cardiomyoplasty]. / Utilidad de la electrofisiología en un paciente sometido a cardiomioplastía.

The cardiomyoplasty is a new surgical procedure that uses a skeletal muscle electrostimulated in order to reinforce or even substitute partially the cardiac muscle. We present the electrophysiology aspects in a patient with dilated cardiomyopathy that underwent cardiomyoplasty. First the latissimus dorsi muscle was prepared with a neurostimulant ITREL II. During the surgical procedure a dual-chamber pacemaker mode DDD brand CPI was placed. After three months, ablation radiofrequency of the AV node was performed in order to control the atrial fibrillation that caused heart failure. By means of the AV block we obtained synchrony between the ventricular stimulation and the latissimus dorsi muscle, and by this the patient improved. Using the modern pacemakers and radiofrequency we can control the bradyarrhythmias as well as the tachyarrhythmias frequent in patients with dilated cardiomyopathy, increasing the success rate of cardiomyoplasty.

[The use of endocavitary fulguration in the treatment of common auricular flutter]. / Uso de la fulguración endocavitaria en el tratamiento del flutter auricular común.

Between April 1990 and July 1991, 10 patients, were fulgurated after right atrial endocardial mapping with the purpose of destroying or modifying the site of origin of atrial flutter. Mean age, 47 years old (23-61), 9 males. All patients suffered "common" atrial flutter episodes with very rapid ventricular response (greater than or equal to 150 beats per minute) refractory to pharmacological therapy. All patients had pathologic potentials with prolonged duration between 90 and 160 ms (m = 109) which preceded other reference electrodes in the high right atrium and His position. Electrical stimulation from that zone provoked the capture entrainment and termination of the flutter; the same configuration of the arrhythmia was obtained with electrical stimulation from the suspected zone. With the catheter in that situation one or two direct current cathodic, unipolar shocks were given with energy of 60-150 Joules (m = 117). In the follow up (16-73 weeks), 8 patients are free of symptoms without drugs, one suffered a new episode after 7 weeks, His fulguration was performed and a permanent pacemaker implanted. The other patient has failed two session and is still on treatment.

[The treatment of intranodal tachycardias with intracavitary fulguration]. / Tratamiento de las taquicardias intranodales con fulguración intracavitaria.

The electrical ablation of the His bundle with proximal intracardiac shocks of low energy was performed through an electrical catheter, to 14 patients with AV nodal reentry tachycardias refractory to pharmacological therapy, to whom at least 3 antiarrhythmic drugs were previously administered. The electrical energy applied oscillated between 10 to 150 Joules (114 average). 11 patients (72%) recovered the normal atrioventricular conduction and in the electrophysiological evaluation was found: 1--Increase in the duration of the AH interval. 2--No existence of two AV nodal pathways. 3--Absence of retrograde conduction. 4--Impossibility to induce tachycardia. The PR interval was prolonged (60 ms average) after the electrical shocks. These criteria defined the total effectiveness of the procedure. In the 3 remaining patients (28%) a permanent atrioventricular complete block was induced and the implantation of the permanent pacemaker was required. It was concluded that the electrical fulguration of the atrioventricular junction with low energy is an effective technique as curative treatment for intranodal reentry tachycardias, which can be applied without induction of permanent cardiac block.

[Experience with the use of an implantable automatic cardioverter defibrillator]. / Experiencia en el uso del desfibrilador cardioverter automático implantable.

An automatic implantable cardioverter-defibrillator with pacemaker was implanted in Cuba, in ten patients with malignant ventricular arrhythmias, sudden cardiac collapse, and ventricular tachycardia with syncope, after a previous electrophysiological study for analysis of the arrhythmia and pharmacological evaluation. The patients were 9 males, ranging in age from 23 a 70 years, with a mean of 48 years, and an ejection fraction of 32% (18-62%). The etiologies were: an old myocardial infarction (7 cases) and dilated cardiomyopathy (3 cases). During the follow-up, mean from 2 to 25 months, four patients received effective shocks for rapid palpitations and presyncope. Two patients died, one due to incessant ventricular tachycardia and one of a cause unrelated to device. We concluded that the GUARDIAN 4201 and 4202 device are useful to prevent sudden cardiac death in high risk patients who experienced a life threatening arrhythmia.

[Surgery for Wolff-Parkinson-White syndrome. Cuban experience]. / Cirugía en el síndrome de Wolff Parkinson White. Experiencia cubana.

Surgery is a recent approach in the treatment of arrhythmias. The first successful surgery of this type was the interruption of the accessory pathway in a patient suffering from the Wolff Parkinson White syndrome. In 25 consecutive patients who underwent surgery, 28 accessory AV pathways were identified with classical endocardial and epicardial mapping. Only three patients experienced recurrence of preexcitation without symptoms; one patient had AV block; and another patient died. In all cases we successfully used either an endocardial or an epicardial approach. The purpose of this paper is to report the Cuban experience with this procedure.

Effects of manganese chloride, verapamil, and hypoxia on the rate-dependent increase in internal longitudinal resistance of rabbit myocardium.

The effects of high rates of stimulation on the internal longitudinal restivity (Ri) and conduction velocity (theta) were studied on rabbit papillary muscle preparations using a silicon-oil chamber. Increasing the rate from 75 to 150/min caused Ri to rise and theta to decrease. The maximum rate of depolarization and action potential duration were also decreased. At a rate of 300/min the effects were more pronounced. Blockade of the slow inward current (Isi) and of the Na-Ca exchange by MnCl2 (5 mmol/L) did not prevent rate-induced changes in these variable. Verapamil (0.02 mmol/L) was also ineffective. Hypoxia (PO2 = 5.3 kPa) at 75/min induced changes in Ri and theta which were similar to those recorded at 150/min under aerobic conditions. The effects of high rates of stimulation were potentiated under hypoxia. From the present results it is suggested that Isi and the Na-Ca exchange are not the main determinants of the rate-induced increase in Ri, which could be determined by other intracellular Ca-release mechanisms or by a decrease in myoplasmic pH.

Effects of manganese chloride on the outward currents in frog atrial trabeculae.

The effects of MnCl2 on outward currents in frog atrial muscle were investigated under voltage-clamp conditions. MnCl2 (3 mmol/L), which completely abolished the slow inward current, produced a decrease in the outward background current (Ib) at potentials positive to -50 mV. The delayed outward current (Ix, time dependent) was not altered by Mn. "Isochronic activation curves" for Ix and decay of current tails at -40 mV remained unaffected after Mn. Effects on Ib probably reflect a decrease in IK1 related to the decrease in Ca influx as well as a reduction in the Na-Ca exchange current.

Role of the slow inward current during the repolarisation process in frog atrial trabeculae.

Voltage clamp experiments were performed to analyse the influence of the slow inward current (isi) on the repolarisation process in frog atrium. MnCl2 was used as isi blocker. The action potential was prolonged by depolarising pulses applied during the plateau. This was an expected result considering that, at positive potentials the time constant for isi inactivation increases. This effect was abolished by Mn ions which in turn block isi. The results suggest that inactivation of isi is of primary importance in determining the repolarisation rate. The action of Mn was not selective, since it reduced the background K current. This effect seems to be related to the decrease in Ca influx.

Effects of moderate hypoxia on premature action potentials of rabbit papillary muscle.

Experiments were performed to study the effects of hypoxia on the characteristics of premature action potentials of rabbit papillary muscles. At normal resting potential, the duration of the premature action potential at the shortest coupling intervals was always greater than that of the control response. As the coupling interval was increased beyond 150 ms, the duration of the premature action potential regained control values. In cells depolarized to -70 mV by KCl, early lengthening of the premature response was attenuated. After 60 min of hypoxia, recovery of action potential duration at normal and reduced resting potentials was accelerated. The maximum rate of depolarization and its reactivation time constant were not affected by 60 min of hypoxia. It is suggested that intracellular free Ca is important in the control of action potential duration via the outward background potassium current.

Changes in electrical and mechanical activities of rabbit papillary muscle during hypoxic perfusion.

The influence of moderate hypoxia (p02 : 70 mmHg) on action potential and contraction of isolated rabbit papillary muscles was analyzed. 1. Action potential duration, maximum twitch tension and time-to-peak tension decreased during 60 min of hypoxic perfusion, while resting tension increased and resting potential, overshoot and fast depolarization of the action potential remained constant. 2. MnCl2 (5 mM), after 60 min of hypoxia, abolished overshoot increased resting potential, and further reduced action potential duration. "Slow"action potentials induced by isoproterenol (2.5 X 10(-6) M) in KCl (20 mM) depolarized muscles, were highly resistant to hypoxic perfusion. This resistance indicates that the inflow of cations through slow channels persists under these hypoxic conditions. 3. CsCl (2-4 mM) increased action potential duration in hypoxic fibers to control (O2) values. These results suggest that an increase in membrane background K conductance could account for the reduction in action potential duration under hypoxic incubation. A possible relationship between changes in internal free calcium concentration and background K conductance during hypoxia is considered.

Effects of low pH on the action potential and contraction of normal and hypoxic papillary muscles.

The effects of low pH (6.5) on action potentials and contractions of rabbit papillary muscles were examined under aerobic and hypoxic conditions (pO2 = 65- 75 mmHg, 8.6-10.0 kPa). An acid medium reduced overshoot, Vmax of phase O and action potential duration, without changing the resting potential, under aerobic aerobic conditions. Maximum twitch tension was reduced and resting tension was increased by 40% and 6% respectively of control values. Upon returning to normal Tyrode, all parameters returned to control values. The effects of acidosis under hypoxic conditions were essentially the same as those described above; acidosis potentiated the effects of hypoxia. It is concluded that in the given experimental conditions, low pH potentiates the effects of hypoxia on electrical and contractile activity, although probably by different mechanisms. The effects of acid medium on the action potential could be well accounted for the a reduction in slow inward current and by an increase in outward background potassium current, probably in relation to an increase in internal free calcium concentration.

Effects of hydrocortisone sodium succinate on the electrophysiological properties of hypoxic rabbit papillary muscle.

Hydrocortisone sodium succinate (HSS) (50 mg/1) was tested as a protective agent against the effects of hypoxia on rabbit papillary muscle fibres. No effect of HSS was observed on the electrophysiological variables studied in aerobic condition. Hypoxia (65-75 mmHg, 8.66-10.0 kPa) had no effects on the resting potential, amplitude and overshoot, and shortened the action potential at 0 and -60 mV levels of repolarization. In the presence of HSS the resting potential, amplitude and overshoot were also unaffected by the hypoxic condition. However, when measured at -60 mV level the changes on the repolarization phase after 15 and 60 minutes of hypoxia were significantly reduced, 14% and 24% respectively (p less than 0.001) as compared with the values obtained in the series without HSS.

Influence of parasympathetic pathways on early post--infarction arrhythmias.

The close relation between heart rhythm disorders that follow acute myocardial infarction (MI) and autonomic nervous system activity has come into focus recently. In order to evaluate the influence of the parasympathetic outflow on the incidence and characteristics of the early arrhythmias that follow myocardial infarction, the authors developed an experimental model of MI in rabbits by acute occlusion of the left ventricular artery. They have found that after the acute experimental MI an early stage of rhythm disorders is developed in 60% of the animals. In a second group of animals submitted to vagotomy prior to coronary occlusion none of rabbits exhibited arrhythmias. A third experimental series was performed in animals pretreated with atropine before and during the coronary occlusion; in this group the incidence of arrhythmias was the same as in control animals. The haemodynamic data obtained from the animals pretreated with atropine were similar to those obtained in control animals. The influence of vagal afferent and efferent pathways and their role in the genesis of the early arrhythmias is discussed.

Action potential characteristics of rabbit papillary muscle.

The ionic components of the action potential (AP) in rabbit right papillary muscle (RRPM) were determined by simple methods such as changes in external concentrations of sodium and calcium ions and addition of MnCl2 ot the perfusion fluid. Two components (fast and slow) were clearly visible in the upstroke of AP in normal Tyrode solution. MnCl2 (5 mmol/l) eliminated the slow component which forms the overshoot (OS) leaving the fast one unaffected, indicating that the former was related to a slow inward current. Mn also drastically reduced AP duration without changing the slope of phase 3 of repolarization. Reduction of Na concentration to 90 mmol/l did not affect the peak voltage of the OS but shortened AP. This low-Na solution reduced both (Vmax)f and the amplitude of the fast component. Ca-free solution reduced OS and increased AP duration. In high-Ca Tyrode (7.2 mmol/l) OS was increased and AP shortened. The effects of MN were reversed in this solution. The results suggest that the upstroke of the RRPM action potential is determined by two different ionic currents: a fast Na current responsible for the fast component and a slow inward current carried mainly by Ca, this latter being responsible for the slow component in the upstroke and for the plateau phase. The existence of propagated, Ca-dependent slow responses was demonstrated. Emphasis is placed on the fact that the major determination of the repolarization process in this type of AP is probably the inactivation of the slow inward Ca current.

Effects of moderate hypoxia on action potential and contraction of rabbit ventricular muscle.

Experiments were performed on rabbit right ventricular strips in order to investigate the effects of moderate hypoxia on electrical and mechanical activities of this preparation. The results indicate that a slow inward current (Isi) is responsible for overshoot (OS) and the plateau phase of the action potential (AP). Hypoxia (pO2 = 65-70 mmHg; 8.66-10.0 kPa) induced a rapid shortening of AP and an increase in the phase-3 slope. It also markedly reduced twitch tension and time to peak tension, and increased resting tension. The resting potential (RP), OS and maximum rate of depolarization of phase O were not affected during 60 min of hypoxic perfusion. Isoproterenol under this condition had a positive inotropic effect and also increased AP duration (APD) measured at -60 mV, having a less pronounced effect on the plateau phase. MnCl2 in hypoxic conditions drastically reduced OS indicating that even in this condition, Isi was present. These results suggest that an increase in gK is responsible for the hypoxia-induced reduction in APD. This also partially explains the maintenance of RP during hypoxic incubation.

Electrophysiological effects of droperidol on sinoatrial nodal fibers.

The influence of 1 and 5 mg/l of droperidol on rabbit sinus node intracellular recordings was evaluated. At 1 mg/l the drug merely prolonged the spontaneous basic cycle by reducing phase 4 slope of the action potential. At the higher concentration, droperidol induced a more pronounced effect of these variables and after 20 min perfusion, it also decreased the upstroke velocity and the threshold potential. Further exposure continued to reduce spontaneous rate, until irregular failure of impulse initiation and subthreshold oscillations appeared. After 45 min exposure to droperidol, only subthreshold oscillations could be recorded. Isoproterenol (0.2 mg/l) rapidly restored normal action potentials, while acetylcholine (0.5 mg/l) caused an immediate arrest leaving a stable level of membrane potential. The activity of droperidol in 1 mg/l concentration could be dependent on a partial blockade of the sodium leakage current, while at higher concentrations of 5 mg/l the drug seems to provoke a total blockade of Na--Ca slow channels. Subthreshold oscillations could be explained by changes in K conductance together with a remanent of the sodium leakage current.

Rate-dependent action potential changes in rat atrium.

Experiments in isolated left atria from rat hearts were performed in order to study the effects of stimulation rate on the transmembrane action potential. 1. Two components (fast and slow) of the action potential upstroke could be differentiated by adding MnCl2 to the perfusion solution. 2. With the increase in rate of stimulation over the control cycle length (500 msec), amplitude, Vmax and action potential duration at 80% of repolarization (D80) diminished in normal Krebs. In Mn-containing Krebs, only a slight reduction in amplitude was recorded. Resting potential and action potential duration at 20% (D20) and 50% (D50) of repolarization were only slightly affected in normal Krebs and not at all in Mn-Krebs. 3. Low rates of stimulation in normal Krebs increased D50 only slightly; however, D80 increased significantly while other parameters remained constant. No effects were seen in Mn-Krebs. 4. The results with Mn-Krebs indicate the importance of slow inward current on changes induced by stimulation rates. A possible mechanism relating intracellular calcium concentration and the outward K current, depending on the rate of stimulation, is discussed.