Mean Cycle Length Research Articles

In vitro fertilization and embryo transfer: an individualized approach to ovulation induction.

Because of the inherent marked individual responsiveness to ovulatory stimulating agents, a highly individualized approach to ovulation induction for in vitro fertilization has been utilized. The starting time for medication was varied according to the previous mean cycle length. The dose of clomiphene citrate was adjusted to the body weight. The dose and duration of both clomiphene and human menopausal gonadotropin (hMG) were adjusted as early as treatment day 5 in accordance with the ultrasonic findings. The day of human chorionic gonadotropin (hCG) administration was varied according to a combination of ultrasonic findings and plasma estradiol levels. This approach resulted in a mean retrieval of four oocytes per laparoscopy, 75% of which were mature, a fertilization rate of 78%, and a pregnancy rate of 14% of laparoscopies.

Changes in heart rate during breathing interrupted by recurrent apneas in humans.

Heart rate varies with breathing patterns, especially in sleep apnea. To assess the effects on heart rate of recurrent apneas interrupting tidal breathing, we studied five normal awake male subjects. These subjects voluntarily changed their breathing pattern from regular tidal breathing to tidal breathing interrupted by breath holding at end expiration. This recurrent apneic breathing pattern did not change mean heart rate but increased its variance significantly. In addition, the variations in heart rate formed a cyclic pattern of oscillation with a mean cycle length identical to both arterial O2 saturation (SaO2) (R = 0.95; P less than 0.01) and ventilation (R = 0.92; P less than 0.01). Cyclic changes in either SaO2 or ventilation reproduced the oscillatory patterns of heart rate seen with tidal breathing interrupted by multiple apneas, but the amplitude of the variance in heart rate was smaller. Finally, preventing the cyclic declines in SaO2 with supplemental O2 did not significantly alter the heart rate changes seen in tidal breathing interrupted by apneas.

Electrical alternans in wide complex tachycardias

The occurrence of electrical alternation of 0.1 mV or greater of the QRS or T wave was analyzed in 156 electrocardiograms that showed wide QRS complex tachycardias from 91 patients. One hundred thirty-six ventricular tachycardias (VT) were recorded from 74 patients and 20 supraventricular tachycardias (SVT) from 17 patients. Alternans was present in 42 tracings (27%) from 35 patients (38%) and was equally frequent in the patients with VT (39%) and those with SVT (35%). Alternans occurred in 36 VTs (27%) and 6 SVTs (30%). Tachycardias with alternans had a shorter mean cycle length than tachycardians without alternans (339 ± 53 vs 368 ± 85 ms, p < 0.05), but were not associated with a particular QRS morphology or axis. Alternans was most frequent in leads V 2 and V 3 and was seen in more leads during SVT than VT (7.2 ± 2.6 vs 3.7 ± 2.5, p < 0.005). All SVTs with alternans incorporated an atrioventricular bypass tract. Electrical alternans occurs frequently in wide QRS tachycardias. Alone, it does not help differentiate VT from SVT. SVTs utilizing bypass tracts frequently show alternans even if the QRS is wide, and this finding may be useful in determining the mechanism of SVTs with aberrant intraventricular conduction.

The Oscillating 'Vena Cava Syndrome' During Quiet Standing - An Unexpected Observation in Late Pregnancy

While studying the lung function of pregnant women at term in four different postures, we were surprised to note marked cyclic accelerations in the heart rate in two-thirds of the women when in a standing position. The mean cycle length was 105 s (range: 1-4 min) and the amplitude had a mean of 27 beats/min (range: 9-51). Blood flow velocity measurements with ultrasound Doppler over the femoral vein showed that there was an intermittent reduction of flow during quiet standing. When the venous return ceased, maternal heart rate increased, cardiac output decreased and blood pressure fell. After the venous blood flow was restored, maternal heart rate, cardiac output and blood pressure returned to normal until the cycle started again. Concomitant with these maternal heart rate changes, different patterns of fetal heart rate were observed. About 70% of the fetuses showed reduction in the long-term variability, increase in fetal heart rate or periodic accelerations. Although no woman fainted during quiet standing, the maternal circulatory changes were consistent with those seen in the classical vena cava syndrome.

Disruption of estrous cycles in exercise-trained rats.

The female Sprague-Dawley rat was evaluated as an animal model for the menstrual irregularities that are common in women athletes. Daily vaginal smears revealed that estrous cycles were markedly disrupted in rats during a 10-week exercise training program, while cycles remained normal in sedentary rats. Compared to 9 sedentary rats, the 10 exercise-trained rats had longer mean cycle lengths and fewer estrus smears. Six of the exercise-trained rats, but none of the sedentary rats, had an "anestrus period" with more than twice the normal interval between estrus smears; one exercise-trained rat became essentially acyclic. Weight gain during the 10-week training program was lower in exercise-trained rats than in sedentary rats. Colonic temperatures, monitored at rest and during 30 min of exercise, were slightly lower in exercise-trained rats with irregular estrous cycles than in exercise-trained rats with regular cycles, indicating that unusually elevated body temperatures during exercise are not responsible for exercise-related reproductive acyclicity. It is concluded that the female Sprague-Dawley rat may be a useful animal model for the study of menstrual irregularities associated with exercise training.

Subendocardial resection for sustained ventricular tachycardia in the early period after acute myocardial infarction

One hundred nineteen patients with drug-refractory ventricular tachycardia (VT) underwent mappingguided subendocardial resection for control of their arrhythmias from 3 weeks to 10 years after acute myocardial infarction (AMI). Patients were separated into 2 groups: those treated early (within 4 months, group I) and those treated later (after 1 year, group II) after AMI. There were 32 patients in group I and 72 patients in group II. Both groups of patients had similar clinical, angiographic and hemodynamlc characteristics. Patients in group I had VT with a shorter mean cycle length than patients in group II (322 ± 71 vs 349 ± 88 ms, p < 0.05). The groups did not differ with respect to operative mortality (12% vs 7%), late mortality (31% vs 33%, mean follow-up 23 months), or frequency with which subendocardial resection without any adjunctive therapy prevented postoperative spontaneous or inducible VT (21% vs 34%). Group I was further separated into patients who underwent subendocardial resection within 1 month of AMI (n = 7) and those who underwent subendocardial resection with 2 months of AMI (n = 14). Although patients in group I were characterized by having more spontaneous morphologically distinct tachycardias, their operative mortality, total mortality and surgical success rates were comparable to those of patients in group II. The results of the study suggest that in a patient population with drug-refractory VT after AMI, (1) there are no clinical, angiographic, or hemodynamic variables that distinguish patients in whom VT develops early (within 4 months) from those in whom it develops late (longer than 1 year) after myocardial infarction; (2) VT early after AMI tends to have faster rates and increased number of distinct morphologies; and (3) subendocardial resection early (within 4 months, but even within 1 or 2 months) after AMI is associated with acceptable operative mortality and control of VT.

Effects of neutralization of luteinizing hormone on corpus luteum function and cyclicity in Macaca fascicularis.

The primate corpus luteum (including the human) is thought to require continuous exposure to LH for normal progesterone production and menstrual cyclicity. Recently, normal luteal function was reported in rhesus monkeys after postovulatory hypophysectomy or treatment with an antagonist to GnRH. We studied the effects of neutralization of LH by specific antiserum in the fascicularis monkey. A potent antiserum to ovine LH, which cross-reacted with monkey pituitary extract, was produced in rabbits; this antiserum was administered daily to cycling monkeys during the midluteal phase. The pretreatment cycle duration was 32.4 +/- 1.7 (+/- SE) days, and luteal length was 16.5 +/- 0.8 days, with a midluteal progestin peak of 15.28 +/- 2.23 ng/ml. LH antiserum treatment resulted in a precipitous fall in serum progestin within 24 h, which remained low for the remainder of the cycle. All treated monkeys had premature menstrual bleeding, with mean cycle length shortened to 22.8 +/- 1.6 days (P less than 0.0005). These results confirm that the continuous presence of LH is essential for maintenance of corpus luteum function in this species of primate.

Postvagal potentiation of the chronotropic effect of norepinephrine.

Following termination of vagal stimulation, heart rate increases above control (postvagal tachycardia). This phenomenon has been attributed to vagally mediated release of norepinephrine in the sinus node region, although other contributory factors may be important. The possibility that, during the postvagal period, the chronotropic efficacy of norepinephrine is enhanced was investigated. Mongrel dogs (N = 6) were pretreated with reserpine in order to minimize postvagal tachycardia and hence allow reliable detection of enhanced responsiveness to norepinephrine. The dogs were then anesthetized with chloralose, autonomically decentralized, and instrumented to record electrocardiogram, aortic blood pressure, and electrograms from right atrium and right ventricle. Thirty-, forty-, or sixty-second infusions of norepinephrine were administered via the sinus node artery. The mean cycle length decrease produced by norepinephrine alone was 95 msec (which corresponds to a heart rate increase of + 19.6 bpm). After a 30-sec period of vagal stimulation, norepinephrine infusions produced a cycle length decrease of 139 msec (+32.5 bpm). These results are significant at the P less than 0.05 level. It is concluded that norepinephrine infusions produce a significantly greater magnitude of tachycardia when administered postvagally. It is proposed that this postvagal potentiation of the chronotropic effect of norepinephrine may contribute to postvagal tachycardia. Indeed, there may be a synergistic relationship between this phenomenon and vagally mediated release of norepinephrine in the mediation of postvagal tachycardia.

The oscillating 'vena cava syndrome' during quiet standing--an unexpected observation in late pregnancy.

While studying the lung function of pregnant women at term in four different postures, we were surprised to note marked cyclic accelerations in the heart rate in two-thirds of the women when in a standing position. The mean cycle length was 105 s (range: 1-4 min) and the amplitude had a mean of 27 beats/min (range: 9-51). Blood flow velocity measurements with ultrasound Doppler over the femoral vein showed that there was an intermittent reduction of flow during quiet standing. When the venous return ceased, maternal heart rate increased, cardiac output decreased and blood pressure fell. After the venous blood flow was restored, maternal heart rate, cardiac output and blood pressure returned to normal until the cycle started again. Concomitant with these maternal heart rate changes, different patterns of fetal heart rate were observed. About 70% of the fetuses showed reduction in the long-term variability, increase in fetal heart rate or periodic accelerations. Although no woman fainted during quiet standing, the maternal circulatory changes were consistent with those seen in the classical vena cava syndrome.

Life threatening ventricular tachycardias in late survivors of surgically corrected tetralogy of Fallot.

Electrophysiological tests were performed in three patients with surgically corrected tetralogy of Fallot (mean age at evaluation 25 years, mean age at surgical correction 4 years) who had had either a cardiac arrest or transient neurological disturbances (presyncope, syncope) associated with ventricular arrhythmias. All three patients had an excellent haemodynamic result from surgery as judged by echocardiography and cardiac catheterisation. Ambulatory electrocardiographic monitoring and stress exercise testing were normal in two patients and showed complex ventricular ectopy in one. During invasive electrophysiological evaluation all three patients had inducible ventricular tachycardia (monomorphic QRS in two patients, cycle lengths 230 and 240 ms; polymorphic QRS in one patient, mean cycle length 200 ms) with adverse haemodynamic effects in all three patients. These findings suggest that rapid ventricular tachycardia with detrimental haemodynamic consequences, similar to that induced during laboratory study, was the basis for the presenting symptoms in each patient. This possibility was confirmed in one patient who had identical QRS morphology during both spontaneous ventricular tachycardia and that induced during the laboratory study. Thus sudden death or symptoms of syncope postoperatively in patients with surgically corrected tetralogy of Fallot appear to be due to rapid ventricular tachycardia, which may occur despite an apparently excellent surgical result.

Luteolytic potencin in a novel prostaglandin analogue

Estrus induction in cycling sows with exogenous prostaglandin is hindered by the extended refractory period and resistance of swine to the luteolytic action of PG's. The luteolytic potency of a novel PGF 2α analogue, Schering ZK 71677, was assessed at four different dosages in chronically cannulated cycling swine. Dosages totalling 1, 1.5, 3 and 10 mg of ZK 71677 were split into two injections given intramuscularly on day 13 of the estrous cycle. Onset of behavioural estrus and serum levels of progesterone and PGF metabolite were monitored. The three lowest doses did not advance estrus but did cause a transitory decline in serum progesterone concentration on day 13. The 10 mg level advanced estrus in three of four sows although the overall mean cycle length did not differ from pretreatment cycles (18.5 ± 1.3 vs 21.3 ± 0.6 days). Progesterone values droppd steadily in all four sows in the 10 mg treatment group. No level of ZK 71677 affected serum levels of PGF metabolite. The highest level tested of PGF 2α analogue ZK 71677 elicited an uninterrupted decline in serum progesterone concentrations but was inconsistent in its ability to promote early onset of behavioural estrus in swine.

Actions of disopyramide on potential reentrant pathways and ventricular tachyarrhythmias in conscious dogs during the late post-myocardial infarction phase

The effect of intravenous disopyramide (plasma level 3.7 ± 1.6 μg/ml, mean ± standard deviation) on reentrant ventricular tachyarrhythmias was studied by programmed ventricular stimulation in 11 conscious dogs 3 to 8 days after experimental myocardial infarction. Sustained ventricular tachycardia (VT) was induced in 4 dogs (mean cycle length 173 ± 14 ms) and nonsustained VT in 7 (8 ± 4 beats, mean cycle length 136 ± 18 ms). Disopyramide prevented induction of VT in 1 of 4 dogs with sustained VT and 3 of 7 with nonsustained VT, and increased VT cycle length by more than 30 % in 2 dogs with sustained VT and 2 of 7 with nonsustained VT. Disopyramide prolonged refractoriness in the infarct zone, measured by analysis of electrograms from an implanted “composite” electrode, by 38 to 53%, depending on the mode of pacing. These values were significantly greater than the increase produced by disopyramide in ventricular effective refractory period (13 ± 12%), QRS duration and QT interval. Disopyramide has a selective effect on potential reentry circuits in ischemic myocardium, and prolongs refractoriness in abnormal myocardium to a greater extent than its effect on the normal ventricle.

Cardiac effects of cibenzoline.

The effects of cibenzoline were examined in the dog with multifocal ventricular arrhythmias 24 h after ligation of the left anterior descending coronary artery, and on isolated, superfused canine cardiac tissues which were studied using standard microelectrode techniques. In the intact dog, 5 mg/kg cibenzoline consistently exerted antiarrhythmic effects. In all experiments, the percentage of normal sinus beats was greatly increased as the ventricular ectopic cycle length was significantly prolonged. Cibenzoline also slightly decreased the mean sinus cycle length. In isolated, driven Purkinje fibers, cibenzoline (1-5 mg/L) exerted lidocaine-like effects, significantly shortening the plateau of the action potential and decreasing the maximum rate of depolarization. Cibenzoline (2.5 mg/L) did not decrease the rate of normal automaticity in Purkinje fibers (with maximum diastolic potentials [MDPs] greater than - 85 mV), but did slow the rate of fibers pretreated with isoproterenol (0.5-10 microM) for greater than 30 min. It did not slow these fibers via beta-adrenergic blockade, because superfusion of cibenzoline-pretreated fibers with isoproterenol (0.5-10 microM) produced positive chronotropic responses which were as large as those that occurred in these fibers prior to cibenzoline exposure. Cibenzoline, 1-5 mg/L, also significantly slowed "abnormal automaticity" in Purkinje fibers with MDPs of -60 to -40 mV. In experiments on automaticity in fibers with normal MDPs, cibenzoline, 2.5-5.0 mg/L, was found to induce early afterdepolarizations and triggered activity within 16-30 min of the start of exposure. These early afterdepolarizations could be terminated by stimulating the fibers at cycle lengths of 2,000 ms or less. The antiarrhythmic actions of cibenzoline may result from negative chronotropic effects on abnormal automaticity or on catecholamine-induced (triggered) automaticity, or from effects on conduction dependent on its local anesthetic actions.

Clinical efficacy and electrophysiologic effects of cibenzoline therapy in patients with ventricular arrhythmias

Cibenzoline, a new antiarrhythmic agent, was tested in 26 patients who had symptomatic ventricular tachycardia (24 patients) or premature ventricular complexes (2 patients) unresponsive to conventional drugs. Cibenzoline was given orally every 8 hours to maximal doses of 65 mg in 2 patients, 81.25 mg in 22 patients and 97.5 mg in 2 patients. Cibenzoline abolished spontaneous episodes of ventricular tachycardia in 8 of 16 patients with ventricular tachycardia during a 72 hour control electrocardiographic recording, and 7 of 22 patients had greater than 83% decrease in premature ventricular complexes compared with control. The PR interval increased 14% (p less than 0.001), QRS duration increased 17% (p less than 0.001), QT interval did not change and mean ejection fraction in 10 patients did not change. Electrophysiologic studies were performed on 10 patients in the control period and during maximal cibenzoline dosage. Cibenzoline did not affect electrophysiologic properties of the atrium or atrioventricular (AV) node. It prolonged the ventricular effective (223 +/- 16 to 241 +/- 22 ms, p less than 0.02) and functional (247 +/- 18 to 264 +/- 25 ms, p less than 0.02) refractory periods. At control electrophysiologic studies, ventricular tachycardia was induced in 9 of 10 patients (mean cycle length 210 +/- 31 ms). Cibenzoline therapy prevented ventricular tachycardia induction in two patients, and in the other seven patients the mean ventricular tachycardia cycle length increased from 210 to 260 ms. The one patient with no ventricular arrhythmia induced during the control study still had no arrhythmia induced while receiving cibenzoline.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of triple extrastimuli during electrophysiologic study of patients with documented sustained ventricular tachyarrhythmias.

Electrophysiologic studies were performed in 172 consecutive patients for evaluation of documented sustained ventricular tachyarrhythmias. One hundred thirteen patients presented with sustained ventricular tachycardia that was hemodynamically stable, and 59 patients presented with cardiac arrest. Seventy-one patients without previously documented or suspected ventricular arrhythmias were also studied to determine the specificity of our electrophysiologic study protocol. The stimulation protocol included single, double, and triple right ventricular extrastimuli and rapid ventricular pacing at multiple cycle lengths performed at one or more right ventricular sites. Stimulation was performed at one or more left ventricular sites in patients with documented spontaneous arrhythmias when right ventricular programmed stimulation failed to induce sustained ventricular tachycardia. Ventricular tachyarrhythmias were induced in 110 (97%) of the patients who presented with sustained ventricular tachycardia, in 48 (81%) of the patients who presented with cardiac arrest, and in 28 (40%) of the patients without documented spontaneous arrhythmias. Right ventricular triple extrastimuli induced tachycardia in 22% of patients who presented with sustained ventricular tachycardia vs 46% of those who presented with cardiac arrest (p less than .001). Left ventricular stimulation was required for tachycardia induction in 3% of patients with stable tachycardia vs 19% of those with cardiac arrest (p less than .01). Triple extrastimuli induced 57% of tachycardias in the 28 patients without spontaneous arrhythmias, and virtually all of these tachycardias were polymorphic and nonsustained. The cycle lengths of tachycardias induced in each group by double and triple extrastimuli were similar, but the tachycardias induced in patients with cardiac arrest were significantly faster than those induced in the ventricular tachycardia group (mean cycle length 218 vs 291 msec, p less than .001).(ABSTRACT TRUNCATED AT 250 WORDS)

Menstrual patterns in adolescent Swiss girls: a longitudinal study

Menstrual patterns were studied longitudinally in 140 adolescent Swiss girls. The mean cycle length was 32.2 (S.D. 11.24) d in the first year after menarche, and 29.9 (S.D. 7.12) d in the sixth year after menarche. The values of the mean cycle length became essentially constant from the sixth post-menarcheal year, the chronological age of 20 y and the 36th post-menarcheal cycle. No association was found between cycle length and age at menarche. The menarcheal age of mothers and that of their daughters were significantly correlated with each other (r = 0.29, P less than 0.001). The most frequent cycles of 21-27 and 28-34 days constituted 64-81% of all cycles depending on post-menarcheal age. Short cycles (14-20 d), representing 2-6% of all cycles, were present in 14-31% of the girls; long cycles (35-41 d), constituting 10-16% of all cycles, occurred in 46-68% of the girls. The frequency of the long cycles tended to decrease at higher post-menarcheal ages. There were minimal changes in the duration of menstrual flow throughout the first six years after menarche. The mean duration was 5.4 (S.D. 1.72) d for the first year, and 5.1 (S.D. 1.33) d for the sixth year. The most frequent flow duration was 3-7 d, present in 88-94% of cycles. Prolonged bleeding tended to decrease with rising post-menarcheal and chronological age. The intensity of menstrual flow was mild in 11-16%, moderate in 62-78% and severe in 11-25% of the girls. The frequency of these three categories remained essentially unchanged during the first five post-menarcheal years.

A prospective multicentre trial of the ovulation method of natural family planning. III. Characteristics of the menstrual cycle and of the fertile phase

Seven hundred twenty-five women of proven fertility recorded the presence of cervical mucus at the vulva in 7514 menstrual cycles. The mean cycle length of the 6472 "normal" cycles was 28.5 days (standard deviation +/- 3.18). The peak day of mucus discharge was the last day of slippery, raw-egg-white-like mucus and occurred on average on day 15 (+/- 2.6). The fertile period was defined as any day on which mucus was reported before the peak day until 3 days after the peak. Its mean length was 9.6 (+/- 2.6) days. The probability of pregnancy was maximal on the peak day and declined on the days before and after the peak.

Relation of mode of induction and cycle length of ventricular tachycardia: Analysis of 104 patients

One hundred four consecutive patients with ventricular tachycardia (VT) were examined to correlate the cycle length with the mode of initiation of VT (single, double, and triple extrastimuli and rapid pacing). Tachycardias induced with a single extrastimulus were slower (342 ± 72 ms, mean cycle length) than those induced with double (295 ± 60 ms) or triple (282 ± 56 ms) extrastimuli or rapid pacing (293 ± 40 ms). There were no differences among the last 3 groups. In 38 patients who had endocardial catheter mapping to determine the site of origin of VT, distance from stimulation site to the site of origin was estimated and correlated with mode of initiation. There was no difference in mode of initiation when the stimulation site was close (< 3 cm), intermediate (3 to 5 cm), or distant (> 8 cm) from the site of origin. To address the issue of distance from stimulation site to the site of origin somewhat differently, mode of initiation was correlated with site of previous myocardial infarction in 69 patients with VT initiated from the right ventricular apex. Again, mode of initiation did not differ among patients with septal, inferior, lateral, or multiple myocardial infarctions. Thus, cycle length of VT initiated with a single extrastimulus was slower than that initiated with double or triple extrastimuli or rapid pacing and the mode of initiation of VT was unrelated to site of myocardial infarction or distance between stimulation site and site of origin of VT.

Selective blockade of retrograde fast pathway by intravenous disopyramide in paroxysmal supraventricular tachycardia mediated by dual atrioventricular nodal pathways.

Electrophysiological effects of 2 to 2.5 mg/kg iv disopyramide were studied in 10 patients with dual nodal pathways who used a slow pathway for anterograde and a fast pathway for retrograde conduction during paroxysmal supraventricular tachycardia (mean cycle length 308.5 +/- 37 ms; range 260-370 ms). Disopyramide terminated the tachycardia in six cases by production of ventriculoatrial block in five and by sinus overdrive in one. In the remaining four patients cycle length of the paroxysmal supraventricular tachycardia increased significantly from 270 +/- 8 ms to 377.5 +/- 28 ms. In all 10 patients disopyramide depressed retrograde fast pathway conduction manifest by an increase in mean ventricular paced cycle length producing ventriculoatrial block from less than or equal to 296.5 +/- 25 ms to 358 +/- 60 ms, and increase in retrograde fast pathway effective refractory period from less than or equal to 246 +/- 34 ms to 325 +/- 36 ms; the drug abolished ventriculoatrial conduction in two cases. Anterograde slow pathway and fast pathway conduction properties were unchanged after disopyramide (atrial paced cycle length producing AH block 292 +/- 30 to 306.5 +/- 30 ms; effective refractory period of anterograde fast pathway less than or equal to 274 +/- 56 to 284 +/- 44 ms, before and after the drug, respectively) suggesting that anterograde conduction was not crucial either for sustainment or for failure to initiate paroxysmal supraventricular tachycardia after the drug. Paroxysmal supraventricular tachycardia could not be reinduced in six cases after disopyramide. In the other four the ventricular paced cycle lengths producing ventriculoatrial block (318 +/- 41 ms) and effective refractory period of retrograde fast pathway (320 +/- 28 ms) were shorter than the cycle length of reinduced paroxysmal supraventricular tachycardia (367.5 +/- 35 ms) allowing perpetuation of the tachycardia. We conclude that disopyramide breaks atrioventricular nodal re-entrant tachycardia by specific blockade of the retrograde fast pathway though the effect on anterograde atrioventricular nodal conduction is variable.

Effects of flecainide on electrophysiological properties of accessory pathways in the Wolff-Parkinson-White syndrome.

The effect of flecainide in 12 patients with the Wolff-Parkinson-White syndrome was analyzed with respect to the anterograde and retrograde conduction properties of the accessory pathway, the modes of initiation and termination of circus movement tachycardias, and the ventricular response during induced atrial fibrillation. The principal effect of this drug was to depress both anterograde and retrograde conduction of the accessory pathway. In 8/9 cases circus movement tachycardia was terminated by prolongation of the retrograde effective refractory period of the accessory pathway. Flecainide increased the shortest and the mean cycle length during induced atrial fibrillation. It is concluded that the drug may be of potential benefit in patients with paroxysmal supraventricular tachycardias in patients with the Wolff-Parkinson-White syndrome.