伊布利特对人体心房与心室的电生理作用及其频率依赖性研究

目的探讨伊布利特对人体心房、心室的电生理作用及其频率依赖性。方法25例射频消融术后患者于静脉推注伊布利特（0．0167mg／kg）前后测定两种起搏周长（PCL，400ms与600ms）时的右心房、左心房及右心室的有效不应期（RA-ERP、LA-ERP及RV-ERP），其中通过起搏冠状静脉窦远端问接起搏左心房。结果（1）明显延长RA-ERP（PCL=400ms时，由215．20ms延长至259．60ms，P〈0．001；PCL=600ms时，由231．20ms延长至281．20ms，P〈0．001）；（2）明显延长LA-ERP（PCL=400ms时，由216．60ms延长至247．60ms，P〈0．001；PCL=600ms时，由226.40ms延长至262．40ms，P〈0．001）；（3）明显延长RV-ERP（PCL=400ms时，由219．60ms延长至249．60ms，P〈0．001；PCL=600ms时，由233．20ms延长至268.20ms，P〈0．001）；（4）PCL=400ms与PCL=600ms比较，对RA-ERP、LA-ERP及RV-ERP延长程度均差异无统计学意义（P〉0．05）；（5）明显延长QT与QTc间期，其中QTc由384．36ms延长至450．66ms（P〈0．001），对窦性心率〈82次／min与≥82次／min患者的QT与QTc延长程度差异无统计学意义（P〉0．05）。结论伊布利特可明显延长RA-ERP、LA-ERP、RV-ERP及QT、QTc，而且这些电生理作用无频率依赖性。     

The electrophysiological effects of intravenous magnesium on human sinus node, atrioventricular node, atrium, and ventricle

The effects of intravenously (IV) administered magnesium chloride (MgCl) on electrophysiologic and electrocardiographic variables were studied in 13 patients undergoing a routine electrophysiologic assessment for clinical indications. An infusion of 12 mmol of MgCl was given during a 10-min period and relevant electrophysiologic variables were determined before and after the infusion. Serum Mg levels increased from 0.78 +/- 0.03 (mean +/- SEM) before to 1.52 +/- 0.08 ms after the infusion (p less than 0.0001). Magnesium treatment caused a significant prolongation in PR interval (from 151 +/- 8 to 174 +/- 8 ms, p less than 0.001) as well as in QRS duration (from 90 +/- 4 to 101 +/- 6 ms, p less than 0.05). Likewise, intra-atrial (PA) as well as atrioventricular (AV) nodal (AH) conduction times were significantly prolonged (from 33 +/- 3 to 46 +/- 3 ms, p less than 0.01, and from 85 +/- 6 to 94 +/- 6 ms, p less than 0.05, respectively). Mean effective and functional atrial refractory periods increased (from 228 +/- 8 to 256 +/- 10 ms, p less than 0.01 and from 292 +/- 9 to 320 +/- 11 ms, p less than 0.01, respectively), as did mean AV node functional refractory period (from 399 +/- 29 to 422 +/- 27 ms, p less than 0.02). No significant change occurred with regard to sinus node function (as estimated from heart rate, sinus node recovery time, and calculated sinoatrial conduction time) or ventricular refractoriness. It is concluded that IV Mg has several electrophysiologic effects that may be beneficial in the treatment/prevention of supraventricular tachyarrhythmias.     

Reproducibility of electrophysiological parameters of sinus node following autonomic blockade

We investigated the reproducibility of sinus node cycle length (SCL), corrected sinus node recovery time (CSRT) and sino-atrial conduction time (SACT) during the control state and following autonomic blockade in 25 patients (mean age: 56.9 ± 13.8 years). Autonomic blockade was induced by i.v. administration of propranolol (0.2 mg/kg) and atropine (0.04 mg/kg). The electrophysiological study was repeated after 24 hr and the results were compared. The patients were divided into two groups: Group 1 (15) with normal and Group 2 (10) with abnormal intrinsic sinus node function. Following autonomic blockade in Group 1 the daily variations in SCL, CSRT and SACT were very slight whereas in Group 2 there was far greater variability in these parameters. However, in the latter group there were no patients who changed their status from prolonged to normal intrinsic CSRT on the second study, whereas SACT changed its status in 2 patients. In Group 1 the daily variations in sinus node parameters were much slighter following autonomic blockade than during the control state. In Group 2 the variations were very similar during control and following autonomic blockade.These data suggest that: (1) following autonomic blockade the reproducibility of sinus node parameters is very good in Group 1, whereas in Group 2 several patients show marked daily variations in sinus node parameters; (2) following autonomic blockade the sinus node electrophysiological parameters are meaningful in diagnosing an involvement of intrinsic sinus node function; and (3) in patients with abnormal sinus node parameters during control state, but with normal intrinsic sinus node function, the daily variations are mainly due to change in autonomic tone, whereas when the intrinsic sinus node function is abnormal, the day to day variations during control state appear due predominantly to intrinsic sinus node abnormalities.     

Molecular and electrophysiological differences in the L-type Ca2+ channel of the atrium and ventricle of rat hearts.

BACKGROUND: Many pathological conditions induce electrical remodeling, possibly through intracellular Ca2+ overload, but the currently available L-type Ca2+ channel blockers may be detrimental because of their global negative inotropic effects. METHODS AND RESULTS: To determine whether the L-type Ca2+ channel is identical throughout the heart, the distribution of the mRNAs and proteins comprising the L-type Ca2+ channel and its electrophysiological properties were analyzed in rat atria and ventricles. The mRNA of alpha2delta-2 (Cacna2d2) was more abundantly expressed in the atrium (approximately 5-fold) than in the ventricle. In contrast, alpha1C (Cacna1c) (Cav1.2) mRNA was significantly less abundant in the atrium. The level of the alpha1C (Cacna1c) (Cav1.2) protein was decreased (approximately 0.5-fold) and that of alpha2 delta-1 (Cacna2d1) was increased (approximately 2-fold) in the atrium compared with the ventricle. Although the peak ICa,L density showed no significant differences, voltage dependence of inactivation and activation of the current showed a more depolarized shift in the atrium than in the ventricle. CONCLUSION: These results indicate that in the rat heart the L-type Ca2+ channel differs between the atrium and ventricle with regard to gene expression and electrophysiological properties.     

增龄对健康犬心房、肺静脉电生理特性的影响

目的 :探讨犬肺静脉 （PV）、心房电生理特性随年龄变化特点。方法 :健康杂种犬 15只按年龄分成 3个阶段组 :老、中、幼龄组 ,每组 5只。经锁骨下、股静脉穿刺和房间隔穿刺放置导管 ,采用刺激诱发心房纤颤 （AF） ,标测肺静脉PV、上腔静脉 （SVC）、左、右心房电位 ,测量各自有效不应期 （ERP）、功能不应期 （FRP） ,传导时间。结果 :3组AF诱发率分别为幼龄组 0 %、中龄组 2 0 %、老龄组 10 0 % ;起源于PV的AF占 83.3% ,其它为 16 .7% ;ERP :老龄犬PV的ERP显著短于幼龄组 ,为 132± 38msvs2 34± 5 1ms（P <0 .0 1） ,老龄组的PV的ERP显著短于心房的ERP ,为 132± 38msvs2 0 0± 34ms（P <0 .0 5 ） ;老龄犬组SVC的ERP显著短于幼龄组 （P <0 .0 5 ）。老、中、幼 3组PV起搏部位发生递减性传导百分率分别为 89%、33%、31% ,传导时间延长分别为 92± 5 5ms、2 7± 31ms、2 2± 38ms,老龄组与后两者比较均有非常显著差异 （P <0 .0 1）。结论 :PV电生理特点随年龄变化 ,电重构集中发生在老龄阶段 ,主要表现为不应期显著缩短和递减性传导 ,可能是PV致AF的主要原因。     

Observations on the biphasic nature of digitalis electrophysiological actions in the human right atrium

Cardiac electrophysiological effects of a digitalis glycoside have been investigated by right atrial intracardiac stimulation and recording in 12 patients with paroxysmal supraventricular tachyarrhythmias. Measurements were made of atrial effective refractoriness by pacing together with programmed premature extrastimulation. Simultaneous recordings of atrial action potential duration from a site close to the sinoatrial node and from a more distal atrial site were made using an endocardial contact-injury potential technique. All subjects received methyldigoxin 10.0 micrograms X kg-1 intravenously, while half were also pretreated with atropine. A biphasic response to methyldigoxin was observed, with initial action potential prolongation, maximal at 20 min post-infusion, followed by significant action potential shortening which persisted to the end of the study period at 40 min. The initial phase, that of prolongation, was associated with smaller increases in atrial effective refractoriness and increased vulnerability to atrial tachyarrhythmia initiation. During the subsequent phase of action potential shortening, the gap between the termination of effective refractoriness and completion of action potential repolarisation was narrowed, coinciding with diminished vulnerability to tachyarrhythmias. Slight but significant atrioventricular conduction delay was apparent 30 to 40 min after glycoside infusion, indicating enhanced vagal activity during the phase of action potential shortening. Prior atropinisation reduced the magnitude of both early and late components of the biphasic action potential response to digitalis, supporting the proposition that both components are mediated via cardiac muscarinic receptors. Since vagal effects on the atrioventricular junction appeared during the later phase, it is suggested that initial action potential prolongation by digitalis may have been effected via local acetylcholine release, while subsequent action potential shortening may have been caused by a combination of vagally and locally mediated activity.     

增龄对犬心房和肺静脉电生理学特性的影响

目的研究增龄对犬心房和肺静脉电生理学特性影响。方法17只杂种犬按年龄分为两组,成年犬7只,老年犬10只,做12导联同步心电图,测量P波平均时限和P波离散度;放置冠状静脉窦电极,左、右心耳电极,左上、左下、右上、右下肺静脉电极,测量各部位有效不应期（ERP）、ERP离散度及频率适应性。结果与成年犬相比,老年犬的P波平均时限延长,P波离散度增大;右心耳和冠状静脉窦近端ERP延长,左心耳和冠状静脉窦远端以及左上肺静脉ERP缩短;心房各部位及肺静脉ERP离散度增大;左心耳和冠状静脉窦远端及左上肺静脉频率适应性减低。结论增龄对心房和肺静脉电生理影响主要是左心房和左上肺静脉ERP缩短和频率适应性减低,心房及肺静脉ERP离散度增大。     

Frequency-dependent electrophysiological effects of flecainide, nifekalant and d,l-sotalol on the human atrium

To compare the effects of class Ic and III antiarrhythmic agents on the termination and prevention of atrial fibrillation, the present study investigated the use-dependent electrophysiological effects of flecainide, nifekalant and d,l-sotalol on the human atrium. Flecainide significantly prolonged effective refractory period (ERP), intra-atrial conduction time (IACT) and monophasic action potential duration (MAPD), and its effects on ERP and IACT were use-dependent. Nifekalalant significantly prolonged ERP and MAPD, and these effects were reverse use-dependent; however, there was no significant change in IACT. d,l-Sotalol significantly prolonged MAPD and the effect was reverse use-dependent. It significantly prolonged ERP, but the effect was not reverse use-dependent. d,l-Sotalol increased IACT in a use-dependent manner. Thus, for atrial fibrillation, class Ic antiarrhythmic agents might be more effective in termination and class III antiarrhythmic agents might be more effective in prevention.     

Skinned fibers of human atrium and ventricle: myosin isoenzymes and contractility

Different myosin isoenzymes of pig and human atrium and ventricle and rat ventricle were characterized by two approaches: pyrophosphate polyacrylamide gel electrophoresis (PP-PAGE) and analysis of the myosin P light chains by two-dimensional polyacrylamide gel electrophoresis (2D-PAGE). We further investigated the relation between atrial and ventricular myosin isoenzymes of human, pig, and rat, and the maximum (unloaded) shortening velocity (Vmax) and the Ca2+ sensitivity of chemically skinned fibers of the same species. The myosin isoenzymes of both human and pig atrium comigrated in the PP-PAGE with rat V2 isomyosin, whereas the ventricle of human and pig comigrated with rat V3. In both human and pig ventricle, a myosin P light chain polymorphism exists (two phosphorylatable P light chains with the same molecular weight but different isoelectric points). In contrast, we found no P light chain polymorphism in the atrium of human and pig and in the ventricle of rat (one phosphorylatable P light chain only). A correlation exists between Vmax, Ca2+ sensitivity, and atrium- and ventricle-specific myosin isoenzymes of human and pig. Vmax was determined by the slack-test method. Plots of delta l versus delta t of atrial and ventricular skinned fibers were well fitted by a single straight line up to delta l = 15% and delta l = 13%, respectively. Vmax of skinned ventricular fibers was lower than Vmax of skinned atrial fibers in both human and pig. Ca2+ sensitivity of skinned fibers of ventricle, however, was higher than Ca2+ sensitivity of atrial skinned fibers in both human and pig.     

Plasma glucagon and glucose recovery after hypoglycemia: the effect of total autonomic blockade.

The role of the autonomic nervous system in the glucagon response to hypoglycemia has not been fully clarified. We have studied the effect of total pharmacological blockade of the autonomic nervous system (concomitant alpha- and beta-adrenergic blockade with simultaneous atropine injection) and of isolated alpha-adrenergic blockade on hormonal responses to hypoglycemia and on blood glucose recovery after hypoglycemia in healthy subjects. Neither of the pharmacological blockades had any significant effects on plasma glucagon responses to hypoglycemia nor had they any effect on the rate of blood glucose recovery after hypoglycemia. We conclude that the autonomic nervous system has no major influence on the glucagon response to hypoglycemia in healthy man. Changes in autonomic nervous activity are not essential for blood glucose recovery after hypoglycemia in healthy man.     

自主神经对左上肺静脉电生理特征的影响

目的研究迷走神经刺激和心脏自主神经阻断对左上肺静脉(LSPV)电生理特征影响。方法用7只成年杂种犬自身对照,观察基础状态、左侧迷走神经干刺激、阻断迷走神经和阻断自主神经等不同状态下犬的心房和LSPV远端(LSPV-D)、中端(LSPV-M)、近端(LSPV-P)有效不应期(ERP)的变化,以及起搏肺静脉时心房颤动(简称房颤)诱发率的变化。结果①迷走神经刺激时LSPV的ERP均较基础状态下缩短,房颤的诱发率最高(71.4%)。②单用阿托品阻断迷走神经时LSPV-M的ERP较基础状态下延长(125.8±9.1msvs112.9±13.8ms,P<0.05),LSPV-P和LSPV-D无变化,但房颤诱发率较基础状态下和迷走神经刺激时下降(17.1%vs24.8%,71.4%,P<0.05)。③联合应用阿托品和普奈洛尔阻断自主神经时LSPV-D、LSPV-M和LSPV-P的ERP均显著延长,房颤的诱发率最低(7.6%)。④基础状态下LSPV-D的ERP长于LSPV-P(118.6±17.5msvs106.4±10.7ms,P<0.05),阻断自主神经时LSPV-D的ERP短于LSPV-P(135.0±8.2msvs151.4±12.1ms,P<0.05)。结论LSPV的电生理特征存在“异质性”,对阻断自主神经的药物反应性也不同,对房颤的发生和维持有重要作用。而自主神经张力的变化可以改变LSPV的电生理特性,其中交感神经也是主要原因之一。     

Effects of digitalis on the human sick sinus node after pharmacologic autonomic blockade

To study the effects of digitalis on the sinus node and the mechanisms involved, 16 patients with the sick sinus syndrome had electrophysiologic assessment of sinus nodal function during (1) control study, (2) after pharmacologic autonomic blockade with propranolol (0.2 mg/kg body weight and atropine sulfate 0.04 mg/kg intravenously), and (3) 10 minutes after 0.01 mg/kg of intravenous ouabain. The study was completed within 30 minutes of pharmacologic autonomic blockade. During the control study 50 percent of patients had an abnormal corrected sinus nodal recovery time or abnormal sinoatrial conduction time, or both. The effects of ouabain on sinus nodal function were compared with those after pharmacologic autonomic blockade. Ouabain significantly increased both intrinsic sinus cycle length (ouabain 975 ± 194 ms [mean ± standard deviation]; autonomic blockade 1,025 ± 218 ms, probability [p] < 0.001) and corrected sinus nodal recovery time (ouabain 615 ± 503 ms; autonomic blockade 575 ± 536 ms, p < 0.05). In contrast there was no significant change in sinoatrial conduction time after ouabain (ouabain 141 ± 56 ms; autonomic blockade 132 ± 45 ms; difference not significant). The effects of ouabain were similar in patients with both normal and abnormal sinus nodal function.These findings suggest that (1) digitalis in therapeutic doses has a depressant effect on intrinsic sinus nodal automaticity in patients with normal as well as abnormal sinus nodal function; (2) digitalis has no significant effects on sinoatrial conduction; and (3) the effects of digitalis on sinus nodal automaticity are primary and independent of its vagal and antiadrenergic effects.     

Electrophysiological effect of verapamil on human atrium]

To investigate the effect of verapamil on atrial vulnerability, the following measurements were performed before and after the intravenous administration of verapamil (0.15 mg/kg) in 10 subjects with paroxysmal atrial fibrillation (Paf), and 10 subjects without Paf (non-Paf). During the sinus rhythm, 1) intra-/interatrial conduction time (Intra-/Inter- ACT); the initial deflection of high right atrium (HRA) to that of His bundel/coronary sinus were measured. After 8 consecutive HRA stimuli (A1), premature stimulus (A2) was introduced by shortening the coupling interval (A1A2) and we measured 2) conduction delay zone (CDZ); the zone of A1A2 with the prolongation of Inter-ACT, 3) % maximum atrial fragmentation (%MAF); % maximum value of the ratio of HRA activity width at A2 (Awt) against that at A1 (Awc), 4) fragmented atrial activity zone (FAZ); the zone of A1A2 with % value of Awt/Awc more than 150%,5) repetitive atrial response (RAR); more than 2 atrial activities which occur in response to A2. (6) right atrial effective refractory period (RAERP). Verapamil significantly shortened CDZ and %MFA, slightly lengthened RAERP, and had RAR disappear in Paf, while it did not effect any indices significantly in non-Paf. We concluded that verapamil could reduce atrial vulnerability in Paf due to blocking of atrial conduction delay mediated by slow response fibers.     

Unique autonomic profile of the pulmonary veins and posterior left atrium.

OBJECTIVES: The purpose of this study was to investigate the electrophysiologic profile of the pulmonary veins (PVs) and left atrium (LA) in response to autonomic manipulation. BACKGROUND: The parasympathetic innervation of the PVs and posterior left atrium (PLA) is thought to contribute to focal atrial fibrillation (AF). We hypothesized that autonomic effects would be more prominent in these regions. METHODS: In 14 dogs, epicardial mapping was performed in the PVs, PLA, and left atrial appendage (LAA) under the following conditions: baseline, 20-Hz cervical vagal stimulation (VS), propranolol (P), P + VS, and P + atropine. Effective refractory periods (ERPs) were measured, and conduction vectors were computed at multiple sites. Western blotting and immunostaining were performed for IKAch (Kir3.1/3.4). RESULTS: The VS and P + VS caused more ERP shortening in the PV and PLA than in the LAA. The P + atropine caused greatest ERP prolongation in the LAA. Cumulative ERP change (ERP difference between P + VS and P + atropine) was greatest in the LAA and corresponded with expression of Kir3.1/3.4 (LAA > PLA > or = PV). The ERP change in response to vagal manipulation was most heterogeneous in the PLA; this corresponded with a pronounced heterogeneity of Kir3.1 distribution in the PLA. With VS and/or P, there was evidence of regional conduction delay in the PVs with a significant change in activation direction. Similar activation changes were not seen in the PLA and LAA. CONCLUSIONS: The PVs and PLA demonstrate unique activation and repolarization characteristics in response to autonomic manipulation. The heterogeneity of vagal responses correlates with the pattern of IKAch distribution in the LA. The peculiar autonomic characteristics of the PVs and PLA might create substrate for re-entry and AF.     

Monophasic action potentials of right atrium and electrophysiological properties of AV conducting system in patients with hypothyroidism.

In 12 patients with manifest hypothyroidism right atrial monophasic action potentials showed a significant prolongation in comparison with data from normal or euthyroid patients. Atrial effective refractory periods were also significantly prolonged. After thyroid treatment the monophasic action potential duration and the effective refractory period of the right atrium were within normal ranges. In 6 hypothyroid patients studies of AV conduction with the aid of His bundle electrography and atrial pacing showed a supraHisian conduction delay which was manifest in one case and latent in another two. InfraHisian conduction delay was encountered in 2 cases.     

Differential effects of functional autonomic blockade on the variables of sinus nodal automaticity in sick sinus syndrome

To study the pathophysiologic mechanism of sick sinus syndrome and to establish the relation of intrinsic heart rate, corrected sinus nodal recovery time and sinoatrial conduction time in this syndrome, electrophysiologic studies were conducted in 22 men (mean age 60 ± 12 years) with the clinical diagnosis of sick sinus syndrome. Measurements were determined before and after autonomic blockade with propranolol (0.2 mg/kg body weight) and atropine sulfate (0.04 mg/kg). Fifty-nine percent of patients (Group I) had an abnormal intrinsic heart rate, suggesting intrinsic abnormality of sinus nodal automaticity; 41 percent (Group II) had a normal intrinsic heart rate after autonomic blockade, suggesting disturbed autonomic regulation. One patient with an observed intrinsic heart rate higher than the upper limit of predicted intrinsic heart rate was also included in Group II. The mean corrected sinus nodal recovery time before autonomic blockade was 751 ± 502.8 ms and was abnormal (more than 450 ms) in 10 of the 13 patients in Group I and 2 of the 9 patients in Group II. After autonomic blockade this interval was 694 ± 638.7 ms and was abnormal in 12 of the 13 patients in Group I and in 2 of the 9 patients in Group II. The patients in each group could be further classified into three groups on the basis of normal or abnormal corrected sinus nodal recovery time before or after autonomic blockade. Not all patients with abnormal intrinsic heart rate (Group I) had abnormal corrected sinus nodal recovery time and vice versa. Patients in Group II were younger in age, had a lesser incidence of organic heart disease and were more severely symptomatic.Mean sinoatrial conduction time during control studies was 210.4 ±96.3 ms and decreased significantly (143.2 ± 59.6 ms, p < 0.005) after autonomic blockade. This interval was abnormal in 3 of the 13 patients in Group I and in 6 of the 9 patients in Group II during control studies; after autonomic blockade it remained abnormal in 3 patients in Group I and in 1 patient in Group II.It is concluded that determination of heart rate and corrected sinus nodal recovery time after autonomic blockade increases the sensitivity of electrophysiologic testing and offers some insight into the pathophysiology of sick sinus syndrome. Patients with sick sinus syndrome who have a normal intrinsic heart rate have a greater incidence of abnormal sinoatrial conduction time than do those with an abnormal intrinsic heart rate. Thus, abnormal sinoatrial conduction time is usually due to extrinsic autonomic influences.     

Electrophysiological properties of the human atrium in atrial fibrillation

It has been reported that ectopic foci from the pulmonary veins can initiate atrial fibrillation (AF) and can also act as drivers for maintaining AF. However, not all patients with atrial arrhythmias initiate AF. A substrate for atrial propensity to AF is required for AF initiation and maintenance. Thus, we reviewed and discussed mainly the electrophysiological properties observed in AF. Abnormal atrial electrograms during sinus rhythm and abnormal responses of the atrium elicited by programmed stimulation have been observed more frequently in patients with paroxysmal AF than in those without. A shorter atrial effective refractory period, greater dispersion of the atrial refractoriness and atrial conduction delay are also of electrophysiologic significance in the genesis of AF. Electrical remodeling is likely to be a final common pathway that ultimately supervenes. Even if atrial electrical remodeling facilitates AF initiation and AF perpetuation, the initiation of AF requires a trigger. Further investigation into the electrophysiological properties in AF will be needed in order to contribute to the future development of an appropriate treatment.     

Discordant temporal changes in electrophysiological properties during electrical remodeling and its recovery in the canine atrium

Prolonged rapid atrial excitation gives rise to atrial electrical remodeling, which perpetuates atrial fibrillation (AF). However, there has been controversy regarding the nature of temporal changes in conduction characteristics during the development and recovery of electrical remodeling. This study was designed to clarify the nature of the development and recovery of electrical remodeling in relation to AF inducibility in dogs subjected to rapid atrial pacing. Eleven dogs underwent rapid atrial pacing (400/min) for 28 days. The electrophysiological study was performed on the day just prior to the commencement of pacing, on days 2, 7, 14, and 28 of rapid pacing, as well as 1 and 7 days after the cessation of pacing. In response to rapid atrial pacing, atrial effective refractory period (ERP), conduction velocity and wavelength decreased significantly (p < 0.05). ERP had shortened significantly and rapidly within 2 days of pacing, while conduction velocity decreased more gradually. During the recovery, ERP returned to almost baseline levels within a day, whereas conduction velocity returned to baseline by day 7. Sustained AF became inducible in 37% of the dogs from 7 days of pacing until 1 day after the cessation, when wavelength fell below 8.7 cm. In conclusion, rapid atrial excitation causes a progressive but discordant temporal pattern of a decrease in ERP and conduction velocity. The resultant shortening of the wavelength determines the inducibility and maintenance of AF. The electrophysiological changes produced by one month of rapid atrial pacing can be fully reversed within a week, although in a discordant temporal pattern.     

Influence of digitalis on cardiac function before and after autonomic blockade.

The influence of Deslanoside C (D), 1.2 mg intravenously on the systolic time intervals (STI) was assessed in 15 individuals with right ventricular pacemakers, who were studied on two occasions, ten days apart. In the first case D was given under basal conditions, and in the second after autonomic blockade (with practolol 20 mg intravenously and atropine 1.5 and 1.0 mg intravenously) at 1 hour's interval. There were similar changes of the STI with digitalis administration both before and after automic blockade. Autonomic blockade is not necessary for full expression of digitalis action on the human heart, as advocated by some authors to be the case in experimental animals.