Cognitive Structure of Origami Imagery

While previous studies found that origami, when used for cognitive training and education, can improve spatial ability, the underlying mechanisms of this change, presumably associated with the origami folding process, remain unclear. In the present study, we focused on origami imagery in which participants imagined the process of folding paper to create a work of art; and we examined the cognitive factors involved in the imagery process and their association with mental transformations and the extent to which visual imagery was vivid. We identified four specific relevant cognitive factors in origami imagery: (a) controllability of origami transformations, (b) visual imagery of shapes, (c) hand sensations, and (d) visual imagery of colors. We associated the first two of these with non-rigid transformations: the controllability of origami transformations and the visual imagery of shapes. Moreover, vividness of visual imagery was related to all four cognitive factors. We propose this cognitive model of origami as one that considers the key relationships between origami imagery, mental transformations, and vividness of visual imagery.

[Human resource capacity building on TB laboratory work for TB control program--through the experience of international TB laboratory training course for TB control at the Research Institute of Tuberculosis, JATA, Japan]

The international training course on TB laboratory work for national tuberculosis program (NTP) has been conducted at the Research Institute of Tuberculosis since 1975 funded by Japan International Cooperation Agency in collaboration with WHO Western Pacific Regional Office. The aim of the course is to train key personnel in TB laboratory field for NTP in resource-limited countries. The course has trained 265 national key personnel in TB laboratory service from 57 resource-limited countries in the last 33 years. The number of participants trained may sound too small in the fight against the large TB problem in resource-limited countries. However, every participant is playing an important role as a core and catalyst for the TB control program in his/her own country when they were back home. The curriculum is composed of technical aspects on TB examination, mainly sputum microscopy in addition since microscopy service is provided at many centers that are deployed in a widely spread area, the managerial aspect of maintaining quality TB laboratory work at the field laboratory is another component of the curriculum. Effective teaching methods using materials such as artificial sputum, which is useful for panel slide preparation, and technical manuals with illustrations and pictures of training procedure have been developed through the experience of the course. These manuals are highly appreciated and widely used by the front line TB workers. The course has also contributed to the expansion of EQA (External Quality Assessment) system on AFB microscopy for the improvement of the quality of TB laboratory service of NTP. The course is well-known for not only having a long history, but also for its unique learning method emphasizing "Participatory Training", particularly for practicum sessions to master the skills on AFB microscopy. The method in learning AFB microscopy, which was developed by the course, was published as a training manual by IUATLD, RIT and USAID. As it is mentioned, the course has been contributing to human resource capacity building including management of laboratory service to improve NTP in the resource-limited countries. Currently, expansion of technology transfer on culture examination for drug susceptibility test has been attempted to the resource-limited countries due to the occurrence of MDR-TB (Multi drug-resistant tuberculosis) and XDR-TB (Extensively drug-resistant tuberculosis) cases. However, since sputum smear examination is most effective method of detection of infectious TB, the writers believe it is still a core component of TB control, unless a new diagnostic tool that is practicable and effective in the resource-limited countries is developed. Therefore the course will keep focused on the smear examination as the basic curriculum. The course is highly appreciated by international experts and it is our responsibility to answer the expectation from them.

[Stability for long-term storage and reproducibility of positivity in the panel test slide prepared with the polyacrylamide-based artificial sputum]

OBJECTIVE

A novel artificial sputum has been developed using polyacrylamide, cultured THP-1 cell and BCG-Pasteur. Smears prepared with this artificial sputum are similar to actual sputum and has feasibility to set any positivity grades. Long-term storage and reproducibility of the positivity was examined to support further availability.

METHOD

The artificial sputa were stored for up to 9 months at room temperature, 4 degrees C and -20 degrees C. Then, smears were prepared and their macroscopic and microscopic appearance were examined compared with smears from freshly prepared artificial sputum. Furthermore, smears with different positivities (+/-, 1 +, 2 + and 3 +) were prepared and examined by several trained technicians, and the reproducibility of the original sputum positivity was determined.

RESULTS

Macroscopic and microscopic appearance of smears prepared from long-term stored artificial sputum showed little changes compared with smears of freshly prepared artificial sputum. The positivity of these smears fell in their original grade. A total of 91 smears were prepared from artificial sputum with different positivity and examined by trained technicians. Although 3 out of 36 +/- smears were determined as negative, all of the remaining smears were evaluated correctly.

DISCUSSION

This study confirmed that the artificial sputum and the smears have long-term storage stability and reproducibility in the positivity. These results suggest that the artificial sputum can be widely used to perform external quality assessment in many countries, including high prevalence countries.

The national tuberculosis drug resistance survey in Cambodia, 2000-2001

SETTING

Cambodia has a high incidence of tuberculosis (TB). Hospital-based DOTS was predominant throughout the country from 1994 to 2002.

OBJECTIVES

To determine the prevalence of resistance to four major anti-tuberculosis drugs, isoniazid (INH), rifampicin (RMP), ethambutol (EMB) and streptomycin (SM), among new cases as a baseline before a new National Tuberculosis Programme strategy with decentralised ambulatory DOTS was widely implemented.

DESIGN

A cluster sampling of TB diagnostic centres with probability proportional to the number of new cases in a diagnostic centre in 1999 was used. Intake of cases took place from October 2000 to April 2001.

RESULTS

From 734 isolates collected, drug susceptibility test results were obtained for 638 new cases. The prevalence of resistance to any of four drugs was 10.1% (95%CI 7.7-13). Resistance to INH was 6.1% (95%CI 4.3-8.4) and resistance to RMP 0.6% (95%CI 0.2-1.6). No multidrug-resistant (MDR) case was found among the new cases (95%CI 0.0-0.6). Three of 96 previously treated cases had MDR (3.1%, 95%CI 1.0-9.0).

CONCLUSION

The first survey indicates that the current prevalence of MDR is low. It is necessary to track resistance trends when restructuring a DOTS-based programme.

Nationwide survey on the prevalence of anti-tuberculosis drug resistance in the Republic of Yemen, 2004

OBJECTIVES

To determine the prevalence of resistance to the four major anti-tuberculosis drugs, isoniazid, rifampicin, streptomycin and ethambutol, in Yemen.

METHODS

Cluster sampling with probability proportionate to size was applied. Susceptibility to four major anti-tuberculosis drugs was examined. The proportion method using Löwenstein-Jensen medium or Ogawa medium was carried out.

RESULTS

A total of 790 primary culture isolates from tuberculosis (TB) cases enrolled at the National Tuberculosis Institute, Yemen, were examined. In the confirmation culture at the supranational reference laboratory, 227 of them failed to grow on the secondary culture or were proved to be mycobacteria other than Mycobacterium tuberculosis and were excluded from further analysis. Among 563 cultures, 510 were obtained from new cases and 53 from previously treated cases. The prevalence of resistance to any four drugs was 9.8% (95%CI 7.0-12.5) among new cases and 17.4% (95%CI 12.0-33.5) among previously treated cases. The prevalence of multidrug-resistant TB was 3.0% (95%CI 1.5-4.5) among new cases and 9.4% (95%CI 0.2-18.7) among previously treated cases.

CONCLUSION

The first nationwide prevalence survey on resistance to the four major anti-tuberculosis drugs in Yemen showed a relatively low prevalence of drug-resistant cases, but a high prevalence of multidrug resistance among new cases.

Operational conditions influencing the proficiency of AFB microscopy services in the Philippines

SETTING

The microscopy services of the Philippine National Tuberculosis Programme (NTP).

OBJECTIVE

To investigate how operational conditions in field microscopy centres (MC) affect proficiency.

DESIGN

In 2004, a newly developed external quality assessment system (blinded rechecking) for acid-fast bacilli (AFB) microscopy employing lot quality assurance sampling (LQAS) was introduced into the NTP by the Philippine government. Performance reported by the quality assurance centres (QACs) of the four provinces and four cities was analysed.

RESULT

There was no significant difference in rechecking results between small MCs examining fewer than 166 slides (500 slides/3 sputum samples per suspect) and larger MCs in the provinces. City MCs recorded better performance than those of the provinces. A city QAC covers only five MCs in average, whereas a provincial QAC covers 38. The average distance between city QACs and MCs is much shorter (3.2 km) than in the provinces (60.5 km).

CONCLUSION

The number of MCs to be covered by each QAC and the distances between QAC and MCs are the dominant factors influencing the quality of AFB microscopy. Combining a few neighbouring MCs to reduce the number of MCs and/or provision of sufficient travel funds and timely use of vehicles, particularly in the provinces, are recommended.

Preparation of mycobacteria-containing artificial sputum for TB panel testing and microscopy of sputum smears

SETTING

Panel testing, blinded cross rechecking and on-site evaluation are the three methods for external quality assessment (EQA) of acid-fast bacilli (AFB) smear microscopy. Panel testing can provide data on laboratory capabilities prior to implementing a rechecking programme, assess the current status of laboratory performance and detect problems associated with diagnostic performance. Thus far, two methods for preparing panel test slides have been reported: these use real AFB-positive and -negative sputum treated with sodium hydroxide (NaOH) or N-acetyl-L-cysteine (NALC).

OBJECTIVE

To evaluate the above methods and to develop a new method to prepare panel test slides with artificial sputum.

DESIGN

Panel test slides were prepared using the NaOH and NALC methods. New artificial sputum preparation methods were developed and examined using a cultured monocyte cell line, cultured avirulent mycobacteria and methylcellulose or polyacrylamide gel as substrate. Smears prepared by the four methods were compared.

RESULTS

Panel test slides prepared with NaOH and NALC methods are not macroscopically or microscopically similar to real smears. Our new artificial sputum is similar to real sputum in viscosity and macroscopic and microscopic appearance; it is also consistent in panel positivity grades.

CONCLUSION

The artificial sputum described here could contribute to the EQA and training in tuberculosis laboratories or microscopy centres.

Tuberculosis drug resistance and treatment outcomes under DOTS settings in large cities in the Philippines

SETTING

Two large cities in the Philippines.

OBJECTIVES

To describe the problems of drug-resistant tuberculosis (TB) in an urban setting, with special emphasis on their potential impact on the treatment services provided by the National TB Control Programme.

DESIGN

Cross-sectional survey and cohort analysis of treatment outcomes.

METHODS

All patients with positive sputum smear examination results in Cebu and Mandaue cities during the survey period were included. The survey procedures of the World Health Organization and the International Union Against Tuberculosis and Lung Disease were strictly applied. Treatment outcome data were also collected.

RESULTS

Of 306 cases enrolled, 255 were new cases, 28 were previously treated and for 23 treatment history was unknown. Of the new cases, 72.2% were pan-susceptible to all four first-line anti-tuberculosis drugs. Resistance in new cases was 16.9% to isoniazid (INH), 4.7% to rifampicin (RMP), 3.1% to ethambutol, 18.0% to streptomycin, and 3.9% to at least both INH and RMP (multidrug-resistant [MDR]). Over 90% of the new cases, either pan-susceptible or mono-resistant, were successfully treated with the standard regimen, but four of nine MDR new cases could not be cured.

CONCLUSION

The drug resistance level was high in this population, but treatment outcome using the standard treatment regimen was not seriously affected unless the patients were MDR.

New quantitative methods for evaluation of dynamic changes in QT interval on 24 hour Holter ECG recordings: QT interval in idiopathic ventricular fibrillation and long QT syndrome

OBJECTIVES

To introduce a nomogram of the normal QT interval at various heart rates measured from 24 hour Holter ECG recordings in healthy subjects with respect to age and sex and to use the nomogram to characterise dynamic changes in QT interval in patients with idiopathic ventricular fibrillation (IVF) and the long QT syndrome (LQT).

METHODS

The study group consisted of 422 subjects: 249 healthy men ranging in age from 21-88 years (mean (SD) 47 (20) years) and 173 healthy women ranging in age from 21-85 years (47 (19) years). In addition, seven men with IVF ranging in age from 33-53 years (43 (9) years) and five women with LQT ranging in age from 20-55 years (37 (14) years) were studied. For each subject, QT interval and heart rate were determined automatically from 24 hour Holter ECG digital data-namely, QT interval was measured from signal averaged ECG waves obtained by averaging consecutive sinus beats during each 15 second period over 24 hours. Data were grouped and averaged at an interval of 5 beats/min for heart rates ranging from 46-120 beats/min.

RESULTS

In healthy subjects aged < 50 years and > or = 50 years QT intervals were longer in women than in men. QT intervals were longer in both men and women aged > or = 50 years than in ages < 50 years. From these findings a nomogram of QT interval at varying heart rates adjusted for age (younger group aged < 50 years or older group aged > or = 50 years) and sex was determined. In patients with IVF, QT intervals were significantly shorter at slower heart rates than normal values obtained from the nomogram. In patients with LQT, QT intervals were significantly longer at both faster and slower heart rates than normal values.

CONCLUSIONS

The nomogram of QT interval at varying heart rates adjusted for sex and age could be used to assess dynamic changes of QT interval of various pathological conditions. For example, patients with IVF had shorter QT interval at slower heart rates, a finding suggestive of arrhythmogenicity of this specific syndrome at night. Patients with LQT had prolonged QT interval at specific heart rate ranges depending on their genotype.

The nationwide tuberculosis drug resistance survey in Mongolia, 1999

SETTING

Mongolia, a country in the Western Pacific Region burdened with many cases of tuberculosis, with rapid expansion of DOTS over the last several years.

OBJECTIVE

To determine the prevalence of resistance to major anti-tuberculosis drugs among tuberculosis patients who have never been treated previously.

DESIGN

Sputum specimens were collected from all smear-positive tuberculosis patients identified from 1 November 1998 to 1 May 1999.

RESULTS

Resistance to any of the four major drugs (streptomycin, isoniazid, rifampicin, and ethambutol) was as high as 28.9% (95%CI 24.7-33.5), primarily due to high streptomycin resistance of 24.2% (95%CI 20.3-28.6). Isoniazid resistance was also high, at 15.3% (95%CI 12.1-19.1). Resistance levels to ethambutol and rifampicin were relatively low, at 1.7% (95%CI 0.8-3.5) and 1.2% (95%CI 0.5-2.9), presumably because these drugs were only recently introduced into Mongolia. Multidrug resistance was also rare, at 1.0% (95%CI 0.1-1.8). Drug resistance rates were higher in middle-aged patients than in younger and older age groups combined (P = 0.006). Males tended to have higher resistance than females, although this was of statistically marginal significance (P = 0.08). No significant regional differences in drug resistance were found.

CONCLUSION

While multidrug resistance was rare, isoniazid resistance was very common, which necessitates closer monitoring of the treatment outcomes of individual patients as well as long-term follow-up for drug resistance on a nationwide scale.

Quality control of sputum smear examination in Cebu Province

SETTING

Rural Health Units (RHUs) in Cebu Province, Philippines.

OBJECTIVE

To assess and improve the on-going quality control of tuberculosis activities in Cebu Province.

METHODS

During the period of the study, from January 1996 to December 1997, positive slides (100% in 1996 and 20% or 100% in 1997) and 20% of negative slides selected from all of the slides examined at the RHUs were assessed on the quality of smear preparation. The readings were blindly cross-checked by the provincial assessors.

RESULTS

In 1997, 1) 90% of RHUs participated in the quality control activity; 2) the proportion of good quality smears increased markedly; and 3) the false positive and false negative rates did not change during the period, but most of the false positives were observed among the scanty positives of the field reading, and no false negatives were noted among the heavily positive slides.

CONCLUSION

Although the false positive and negative rates did not decrease during the period, the quality control procedure resulted in marked improvements in smear preparation, a high participation of RHUs in the quality control programme and the elimination of large discrepancies between readers on positive slides in 1997. It is considered to have significantly improved the NTP's smear microscopy service in Cebu Province.

Spontaneous onset of torsade de pointes in long-QT syndrome and the role of sympathovagal imbalance

The net effects of sympathetic and vagal activity on the QT interval and the mode of spontaneous onset of torsade de pointes (TdP) are still unclear in long-QT syndrome. Two patients with long-QT syndrome had syncope while undergoing Holter ECG investigation. The spontaneous onset of TdP in these patients was analyzed with respect to the relation between the RR and QT intervals. Both patients were high-school students (16- and 17-year-old boys) who had been diagnosed as long-QT syndrome and followed up without medical treatment because they had had neither a history of syncope nor arrhythmia induction by treadmill exercise tests. The first episode of syncope in both patients occurred during ordinary daily life and was not related to exercise or psychological stress. The dynamic changes between the RR and QT intervals associated with the spontaneous onset of TdP were analyzed by Holter ECG. Both patients showed sinus tachycardia followed by abrupt sinus bradycardia immediately before the onset of TdP. The enhanced rate of the adaptive response of the QT interval that occurred during the deceleration of the heart rate preceded the onset of TdP. These observations suggest that the complex situation that follows sympathovagal imbalance may have an important role in the dynamic change in the QT interval and initiation of TdP in patients with long-QT syndrome.

Spectral characteristics of human atrial fibrillation waves of the right atrial free wall with respect to the duration of atrial fibrillation and effect of class I antiarrhythmic drugs

The aim of this study was to use fast Fourier transform analysis to clarify the characteristics of human atrial fibrillation (AF) waves with respect to the duration of AF and the effect of class I antiarrhythmic drugs. Twenty-two patients (10 paroxysmal AF, 12 persistent AF) without organic heart disease were studied by conventional electrophysiological methods. Electrograms were recorded from the right atrial free wall during AF and spectral analysis was performed for 35s (16 consecutive 4096-ms epochs with 50% overlap) and the fibrillation cycle length (FCL) was calculated from the peak frequency. Mean FCL and SD were determined from 16-epoch data, and the temporal variability of FCL was defined as the SD of FCL. Paroxysmal AF had a longer mean FCL than persistent AF (178+/-26ms vs 139+/-16 ms, p<0.001) and AF duration had a significant inverse correlation with mean FCL (r=-0.79, p<0.001). The temporal variability of FCL was significantly greater in paroxysmal AF than in persistent AF (p<0.05) and there was a significant positive correlation between the mean FCL and the temporal variability of FCL (r=0.66, p<0.001). In 8 of 18 patients given a class I antiarrhythmic drug (cibenzoline or procainamide), AF was terminated and in those patients the mean FCLs before administration of class I drugs were significantly greater than in patients without AF termination. With respect to mean FCL before drug administration, conversion occurred in 100% of patients with FCL > or =168 ms and in 17% of those with FCL <168 ms. A longer duration of AF shortens the mean FCL, which is consistent with atrial electrical remodeling. Class I drugs prolong the mean FCL above a critical level and will terminate AF, which can be estimated from the mean FCL before drug administration.

Radiofrequency ablation at the coronary sinus ostium interrupts the vagal efferent input to the atrioventricular node in the canine heart

The fat pad at the junction of the inferior vena cava and inferior left atrium is the area of convergence of vagal projections into the atrioventricular node (AVN) region. The present study investigated whether radiofrequency (RF) ablation applied to the area around the coronary sinus (CS) ostium would impair vagal input to the AVN in the canine heart. Twenty-four dogs were anesthetized by sodium pentobarbital and RF energy was delivered at 20W for 5-10s. In the baseline state without vagal stimulation (10Hz, 2ms), the electrophysiological variables did not change significantly after RF ablation. Vagally induced changes in the sinus cycle length and effective refractory period of the right atrium and left ventricle did not differ after RF ablation. However, the effects of vagal stimulation on the AVN function were impaired after RF ablation to the CS area from the ostium to 10mm within the ostium. After ablation was applied to the fast pathway area, the vagally induced changes in the AVN function decreased, but these changes were not affected after RF ablation in the slow pathway area. RF ablation in the vicinity of the CS would attenuate vagal input to the AVN.

Relation of Fibrillatory Wave Amplitude With Hemostatic Abnormality and Left Atrial Appendage Dysfunction in Patients With Chronic Nonrheumatic Atrial Fibrillation

Large left atrium (LA) and LA appendage (LAA) dysfunction are known to relate to cardiogenic thromboembolism, so the present study investigated the relation of the atrial fibrillatory wave (F wave) amplitude to hemostatic markers and LAA function. Transthoracic and transesophageal echocardiographic studies were performed in 82 consecutive patients with chronic, nonrheumatic atrial fibrillation (AF). Patients were divided into 2 groups according to F wave amplitude in lead V1 on the 12-lead ECG: coarse AF (the greatest amplitude of F wave > or =1 mm, n=44) and fine AF (<1 mm, n=38). Plasma levels of thrombin-antithrombin III complex, D-dimer, platelet factor 4 and beta-thromboglobulin were determined. Compared with patients with coarse AF, those with fine AF had lower LAA peak flow velocity (p<0.05) and higher prevalence of embolic cerebral infarction (50% vs 27%, p<0.05). Platelet activity did not differ between the 2 groups; however, plasma levels of thrombin-antithrombin III complex and D-dimer were significantly higher in patients with fine AF than in those with coarse AF (p<0.05). Multiple logistic regression analysis showed that fine AF was independently associated with cerebral embolism. Therefore, the presence of fine F wave in V1 would be a useful marker of LAA dysfunction and hypercoagulability, and indicate a risk for cerebral embolism in patients with chronic, nonrheumatic AF.

[Abnormal Q wave in the right precordial leads unmasked during right bundle branch block in a patient with anteroseptal myocardial infarction: a case report]

Electrocardiography in a 77-year-old woman showed small R waves in leads V1-V3 3 hours after the onset of acute anteroseptal myocardial infarction. Abnormal Q waves appeared in leads V1-V3 only during intermittent right bundle branch block. The normal septal force disappeared after transmural septal infarction and a small force of right ventricle origin became apparent as a small R wave in V1. Right bundle branch block delayed activation of right ventricle, and thereby deleted the initial R wave and unmasked the Q wave of the septal infarction. Appearance of a Q wave in leads V1-V3 with right bundle branch block should not be assumed to reflect the extension of myocardial infarction.

Electrophysiological mechanisms of conversion of typical to atypical atrioventricular nodal reentrant tachycardia occurring after radiofrequency catheter ablation of the slow pathway

This report presents an adult patient with conversion of typical to atypical atrioventricular nodal reentrant tachycardia (AVNRT) after slow pathway ablation. Application of radiofrequency energy (3 times) in the posteroseptal region changed the pattern of the atrioventricular (AV) node conduction curve from discontinuous to continuous, but did not change the continuous retrograde conduction curve. After ablation of the slow pathway, atrial extrastimulation induced atypical AVNRT. During tachycardia, the earliest atrial activation site changed from the His bundle region to the coronary sinus ostium. One additional radiofrequency current applied 5 mm upward from the initial ablation site made atypical AVNRT noninducible. These findings suggest that the mechanism of atypical AVNRT after slow pathway ablation is antegrade fast pathway conduction along with retrograde conduction through another slow pathway connected with the ablated antegrade slow pathway at a distal site. The loss of concealed conduction over the antegrade slow pathway may play an important role in the initiation of atypical AVNRT after slow pathway ablation.

Effects of unilateral stellate ganglion block on the spectral characteristics of heart rate variability

The effect of unilateral stellate ganglion block on cardiovascular regulation remains controversial, so the present study used power spectral analysis of heart rate variability to investigate its effect on the autonomic neural control of the heart. In 20 young healthy volunteers (mean age: 25 years), heart rate variability was determined before and after unilateral stellate ganglion block (right side 11, left side 9) using 8 ml of 1% mepivacaine during supine rest. Using autoregressive spectrum analysis, power spectra were quantified by measuring the area in 3 frequency bands: high-frequency power (lnHF, parasympathetic influence) from 0.15 to 0.40 Hz, low-frequency power (lnLF, predominantly sympathetic influence) from 0.04 to 0.15 Hz, and total-frequency power (lnTF) less than 0.40 Hz. Right stellate ganglion block decreased not only the lnLF component from 6.55+/-0.84 to 5.77+/-0.47 but also the lnHF component from 4.40+/-0.95 to 3.42+/-1.12 (p<0.05). In contrast, left stellate ganglion block changed neither the lnLF nor the lnHF component. The lnTF component was also decreased significantly by right stellate ganglion block from 7.80+/-0.95 to 7.01+/-0.36 (p<0.05), but was unchanged following left stellate ganglion block. Neither right nor left stellate ganglion block induced any significant change in both the RR and corrected QT intervals. However, changes in the RR interval induced by right stellate ganglion block showed significant positive correlation with changes in lnHF (p<0.005) and lnTF (p<0.05). These results suggest that (1) autonomic innervation to the sinus node is mainly through the right-sided stellate ganglion, (2) pharmacological right-sided stellate ganglion block may attenuate not only sympathetic but also parasympathetic activity and (3) following right stellate ganglion block the decrease in both the sympathetic and parasympathetic influence on the sinus node may inconsistently counterbalance and change the RR interval.

Successful radiofrequency catheter ablation of incessant ventricular tachycardia with a delta wave-like beginning of the QRS complex

Ventricular tachycardia with a delta wave-like beginning of the QRS complex is considered to be refractory to endocardial catheter ablation because it originates from the epicardial region. A 45-year-old woman had incessant ventricular tachycardia with a delta wave-like beginning of the QRS complex which was resistant to several antiarrhythmic drugs. The origin of the arrhythmia was at the mitral annulus on the antero-lateral left ventricular wall. The earliest endocardial activation preceded the QRS complex by 18 msec. After 7 sec of endocardial radiofrequency application ventricular tachycardia was terminated. During a 2 year follow-up ventricular tachycardia did not recur and only small numbers of premature ventricular contractions (< 100/day) were noted. VT with delta wave-like QRS morphology which originates from the basal region of the ventricle may be treated successfully with radiofrequency catheter ablation using an endocardial approach.

Changes in autonomic nervous activity after catheter ablation of right ventricular outflow tract tachycardia

Idiopathic right ventricular outflow tract (RVOT) tachycardia is prone to occur when sympathetic nervous activity increases. The effects of catheter ablation on the arrhythmia may be modified by changes in the sympathovagal balance induced by the ablation. In 8 patients with RVOT tachycardia, analyses of heart rate variability (HRV) were performed before, early (1-3 days, POST1) and late (7-14 days, POST2) after the ablation. From 24-h ambulatory Holter monitoring, RR intervals of a 2-h period during sleep (00.00-06.00 h) were analyzed. MSSD and pNN50 were increased along with a decrease in the frequency of ventricular arrhythmias at both POST1 and POST2 after successful ablation. In contrast, high frequency power (HF) was increased, and low frequency power (LF) and LF/HF were decreased only at POST2 in the 8 patients. In 4 patients in whom the initial ablation had been unsuccessful, the indices of HRV did not change significantly after the unsuccessful ablation, but after successful ablation they changed as in the other 4 patients. After successful catheter ablation of the RVOT tachycardia, sympathetic nervous activity was decreased and parasympathetic nervous activity was increased along with decrease in the frequency of ventricular arrhythmias. The presence of ventricular tachyarrhythmia could, therefore, elicit sympathetic predominance and consequently modify arrhythmogenesis.

Circadian variation of idiopathic ventricular tachycardia originating from right ventricular outflow tract

We determined circadian variation of isolated ventricular premature complexes (VPCs), 2 to 4 consecutive VPCs, and ventricular tachycardia (5 consecutive VPCs) originating from the right ventricular outflow tract in patients without apparent structural heart diseases. There was apparent circadian variation with 2 prominent peaks for these ventricular arrhythmias, and blockade abolished ventricular tachycardia and attenuated the circadian variation of consecutive VPCs.

ST segment elevation in the right precordial leads induced with class IC antiarrhythmic drugs: insight into the mechanism of Brugada syndrome

We evaluated two patients without previous episodes of syncope who showed characteristic ECG changes similar to Brugada syndrome following administration of Class IC drugs, flecainide and pilsicainide, but not following Class IA drugs. Patient 1 had frequent episodes of paroxysmal atrial fibrillation resistant to Class IA drugs. After treatment with flecainide, the ECG showed a marked ST elevation in leads V2 and V3, and the coved-type configuration of ST segment in lead V2. A signal-averaged ECG showed late potentials that became more prominent after flecainide. Pilsicainide, a Class IC drug, induced the same ST segment elevation as flecainide, but procainamide did not. Patient 2 also had frequent episodes of paroxysmal atrial fibrillation. Pilsicainide changed atrial fibrillation to atrial flutter with 2:1 ventricular response, and the ECG showed right bundle branch block and a marked coved-type ST elevation in leads V1 and V2. After termination of atrial flutter, ST segment elevation in leads V1 and V2 continued. In this patient, procainamide and quinidine did not induce this type of ECG change. In conclusion, strong Na channel blocking drugs induce ST segment elevation similar to Brugada syndrome even in patients without any history of syncope or ventricular fibrillation.

Different effects of class Ic and III antiarrhythmic drugs on vagotonic atrial fibrillation in the canine heart

Effects of class Ic drug pilsicainide and class III drug MS-551 were determined in the canine model of atrial fibrillation (AF) induced under vagal stimulation. Pilsicainide injected intravenously at a dose of 1.0 mg/kg over 3 min terminated AF in six of six dogs. After pilsicainide injection, the effective refractory period (ERP) of the right atrium (RA) increased (104 +/- 22 to 122 +/- 31 ms; p < 0.05), and intraatrial conduction time (CT) increased (24%; p < 0.05) in the RA during vagal stimulation. Wavelength index (WLI; ERP/CT), an estimate of the wavelength for reentry, was decreased slightly but significantly (-2%; p < 0.05) in the RA after pilsicainide. MS-551 injected intravenously at a dose of 0.5 mg/kg over a 3-min period terminated AF in three of eight dogs. An additional dose of 0.5 mg/kg of MS-551 terminated AF in three of the remaining five dogs. After MS-551 injection, ERP increased (100 +/- 30 to 143 +/- 28 ms; p < 0.05), but CT remained unchanged in the RA, and therefore WLI was increased significantly (48%; p < 0.01). Immediately before termination of AF with test drugs, mean AF intervals (FF intervals) increased, whereas the standard deviation of FF intervals did not change significantly. In conclusion, both pilsicainide and MS-551 effectively terminated vagotonic AF after an increase in FF intervals. However, changes in WLI were different between the two test drugs. Vagotonic AF could, therefore, be terminated either by prolongation of ERP or suppression of conduction with antiarrhythmic drugs.

Role of sympathovagal balance in the initiation of idiopathic ventricular tachycardia originating from right ventricular outflow tract

VT originating from the right ventricular outflow tract (RVOT) is prone to occur when sympathetic nervous activity is increased. beta-Blockade is, therefore, effective in suppressing this VT. The purpose of this study was to determine the role of sympathovagal balance assessed by heart rate variability (HRV) in the spontaneous initiation of repetitive premature ventricular contractions (PVCs) and VT (five or more consecutive PVCs) arising from RVOT in seven patients without structural heart diseases. Frequency-domain measures of HRV were determined by analyzing 24-hour Holter electrocardiographic recording with the maximum entropy method over a 1,280-second period immediately before the onset of 35 single PVCs, 26 episodes of 2-4 consecutive PVCs, and 21 episodes of VT. High frequency component (HF: 0.15-0.40 Hz) was used as an index of parasympathetic activity, and the ratio of low frequency component (LF: 0.04-0.15 Hz) to HF (LF/HF ratio), as an index of sympathovagal balance. NN50(%), a time-domain variable of parasympathetic activity, was also determined. Mean RR interval and any measures of HRV did not change significantly before single PVCs. Mean RR interval shortened and HF decreased prior to repetitive PVCs and VT. The LF/HF ratio, however, increased only before the onset of VT. NN50(%) tended to decrease before repetitive PVCs and decreased significantly before VT. With propranolol (30-60 mg/day), frequency of repetitive PVCs was suppressed from 2,048 +/- 1,201 to 746 +/- 658/day and VT was totally abolished, but frequency of single PVCs did not change significantly. In conclusion, sympathetic predominance plays an important role in the initiation of repetitive PVCs and VT originating from RVOT in patients without structural heart diseases.

Essential pathway of reentry in the canine model of atrial flutter. Analysis using radiofrequency ablation

In humans, the isthmus in the low right atrium between the tricuspid annulus and the inferior vena cava or the coronary sinus ostium is a well-established target of catheter ablation of common atrial flutter. In the canine model of atrial flutter with a Y-shaped incision, the tricuspid annulus was thought to constitute the essential reentrant pathway. The present study was designed to determine whether the supravalvular tissue around the tricuspid annulus is essential to atrial flutter in the canine model with an intercaval obstacle on the basis of the results of radiofrequency ablation. Epicardial approach of radiofrequency ablation was tested in 4 groups of dogs. Group A (5 dogs): Single application of radiofrequency energy (20 W) for 5 sec to the mid right atrial free wall. Group B (9 dogs): One to two applications to the tricuspid annulus. A ligature was also placed encircling the tricuspid annulus from the supravalvular atrial tissue to the subvalvular ventricular tissue. Group C (9 dogs): Linear transverse applications to the mid right atrial free wall between the tricuspid annulus and the intercaval obstacle. Group D (10 dogs): The isthmus between the inferior vena cava and the tricuspid annulus was ablated. After the experiment, the heart was excised for anatomical and histological studies. Atrial flutter was never abolished in all dogs in Groups A and B. A ligature encircling the tricuspid annulus also failed to terminate atrial flutter in 2 dogs tested. In contrast, atrial flutter was successfully abolished in 6 dogs (67%) of Group C and in 7 dogs (70%) of Group D. Total energy delivered was significantly higher in Group C than in Group D (364 +/- 133 versus 139 +/- 65 joules, p < 0.003). The total energy required for successful ablation was related to the cross sectional area of the ablation site (r = 0.55, p < 0.05). These results indicate that the tricuspid annulus is not an essential part of the reentrant pathway in the canine model of atrial flutter with an intercaval obstacle. The entire atrial tissue between the anatomical barriers could be involved in the reentrant pathway, and should therefore be ablated transmurally for successful ablation.

Electrophysiologic effects of SD-3212, a new class I antiarrhythmic drug, on canine atrial flutter and atrial action-potential characteristics

SD-3212 (levo-semotiadil fumarate) is a newly developed compound that exhibits potent antiarrhythmic activity because of its inhibitory action on sodium and calcium channels. In animal models, SD-3212 suppressed ventricular tachyarrhythmias, but the effects of this drug on atrial tachyarrhythmias have not been reported. We investigated the electrophysiologic effects of SD-3212 on canine atrial flutter induced after placement of the intercaval obstacle and on atrial action-potential characteristics. In all seven dogs, SD-3212 (1.9 +/- 0.3 mg/kg) terminated atrial flutter after significant increase in atrial flutter cycle length from 126 +/- 5 to 166 +/- 14 ms (increase, 31 +/- 8%; p < 0.005). SD-3212 increased right atrial effective refractory period (RAERP) significantly from 126 +/- 7 to 149 +/- 11 ms at a basic cycle length of 300 ms. The increases in RAERP after SD-3212 at basic cycle lengths of 300, 200, and 150 ms did not differ (increase, 18 +/- 4%, 17 +/- 3%, and 19 +/- 3%, respectively). Interatrial conduction time (IACT) was prolonged after SD-3212 from 63 +/- 4 to 81 +/- 6 ms (increase, 31 +/- 6%) at a basic cycle length of 150 ms. Prolongation of IACT was frequency dependent. The plasma concentration of SD-3212 after the termination of atrial flutter was 187 +/- 56 ng/ml in four dogs tested. In vitro study by using standard microelectrode techniques showed SD-3212 at concentrations of 1-3 microM significantly prolonged action-potential duration at 90% repolarization. Vmax was decreased by SD-3212 in a concentration-dependent manner (0.3-3 microM), and the inhibitory effect on Vmax was greatest at the highest stimulation frequency of 3.3 Hz. These results indicate that a new antiarrhythmic drug, SD-3212, is effective in interrupting canine atrial flutter, possibly by suppressing atrial conduction, and might be effective for the treatment of clinical atrial tachyarrhythmias.

Electrophysiologic mechanisms of adverse effects of class I antiarrhythmic drugs (cibenzoline, pilsicainide, disopyramide, procainamide) in induction of atrioventricular re-entrant tachycardia

We evaluated the electrophysiological mechanisms of adverse effects of class I antiarrhythmic drugs (cibenzoline in seven patients, pilsicainide in two, and disopyramide in two, and procainamide in three) in the induction of orthodromic atrioventricular re-entrant tachycardia (AVRT). In 14 patients (10 males, 4 females; mean age 37 +/- 18 years) who had inducible AVRT despite the administration of class I drugs, electrophysiological effects of class I antiarrhythmic drugs were evaluated using programmed electrical stimulation techniques. In 4 out of 6 patients with a manifest accessory pathway, class I drugs induced unidirectional conduction block of the accessory pathway (antegrade conduction block associated with preserved retrograde conduction) and enhanced the induction of AVRT with atrial extrastimulation. In eight patients with a concealed accessory pathway, the outward or inward expansion of the tachycardia induction zone was observed in patients who had greater prolongation of the conduction time than the refractory period of the retrograde accessory pathway after class I drugs. During ventricular extrastimulation, the induction of bundle branch re-entry after class I drugs initiated the AVRT in patients with either manifest or concealed accessory pathways. We conclude that the adverse effects of class I drugs are mainly due to induction of unidirectional retrograde conduction of the manifest accessory pathway and the greater prolongation of the retrograde conduction time of the concealed accessory pathway than the refractory period, regardless of the sub-classification of class I drugs.

Left ventricular dimensions and autonomic balance during head-up tilt differ between patients with isoproterenol-dependent and isoproterenol-independent neurally mediated syncope

OBJECTIVES

This study sought to elucidate differences in mechanisms of neurally mediated syncope between patients with syncope induced by head-up tilt alone and those requiring isoproterenol infusion to induce syncope during head-up tilt.

BACKGROUND

Some patients with neurally mediated syncope require isoproterenol to induce syncope during head-up tilt (isoproterenol dependent), and others do not (isoproterenol independent). Differences in mechanisms between these two groups have not been well elucidated.

METHODS

A 60 degrees head-up tilt test was performed in 13 patients with isoproterenol-independent syncope (Group I, mean [+/- SD] age 28 +/- 12 years), 14 patients with isoproterenol-dependent syncope (Group II, mean age 34 +/- 14 years) and 20 control subjects without syncope (Group III, mean age 32 +/- 12 years). Left ventricular size and contractility were determined by echocardiography, and sympathovagal balance was determined with power spectral analysis of heart rate variability using a maximal entropy method.

RESULTS

Group I patients had smaller left ventricular dimensions than Group II and III during baseline tilt. During head-up tilt with isoproterenol infusion (0.01 to 0.04 microgram/kg body weight per min), left ventricular dimensions decreased to the same extent in Groups II and III, but fractional shortening was greater in Group II than in Group III at the end of the tilt. The ratio of low (0.05 to 0.15 Hz) to high frequency (0.15 to 1.0 Hz) component became greater in Group I than in Groups II and III during the last period of baseline tilt. However, the ratio was greater in Group II than in Group III during the last period of the tilt with isoproterenol.

CONCLUSIONS

Patients with isoproterenol-independent syncope had an exaggerated decrease in left ventricular size and sympathetic predominance preceding syncope during head-up tilt. In contrast, in patients with isoproterenol-dependent syncope, similar changes in autonomic nervous balance were evident only during isoproterenol infusion in addition to head-up tilt.

[A transient sinus arrest after right stellate ganglion block--assessment of autonomic function by heart rate spectral analysis]

We experienced a case of sinus arrest probably induced by right stellate ganglion block (SGB). A healthy medical student volunteered in our study of the cardiac autonomic nervous system and received the SGB. After the Holter ECG had been attached, the SGB was performed with mepivacaine 8 ml. Horner's sign was observed after about 3 minutes. A transient (15 s) sinus arrest occurred suddenly after about 6 minutes of the tilt test probably due to a vasovagal reflex, and the subject lost consciousness. From spectral analysis of the Holter ECG recording, the right SGB may be closely involved in the induction of the sinus arrest. Our present case suggests that sinus arrest may occur if a patient stands up after right SGB.

Long-term outcome of operative treatment of focal atrial tachycardia

BACKGROUND

This study examined the long-term clinical outcome of patients with focal atrial tachycardia who were treated surgically. Focal atrial tachycardia is a relatively rare arrhythmia that is often difficult to control with conventional medical therapy. Therapeutic modalities are not well defined because of the scarcity of long-term data of treated patients, including pathologic findings.

STUDY DESIGN

Nine patients, six men and three women, ranging in age from 16 to 50 years (mean of 34 +/- 14 years), underwent operative treatment for focal atrial tachycardia. The average rate of tachycardia was 167 +/- 22 beats per minute. All patients were treated with antiarrhythmic drugs (mean 2.9 drugs per patient). Concomitant operative procedures were performed upon four patients, including division of the accessory atrioventricular pathway for the Wolff-Parkinson-White syndrome in two patients, plication of the right atrium for idiopathic right atrial dilatation in one patient, and a closure of the atrial septal defect in one patient. Focal ablation was performed in all instances.

RESULTS

There was no early or late death nor postoperative complications. Atrial tachycardia disappeared and there were no episodes of recurrent tachycardia postoperatively during the mean follow-up period of 67 +/- 38 months. Histopathologic findings from four patients revealed a sinus node-like structure, diffuse chronic epimyocarditis, focal myocarditis, and fascicular disarray lesions.

CONCLUSIONS

Excellent long-term result were obtained in patients with focal atrial tachycardia who were treated operatively. Early operative intervention is preferable before the occurrence of impaired ventricular function. From the histopathologic findings, operative therapy should be selected in patients with diffuse atrial lesions.

[Usefulness of body surface potential maps to determine ablation site in patients with WPW syndrome]

We studied body surface potential maps (BSPM) in patients with WPW syndrome before surgical ablation. These BSPM were compared with computerized epicardial mapping using sock and snap electrode. In most patients the location of minima in the early delta wave was a simple and accurate index of the site of accessory pathway. In 4 patients BSPM was useful for the diagnosis of presence of bilateral accessory pathways. We conclude that BSPM may be also useful to determine ablation site of radiofrequency catheter ablation.

Electrophysiologic effects of intravenous E-4031, a novel class III antiarrhythmic agent, in patients with supraventricular tachyarrhythmias

The electrophysiologic effects of intravenous (i.v.) E-4031, a new class III antiarrhythmic drug, were evaluated in 15 patients with supraventricular tachyarrhythmias [11 men, 4 women; mean age 41 +/- 19 (SD) years]. Eleven patients had accessory atrioventricular (AV) pathways, and 4 patients with no accessory pathway had paroxysmal atrial fibrillation. Electrophysiologic studies were performed before and after E-4031 administration (loading infusion 9 micrograms/kg for 5 min + maintenance infusion 0.15 microgram/kg/min). QT and QTc intervals were significantly prolonged by E-4031 from 0.40 +/- 0.03 (mean +/- SD) to 0.46 +/- 0.03 s (p < 0.0001) and from 0.43 +/- 0.03 to 0.49 +/- 0.04 s (p < 0.0001), respectively. No effect was observed on RR interval, PR interval, QRS duration, or AH and HV intervals. The effective refractory periods (ERPs) of the right atrium and ventricle were significantly prolonged from 219 +/- 27 to 236 +/- 26 ms (p < 0.001) and from 230 +/- 12 to 249 +/- 11 ms (p < 0.001), respectively. The ERP of the AV node did not change significantly after E-4031 administration. In patients with ventricular preexcitation, E-4031 significantly prolonged the ERP of the antegrade accessory pathway conduction from 340 +/- 101 to 362 +/- 106 ms (p < 0.001), but not retrograde accessory pathway conduction. AV reentrant tachycardia was induced in 3 of 11 patients with an accessory pathway, and repetitive atrial firing was induced in 3 of 4 patients with paroxysmal atrial fibrillation. E-4031 could prevent repetitive atrial firing in only 1 patient and could not prevent induction of AV reentrant tachycardia.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of acute ischemia on anisotropic conduction in canine ventricular muscle

The effects of acute ischemia on conduction velocities in the longitudinal (theta L) and transverse (theta T) fiber axis were determined from epicardial activation patterns, recorded with 48 bipolar electrodes (plaque electrode, 25 x 35 mm) on the left anterior ventricular wall of eight dogs and the posterior wall of seven dogs. During left ventricular stimulation (cycle length = 300 msec) in the center of the plaque electrode, theta L, theta T, and the ratio of longitudinal to transverse conduction velocities (theta L/T) were measured before and 2 to 5 minutes after occlusion of the left anterior descending coronary artery or the left circumflex coronary artery. During the control state theta L was greater than theta T demonstrating anisotropic properties of cardiac muscle, not only in the anterior but also in the posterior wall. During acute ischemia theta L and theta T were decreased from the control value and theta T was decreased by a greater extent than theta L resulting in an increase in theta L/T from 1.83 +/- 0.31 (mean +/- SD) to 2.19 +/- 0.36 in the anterior wall and from 1.58 +/- 0.17 to 1.92 +/- 0.28 in the posterior wall. During ventricular fibrillation some lines of conduction block were parallel to the long axis of epicardial muscle fiber bundle and the others were perpendicular. In conclusion, acute ischemia increased anisotropic conduction (theta L/T) in the epicardial ventricular muscle mainly due to greater reduction in theta T, in the anterior and the posterior wall. This augmented anisotropic ventricular conduction may have some relation to the initiation of ventricular fibrillation during acute ischemia.

Effects of diltiazem on concealed atrioventricular nodal conduction in relation to ventricular response during atrial fibrillation in anesthetized dogs

By means of a new quantitative index for concealed conduction, we evaluated the effects of diltiazem on atrioventricular (AV) node concealment and correlated this index with the variability of the ventricular response during atrial fibrillation in 16 anesthetized mongrel dogs. After determination of the atrial effective refractory period (ERP), AV nodal ERP (AVNERP), concealment zone, and concealment index (AVNERP of blocked atrial extrasystole/AVNERP of conducted atrial extrasystole), the R-R intervals during atrial fibrillation induced by electrical stimulation were measured. Both low (0.1 mg/kg) and medium (0.2 to 0.4 mg/kg) doses of diltiazem prolonged the AVNERP and increased the mean R-R interval during atrial fibrillation. Only medium doses of diltiazem increased the degree of concealed conduction in the AV node and accentuated the variability of R-R intervals. There was a good positive correlation between the variability of the ventricular response during atrial fibrillation and the concealment index. In conclusion, medium doses of diltiazem are more effective in reducing heart rate during atrial fibrillation than a low dose. However, medium doses also increase the degree of concealed conduction in the AV node and enhance the irregularity of the ventricular response during atrial fibrillation. Measurement of the concealment index is useful for quantitating the degree of concealed conduction in the AV node, which is actually an important determinant of the ventricular response during atrial fibrillation.

Transient terminal U wave inversion as a more specific marker for myocardial ischemia

Transient U wave inversion can be caused either by regional myocardial ischemia or by an elevation of systemic blood pressure. The characteristics of U wave inversion during chest pain attacks in 21 patients with variant angina were compared with those observed in 38 patients with hypertension without apparent ischemic heart disease. Differentiation was possible according to the ECG phase in which U wave inversion appeared. U wave inversion was considered to be significant if there was a discrete negative deflection of more than 0.05 mV within the TP segment. U wave inversion proceeded to positive deflection of U wave in patients with hypertension without ischemic heart disease (initial U wave inversion). In contrast, inverted U wave occurred after positive U wave deflection during attacks in patients with variant angina (terminal U wave inversion). When cold pressor test was performed in patients with variant angina during treatment with calcium entry blockers, no patient had either anginal attacks or ischemic ST-segment deviation, but 9 of 21 patients (43%) had transient initial U wave inversion, which was followed by positive U wave deflection. U wave inversion can be classified as initial U wave inversion and terminal U wave inversion according to the phasic relationship to positive U wave deflection; the latter is observed in association with regional myocardial ischemia. The former seems to be related to elevated blood pressure rather than to myocardial ischemia.

Two different reentrant circuits of ventricular tachycardia in a patient with an extensive anterior infarction: evaluation using electrical catheter ablation techniques

Two morphologically distinct sustained ventricular tachycardias were initiated by programmed stimulation during attempted catheter ablation in a patient with an old anterior myocardial infarction. Right bundle branch block configuration of ventricular tachycardia, which was identical to the spontaneously occurring tachycardia, was initiated and displayed fragmented mid-diastolic potential at the apicolateral left ventricular site. Evidence of a critical slow conduction area was observed during delivery of electrical stimuli to this area. Following a 150-joule electrical shock delivered to this area, right bundle branch block pattern of ventricular tachycardia was no longer inducible but a new sustained monomorphic ventricular tachycardia with left bundle branch block pattern was initiated. The mid-diastolic fragmented activity at the ablation site became electrical activation of bystander area that was not participating in the left bundle branch block type of the ventricular tachycardia circuit. The critical slow conduction area was identified at the apicoseptal left ventricular site that was separated more than 5 cm from the ablation site. We speculate that two morphologically distinct sustained monomorphic ventricular tachycardias may be due to two different reentrant circuits and not the different expression of the same circuit.

Effects of chronotropic responsive cardiac pacing on ventilatory response to exercise in patients with complete AV block

To identify the effect of chronotropic responsive cardiac pacing on the ventilatory response to exercise, ten selected patients with complete atrioventricular block underwent paired cardiopulmonary exercise tests in fixed rate ventricular (VVI) and dual chamber (DDD) or rate responsive ventricular (VVIR) pacing modes. Compared to VVI pacing, DDD or VVIR pacing increased peak oxygen uptake (P < 0.005) and augmented anaerobic threshold (P < 0.001). In eight patients, dyspnea was the major symptom limiting exercise with VVI pacing and this was markedly attenuated with DDD or VVIR pacing. In all patients, ventilation (VE) and the ratio of ventilation to CO2 production (VE/VCO2) were consistently higher with VVI pacing during exercise. To compare the response of the two pacing modes at the same workloads in an aerobic condition, we measured ventilatory variables 1 minute prior to the anaerobic threshold obtained with VVI pacing. When DDD or VVIR pacing was compared with VVI pacing, VE and VE/VCO2 significantly decreased from 20.5 +/- 5.3 L/min to 18.3 +/- 5.0 L/min (P < 0.005) and from 35.9 +/- 5.8 to 31.9 +/- 5.0 (P < 0.001), respectively. Respiratory frequency rose significantly more with VVI pacing (P < 0.001) despite an unchanged tidal volume. Although peak VE did not differ between the two pacing modes, VE/VCO2 at the peak exercise increased significantly more with VVI pacing (P < 0.005). Respiratory frequency also rose more with VVI pacing (P < 0.005) and tidal volume did not change. This study suggests that chronotropic responsive cardiac pacing attenuates the exertional dyspnea by improving the ventilatory response to exercise as well as increasing the cardiac output in patients with complete atrioventricular block.

Electrophysiologic effects and efficacy of cibenzoline in patients with supraventricular tachycardia

Electrophysiologic effects of intravenous (i.v.) cibenzoline were evaluated in 18 patients with accessory pathways or dual atrioventricular (AV) nodal pathways (12 men and 6 women with a mean age of 44 +/- 18 years). Twelve patients had accessory AV pathways, including 6 patients with a manifest accessory pathway. Six patients had AV nodal reentrant tachycardia (AVNRT). Electrophysiologic studies were performed before and after cibenzoline (1.4 mg/kg i.v.) infusion for 5 min. Sinus cycle length did not change significantly after cibenzoline administration. Cibenzoline increased both the AH (85 +/- 20 vs. 91 +/- 21 ms, p less than 0.05) and HV intervals (41 +/- 10 ms vs. 53 +/- 11 ms, p less than 0.001). Neither the atrial nor ventricular effective refractory period (ERP) was altered by cibenzoline. Complete block in the accessory pathway occurred antegradely in 4 patients and retrogradely in 1 patient. Cibenzoline prevented induction of AV reentrant tachycardia (AVRT) in 3 of 8 patients with sustained orthodromic AVRT by abolishing retrograde accessory pathway conduction or prolonging the retrograde accessory pathway ERP. Of 5 patients who continued to have inducible AVRT before and after cibenzoline administration, the tachycardia cycle length was increased in 3, mainly due to the increase in retrograde accessory pathway conduction time. Cibenzoline prevented induction of sustained AVNRT in 4 of 5 patients by prolonging the minimum pacing cycle length, maintaining 1:1 ventriculoatrial (VA) conduction through the retrograde fast AVN pathway or shortening the antegrade fast AVN pathway ERP equal to the slow AVN pathway. In one patient who had an uncommon type of AVNRT, sustained tachycardia was induced by cibenzoline.(ABSTRACT TRUNCATED AT 250 WORDS)

Active and passive electrical properties of isolated canine cardiac Purkinje fibers under conditions simulating ischaemia: effect of diltiazem

The effect of a calcium channel blocker diltiazem on the electrical properties of canine Purkinje fibers superfused in a milieu similar to that occurring in acute myocardial ischaemia was studied. Action potential parameters, passive electrical properties, and conduction velocity were measured using conventional microelectrode techniques. Superfusion with glucose-free Tyrode's solution containing 9 mM K+, gassed with 100% N2 at pH = 6.5 ('ischemic solution') significantly reduced the maximal diastolic potential, action potential duration, maximal upstroke velocity, conduction velocity and length constant, while input resistance and longitudinal resistance were elevated and membrane resistance remained unchanged. Diltiazem (1 microM) alone reduced only the action potential duration, while all other parameters were unaffected. Pretreatment with diltiazem did not fully prevent the effects of ischemic superfusion; however, the ischaemia-induced decrease in length constant was not significant in the presence of diltiazem. In addition, the increase in longitudinal resistance during ischaemia was significantly reduced following diltiazem pretreatment. This decrease in longitudinal resistance may contribute to the improvement of ischaemia-induced conduction delay observed in intact animals and may be related to a reduction of ischaemia-induced increase in intracellular free Ca2+.