1st Degree Atrioventricular Block Research Articles

Atrial pacing site and atrioventricular conduction in patients paced for sinus node disease.

Unnecessary ventricular pacing in sinus node disease (SND) must be avoided. To test the hypothesis that in SND, with or without 1st degree atrioventricular (AV) block, cumulative percent ventricular pacing (cum%VP) can be limited by low right atrial septal (LRAS) instead of right atrial appendage (RAA) pacing. We studied 102 dual-chamber pacemaker recipients with SND. The PQ interval on 12-lead electrocardiogram and the atrial paced to ventricular sensed interval (Ap-Vs) during LRAS and RAA pacing were measured and compared at implantation, 3 months and 1 year of follow-up. Group 1 included 62 patients with baseline PQ interval <200milliseconds during LRAS (n = 28) versus RAA (n = 34) pacing. Group 2 included 40 patients with baseline PQ ≥200 milliseconds during LRAS (n = 20) versus RAA (n = 20) pacing. cum%VP were measured at 3 months and 1 year. The characteristics and AV conduction properties were similar and the Ap-Vs interval was significantly shorter in the LRAS than in the RAA pacing group up to 1 year (193 ± 32 milliseconds vs. 220 ± 27 milliseconds in Group 1; P = 0.003, 222 ± 41 milliseconds vs. 281 ± 30 milliseconds in Group 2; P < 0.001). While cumulative percent atrial pacing was consistently similar, cum%VP was significantly smaller during LRAS than RAA pacing (1 ± 1% vs. 8 ± 18% in Group 1; P = 0.03, 7 ± 10% vs. 48 ± 38% in Group 2; P < 0.001). Similar observations were made with or without left atrial (LA) enlargement. Compared with RAA, LRAS pacing showed shorter AV interval in SND patients with or without 1st degree AV block and LA enlargement. This beneficial effect persisted through 1-year follow-up, and decreased cum%VP significantly.

Coronary Artery to Right Atrium Fistula Associated With First Degree Atrioventricular Block: A Rare Association.

A 40 year-old man with no significant past history except for asymptomatic 1st degree heart block presented for general health screen. Clinical examination revealed a loud continuous murmur with diastolic accentuation in the left precordium, noncollapsing pulse, and no differential pulses in the upper and lower limbs. The ECG showed normal sinus rhythm with PR interval of 220 milliseconds. Transthoracic echocardiogram (Figure ​(Figure1)1) showed a dilated right coronary artery that was enlarged, forming multiple saccular aneurysms distally that drain into the roof of right atrium. The right heart was normal in size and function. CT angiogram (Figure ​(Figure2)2) later confirmed the presence of a coronary artery fistula from the right coronary artery draining into the right atrium. Right coronary artery is dilated and the distal segment of the RCA is tortuous and aneurismal. Nuclear myocardial perfusion imaging showed no inducible ischemia during exercise stress. He declined cardiac catheterization, and was advised for corrective surgery. This case illustrated a rare saccular aneurysm formation in a right coronary artery to right atrium (coronary-cameral) fistula associated with 1st degree atrioventricular (AV) block. Coronary arteriovenous fistula (CAVF) arises as a persistence of sinusoidal connections between the lumens of the primitive tubular heart in the early embryologic period. It is reported in 0.1%–0.2% of all cases of selective coronary angiography[1]. Most fistulae originate from the right coronary artery (60%) and terminate in the right side of the heart such the right ventricle or atrium, coronary sinus, and pulmonary vasculature. Most often congenital, a CAVF may rarely arise as a consequence of surgical complication, endomyocardial biopsy, invasive procedures[2, 3] or penetrating trauma. It could cause myocardial stealing due to run-off from the coronary vasculature to a low-pressure receiving cavity. Coronary artery that feeds the fistula progressively dilates, leading to complications of frank aneurysmal formation and mural thrombosis. Hence, all CAVF ought to be closed except for trivial ones. The evolution of 1st degree AV block in our case may reflect a flow limitation to atrioventricular (AV) node directly caused by the CAVF. CT angiogram has now emerged as an excellent imaging technique to delineate the lesion anatomy[4-6] CAVF generally requires closure. Transcatheter embolization techniques using coils, bags, or other devices can be performed successfully and safely, and are now the treatment modality of choice [7]. CAVFs with multiple connections, circuitous routes, and acute angulations may however be better treated surgically. Figure 1. Transthoracic echocardiogram performed showed the tubular structure coming off the right coronary cusp (bold arrow, image A); saccular formations adjacent to the aortic root in short axis and apical 4 chamber view (bold arrows, image B and C); as well as predominantly diastolic turbulent flow within the saccular formations (image D). Figure 2. Cardiac multidetector computed tomography (MDCT) angiogram volume rendering reconstruction of cardiac structures (images A-B) and multiplanar reconstruction images (images C-D) showed a dilated, tortuous right coronary artery (RCA) that eventually gave off a fistulous connection into the right atrium (RA).

Cardiac conduction system abnormalities in ankylosing spondylitis: a cross-sectional study

BackgroundCardiac conduction disturbances are common in spondyloarthropathies such as ankylosing spondylitis (AS). Whether their occurrence can be linked to signs and symptoms of rheumatic disease activity is an unsettled issue addressed in this study.MethodsIn this cross-sectional study patients with AS according to modified New York criteria but without psoriasis, inflammatory bowel disease, dementia, pregnancy, other severe diseases such as malignancy and difficulties in answering questionnaires were invited; and 210 participated (120 men), mean age 49 years (SD 13; range: 16–77). Questionnaires, physical examination, ECG, and laboratory tests were performed at the same visit.ResultsCardiac conduction disturbances were common and diagnosed in 10-33%, depending on if conservative or less conservative predefined criteria were applied. They consisted mostly of 1st degree atrio-ventricular block and prolonged QRS duration, but one patient had a pacemaker and 7 more had complete bundle branch blocks. Conduction abnormalities were associated mainly with age, male gender and body weight, and not with laboratory measures of inflammation or with Bath Ankylosing Spondylitis Disease Activity Index. Neither were they associated with the presence of HLA B27, which was found in 87% of all patients; the subtype B270502 dominated in all patients.ConclusionsCardiac conduction abnormalities are common in AS, but not associated with markers of disease activity or specific B27 subtypes. Even relatively mild conduction system abnormalities might, however, indirectly affect morbidity and mortality.

Is atrioventricular nodal reentrant tachycardia possible in patients with first degree AV block?

Purpose of the study: Typical Atrioventricular (AV) Node Re-entrant Tachycardia (AVNRT) occurs in patients with dual AV nodal pathway, a rapid pathway used for retrograde conduction and a slow pathway used for the anterograde conduction. In sinus rhythm the patients have generally the signs of conduction through the rapid pathway with a normal or short PR interval. The purpose of the study was to evaluate the prevalence of patients with 1st degree AV block and with AVNRT and their clinical characteristics. Methods: 1040 patients, 366 males, 665 females were admitted for typical AVNRT. They were aged from 6 to 90 years (mean age 50±19). Initial ECG and clinical data were collected. Electrophysiological study was systematic. Results: Spontaneous 1st degree AV Block (AVB) was rare and noted in 8 patients. The prevalence of the association 1st degree AV Block and AVNRT was 0.8%. AVB was suprahisian in 7 of 8 and infrahisian in one of them. Five patients complained of AVNRT at exercise. Two patients had an ischemic heart disease. Patients with AVB were significantly older (71.5±16 years) than patients without AVB (50±19) (p<0.002). AVNRT was induced in control state in 5 patients. The rate of tachycardia was slow between 130 and 160 bpm. AVNRT was induced after isoproterenol in 3 patients and the rate was higher (180 to 200 bpm). Ablation of slow pathway was performed in 7 patients. Transitory 2nd degree AVB was noted in 1 patient. AVNRT was not inducible after ablation. PR interval remained unchanged. At atrial pacing, the rate of 2nd degree AVB occurrence decreased, due to the disappearance of the conduction through the slow pathway. Two patients developed transitory well-tolerated 2nd degree AVB one day after ablation. One patient presented apparent sinus bradycardia related to a concealed conduction through AV node. One year after ablation none of the patients required pacemaker implantation and patients were free of tachycardia. Conclusions: The occurrence of AVNRT in patients with 1st degree AV block is exceptional and concerns old patients. The prevalence was 0.8%. Ablation of slow pathway might be safely performed without a need of pacemaker implantation. Transitory 2nd degree AVB can be noted the day after ablation.

Bradyarrhythmias and Pacemaker Therapy in Dogs with Chagas Disease

Chagas disease (Trypanosomiasis) is a cause of myocarditis in the southern United States causing cardiac conduction abnormalities, arrhythmias, and heart failure. To report clinical findings and outcome in Chagas positive (CP) dogs requiring pacemaker implantation for bradyarrhythmias. One hundred and forty-four client-owned dogs requiring pacemaker implantation. Retrospective case series. Information regarding history, physical exam, laboratory and diagnostic imaging findings, treatment, and survival were obtained from medical records, with additional follow-up information obtained by contacting referring veterinarians and owners. Of the 144 dogs requiring pacemaker implantation from January 2001 to May 2010, 83 (57.6%) had a Chagas titer performed and 9 (10%) were CP. Concurrent ventricular arrhythmias (odds ratio 1.61, P = .005) or atrioventricular (AV) block (odds ratio 4.18, P < .001) increased the likelihood that a Chagas titer was submitted. Median age for CP dogs was 6.2 years (range, 0.3-10); 7 were male. Bradyarrhythmias included high-grade 2nd or 3rd degree AV block (n = 8) and sinus bradycardia with 1st degree AV block (n = 1); 5 had concurrent ventricular arrhythmias. A positive Chagas titer had a negative impact on survival (hazard ratio 4.04; 95% CI 1.36-12.1, P = .012) with a reported median survival time of 365 days (interquartile range, 84-973 days). Bradyarrhythmias can result in clinical signs requiring pacemaker implantation in CP dogs, and although the diagnosis negatively impacts survival, pacemaker therapy is a viable treatment option.

A Case of Heart Failure Effectively Treated by Generator Exchange to Obtain Minimal Ventricular Pacing Algorhythm

A 75 years old woman with diabetes mellitus, diabetic nephritis and hypertension was implanted DDD pacemaker (Symphony DR, Ela medical Inc) due to sick sinus syndrome (Rubenstein type 2). She also had 1st degree atrioventricular block. After she was implanted pacemaker, she developed anteroseptal acute myocardial infarction and sequential atrial fibrillation. She was treated with percutaneous coronary intervention and was prescribed amiodarone to maintain sinus rhythm. After amiodarone was prescribed, atrioventricular block became prominent and ventricular pacing was induced in DDD/AMC mode.

Electrocardiogram in Athletes

Changes in the resting electrocardiogram(ECG) as a result of training are common and can cause difficulties for the differential diagnosis. Recently updated guidelines from the European Society of Cardiology (ESC) differentiate between common, training-related and rare, potentially pathological changes (1). These new international recommendations were omitted from the article on the pre-participation examination for leisure time physical activity (2), presumably because they were not yet available at the time the manuscript was accepted. I wish to add them at this point. The following changes on ECG are classed as training-related in the absence of other distinctive features: sinus bradycardia, 1st degree atrioventricular block, incomplete right bundle block, early repolarization, isolated increased QRS voltages (increased Sokolow-Lyon index). These changes may occur in up to 80% of athletes. The prevalence is highest in endurance athletes with physiological remodeling of the heart, but the changes may also be found in other athletes and are notably more common in men than in women, and in black people than in white (Caucasian) people (3, 4). Isolated increased QRS voltages are responsible for 60% of training-related changes in athletes (4). In addition to cardiac adaptations, athletes often have favorable conditions for ECG leads owing to a lower proportion of body fat. Early repolarization of at least 0.1 mV, mostly located in the precordial leads (V2)V3–V4, is also common. In athletes of Afro-Caribbean origin, these ST elevations may be followed by negative T waves (3). As far as AV blocks are concerned, I would, by contrast to the authors, be very reticent to classify a 3rd degree AV block in elite athletes as normal (Box 3). I am not familiar with any such findings in athletes who are proven to be healthy. It is to be expected that the current ESC recommendations will notably lower the rate of false positive findings on athletes’ ECGs.

Rapidly Progressive Cardiac Manifestation of Behçet's Disease Involving Conduction System and Aortic Valve

Cardiac conduction system impairment is a rare clinical manifestation of Behçet's disease. We report a patient who showed 1st degree atrioventricular block at first presentation, and showed aggravated finding of 3rd degree atrioventricular block on five months later. His cardiac manifestation finally developed to acute severe aortic regurgitation on six months later from his first cardiac manifestation. We observed this rapid progression during 6 months and successfully improved symptom and disease severity of the patient with treatment targeting Behçet's disease.

Managing the fetus with atrioventricular block

e b ntroduction ith the arrival of ultrasound imaging to noninvasively iagnose and monitor the evolution of pregnancy abnormalties, the fetus has increasingly become the target of intenional in-utero treatment. The prenatal diagnosis of electrial atrioventricular (AV) conduction abnormalities relies on he analysis of the timing of atrial and ventricular systolic echanical events by Doppler echocardiographic methods. imilar to the electrocardiographic characterization of AV lock after birth, mechanical AV conduction abnormalities n the fetus can be delayed for gestational age and heart rate 1st-degree AV block), or intermittently (2nd-degree AV lock), or completely blocked (3rd-degree AV block; AVB). In CAVB, the most common conduction disorder f the fetus, the ventricles typically beat at rates between 35 nd 80 beats/min. Related to the slowed ventricular rate and ssociated structural anomalies or disease of the myocarium, the cardiac output may become critically comproised. Different prenatal treatment strategies have been ttempted to improve the outcome of AV block, including he administration of pharmaceuticals to the fetus via the aternal circulation. The primary focus of this article is to eview the results and risks of transplacental treatment of solated fetal AV block, which in the absence of universally ccepted management guidelines remains controversial.

Muscle MRI findings in patients with an apparently exclusive cardiac phenotype due to a novel LMNA gene mutation

The case of a family in which several members displayed conduction defects inherited as a dominant trait is reported. The proband was a young woman with a 1st degree atrio-ventricular block and high serum creatine kinase. Several members of the family featured cardiologic symptoms. All adult family members were clinically evaluated and blood tests including serum creatine-kinase levels, standard and Holter ECG, echocardiogram and muscle MRI were performed.LMNA gene analysis was carried out and a novel missense mutation consisting in substitution of exon 4 c.799 T/C, p.Tyr267His was revealed. The mutation was present in seven family members, five of whom displayed cardiac defects alone with no involvement of the skeletal muscle.In all mutated individuals muscle MRI featured a pattern of skeletal muscle involvement similar to that observed in autosomal dominant Emery Dreifuss muscular dystrophy, suggesting that even patients bearing a LMNA gene mutation associated to an apparently selective cardiac phenotype may present subclinical skeletal muscle involvement.

Third‐Degree Atrioventricular Block in a Horse Secondary to Rattlesnake Envenomation

Third‐Degree Atrioventricular Block in a Horse Secondary to Rattlesnake Envenomation

Continuous infusion in adult females dogs submitted to ovariohysterectomy with midazolam-xylazine and/or medetomidine pre-treated with methotrimeprazine and buprenorphine

To compare, by continuous infusion of ketamine or medetomidine combined to methotrimeprazine and buprenorphine, ketamine and midazolam, the degree of hypnosis, myorelaxation, anesthetic quality and surgical feasibility through evaluation of possible parametric alterations and recovery quality. 20 healthy adult females dogs, aged 3 to 5 years, body weight between 7 and 15 kg, were assigned randomly and homogenously to 2 groups of 10 animals each (n=10), group 1 (G1) and group 2 (G2), respectively. Animals of G1 were subjected to a pre-treatment with intravenous 1.0 mg/kg methotrimeprazine and or 3ì/kg. After 15 minutes, a 5.0 mg/kg ketamine and 0.2 mg/kg midazolam were intravenously injected. Immediately after induction, an anesthetic combination of 0.4 mg/kg/h midazolam, 20 mg/kg/h ketamine and 1.0 mg/kg/h xylazine, was continuously and intravenously administered for 30 minutes. The same techniques were used in G2 except for the substitution of xylazine for 30ìg/kg/h medetomidine. In G1 there was a 1st and 2nd degree atrioventricular heart block, a longer recovery period and lower quality. In G2 a 1st degree atrioventricular heart block occurred but isolated and ephemeral. The continuous infusion method, besides reducing drugs utilization, prevented collateral effects allowing a more tranquil recovery with no excitations, both protocols permitted the surgical procedure (ovary-hysterectomy) bringing about a reduction in hypnosis and an accentuated myorelaxation. Xylazine and medetomidine showed a similar pharmacodynamic behavior but with different clinical aspects. The electrocardiographic alterations observed in G2 and in a lower degree in G1 must be well studied. Describers: dogs, ketamine, methotrimeprazine, medetomidine, midazolam and xylazine.

The value of the electrocardiogram and chest X‐ray for confirming or refuting a suspected diagnosis of heart failure in the community

There is a common assumption that a normal ECG or a normal heart size on chest X-ray virtually rules out a diagnosis of heart failure. To assess the value of the electrocardiogram and chest X-ray in identifying patients with chronic heart failure in the community. This study was a secondary analysis of data prospectively collected at the time of patient's enrollment in the EPICA study, an epidemiological study of the prevalence of heart failure in Portugal. A total of 6300 subjects were clinically evaluated. Patients who presented with symptoms or signs of heart failure, and/or were receiving diuretics for chronic heart failure (CHF) had a chest X-ray, ECG, and echocardiogram. The diagnosis of heart failure was confirmed in 551 cases. Patients with right atrial enlargement, atrial flutter, atrial fibrillation, 2nd degree-Mobitz I atrioventricular block, 1st degree atrioventricular block, left bundle branch block, lung interstitial oedema, and bilateral pleural effusion were more likely to be diagnosed with heart failure. For the diagnosis of heart failure, in the Portuguese population aged over 25 years, an abnormal electrocardiogram had an estimated sensitivity of 81%, and negative predictive value of 75%; an abnormal chest X-ray had an estimated sensitivity of 57%, and negative predictive value of 83%. Twenty five percent of patients with CHF had a normal ECG or chest X-ray. Our results show that electrocardiographic and roentgenographic features are not sufficient to allow heart failure to be reliably predicted in the community and support the recommendation that all patients with suspected heart failure should undergo echocardiography.

108th ENMC International Workshop, 3rd Workshop of the MYO-CLUSTER project: EUROMEN, 7th International Emery-Dreifuss Muscular Dystrophy (EDMD) Workshop, 13–15 September 2002, Naarden, The Netherlands

Inserm UR582 (ex 523), Institut de Myologie, Bâtiment Babinski, G.H. Pitie-Salpetriere, 47, boulevard de l’Hopital, 75 651 Paris Cedex 13, France Laboratoire de Genetique Moleculaire et Chromosomique, IURC, Montpellier, France Institute of Cardiology, University of Bologna, Bologna, Italy Department of Paediatrics and Neonatal Medicine, Imperial College School of Medicine, Hammersmith Campus, London, UK Department of Neurology, Academic Medical Centre, Amsterdam, The Netherlands Service de Cardiologie, GH Cochin, Paris, France Randall Center, Kings College, London, UK Neuromuscular Unit, M.R.C. Polish Academy of Sciences, Warsaw, Poland ITOI, Unit of Bologna, c/o IOR, Bologna, Italy Istituto Ortopedico Rizzoli, Neuromuscular Unit, Bologna, Italy MRIC, North East Wales Institute, Wrexham, UK Department of Internal Medicine and Cardiology Medical University of Warsaw, Warsaw, Poland Department of Cardiology, University Hospital Maastricht, Maastricht, The Netherlands Dipartimento di Biopatologia e Diagnostica per Immagini, Rome, Italy Istituto di Genetica Biochimica ed Evoluzionistica, CNR (IGBE-CNR), Pavia, Italy Division of Medical Genetics, University of Leicester, Leicester, UK Institute of Human Genetics, Greifswald, Germany

The response of atrioventricular junctional tissue to temperature.

To determine the optimal temperature for catheter heat mapping without damaging cardiac tissue, we studied the electrophysiologic and histologic responses of the atrioventricular (AV) conduction system exposed to a specific range of temperatures. In 18 closed-chest dogs, an electrode catheter with a thermistor, tip was positioned transvenously at the AV junction. Radiofrequency current (RFC) was applied in incremental temperature steps until transient 2nd-degree AV block was induced. Catheter tip temperature (CTT) was measured at each step. RFC was immediately discontinued when AV block occurred. AV conduction was evaluated before and 4 weeks after the procedure. Acute transient 2nd-degree AV block was induced in 45 applications, during which the average CTT was 48.7 +/- 2.7 degrees C. In another 40 applications in which 2nd degree AV block was not induced, the average CTT was significantly lower [46.3 +/- 2.5 degrees C] (p < 0.001). Eleven of 16 dogs showed acute 2nd-degree AV block, but had normal AV conduction at 4 weeks (Group A). In the other 5 dogs, 1st-degree AV block was seen at 4 weeks (Group B). The lowest CTTs in Groups A and B were 45 and 49 degrees C, respectively. Histologic findings in 2 dogs from Group A revealed that 10-15% (by area) of the AV node was fibrotic. These findings suggest that the induction of fully reversible AV block can be achieved by titration of RFC, during the application of RFC to the AV junction. In conclusion, RF energy was used to produce a tip temperature of between 45 degrees C and 49 degrees C, which induced reversible and significant interruption of conduction of in tissue in the AV junction, and presumably also in target sites in clinical RF ablation.

Mortality in relation to Minnesota code items in elderly subjects. Sex-related differences in a cardiovascular study in the elderly.

The prognostic value of electrocardiographic abnormalities has not been widely studied in the elderly. We examined the Minnesota code ECG items in 2254 elderly subjects of the Cardiovascular Study in the Elderly (CASTEL), performed on an Italian general population. In our experience, codes for ischaemia, 1st-degree atrio-ventricular block, bundle branch blocks, myocardial infarction, atrial fibrillation or sinus tachycardia were predictors of overall mortality in females, while only the former three items were predictors in men. Although ischaemia, left bundle branch block and atrial fibrillation were predictors of cardiovascular mortality in both sexes, right bundle branch block, supraventricular arrhythmias and left ventricular hypertrophy were predictors only in men, and 1st-degree atrio-ventricular block were predictors only in women. Surprisingly, left anterior haemiblock and bifascicular blocks were not predictive of mortality.

Electrocardiographic evidence for cocaine cardiotoxicity in cat

Recent case studies suggest that cocaine overdose may produce life-threatening cardiac arrhythmias. We therefore investigated its effects on the electrocardiogram (leads II and V1) and arterial blood pressure in cats anesthetized with pentobarbital. Cocaine was administered by intravenous infusion over a 2-min interval at 1 mg/kg in 10 cats. In 5 out of 10 cats an additional infusion of 3 mg/kg cocaine was also administered after hemodynamic and electrocardiographic parameters had returned to control values (i.e., within 10 min). During and following infusion of 1 mg/kg cocaine, no significant change in heart rate or systolic or diastolic blood pressure were found, however the QRS duration increased by 38% (from 46 +/- 5 to 64 +/- 12 ms) (p less than 0.01). Evidence for bundle branch block and (or) premature ventricular beats was observed in 9 out of 10 cats after 1 mg/kg cocaine. Infusion of a further 3 mg/kg cocaine in five cats significantly lowered diastolic blood pressure (from 98 +/- 18 to 64 +/- 28 mmHg; 1 mmHg = 133.3 Pa) (p less than 0.01), and further prolonged QRS to 79 +/- 14 ms, a 75% increase from the mean control value (p less than 0.01). In addition, 1st and 2nd degree atrioventricular block, ventricular extrasystoles, and ectopic rhythms (AV junctional or idioventricular) were observed in four out of five cats given 3 mg/kg cocaine. Mean plasma concentrations of cocaine were 1.37 +/- 0.39 micrograms/mL (4.28 +/- 1.22 microM) (n = 5) at the end of a 1 mg/kg infusion and 2.93 +/- 0.43 micrograms/mL (9.16 +/- 1.34 microM) after a 3 mg/kg infusion (n = 3).(ABSTRACT TRUNCATED AT 250 WORDS)

Prevention of electrocardiographic and histopathologic alterations in the murine model of Chagas' disease by preinoculation of an attenuated Trypanosoma cruzi strain

The effects of infection with Trypanosoma cruzi on the electrocardiographic tracings of mice were studied in 4 groups of animals: (1) normal; (2) infected with a pathogenic T. cruzi strain (TS COB); (3) immunized with 3 intraperitoneal inocula of 10(6) attenuated T. cruzi epimastigotes (TCC) and (4) immunized-infected, which sequentially received the treatments of groups 3 and 2. Infection and protection were confirmed by xenodiagnosis and histopathology. Isolated alterations such as extrasystolia, 1st degree atrioventricular block, arrhythmia and ST elevation were observed in normal as well as infected mice. However, tracings taken repeatedly on each mouse over a 293 day period revealed a set of alterations which were more frequently seen in infected (14/22) than in normal (4/27) animals (p = 0.00048). These alterations consisted of supraventricular tachycardia, sinus bradycardia and persisting, first degree AV blocks, often associated to pacemaker changes. Inoculation of attenuated T. cruzi (group 3) did not increase these alterations (2/27 mice) but significantly prevented their development after challenge with the pathogenic strain (1/19 versus 14/22 mice, p = 0.000095). Thus, preimmunization reduced not only parasitemia but also a pathogenic consequence of T. cruzi infection. This evidence is relevant for immunoprevention studies against Chagas' disease.

Course of Symptoms and Spontaneous ECG in Pacemaker Patients: A 5‐Year Follow‐up Study

We investigated the course of symptoms and the spontaneous ECG retrospectively in 308 patients who had received a pacemaker because of atrioventricular (AV) block (n = 115), sick sinus syndrome (SSS, n = 107), bradyarrhythmic atrial fibrillation (bradyarrhythmia, n = 51), carotid sinus syndrome (CSS, n = 16), complete bifascicular block associated with 1st degree AV block (n = 13) and with other indications (n = 6). The mean implantation time was 63 months. The clinical state of 93% of all patients improved after pacemaker implantation; their symptoms decreased markedly. Persisting syncopy in some patients with SSS, however, supports a restricted implantation policy. We rarely saw improved AV conduction in patients with AV block (11%). Furthermore, in patients with SSS, atrial fibrillation occurred significantly more often (35%) than in those with AV block (17%; P less than 0.01). Only 3% of patients with SSS developed 2nd and 3rd degree AV block within the observation period. In all patients with initial bifascicular block and additional 1st degree AV block, pacing prevented further syncopal attacks; four of them showed 3rd degree AV block at control, indicating that pacemaker implantation is mandatory in symptomatic patients with bifascicular disease and 1st degree AV block.