The normal variants in the left bundle branch system.

This article reviewed the main anatomic and physiopathological aspects of the left bundle branch from its origin in the His bundle and its intraventricular distribution on the left endocardial surface. The results are based on the relevant literature and on personal observations executed on 206 hearts distributed as follows: 67 dogs, 60 humans, 45 sheep, 22 pigs, 10 cows, 2 monkeys, 1 guanaco, and 1 sea lion. The main anatomical features of the His-Purkinje conducting system may be summarized as follows: The bundle of His is composed by two segments: the penetrating and branching portions. LBB originates in the branching portion located underneath the membranous septum. There is no true bifurcation of the bundle of His in a human heart. Short after its origin the LBB gives rise to its two main fascicles, anterior and posterior, both heading the anterior and posterior papillary muscles, respectively. The anterior division is thinner and longer than the posterior one. The RBB and the most anterior fibers of the LBB arise at the end of the branching portion. In some cases a well-defined left septal fascicle can be identified, usually arising from the posterior division. Each division gives off small fibers and false tendons crossing the left ventricular cavity connecting the papillary between them or the papillary muscles with the septal surface. From each division of the LBB, their corresponding Purkinje networks emerge covering the subendocardium of the septum and the free wall of the left ventricles. There are critical relationships of the proximal segments of the His-Purkinje system with the surrounding cardiac structures whose pathologic processes may damage the conducting tissue.

Differential profile and biochemical effects of antiautonomic membrane receptor antibodies in ventricular arrhythmias and sinus node dysfunction.

BACKGROUND: The relationship between anti-beta-adrenergic (anti-betaR) and anti-M(2)-cholinergic (anti-M2R) receptor antibodies (Abs) and cardiac arrhythmias and their biochemical effects have not been systematically investigated. METHODS AND RESULTS: We studied 41 patients, 28 with ventricular arrhythmias (primary or due to Chagas' heart disease or idiopathic dilated cardiomyopathy; group I), 13 with sinus node dysfunction (primary or caused by Chagas' heart disease; group II), and 10 healthy controls (group III). The chronotropic effects of the IgG and immunopurified anti-beta(1)RAbs or anti-M2RAbs were assessed on cultured cardiomyocytes before and after exposure to atropine and propranolol. The biochemical effects of the IgG from 9 patients from group I, 6 from group II, and 6 controls were evaluated on COS7 cells transfected with genes encoding for beta(1),beta(2)-adrenergic receptors (cAMP increment) or M(2)-cholinergic receptors (phosphatidylinositol increment). The IgG from group I patients exerted a positive chronotropic action, with a high prevalence of anti-betaRAbs (75%) and low prevalence of anti-M2RAbs (10.7%) and induced a clear-cut and long-lasting increment in cAMP. The IgG from group II patients depressed chronotropism, with a high prevalence of anti-M2RAbs (76.9%) and low prevalence of anti-betaRAbs (15.4%) and evoked a marked augmentation of phosphatidylinositol. CONCLUSIONS: Our results demonstrate a strong correlation between anti-betaRAbs and ventricular arrhythmias and anti-M2RAbs and sinus node dysfunction. Anti-betaRAbs increase and anti-M2RAbs inhibit cAMP production. These findings offer new insight into the etiology and pathophysiology of cardiac arrhythmias, with therapeutic implications.

Contrasting effects of verapamil and procainamide on rate-dependent bundle branch block: pharmacologic evidence for the role of depressed sodium channel responses.

The mechanisms responsible for intermittent bundle branch block are still under debate. The role of the time-dependent behavior of the slow calcium channel has recently been emphasized. To test this hypothesis and ascertain the possible involvement of the fast sodium channel, the effects of the slow calcium channel blocker verapamil and the fast sodium channel blocker procainamide were compared in 10 patients with intermittent bundle branch block. All 10 patients showed bundle branch block during spontaneous sinus rhythm. Maneuvers to slow cardiac rate (that is, carotid sinus massage, Valsalva maneuver) were performed to identify normal conduction as well as phase 4 bundle branch block. Thus, the ranges of diastolic intervals (RR) resulting in phase 3 (tachycardia-dependent) bundle branch block, phase 4 (bradycardia-dependent) bundle branch block and normal conduction were measured in two control studies performed before intravenous administration of verapamil (control 1) and procainamide (control 2) and at the peak effect of both drugs. In the control studies, all 10 patients showed phase 3 bundle branch block, whereas phase 4 bundle branch block occurred in only 4 patients. The ranges of phase 3 bundle branch block, phase 4 bundle branch block and normal conduction were very similar in control studies 1 and 2. The phase 3 bundle branch block range was slightly shortened by verapamil (983 +/- 83.5 ms in control 1; 930 +/- 69.4 ms at the peak effect of verapamil), whereas phase 4 bundle branch block remained unchanged. In contrast, conduction was systematically worsened by procainamide.(ABSTRACT TRUNCATED AT 250 WORDS)

Overdrive prolongation of refractoriness and fatigue in the early stages of human bundle branch disease.

OBJECTIVES: The aim of this study was to assess the response of refractoriness in normal and diseased human bundle branches to changes in cycle length, as well as during a long period of continuous overdrive pacing. BACKGROUND: The anterograde refractory period of the bundle branches in patients with functional bundle branch block shortens as the rate is increased. The rate-dependent response of refractoriness in diseased bundle branches is quite different. However, this difference has not been precisely delineated, and its physiologic meaning is uncertain. METHODS: Refractoriness of the bundle branches was measured by the extrastimulus technique in 16 patients with tachycardia-dependent bundle branch block and 10 patients with functional bundle branch block, both after basic trains of 8 atrial-paced impulses at different cycle lengths and during a 10-min period of continuous overdrive pacing. RESULTS: The baseline refractory period in the bundle branches of patients with functional bundle branch block measured 430 +/- 32 ms (mean +/- SD) and shortened to 368 +/- 30 ms at the shortest cycle length. The maximal effect was reached within the 1st min of overdrive pacing. The baseline refractory period of the bundle branches was significantly longer in patients with tachycardia-dependent bundle branch block (611 +/- 184 ms) and demonstrated a cumulative overdrive prolongation in 15 (83%) of 18 studies with typical manifestations of fatigue. In two other studies, this occurred only after ajmaline administration. CONCLUSIONS: A rate- and time-dependent prolongation of refractoriness frequently occurs in diseased human bundle branches. When absent, this response may be induced under the effects of sodium channel blockers. This would suggest that an abnormality in the recovery from inactivation of the sodium channel might underlie the early stages of bundle branch disease.

High prevalence of antibodies against beta 1- and beta 2-adrenoceptors in patients with primary electrical cardiac abnormalities.

OBJECTIVES: This study sought to determine the prevalence of autoantibodies directed against the beta-adrenoceptors in patients with primary electrical cardiac abnormalities, including atrial arrhythmias, ventricular arrhythmias and conduction disturbances, in the absence of any other cardiac abnormality. BACKGROUND: Using synthetic peptides corresponding to the predicted sequences for the second extracellular loop of the human beta 1- and beta 2-adrenoceptors as antigenic targets, autoantibodies directed against the beta-adrenoceptors were recently shown to occur in patients with idiopathic dilated cardiomyopathy and Chagas' heart disease. METHODS: Eighty-six patients (57 with primary electrical abnormalities, 29 with idiopathic dilated cardiomyopathy) and 101 healthy and cardiopathic control subjects were studied. Antibodies against the beta 1- and beta 2-peptides were detected with an enzyme immunoassay performed in blinded manner. In nine selected (seropositive) cases, the immunoglobulin G (IgG) fraction was tested for functional effects on the rate of beating of cultured neonatal rat cardiomyocytes. RESULTS: Antibodies recognizing the beta 1- and beta 2-peptides were found in 11 (52.3%) of 21 patients with ventricular arrhythmias (p < 0.01), 5 (35.7%) of 14 patients with conduction disturbances (p < 0.05), 3 (13.6%) of 22 patients with atrial arrhythmias (p > 0.05) and 11 (37.9%) of 29 patients with dilated cardiomyopathy (p < 0.05) compared with 15 (14.8%) of 101 control subjects. A rapid increase in the rate of beating of the cultured cardiomyocytes was induced by IgG from a selected group of patients, suggesting an agonist-like interaction with a functional epitope. This response was mediated by stimulation of both the beta 1- and beta 2-adrenoceptors in the patients with primary ventricular arrhythmias but only the beta 1-adrenoceptors in the patients with idiopathic dilated cardiomyopathy. CONCLUSIONS: Primary ventricular arrhythmias and conduction disturbances, like idiopathic cardiomyopathy, show a high prevalence of antibodies interacting with functional epitopes of the beta-adrenoceptors, suggesting a common or similar abnormal immunoregulatory process.

Lidocaine-sensitive atrial tachycardia: lidocaine-sensitive, rate-related, repetitive atrial tachycardia: a new arrhythmogenic syndrome.

OBJECTIVES: The goal of this study was to report a variety of atrial tachycardia that might be caused by an unusual electrophysiologic substrate. BACKGROUND: The mechanism of atrial tachycardias is attributed to re-entry, abnormal automaticity or triggered activity, based on their electropharmacological responses. A rate-related and lidocaine-sensitive atrial tachycardia has not been reported. METHODS: Eight patients (3 women and 5 men, aged 14 to 60 years) with repetitive, uniform atrial tachycardias were studied. In six patients the arrhythmia had been refractory to at least three antiarrhythmic agents (class 1A and C sodium channel blockers, amiodarone, beta-adrenergic blocking agents, verapamil, digoxin). Conventional electrocardiograms, Holter recordings and B mode echocardiograms were performed in each patient. Intravenous lidocaine and verapamil were tested in the eight patients. Six patients underwent an electrophysiologic study. RESULTS: The baseline electrocardiogram showed nearly incessant runs of atrial tachycardia in all patients. The mean atrial ectopic cycle length ranged from 376 to 502 ms. In seven patients a progressive prolongation of the cycle length from the beginning to the end of the salvos was documented. The arrhythmia was suppressed by increments of sinus node rate and by atrial pacing at cycle lengths longer than that of the atrial tachycardia. In all patients the arrhythmia was abolished by intravenous lidocaine, whereas intravenous verapamil was ineffective. Four symptomatic patients were successfully treated with radiofrequency ablation of the ectopic focus, and two patients were treated with oral mexiletine. CONCLUSIONS: The peculiar electropharmacological responses of this arrhythmia suggest an uncommon underlying mechanism that remains to be elucidated.

Supernormal conduction in the accessory pathway of patients with overt or concealed ventricular pre-excitation.

It was recently shown that supernormal conduction in the diseased His-Purkinje system is more common than previously thought, and is always associated with prolongation of refractoriness. To assess whether supernormal conduction could also occur in the accessory pathway of patients with ventricular pre-excitation, 21 patients with manifestly prolonged refractoriness in the accessory pathway were studied. Under these conditions, programmed atrial stimulation revealed a phase of supernormal conduction in 16 (76%) of the 21. Therefore, what was believed to be a nonexistent or exceptional physiologic event was shown to be a rather common finding, at least under certain circumstances. Supernormal conduction occurred in all 7 patients with an anterograde refractory period of 480 to 980 ms, and in 5 of 10 patients with a refractory period greater than 1.0 second or with no anterograde conduction. Supernormal conduction could not be demonstrated in four patients with a refractory period less than or equal to 440 ms, but appeared in all four patients after the refractory period was prolonged by a rapid rate of stimulation or administration of ajmaline. The electrophysiologic changes underlying the occurrence of supernormal conduction in the accessory pathway are similar to those previously reported for the bundle branch system. The demonstration of supernormal conduction in the accessory pathway may uncover the presence of concealed ventricular pre-excitation. Supernormal conduction over the accessory pathway may facilitate a rapid ventricular response during atrial fibrillation, even if the refractory period is prolonged.

Comparative antiarrhythmic efficacy of verapamil, 17-monochloracetylajmaline, mexiletine and amiodarone in patients with severe chagasic myocarditis: relation with the underlying arrhythmogenic mechanisms.

The antiarrhythmic effects of verapamil, 17-monochloracetylajmaline, mexiletine and amiodarone were compared in 14 patients with chagasic myocarditis. Drugs and placebo were administered orally in the following order: placebo and verapamil, placebo and 17-monochloracetylajmaline, placebo and mexiletine (1 week each) and placebo and amiodarone (4 weeks each). A 24 hour ambulatory electrocardiographic recording was obtained after administration of each placebo and drug. Verapamil had no effect on the number of ventricular premature complexes, ventricular couplets and runs of ventricular tachycardia. 17-Monochloracetylajmaline did not reduce the number of ventricular premature complexes and ventricular couplets but caused a moderate reduction in runs of ventricular tachycardia. Mexiletine failed to significantly reduce ventricular premature complexes but caused a moderate decrease in both ventricular couplets and runs of ventricular tachycardia. Amiodarone was the only one of the four drugs that caused a substantial reduction of ventricular premature complexes (logarithmic mean 97.8%; p less than 0.001), total suppression of runs of ventricular tachycardia in 11 of 11 patients and suppression of ventricular couplets in 8 of 14 patients and a significant reduction in the remaining 6 patients. The much greater efficacy of amiodarone as compared with the two sodium channel modifiers (17-monochloracetylajmaline and mexiletine) and one calcium channel blocker (verapamil) suggests that its potent antiarrhythmic activity is probably related to other peculiar and still undefined electrophysiologic and pharmacologic properties.

Outcome of Hispanic patients treated with thrombolytic therapy for acute myocardial infarction: results from the GUSTO-I and III trials. Global Utilization of Streptokinase and TPA for Occluded Coronary Arteries.

OBJECTIVES: We sought to describe the differences in the process of care and clinical outcomes between Hispanics and non-Hispanics receiving thrombolytic therapy for myocardial infarction (MI). BACKGROUND: Hispanics are the fastest growing and second largest minority in the U.S. but most cardiovascular disease data on Hispanics has been derived from retrospective studies and vital statistics. Despite their higher cardiovascular risk-factor profile, better outcomes after MI have been reported in Hispanics. METHODS: We studied the baseline characteristics, resource use and outcomes of 734 Hispanics and 27,054 non-Hispanics treated for MI in the GUSTO-I and -III trials. The primary end point of both trials was 30-day mortality. RESULTS: Hispanics were younger, shorter, lighter and more often diabetic and began thrombolysis 9 min later, compared with non-Hispanics. Measures of socioeconomic status (educational level, employment and health insurance) were lower among Hispanics. Fewer Hispanics than non-Hispanics underwent in-hospital angiography (70% vs. 74%, p = 0.013) or bypass surgery (11% vs. 13.5%, p = 0.04). Hispanics received more angiotensin-converting enzyme (ACE) inhibitors and less calcium-channel blockers, prophylactic lidocaine and inotropic agents. Mortality at 30 days and at one year did not differ significantly between Hispanics and non-Hispanics (6.4% vs. 6.7% and 9.0% vs. 9.7%, respectively). We noted no interactions between thrombolytic strategy and Hispanic status on major outcomes (30-day death, stroke and major bleeding). CONCLUSIONS: The care of Hispanics with MI differed slightly from that of non-Hispanics. Nevertheless, these differences in care did not affect long-term outcomes.

Electrotonic modulation of the T wave and cardiac memory.

Alterations in the sequence of ventricular activation (left bundle branch block occurring spontaneously or induced by atrial pacing; right ventricular pacing) were studied and shown to induce two opposite changes in the order of ventricular repolarization. One, which causes classic secondary T wave changes, occurs and disappears instantaneously, and is proportional in magnitude to the QRS complex but of opposite direction. The other, which requires a long time to reach its maximal effect and to be dissipated, shows the same direction as the abnormal QRS forces but becomes apparent only when normal activation is restored. The former is a well known consequence of prolongation of the activation time, but the latter appears to be modulated by electrotonic interactions occurring during cardiac activation, in such a way that repolarization is delayed in sites where depolarization begins, and accelerated in sites where depolarization terminates. Our study suggests that electrotonically modulated T wave changes show accumulation and memory, and may persist for days or weeks after the provoking stimulus (the change in the activation sequence) is discontinued. The fact that any shift of the activation sequence may produce "pseudoprimary" T wave changes that may persist long after cessation of the triggering factor has wide clinical implications. Electrotonic modulation of ventricular repolarization is a basic electrophysiologic mechanism that may account for several features of normal and abnormal T waves, and for the possible existence of a heart memory.

Comparative effects of ajmaline on intermittent bundle branch block and the Wolff-Parkinson-White syndrome.

Phase 4 or phase 3 block or both occurred in the His bundle branch system of 11 patients with intermittent bundle branch block and in the anomalous bundle of 6 of 46 patients with the Wolff-Parkinson-White syndrome (13%). Administration of a single dose of ajmaline (50 mg intravenously) in these patients caused a similar response: expansion of the range of phase 3 and phase 4 block at the expense of the intermediate normal conduction range and total interruption of conduction in the affected fascicle when the effect of the drug was maximal. The great similarity in physiologic behavior and pharmacologic response in these groups of patients suggests that the anomalous bundle was probably diseased or abnormal in the six patients with Wolff-Parkinson-White conduction. In addition, ajmaline caused the first appearance of phase 4 or phase 3 block, or both, but not total interruption of conduction in 26 of the 46 patients with Wolff-Parkinson-White conduction (56.5%). Ajmaline does not cause fascicular block in normal subjects; thus this finding suggests either that the anomalous bundle is diseased or that the safety margin for conduction in the anomalous bundle is much narrower than in the bundle branch system. The conduction-depressing action of ajmaline may be greater at relatively rapid or relatively slow rates of stimulation, and smaller or absent at intermediate rates.

Electrocardiographic changes evoked by ajmaline in chronic Chagas' disease with manifest myocarditis.

Conversion from Chagas' infection to chagasic myocarditis occurs slowly and the earliest signs of myocardial involvement are hard to define. To obtain new information on this difficult clinical problem, ajmaline was administered (1 mg/kg body weight intravenously) to 101 patients with Chagas' infection and to 46 patients without such infection (control group). In 3 patients in the control group left anterior hemiblock alone occurred whereas in the group with Chagas' infection, ajmaline caused the occurrence of right bundle branch block, left anterior hemiblock, or both, in 32 patients (31.6 percent), ventricular extrasystoles in 8 (7.9 percent) and ischemic ST-T changes in 7 (6.9 percent). Ajmaline may thus evoke the most typical electrocardiographic changes of chronic chagasic myocarditis in patients without signs of myocardial involvement or only minor nonspecific signs. A positive ajmaline test, defined in the present context as the occurrence of a fascicular block, ventricular arrhythmias or ischemic ST-T changes, may indicate the existence of localized areas of injured myocardial tissue, not enough to alter the electrocardiogram by itself, but able to give rise to severe abnormalities after exposure to the drug. The test may therefore be used as a nonspecific detector of myocardial damage, and thus may have a much broader scope of clinical application. In chronic Chagas' infection, the ajmaline test is a relatively simple and apparently safe procedure that may serve to unveil the earliest signs of chagasic myocarditis.

Clinical efficacy of amiodarone as an antiarrhythmic agent.

Amiodarone, administered orally in doses of 200 to 600 mg/day, was remarkably effective in the treatment and prevention of a wide variety of atrial and ventricular arrhythmias. Total suppression and control was provided in 98 (92.4 percent) of 106 patients with supraventricular arrhythmias and in 119 (82 percent) of 145 patients with ventricular arrhythmias. The rates of total control of the arrhythmia were: 96.6 percent in 30 patients with recurrent atrial flutter or fibrillation, 96.6 percent in 59 patients with repetitive supraventricular tachycardia, 100 percent in 27 patients with Wolff-Parkinson-White syndrome and 77.2 percent in 44 patients with recurrent ventricular tachycardia unsuccessfully treated with other drugs. Excellent results were obtained in 6 to 8 patients with repetitive ventricular tachycardia and ventricular fibrillation related to postinfarction ventricular aneurysm and in 12 of 14 patients with ventricular extrasystoles and ventricular tachycardia related to Chagasic myocarditis. Amiodarone proved safe in patients with severe congestive heart failure and severe myocardial damage. Its clinical efficacy was related to its electrophysiologic properties and to two unique properties: its wide safety margin and its cumulative effect. The latter liberates patients from a rigid hourly schedule and provides for continuous antiarrhythmic control, days and even weeks after treatment is discontinued.

Usefulness of the ajmaline test in patients with latent bundle branch block.

Twelve patients were studied with intermittent bundle branch block whose conduction disturbance disappeared completely and could no longer be recorded even after provoked changes in heart rate. Premature atrial stimulation and atrial pacing at rapid rates were performed in nine patients; in none of these nine were these procedures able to evoke the complete bundle branch block pattern that all patients exhibited before the spontaneous normalization of conduction. In marked contrast, the administration of ajmaline (1 mg/kg body weight, intravenously in 90 seconds) caused the bundle branch block pattern to reappear in 10 (83.3 percent) of the 12 patients 30 to 120 seconds after the end of the injection, and in 11 patients (91.6 percent) when additional atrial stimulation was performed in 1 of the 2 "failures." This pharmacologic test was much more rapid and simple than electrophysiologic testing and it was noninvasive. Results of this study suggest that some form of subclinical fascicular injury was present (or had persisted) at a time when intraventricular conduction was persistently normal even though no significant physiologic alteration could be demonstrated by the atrial stimulation techniques. The ajmaline test may become a valuable tool for uncovering cases of latent bundle branch block and furthering our knowledge of the early natural history of intraventricular block.

Supernormal excitability and conduction.

The authors examine circumstances in which supernormality causes specific electrocardiographic events. True supernormal conduction is much more common than previously thought. A complete scanning of the cardiac cycle in patients with phase 3 BBB or with second-degree or advanced infranodal AV block would reveal that a much larger number of cases of supernormal conduction would be uncovered.

Efficacy of amiodarone for the termination of chronic atrial fibrillation and maintenance of normal sinus rhythm: a prospective, multicenter, randomized, controlled, double blind trial.

OBJECTIVE: We sought to assess the efficacy and safety of amiodarone for restoration and maintenance of sinus rhythm in patients with chronic atrial fibrillation in a prospective, randomized, double blind trial. BACKGROUND: Restoration and preservation of sinus rhythm is difficult in patients with chronic atrial fibrillation. The efficacy of oral amiodarone has not been conclusively established. METHODS: Ninety-five patients with chronic atrial fibrillation, lasting an average of 35.6 months, were randomized to either amiodarone (600 mg/d) (47 patients) or placebo (48 patients) during four weeks. Nonresponders underwent electric cardioversion, and those who reverted continued with amiodarone (200 mg/d) or placebo. End-points were successful cardioversion and sinus rhythm maintenance. RESULTS: Sixteen patients (34.04%) in the amiodarone group reverted within 27.28 +/- 8.85 days in comparison with 0% in the placebo group (P < 0.000009). The conversion rate rose to 51.72% in patients with chronic atrial fibrillation lasting less than 12 months. Twenty-eight patients in the amiodarone group and 39 in the placebo group underwent electric cardioversion, which was successful in 19 patients (67.8%) of the amiodarone group and in 15 (38.46%) of the placebo group (P = 0.017). Altogether, conversion was obtained in 79.54% of the amiodarone group patients and in 38.46% of the placebo group patients (P < 0.0001). During follow-up, atrial fibrillation relapsed in 13 (37.14%) of 35 patients of the amiodarone group within 8.84 +/- 8.57 months and in 12 (80%; P = 0.009) of 15 patients of the placebo group within 2.74 +/- 3.41 months. CONCLUSIONS: Oral amiodarone restored sinus rhythm in one third of patients with chronic atrial fibrillation, increased the success rate of electric cardioversion, decreased the number of relapses and delayed their occurrence.

Intraventricular conduction disturbances in civilian flying personnel: left anterior hemiblock.

We undertook a retrospective study of the natural history, clinical significance, prognosis, associated conduction disturbances, and pathology, as well as flying fitness qualification of 247 cases of left anterior hemiblock (LAH), detected in a presumably healthy population of 8,915 male individuals engaged in civilian flying activities (prevalence: 2.77%). The cases were divided into three groups according to the electrical axis value of the first electrocardiogram (ECG). The group with the slow mode of appearance of LAH was the most common. If associated with right bundle branch block, LAH usually evolves first. LAH could not be ascribed to any definite pathology; neither was it a forerunner of left bundle branch block nor complete atrioventricular block. Not one episode of syncope nor of sudden incapacitation was reported. As a mere ECG finding, LAH does not modify an aviator's fitness qualification. If another conduction disturbance develops, qualification will depend on the results of complementary studies, non-invasive or invasive, according to any associated conduction disturbance.

[Chagasic myocardiopathy: historical perspective]. / La miocardiopatía chagásica perspectiva histórica.

Considerable advances in the clinical pathological and pathogenic aspects of Chagas disease have been made since the Brazilian physician Carlos Chagas described the disease in 1909. The disease caused by the flagellate protozoon parasite Trypanosoma cruzi is transmitted to humans by a blood sucking triatomine and much less frequently by blood transfusion. It is estimated that 18 million are infected and that about 100 million people from Latin America are at risk of contracting T. cruzi infection. One of the most important contributions to the knowledge of Chagas' disease has been the recognition of the natural history of the disease, which can be divided into three well defined periods: 1. The acute stage; 2. An undetermined or undifferentiated stage and 3. The chronic stage. The primary infection (first stage) occurs mostly unrecognized and clinically apparent acute chagasic myocarditis may appear in less than 5% of the infected individuals, usually children living in endemic areas. The majority of the cases of acute myocarditis are mild and reversible. Autopsied cases of acute chagasic myocarditis are uncommon and correspond to exceptionally severe or fulminant forms showing diffuse myocardial damage with myocytolisis, degenerative changes of myocardial fibers and marked intersticial cellular infiltration. The acute clinical manifestations of the infected individuals include fever, muscular pain, sweating, swollen lymph nodes, hepatospienomegaly. Following this initial stage, all patients enter the undifferentiated or undetermined stage of the chronic period (second stage), which lasts between 10 to 20 years. Of these, 20 to 30% (depending on marked geographical differences) develop symptoms or signs of visceral damage conforming the cohort that enter the third stage. Although megaesophagous and megacolon are not uncommon (mainly in Brazil), the most frequent and important clinical manifestation is a dilated cardiomyopathy. Thus, 70% or more of the infected individuals will never show any clinical manifestation of the disease. The ajmaline test and the endomyocardial biopsy are, probably, the most sensitive methods to unmask latent forms of chagasic myocarditis during the undifferentiated stage. In the most advanced stages of chronic chagasic myocarditis, pathological findings are those of a dilated cardiomyopathy. At autopsy, the apical aneurysm with thrombus in it is a frequent and distinctive finding. The histopathological picture is that of an active and chronic microfocal and disseminated myocarditis. In some cases fibrosis may be confluent, which accounts for the electrocardiographic patterns of myocardial necrosis. The widespread distribution of cardiac lesions also constitute the substrate for atrioventricular and intraventricular conduction disturbances and for atrial and ventricular arrhythmias. The clinical diagnosis of Chagas' heart disease is based on a triad of: positive epidemiology, positive serology and a combination of clinical findings (suggestive electrocardiograhic abnormalities, apical aneurysm, cardiac enlargement). The electrocardiogram in the most advanced forms, usually shows sinus bradycardia, right bundle branch block with or without left anterior hemiblock, primary T wave abnormalities, pathological Q waves and multiform ventricular premature beats. The pathogenesis of the myocardial lesions of acute and also chronic chagasic myocarditis appears to be related in large part to autoimmune mechanisms. The lack of correlation between the location and number of parasitized fibers and the severity, type, and extension of degenerative and inflammatory lesions supports this assumption. Experimental and clinical studies have demonstrated the presence of antibodies directed against different components of T. cruzi and crossreacting with human antigens in patients with chronic chagasic myocarditis. Microvascular dysfunction, myocardial ischemia and autonomic nervous system impairment have also been implica