Dynamics of, and alternating Wenckebach periods during, 4:1 and 6:1 atrioventricular block.

In summary, the irregular dynamics of progression of 4:1 AV block in atrial flutter, presumably different from those observed in similar degrees of rate-dependent block, most likely reflected the complex electrophysiologic mechanisms operating during the highest degrees of AV nodal block. Occurrence of previously undescribed arrhythmias, namely Wenckebach periods during 4:1 and 6:1 block, tends to support the multilevel block hypothesis.

Second degree His-Purkinje block during his bundle pacing.

This report presents, for the first time, clear evidence supporting the occurrence of Wenckebach and 2:1 H-V block during His bundle pacing. The simultaneous recording of various intracardiac electrograms, as well as the comparison of the effects produced by selective His bundle pacing and high right atrial pacing at the same rates, permitted the identification of conduction disturbances located distal to the paced His bundle site. This could be done although one criterion usually required to diagnose selective His bundle pacing (namely, stimulus-V intervals of constant duration) was not present.

Atrioventricular block after reciprocating atrioventricular junctional tachycardia.

Short runs of symptomatic atrioventricular (A-V) block occurred after spontaneous cessation of reciprocating A-V junctional tachycardia in a patient with right bundle branch block, normal H-V interval and sinus nodal dysfunction. These episodes were characterized by long (more than 1 sec) P-P intervals during which the A deflections were not followed by His bundle electrograms. Three possible explanations are: (1) a posttachycardia-induced period of abnormally prolonged A-V nodal refractoriness; (2) pseudo-A-V block produced by concealed A-V junctional tachycardia, or (3) bradycardia-dependent (phase 4) A-V block at the "upper" His bundle, above the site from which the H deflection was recorded.

Dynamics of the uncorrected QT interval during vagal-induced lengthening of RR intervals.

Analysis of 21 episodes of vagal-induced atrioventricular block showed that the uncorrected QT intervals at the end of the corresponding RR pauses were not prolonged, in reference to the pre-block QT intervals, with pauses shorter than 1,280 ms. Subsequently, they gradually lengthened as the RR pauses progressively increased to 13,710 ms. This dynamic behavior of the QT interval in subjects without structural heart disease could have resulted from a complex interaction between the cumulative effects of previous cycle lengths (memory effect?) and the autonomic nervous system.

Spontaneous paroxysmal atrioventricular block in patients with positive tilt tests and negative electrophysiologic studies.

A subgroup of patients with neurocardiogenic syncope and negative electrophysiologic studies and adenosine tests (in 5 of 6 cases), who developed symptomatic paroxysmal atrioventricular block in the natural, ambulatory state, had positive tilt tests without advanced block. Lack of concordance between electrocardiographic changes may have reflected differential effects of the autonomic nervous system in the sinus and atrioventricular nodes, occurring in diverse circumstances and less likely because of the protocol used for tilt testing.

Primary cardiomyopathy in identical twins.

Seventeen year old identical twin brothers with no family history of cardiopathy began experiencing palpitations almost simultaneously. In both, examination revealed marked cardiomegaly and hypokinesia of the ventricular walls, and clinical and radiologic signs of progressive cardiac failure developed a few days later. Both boys died suddenly, 49 days and 5 months, respectively, after the initial examination. Electrocardiographic and vectorcardiographic studies revealed a severe intraventricular conduction disturbance that coincided with histologic changes in the myocardial tissue, including profuse interstitial fibrosis, hypertrophy and degeneration of the myocardial fibers, aberrant arrangement of the muscular fibers and considerable alteration of the structure of cardiac tissue. In the absence of hereditary and chromosomal factors, and excluding possible viral intervention during fetal life, it is believed that a teratogenic factor can produce the structural alterations of the tissue and derangement of the fibers observed in these hearts. The irregular contractions of the heart at the level of the net-like meshwork, disarrangement of myocardial fibers, and adaptative mechanisms of the heart inherent in the destruction of the contractile tissue contributed to the functional cardiac disorders that resulted in congestive heart failure and sudden death in these twins.

One to one atrioventricular conduction during atrial pacing at rates of 300/minute in absence of Wolff-Parkinson-White Syndrome.

One to one atrioventricular (A-V) or atrio-His bundle (A-H) conduction occurred during right atrial pacing at rates of 300/min in two patients with short P-R (and A-H) intervals, narrow QRS complexes and recurrent supraventricular tachyarrhythmias. Patient 1 had episodes of reciprocating A-V tachycardia and of atrial fibrillation with very fast rates (270 to 290/min) that were slowed to 100 to 135/min after administration of intravenous verapamil. Enhanced A-V (A-H) conduction was exposed only during stimulation from the high right atrium, but not from the low lateral right atrium or coronary sinus. Patient 2 had episodes of atrial flutter with 1:1 A-V conduction and rates of 290/min. The H-V interval was short (25 ms) during sinus rhythm and atrial pacing presumably because conduction occurred through an atrio-"distal" His bundle (atriofascicular) tract. In contrast, the H-V interval was normal (40 ms) in echo beats or when the "proximal" His bundle was stimulated. In these two patients, having as "common denominators" short P-R (and A-H) intervals, narrow QRS complexes and recurrent supraventricular tachyarrhythmias, enhanced A-V (A-H) conduction was (1) possible due to different electrogenetic mechanisms; (2) pacing-site dependent; (3) manifested, during atrial fibrillation and atrial flutter, by extremely fast ventricular rates; and (4) unrelated to the rate of reciprocating A-V tachycardias because the latter was predominantly a function of anterograde conduction through the "slow" nodal pathway.

Reverse alternating Wenckebach periods and other modes of regression of > or = 8:1 to 2:1 atrioventricular block.

The modes of regression of very high degrees of atrioventricular nodal block (> or = 8:1) were studied in patients with atrial flutter and a specific variant of the tachycardia-bradycardia syndrome. The occurrence of reverse alternating Wenckebach periods, previously reported only in 2:1 atrioventricular block, emphasizes the complexities of multilevel block.

Heart rate variability in inappropriate sinus tachycardia.

Analysis of heart rate variability in patients with inappropriate sinus tachycardia showed a 24-hour decrease in all temporal and spectral indexes, even after attempted correction to a rate of 75 beats/min. This may have resulted from a global decrease in parasympathetic activity or from a rapid sinus rate produced by other ill-defined mechanisms.

Decreased heart rate variability in appropriate sinus tachycardia and effects of rapid rate.

This study revealed that conventional temporal and spectral indexes of heart rate variability were reduced in patients with sinus tachycardia due to various, easily detectable, causes. These findings were attributed to the fast rates, per se, regardless of the cause, without reflecting a particular shift in the degree of autonomic activity and tone.

Sustained ventricular tachycardia in chronic chagasic myocarditis: electrophysiologic and pharmacologic characteristics.

Sustained ventricular tachycardia (VT) develops in many patients with chronic Chagasic myocarditis. Programmed stimulation was used to study the electrophysiologic characteristics of VT in 15 patients with Chagas' cardiomyopathy. Nine patients were in New York Heart Association functional class I, 5 were in class II and 1 patient was in class III. The average ejection fraction was 56 +/- 7%, which is somewhat better than that reported in patients with VT owing to idiopathic cardiomyopathy. In 11 patients VT could be reproducibly initiated and terminated by programmed stimulation. Intravenous mexilitene prevented induction of VT in 7 of 8 patients; amiodarone did not prevent induction in 3 of 4 patients. Our data indicate that the mechanism of VT is likely to be reentrant in many patients, and therefore VT can be produced by extrastimuli. Electrophysiologic study is therefore useful for establishing the diagnosis of sustained VT and may be useful for guiding initial therapy in selected cases of Chagas' disease.

Annihilation, entrainment and modulation of ventricular parasystolic rhythms.

Annihilation and one-to-one entrainment of modulated parasystolic rhythms in humans has not been previously discussed. In 9 nonmedicated patients, it was possible to measure the intrinsic, parasystolic ectopic cycle length given by the intervals between 2 consecutive parasystolic beats without any interposed nonparasystolic beat. The corresponding values varied between 960 and 2,350 ms (corresponding to rates between 62 and 26 beats/min). In addition, modulation could be determined, because nonparasystolic beats falling during the initial 59% of the cycle prolonged the parasystolic cycle length (by 12 to 37.5%), whereas those that fell later in the cycle shortened it (by 9 to 25%). Plotting this prolongation or shortening as a function of the temporal position of the nonparasystolic beats in the cycle yielded biphasic response curves, of which 7 were symmetric and 2 asymmetric. In 2 patients, episodes of concealed one-to-one entrainment were initiated by late nonparasystolic (sinus) beats and, later on, terminated by early ventricular extrasystoles. In 2 other patients (and in 2 separate occasions) nonparasystolic beats, falling in part of the cycle located in between those of maximal delay and acceleration, produced pacemaker annihilation (cessation of automatic activity for the remaining monitoring time). Parasystolic annihilation and concealed entrainment may be one of the causes that can explain the large, spontaneous, day-to-day variability in the incidence of ectopic ventricular beats reported in Holter recordings. Nevertheless, future prospective studies performing interventions that can change the sinus and ectopic rates are required to corroborate our finding.

Left anterior hemiblock of the 2:1 type in the presence of inferior wall myocardial infarction.

A case of inferior wall myocardial infarction (IWMI) with left anterior hemiblock (LAH) is presented. The LAH became type 2:1 in the course of the disease. Electrocardiographic signs of LAH in the presence of IWMI are outlined, and the behavior and etiology of the T-wave changes are analyzed.

A different approach to the analysis of pure ventricular parasystole.

Until recently, it had not been recognized that predictions regarding the number of sinus beats interposed between two consecutive parasystolic beats could be made. In a case of perfect, pure parasystole resulting from unintentional fixed rate ventricular pacing, the following was observed: there were consistently three different values (0,2,3) for the number of interposed sinus beats; only one of these values was odd, and the sum of the two smaller values was one less than the larger value. Our findings, which are in keeping with those obtained in an mathematical model, may be of additional help in the diagnosis of this elusive arrhythmia.

Electrophysiologic studies in a patient with atrial flutter and 1:1 atrioventricular conduction.

Intracardiac electrophysiologic studies were performed in a patient having paroxysms of atrial flutter with 1:1 atrioventricular (A-V) conduction. Although duration of conduction intervals was normal during sinus rhythm, the atrio-His (A-H) interval did not show the expected increase when the atria were stimulated at progressively higher rates. The results of pacing with the extrastimulus technique also indicated that the refractory periods of the A-H tissues were shorter than normal. Yet, intravenously administered ouabain produced a significant increase in these refractory periods. The findings in the case are compatible with a partial A-V nodal bypass with a shorter refractory period than the A-V node or with an A-V node with unusual capacity for rapid conduction. The response to ouabain therapy was that of A-V nodal tissues.

Paradoxical behavior of the QT interval during exercise and recovery and its relationship with cardiac memory.

BACKGROUND: Few studies have dealt with the behavior of the corrected (QTc) and uncorrected QT intervals during exercise and recovery. HYPOTHESIS: Based on previously published dynamics of the QT interval during treadmill testing, this study attempted to reevaluate the computer-proposed underlying mechanisms of these dynamics and to determine whether the so-called memory phenomenon could be operative in some subjects without evidence of structural heart disease. METHODS: This study included 42 unmedicated healthcare volunteers, 23 men and 19 women aged between 20 and 42 (mean 31.7) years. All had normal physical examinations, x-rays, and transthoracic echocardiograms. The electrocardiograms were also normal with 12-lead QT interval dispersions of < 90 ms. RESULTS: During exercise and recovery, the behavior of the QT intervals permitted the categorization into two groups. In Group 1 (31/42; 73.8% of subjects) the uncorrected QT interval showed a biphasic pattern consisting of a gradual decrease during incremental exercise followed by a gradual increase during recovery. In contrast, the QTc interval had a triphasic pattern resulting from a slight increase during the early phase of exercise, a gradual decrease at the highest rates, and a final increase during recovery as the rate slowed to control values. In Group 2 (11/42; 36.2% of subjects) the behavior was considered as paradoxical since the uncorrected QT interval displayed in a triphasic pattern whereas the QTc interval yielded a tetraphasic pattern due to the fact that both showed a second decrease during recovery while the rate was decreasing. CONCLUSIONS: Analysis of dynamics behavior of the QTc and the uncorrected QT intervals during exercise showed that some normal subjects had a paradoxical behavior which, because of its temporal relation to the phases of exercise, could be an expression of the so-called memory phenomenon.

[The usefulness of the application of nonlinear dynamics in the analysis of electrocardiograms in Chagas' disease patients]. / Utilidad de la aplicación de técnicas de modelado no lineal en el análisis de electrocardiogramas de pacientes con infección chagásica.

INTRODUCTION AND OBJECTIVES: The application of nonlinear techniques allows the definition of early risk markers in patients with Chagas infection and without any evidence of cardiac involvement evaluated by standard diagnostic test. Nonlinear modeling techniques have proved to be effective in cardiac rhythm analysis, thereby justifying its use in Chagas' disease. PATIENTS AND METHOD: The routine noninvasive test and heart rate variability analysis were performed in Chagas' disease patients and in a group of healthy subjects. In a second phase we used nonlinear analysis in the evaluation of patients with Chagas infection and no evidence of heart disease, Chagasic patients with minimal electrocardiographic abnormalities and healthy controls. RESULTS: Twenty-four-hour electrocardiographic ambulatory monitoring and heart rate variability allowed us to establish differences between the healthy subjects and patients with Chagas infection without evidence of cardiac disease (p c 0.05 and p <0.005). In sharp contrast nonlinear analysis characterized 4 subgroups in Chagasic patients without cardiac involvement (sensitivity and specificity of 1 00%). CONCLUSIONS: Our findings suggest that nonlinear modeling techniques have a high sensitivity and specificity in the early detection of cardiac involvement and very early autonomic disturbance. We recommend that these techniques be applied to patients with high risk of cardiac disease other than Chagasic myocarditis. Our findings should be corroborated with studies in larger populations. We are currently developing a prospective study to this end.

Characterizing atypical patterns of Heart Rate before Paroxysmal Ventricular Tachycardia.

Results of a comparative analysis between Heart Rate (HR) patterns occurring before the onset of Paroxysmal Ventricular Tachycardia (PVT) and from healthy subjects are shown. Two study groups were made after electrocardiographic dynamical monitoring (Holter) of volunteers. The first group includes 100h from 27 healthy control subjects, and the second group consists of 88h, ending with self-terminating episodes of PVT from 55 patients. Patterns are defined as sequences of consecutive RR intervals, while atypical patterns are defined as corresponding to unlikely behavior of Heart Rate in healthy subjects. We investigated spatial and temporal distributions of these patterns in order to find early signs of PVT. We found that they can be grouped on a reduced number of clusters, and the number of atypical patterns increases as we approach the onset of the episode.