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.

Paradoxical behavior of PR interval dynamics during exercise and recovery and its relationship to cardiac memory at the atrioventricular node.

This preliminary study deals with the dynamics of the PR interval during exercise testing by using a Bruce protocol in 31 nonmedicated, normal patients with ages of 33 +/- 14 years. The behavior of the PR interval permitted its categorization into 2 groups. In Group I (27 of 31, 87.1% of patients) the PR interval showed the expected biphasic behavior with a gradual shortening with increasing exercise and a gradual lengthening during recovery. In contrast, the PR interval in Group II (4 of 31, 12.9% of patients) showed a triphasic behavior since, toward the end of recovery, there was a second decrease in duration. Because of this temporal relation to the phases of exercise, this paradoxical response, in analogy to what happened to the QT interval during exercise, could have been caused by a form of short-term memory or to varying, but normal, intergroup differences in autonomic function. However, further studies involving a greater number of patients are required to reach definite conclusions.

Patterns of acute inferior wall myocardial infarction caused by hyperkalemia.

This is one of the first published articles dealing with two patients with hyperkalemia showing, not only a pattern of acute anteroseptal myocardial infarction, but of inferior myocardial infarction as well. This was attributed to uneven effects of high potassium in different regions of the heart. Marked reduction of resting potential of a large group of cells from the most affected regions could produce areas of inexcitability, capable of generating abnormal q waves. Likewise, ST-segment elevation could be attributed to a hyperkalemic diastolic current of injury (due to depolarization of resting potential) and to a combination of diastolic and systolic current of injury (due to a reduction of action potential amplitude). In addition, current flowing down voltage gradients on either side (epicardial and endocardial) of the M cell region could be responsible for the T wave, and even, to some extent, to the ST-segment changes. However, it cannot be excluded that the previously described changes may have resulted from coronary spasm without chest pain. In fact, an intriguing possibility, namely that hyperkalemia could trigger coronary spasm has to be considered also.

Sobre las causas de la caída nocturna de la presión arterial sistólica y diastólica / About the causes of the tumble nocturnal of the systolic pressure arterial and diastolic

Es bien conocido que la bradicardia reduce la presión diastólica por aumento del tiempo de escurrimiento diastólico, sin embargo, ella puede no disminuir la presión sistólica al provocar un concomitante aumento del volumen latido. Por otra parte, se sabe que la presión arterial desciende durante la noche, al igual que la frecuencia cardíaca. Este fenómeno se relaciona con los cambios del sistema nervioso autónomo que ocurren durante el reposo y el sueño. Sin embargo, la caída nocturna de la presión diastólica disminuye con la edad en mayor grado que la caída de la presión sistólica. De igual manera la caída de la frecuencia cardíaca disminuye con la edad, lo cual sugiere interacción directa entre la bradicardia nocturna y la hipotensión diastólica. Con el objeto de estudiar las relaciones entre bradicardia nocturna e hipotensión sistólica durante el sueño, nosotros estudiamos los cambios nocturnos de estas variables en 50 sujetos jóvenes y sanos, mediante registradores oscilo-métricos de presión arterial colocados durante 24 horas. Los descensos de la presión diastólica fueron mayores que los de la sistólica, en esta población joven con caídas significativas de la frecuencia cardíaca nocturna. Se encontraron correlaciones más elevadas entre la bradicardia nocturna y la caída nocturna de presión diastólica que entre dicha bradicardia y la caída de presión sistólica durante la noche. Este resultado sugiere que en la hipotensión diastólica nocturna debe existir un componente ligado directamente a la bradicardia nocturna, el cual podría explicar la menor hipotensión diastólica que ocurre en los sujetos de edad avanzada, en las cuales la bradicardia nocturna es de escasa magnitud. El nivel de la bradicardia nocturna debe ser evaluada a la hora de interpretar alteraciones del patrón circadiano de la presión arterial en sujetos non dipper"

[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.

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.

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.

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.

Sudden Wenckebach periods and their relationship to neurocardiogenic syncope.

Throughout a 9-month period during which 1,125 Holter tapes were reviewed prospectively we identified 13 nonmedicated patients with an arrhythmia, which for the purposes of this presentation was categorized, because of their mode of initiation, as sudden Wenckebach periods (WP). The episodes emerged abruptly from a normal (< or = 200 ms) PR interval with sudden prolongation of PR and PP intervals (and reversed PR-RP relationship) that took place over 1-8 cycles. The postpaced PR interval was shorter than that of the last conducted beat. The episodes were separated into two groups. Group I included 11 patients with symptoms other than syncope and Group II included 2 patients with syncope. There were 26 episodes of sudden WP in Group I. Twenty-five terminated in a single (and one in double) blocked P waves. Most episodes occurred between 10 PM and 7 AM. Symptoms did not correlate with the episodes. Mean 24-hour rates were < 90. In Group II there were 22 episodes, all occurring between 6 AM and 10 PM. The mean sinus cycle lengths before the phenomenon started to occur in Group I (861 +/- 185 ms) as well as the cycle lengths at the onset of block (1,096 +/- 215 ms) were statistically longer than those in Group II (591 +/- 40 ms and 747 +/- 63 ms, respectively, P < 0.0001). Although the mode of onset in the episodes in Group II was similar to Group I, 16 episodes terminated in 2-6 blocked P waves. Thus, the entire number of episodes could be categorized as an unusual type (because of the PR prolongation) of paroxysmal, or advanced second degree AV block. Because these patients had negative electrophysiological studies, positive tilt tests, and absent syncope after oral propranolol therapy, they were considered as having neurocardiogenic syncope. In addition, the faster than normal (> 100) mean 24-hour rates) suggested that they also had so-called inappropriate sinus tachycardia. In summary, Group I consisted of patients with a normal, benign, vagal-induced second-degree AV block, whereas the Holter findings in Group II appeared to reflect unusual (but natural, i.e., nonprovoked) electrocardiographic manifestations of certain patients with neurocardiogenic syncope.

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.

Intermittent parasystole with exit block.

A 53-year-old patient had a complex ventricular arrhythmia, which most likely was an intermittent pure (nonmodulated) parasystole, due to protection limited to the first part of the cycle coexisting with exit block. However, other interpretations of the observations were possible. Foremost among these was modulated parasystole with partial protection or with an attenuated or nondetectable early delaying phase, with exit block. Interestingly, the parasystole appeared to have fulfilled the dynamic rules regarding the number of sinus beats interposed between manifest parasystolic beats, as has been reported for pure or weakly modulated parasystole. This case corroborates unusual manifestations of an arrhythmia, which because of its newly found complexities and various possible interpretations seems to be discussed with decreasing frequency in most textbooks on general cardiology.

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.

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.