The effects of cigarette smoking on ventricular repolarization in adolescents / O tabagismo altera a repolarização ventricular em adolescentes

ABSTRACT Objective To assess the association between cigarette smoking and ventricular arrhythmias in adolescents. Novel electrocardiographic parameters -Tp-e interval, as well as Tpe/QT and Tpe/QTc ratios - were used to make this assessment. Methods The study population consisted of 87 subjects aged between 16-19 years. Fifty-one adolescent smokers with no risk of arrhythmia comprised the Smoker Group, and 36 adolescents who had never smoked cigarettes comprised the Control Group. Smokers were defined as patients smoking more than three cigarettes per day, for at least 1 year. Body mass index, systolic, diastolic and mean blood pressures were measured, and electrocardiograms were performed on all subjects. Heart rate, PR and Tp-e intervals, and Tpe/QT, Tpe/QTc ratio were digitally measured. Results Adolescents in Smoker Group had smoked cigarettes for 2.9±1.4 years (range 1 to 6 years). The mean age at starting smoking was 13.8±1.4 years. There were no differences between smokers and Control Group as to baseline clinical variables (p>0.05). The PR, QT and QTc intervals were similar in all groups. Tp-e interval (98.4±12.7ms and 78.3±6.9 ms; p<0.001), Tpe/QT (0.28±0.04 and 22±0.03; p<0.01), Tpe/QTc (0.24±0.03 and 0.19±0.01; p<0.001) ratios were significantly higher in Smoker Group. There were no correlations between years of smoking, number of cigarettes per day, Tpe interval, Tpe/QT or Tpe/QTc ratios. Conclusion Cigarette smoking is associated with risk of ventricular arrhytmogenesis with prolonged Tp-e interval and increased Tpe/QT and Tpe/QTc ratios in adolescents.

RESUMO Objetivo Avaliar a associação entre tabagismo e arritmias ventriculares em adolescentes usando novos parâmetros eletrocardiográficos: intervalo Tp-e, e relações Tpe/QT e Tpe/QTc. Métodos A população do estudo incluiu 87 indivíduos de 16 a 19 anos de idade. Cinquenta e um adolescentes fumantes, sem risco de arritmia, formaram o Grupo Fumantes, e 36 adolescentes, que nunca tinham fumado cigarros, formaram o Grupo Controle. Os fumantes foram definidos como pacientes que fumavam mais de três cigarros por dia, há pelo menos 1 ano. O índice de massa corporal, e a pressão arterial sistólica, diastólica e média foram medidos, e foram realizados eletrocardiogramas em todos os participantes. Frequência cardíaca, intervalos PR e Tp-e, e as relações Tpe/QT e Tpe/QTc foram medidas por instrumentos digitais. Resultados Os adolescentes do Grupo Fumante fumavam há 2,9±1,4 anos (variação 1 a 6 anos). A média de idade ao começar a fumar foi 13,8±1,4 anos. Não houve diferença nas variáveis clínicas iniciais entre os Grupos Fumante e controle (p>0,05). Os intervalos PR, QT e QTc foram semelhantes em todos os grupos. O intervalo Tp-e (98,4±12,7ms e 78,3±6,9ms; p<0,001), e as relações Tpe/QT (0,28±0,04 e 22±0,03; p<0,01) e Tpe/QTc (0,24±0,03 e 0,19±0,01; p<0,001) foram significativamente maiores no Grupo Fumantes. Não houve correlação entre anos de tabagismo, número de cigarros por dia, intervalo Tpe e relações Tpe/QT e Tpe/QTc. Conclusão O hábito de fumar está associado ao risco de arritmogênese ventricular, com interval Tp-e prolongado e aumento nas relações Tpe/QT e Tpe/QTc em adolescentes.

La repolarización precoz en el electrocardiograma del futbolista: Prevalencia, características y evolución

La repolarización precoz (RP) en el electrocardiograma (ECG) del deportista ha sido considerada un hallazgo benigno. Algunas publicaciones la han asociado a incremento de riesgo de muerte súbita. Los objetivos del presente trabajo fueron evaluar la prevalencia de RP inferolateral en una población de futbolistas entrenados, describir variables asociadas a esta patente e investigar la aparición de eventos en el seguimiento. Se analizaron ECG de futbolistas sin antecedentes personales y familiares de cardiopatía, con examen físico cardiovascular normal. Se consideró RP a la elevación del punto J ≥ 0.1 mV sobre la línea de base en, al menos, 2 derivaciones inferiores y/o precordiales laterales, asociada o no a deflexión positiva o muesca en la parte final del QRS. Se relacionaron con RP el voltaje de R en V5 o V6, el intervalo PR, la frecuencia cardíaca (FC) y la edad. Fueron contactados a los 60±5 meses de la evaluación inicial con ECG. Estadística: chi cuadrado y test t para datos no apareados. Fueron evaluados 210 ECG de futbolistas hombres, de origen europeo-sudamericano, con entrenamiento de alta intensidad. Edad: 18 ±4.6 años. La RP se encontró en 86 ECG (40.9%), incluida el subtipo inferior en 17 (8.1%). Un ECG mostró RP en cara inferior en forma aislada. Los futbolistas con RP tuvieron mayor edad, menor FC, PR más prolongado y menor voltaje de R. Ninguno de los futbolistas presentó eventos cardiovasculares a los 5 años de la evaluación.

Early repolarization (RP) on the electrocardiogram (ECG) of the athlete has been considered a benign finding. In some publications it has been associated with increased risk of sudden death. The objectives of this study were to evaluate the prevalence of infero-lateral RP in a population of trained players, to describe variables associated with this pattern and investigate the occurrence of events in the follow up. ECG of players with a normal cardiovascular physical examination and without family and personal history of heart disease, were analyzed. RP was considered the J-point elevation ≥ 0.1 mV over baseline in at least 2 inferior and / or lateral precordial leads, associated or not with positive deflection or notch in the end of the QRS. RP is related to the voltage of R in V5 or V6, the PR interval, heart rate (HR) and age. They were contacted at 60 ± 5 months after the initial assessment ECG. Statistics: chi square and t test for unpaired data. We evaluated ECG of 210 soccer players, of European-South American origin, with high intensity training. Age: 18 ± 4.6 years. The RP ECG was present in 86 (40.9%), including the lower subtype in 17 (8.1%). One ECG showed PR in lower face in isolation. RP footballers were older, with less FC, prolonged PR and lower voltage of R. None of the players presented cardiovascular events in a 5 years follow up after this evaluation.

About the specialized myocardial conducting tissue / Acerca del tejido miocárdico especializado de excitoconducción

The chronological succession of discoveries on the location and structure of the atrio-ventricular conducting system are described. The starting point of this system is located in the sinus atrial node, identified by the English scientists A. Keith and M. W. Flack in 1907. The atrioventricular conducting system was pointed out by the Swiss physician Wilhelm His Jr. in 1893. The atrioventricular node (AV) was first identified by the Japanese pathologist Sumao Tawara and his German professor Ludwig Aschoff in 1906. Likewise the structure and routes of the three internodal bundles are described. These bundles include: Bachmann's bundle (1916) connecting the right with the left atrium and the AV node; the middle Wenckebach's bundle (1910) and the posterior or Thorel's bundle (1910), extending from the region of the sinus atrial node towards the posterior margin of the AV node. Lastly, the ventricular left and right conduction systems are detailed. These include the main trunk and their peripheral subdivisions with respective networks. Regarding the controversial existence of the left middle subdivision, it can exist in animal and human hearts. Nevertheless, an intermediate left septal network of specialized fibers seems to act as a functional equivalent of this subdivision.

Se describe, en orden cronológico, la sucesión del descubrimiento de la localización y la estructura de los componentes del sistema de conducción auriculoventricular. El haz de conducción AV fue descrito por el médico suizo Wilhelm His Jr. en 1893. El punto de origen de dicho sistema se halla en el nodo sinoauricular, identificado por los ingleses A. Keith y M.W. Flack en 1907. El nodo auriculoventricular (AV) fue identificado por el patólogo japonés Sunao Tawara y su maestro, el alemán Ludwig Aschoff, en 1906. Asimismo se relatan la estructura y los recorridos de los 3 haces internodales: el anterior o de Bachmann (1916), que conecta la aurícula derecha con la izquierda y el nodo AV; el medio o haz de Wenckebach (1910) y el posterior o haz de Thórel (1910), que se dirige desde la región del nodo sinoauricular hacia la aurícula izquierda y el margen de atrás del nodo AV. Se presentan asimismo, de forma esquemática, los sistemas de conducción ventricular izquierdo y derecho, que comprenden el tronco principal y las subdivisiones periféricas con sus respectivas redes de Purkinje. Respecto a la controvertida existencia de un fascículo izquierdo medio, éste sí puede existir en corazones humanos y de animales. Pero la red septal intermedia de fibras especializadas parece ser un equivalente funcional de dicho fascículo.

Role of the Alternans of Action Potential Duration and Aconitine-Induced Arrhythmias in Isolated Rabbit Hearts

Under conditions of Na+ channel hyperactivation with aconitine, the changes in action potential duration (APD) and the restitution characteristics have not been well defined in the context of aconitine-induced arrhythmogenesis. Optical mapping of voltage using RH237 was performed with eight extracted rabbit hearts that were perfused using the Langendorff system. The characteristics of APD restitution were assessed using the steady-state pacing protocol at baseline and 0.1 microM aconitine concentration. In addition, pseudo-ECG was analyzed at baseline, and with 0.1 and 1.0 microM of aconitine infusion respectively. Triggered activity was not shown in dose of 0.1 microM aconitine but overtly presented in 1.0 microM of aconitine. The slopes of the dynamic APD restitution curves were significantly steeper with 0.1 microM of aconitine than at baseline. With aconitine administration, the cycle length of initiation of APD alternans was significantly longer than at baseline (287.5 +/- 9.6 vs 247.5 +/- 15.0 msec, P = 0.016). The functional reentry following regional conduction block appears with the progression of APD alternans. Ventricular fibrillation is induced reproducibly at pacing cycle length showing a 2:1 conduction block. Low-dose aconitine produces arrhythmogenesis at an increasing restitution slope with APD alternans as well as regional conduction block that proceeds to functional reentry.

Influencia de la madurez sexual y la castración sobre la actividad eléctrica cardíaca en conejos machos y hembras / Influence of sexual maturity and gonadectomy on cardiac electrical activity in male and female rabbits

Es bien conocida la existencia de diferencias en la actividad eléctrica cardíaca asociadas al sexo. Si bien estas diferencias habitualmente se relacionan al efecto de la madurez y de las hormonas sexuales gonadales, todavía existen controversias al respecto. El objetivo de este trabajo fue evaluar el efecto que la madurez sexual y la castración producen sobre los distintos parámetros del electrocardiograma de superficie y de la duración de los potenciales de acción (DPA). Se utilizaron conejos jóvenes (menores de un mes de edad) y adultos (mayores de seis meses de edad). Las diferencias obtenidas en las hembras se observan en la repolarización tardía, mientras que en los machos ocurren en la repolarización temprana. Existiría una relación entre las diferencias observadas en la duración desde el pico máximo hasta el fin de la onda T (Tpf) y las observadas en la DPA al 90% de la repolarización (DPA90) en las hembras, mientras que en los machos la relación existe entre la duración desde el punto J hasta el pico máximo de la onda T (JTp) y la DPA al 30 y 50% de la repolarización (DPA30 y DPA50). Si bien existen diferencias que podrían ser debidas a factores hormonales otras serían debidas a factores no hormonales.

Sex-associated differences in cardiac electrical activity have already been documented. Even though these differences are usually associated with the effect of maturity and sex hormones, there are still some controversial points to this respect. The aim of this study was to evaluate the effects of maturity and gonadectomy on the different parameters of surface electrocardiogram and the duration of the action potential in young and adult rabbits. The differences obtained in females were observed in late repolarization, whereas in males took place in early repolarization. There was a relationship between the differences observed in the duration from the peak to the end of the T wave and those observed in the duration of the action potential to 90% of repolarization in females, whereas in males the relationship exists between the duration from the point J to the peak of the T wave and the duration of the action potential at 30 and 50% of repolarization. Differences could be related to hormonal or non-hormonal factors.

Cardiac pacing in left bundle branch/ bifascicular block patients.

The primary concern in patients with bifascicular block is the increased risk of progression to complete heart block. Further, an additional first-degree A-V block in patients with bifascicular block or LBBB might increase the risk of block progression. Anesthesia, monitoring and surgical techniques can induce conduction defects and bradyarrhythmias in patients with pre-existing bundle branch block. In the setting of an acute MI, several different types of conduction disturbance may become manifest and complete heart block occurs usually in patients with acute myocardial infarction more commonly if there is pre-existing or new bundle branch block. The question that arises is whether it is necessary to insert a temporary pacing catheter in patients with bifascicular block undergoing anesthesia. It is important that an anesthesiologist should be aware of the indications for temporary cardiac pacing as well as the current recommendations for permanent pacing in patients with chronic bifascicular and trifascicular block. This article also highlights the recent guidelines for temporary transvenous pacing in the setting of acute MI and the different pacing modalities that are available for an anesthesiologist.

Slow Ca2+ channels neither contribute to upstroke of action potential nor to pacemaker potential in spontaneously active freshly isolated three day embryonic chick ventricle.

Contribution of slow Ca2+ channels to the upstroke of action potential (AP) and pacemaker potential was studied by observing the effects of Ca2+ channel activators- high [Ca2+]0, Bay-K-8644, isoproterenol, forskolin and dibutyryl-cAMP on spontaneous AP of freshly isolated 3 day embryonic chick ventricle (3 day ECV). The spontaneous APs showed maximal upstroke velocity (+Vmax), maximum diastolic potential (MDP), overshoot (Eov) and AP duration at -20 mv (APD20) of 42.60 +/- 2.40 V/sec, -59.05 +/- 0.95 my, 16.30 +/- 0.53 mv and 70.32 +/- 4.60 msec, respectively (an average value of 35 preparations). Bay-K-8644 (0.1-0.8 microM), isoproterenol (5-10 pM) and forskolin (0.1-2.0 microM) induced a concentration-dependent increase in APD20 and Eov without affecting +Vmax. Dibutyryl-cAMP (1 microM) also enhanced the APD20 and Eov and had no effect on +Vmax. Elevation of [Ca2+]0 from 0.6 mM to 9.6 mM caused a concentration-dependent increase in APD20 and Eov leaving +Vmax unaltered. Elevated [Ca2+] and the other Ca2+ channel activators had no significant effect on MDP in above concentration range. Increase in APD20 and Eov could be explained at least by activation of slow Ca2+ channels but the lack of any change in +Vmax clearly suggests that the slow Ca2+ channels do not contribute to the upstroke of AP. All these interventions reduced the rate of spontaneous firing without any noticeable effect on MDP. This finding shows that the slow Ca2+ channels also do not contribute directly to the generation of pacemaker potential in spontaneously active freshly isolated 3 day ECV.

Aspectos técnicos da cateterização do seio coronariano baseada no componente atrial do eletrograma intracavitário e anatomia radiológica durante o procedimento de implante de marcapasso biventricular / Technical aspects of coronary sinus catheterization based on the atrial component of the intracavitary electrogram and radiological anatomy during the implantation procedure of a biventricular pacemaker

OBJETIVO: Apresentar uma proposição técnica baseada na experiência de 130 implantes utilizando técnica simplificada para cateterização do seio coronariano, baseada no componente atrial do eletrograma intracavi-tário e anatomia radiológica. MÉTODOS: De outubro de 2001 a outubro de 2004 foram realiza-dos 130 implantes de marcapasso biventricular, utilizando-se anatomia radiológica e observação de eletrograma intracavitário, com prioridade ao componente atrial. RESULTADOS: O implante do sistema, utilizando-se a estimulação do ventrículo esquerdo via seio coronariano, não foi possível em 8 pacientes. Em 12 pacientes foram observadas dificuldades na canulação do óstio coronário e em 15 pacientes observaram-se dificuldades de progressão do eletrodo através do seio coronariano. O tempo médio de utilização de radioscopia foi de 18,69 min. CONCLUSÃO: A técnica de implante, utilizando a morfologia do componente atrial do eletrograma intracavitário e anatomia radiológica, demonstrou ser pouco trabalhosa, segura e eficaz para canulação do óstio do seio coronariano, necessitando de reduzido tempo de radioscopia.

Increased beat-to-beat QT variability in patients with congestive cardiac failure.

BACKGROUND: QT interval on the surface electrocardiogram reflects the time for repolarization of myocardium. Prolongation of rate-corrected QT interval, QTc is strongly associated with sudden cardiac death. Recent studies using novel techniques on beat-to-beat QT interval variability have shown that an increase in QT interval variability is associated with increased sympathetic activity and is a predictor of sudden cardiac death. We studied QT variability in patients with congestive cardiac failure, as it is associated with an increase in cardiac sympathetic activity and also sudden death. METHODS AND RESULTS: We compared beat-to-beat heart rate and QT interval data in 2 3 patients with congestive cardiac failure and 19 age-matched normal controls. The electrocardiographic data were acquired in lead II configuration at a sampling rate of 1000 Hz. Heart rate variability was found to be significantly lower while QT variability measures were significantly higher in patients compared to controls. QTvi (a common log ratio of QT variability normalized for mean QT interval squared divided by heart rate variability normalized for mean heart rate squared) was also significantly higher in patients compared to controls. Clinical improvement in some of these patients is associated with a decrease in QTvi, due mainly to an increase in cardiac vagal function. CONCLUSIONS: Our results suggest a decrease in cardiac vagal and an increase in cardiac sympathetic functions in patients with congestive cardiac failure. QTvi may prove to be a useful surrogate end point to evaluate treatment effect in these patients.

En torno al valor clínico del electrocardiograma / On the clinical value of the electrocardiogram

Se hace hincapié en el valor clínico del electrocardiograma, método de exploración cardíaca sencillo, rápido y de bajo costo. Éste da una información de carácter esencialmente funcional y, por ende, refleja de manera fidedigna las características metabólicas y electrolíticas de las fibras miocárdicas. Habitualmente no puede conseguirse esto con otros procedimientos más complejos y costosos. Se ha examinado en particular el cuadro del infarto miocárdico en sus diferentes localizaciones, la manifestación de los cambios posicionales y estructurales que aparecen en la evolución del cor pulmonale crónico de origen obstructivo, ciertas características de las arritmias supraventriculares y ventriculares, la ubicación por datos externos de la zona de preexcitación en el síndrome de WPW y los efectos de la disfunción de los canales iónicos por alteraciones metabólicas o génicas. 1. Existe una buena correlación entre el sitio anatómico y la indicación electrocardiográfica del área de infarto. 2. Los cambios observados en la evolución de una neumopatía obstructiva reflejan modificaciones posicionales: corazón vertical por descenso del diafragma, así como alteraciones estructurales del corazón derecho: crecimiento por hipertrofia y dilatación. 3. Las arritmias ventriculares presentan en general el fenómeno de "salto de onda" entre las dos masas septales y la aberrancia consecutiva de los complejos ventriculares. 4. En el síndrome de WPW, el círculo torácico permite inferir el sitio de la preexcitación en función de la orientación de los primeros frentes de la activación ventricular anómala. 5. Los cambios del intervalo Q-Tc reflejan las variaciones de las concentraciones iónicas celulares de manera más fidedigna que las determinaciones plasmáticas. Todo lo antes dicho da una idea clara de la gran utilidad práctica del electrocardiograma en clínica.

Emphasis is given to the clinical value of the electrocardiogram, a simple, quick and unexpensive method for heart exploration. It provides functional information and reliably reflects the metabolic and electrolytic characteristics of myocardial fibers. Such an information cannot generally be obtained by other more sophisticated and expensive methods. The localization and extension of myocardial infarction, the positional and structural changes observed during the evolution of chronic cor pulmonale of obstructive origin, some characteristics of atrial and ventricular arrhythmias, the site of preexcitation in WPW syndrome and troubles due to a dysfunction of the ionic channels because of metabolic or genic alterations, are particularly examined. 1. A good correlation exists between the anatomical site and electrocardiographic indication of the infarcted area. 2. In the obstructive chronic cor pulmonale, positional and structural changes of the heart are observed. The first ones correspond to a vertical heart, due to a descent of the diaphragm and an increase of lung volume. The structural changes are due to an enlargement of the right heart: dilatation and hypertrophy. 3. Ventricular arrhythmias habitually present the "jumping wave" phenomenon between both septal masses and the consecutive aberrance of the ventricular complexes. 4. In the WPW syndrome, the thoracic circle permits to infer the site of preexcitation by the orientation of the first fronts of anomalous ventricular activation. 5. Modifications in the Q-Tc interval reflect the variations of ionic intracellular concentrations in a more reliable way than the changes of plasmatic concentrations. The aforementioned evidences the great usefulness of the electrocardiogram in the clinical setting. (Arch Cardiol Mex 2003; 73:38-45).

Ritmo hisiano con fenómeno de Wenckebach retrógrado espontáneo y nodo aurículo-ventricular doble asociado a accidente vascular cerebral / Hissian rhythm with spontaneous retrograde Wenckebach fenomena and dual atrio-ventricular node associated to cerebrovascular accident

El fenómeno de Wenckebach se caracteriza por una prolongación progresiva del intervalo P-R hasta que una onda P es conducida por bloqueo a nivel del nodo aurículo-ventricular. En estudios electrofisiológicos se ha demostrado que la estimulación ventricular puede conducirse hacia las aurículas con prolongación progresiva del intervalo V-A, lo que constituye una especie de Wenckebach retrógrado. Se presenta el caso de una mujer de 70 años que posterior a un infarto parietal izquierdo oclusivo presentó ritmo hisiano con conducción ventrículo-auricular, con fenómeno de Wenckebach retrógrado espontáneo y evidencias electrocardiográficas de doble vía nodal. Este conjunto de anormalidades electrofisiológicas no ha sido publicado previamente