Conceptos actuales sobre la clasificación clínica y alteraciones electrofisiológicas en la disfunción del nódulo sinusal / Current concepts about the clinical classification and electrophysiological alterations in the sinus node dysfunction

La disfunción del nódulo sinusal (DNS) es generalmente secundaria a la senescencia del nodo sinusal y del miocardio auricular circundante. Los pacientes con este trastorno son a menudo añosos y en general presentan otras comorbilidades. Los pacientes a menudo buscan atención médica con síntomas de aturdimiento, pre-síncope, síncope y, en pacientes con periodos alternantes de bradicardia y taquicardia, palpitaciones u otros síntomas asociados con una frecuencia cardíaca rápida. Debido a que los síntomas pueden ser de naturaleza variable, inespecíficos y frecuentemente transitorios, a veces puede ser difícil establecer esta relación síntoma-alteración electrocardiográfica. Los hallazgos electrocardiográficos típicos son uno o más episodios de bradicardia sinusal extrema (Rubenstein Tipo I), o pausas sinusales, paro y bloqueo de salida sinoatrial (Rubenstein Tipo II), o episodios de bradicardia y/o pausas alternantes con taquiarritmias auriculares (Rubenstein Tipo III). Las investigaciones basadas en el registro de electrogramas locales auriculares anormalmente prolongados y fraccionados durante el ritmo sinusal y su distribución característica en la aurícula derecha de pacientes con DNS han aportado un conocimiento importante sobre las propiedades electrofisiológicas de la aurícula patológica. El electrograma auricular anormal traduce una conducción auricular irregular, caracterizada por una actividad eléctrica local no homogénea, relacionada con una conducción anisotrópica, no uniforme y retardada a través de un miocardio auricular patológico, en el que se pueden originar arritmias por reentrada. La detección de electrogramas auriculares anormales en la DNS identifica a un grupo de pacientes con vulnerabilidad auricular aumentada y con una incidencia significativamente mayor de episodios espontáneos o inducidos de fibrilación auricular(AU)

Sinus node dysfunction (SND) is often secondary to senescence of the sinus node and surrounding atrial myocardium. Patients with this disorder are frequently elderly and generally have other comorbidities. Patients with SND often seek medical attention with symptoms of lightheadedness, presyncope, syncope, and, in patients with alternating periods of bradycardia and tachycardia, palpitations and/or other symptoms associated with a rapid heart rate. Because symptoms may be variable in nature, nonspecific, and frequently transient, it may be challenging at times to establish this symptom-rhythm relationship. Typical electrocardiographic findings are one or more episodes of extreme sinus bradycardia (Rubenstein type I), or sinus pauses, arrest, and sinoatrial exit block (Rubenstein type II), or alternating bradycardia and atrial tachyarrhythmias (Rubenstein type III). Investigations based on the recording of abnormally prolonged and fractionated local atrial electrograms during sinus rhythm and their characteristic distribution in the right atrium of patients with SND have provided important knowledge about the pathological atrium electrophysiological properties. Abnormal atrial electrogram results in an irregular atrial conduction, characterized by a non-homogeneous local electrical activity, related to an anisotropic, non-uniform and delayed conduction through a pathological atrial myocardium, in which reentry arrhythmias may arise. Abnormal atrial electrograms detection in SND identifies a group of patients with increased atrial vulnerability and a significantly higher incidence of spontaneous or induced episodes of atrial fibrillation(AU)

The Role of the Calcium and the Voltage Clocks in Sinoatrial Node Dysfunction

Recent evidence indicates that the voltage clock (cyclic activation and deactivation of membrane ion channels) and Ca2+ clocks (rhythmic spontaneous sarcoplasmic reticulum Ca2+ release) jointly regulate sinoatrial node (SAN) automaticity. However, the relative importance of the voltage clock and Ca2+ clock for pacemaking was not revealed in sick sinus syndrome. Previously, we mapped the intracellular calcium (Cai) and membrane potentials of the normal intact SAN simultaneously using optical mapping in Langendorff-perfused canine right atrium. We demonstrated that the sinus rate increased and the leading pacemaker shifted to the superior SAN with robust late diastolic Cai elevation (LDCAE) during beta-adrenergic stimulation. We also showed that the LDCAE was caused by spontaneous diastolic sarcoplasmic reticulum (SR) Ca2+ release and was closely related to heart rate changes. In contrast, in pacing induced canine atrial fibrillation and SAN dysfunction models, Ca2+ clock of SAN was unresponsiveness to beta-adrenergic stimulation and caffeine. Ryanodine receptor 2 (RyR2) in SAN was down-regulated. Using the prolonged low dose isoproterenol together with funny current block, we produced a tachybradycardia model. In this model, chronically elevated sympathetic tone results in abnormal pacemaking hierarchy in the right atrium, including suppression of the superior SAN and enhanced pacemaking from ectopic sites. Finally, if the LDCAE was too small to trigger an action potential, then it induced only delayed afterdepolarization (DAD)-like diastolic depolarization (DD). The failure of DAD-like DD to consistently trigger a sinus beat is a novel mechanism of atrial arrhythmogenesis. We conclude that dysfunction of both the Ca2+ clock and the voltage clock are important in sick sinus syndrome.

Long-Term Outcome of Single-Chamber Atrial Pacing Compared with Dual-Chamber Pacing in Patients with Sinus-Node Dysfunction and Intact Atrioventricular Node Conduction

PURPOSE: The optimal pacing mode with either single chamber atrial pacemaker (AAI or AAIR) or dual chamber pacemaker (DDD or DDDR) is still not clear in sinus-node dysfunction (SND) and intact atrioventricular (AV) conduction. MATERIALS AND METHODS: Patients who were implanted with permanent pacemaker using AAI(R) (n = 73) or DDD(R) (n = 113) were compared. RESULTS: The baseline characteristics were comparable between the two groups, with a mean follow-up duration of 69 months. The incidence of death did not show statistical difference. However, the incidence of hospitalization for congestive heart failure (CHF) was significantly lower in the AAI(R) group (0%) than the DDD(R) group (8.8%, p = 0.03). Also, atrial fibrillation (AF) was found in 2.8% in the AAI(R) group, which was statistically different from 15.2% of patients in the DDD(R) group (p = 0.01). Four patients (5.5%) with AAI(R) developed AV block, and subsequently switched to DDD(R) pacing. The risk of AF was lower in the patients implanted with AAI(R) than those with DDD(R) [hazard ratio (HR), 0.84; 95% confidence interval, 0.72 to 0.97, p = 0.02]. CONCLUSION: In patients with SND and intact AV conduction, AAI(R) pacing can achieve a better clinical outcome in terms of occurrence of CHF and AF than DDD(R) pacing. These findings support AAI(R) pacing as the preferred pacing mode in patients with SND and intact AV conduction.

Estudo da função ventricular na técnica de plicatura da parede livre do ventrículo esquerdo em cães / Left ventricular function after plication of the left ventricular free wall in dogs

OBJETIVO: Avaliar os efeitos da técnica na função ventricular esquerda em cães hígidos e com cardiomiopatia dilatada induzida pela doxorrubicina. MÉTODO: De 13 cães, oito receberam doxorrubicina até que a fração de encurtamento (FE) fosse menor que 20 por cento. Destes, quatro animais e os cinco não induzidos foram submetidos à plicatura da parede livre do ventrículo esquerdo (PPLVE). Os demais cães não foram operados. Foram avaliados débito cardíaco (DC), pressão arterial, exame físico, eletrocardiografia, sistema "Holter" e ecocardiografia, por 180 dias. RESULTADOS: Houve redução do volume ventricular esquerdo. Os cães induzidos melhoraram após a operação e a fração de ejeção (FEj) retornou aos valores normais para a espécie. O DC e a FE aumentaram após a operação. Um cão foi a óbito. Nos cães não operados, a FE diminuiu e foram a óbito em torno de 40 dias após a indução; nos cães não induzidos, esta não se alterou. Houve extra-sístoles ventriculares, que se resolveram espontaneamente. CONCLUSÕES: A PPLVE sem circulação extracorpórea reduz o volume ventricular esquerdo e melhora a função cardíaca dos cães com cardiomiopatia dilatada induzida pela doxorrubicina, demonstrando baixa morbidade e mortalidade tardia.

Electrical Injury As A Possible Cause of Sick Sinus Syndrome

Electrical injury is a serious public health problem. Heart is one of the most frequently affected organs. Electrical injury can cause life-threatening cardiac complications such as asystole, ventricular fibrillation, and myocardial rupture. In this case report, we present a 20-yr-old male patient with sick sinus syndrome that developed years after electrical injury.

A cardiac evoked response algorithm providing automatic threshold tracking for continuous capture verification: a single-center prospective study.

BACKGROUND: The AutoCapture algorithm as implemented in Regency and Microny pacemakers (Pacesetter Inc., Sylmar, CA, USA) provides beat-by-beat monitoring of capture based on proper detection of the evoked response, provides high output back-up pulse when loss of capture occurs, performs periodic threshold evaluations and acquires the capture threshold data in a time-based event counter for later retrieval. The safety and efficacy of this algorithm was prospectively evaluated at a tertiary care hospital of north India. METHODS AND RESULTS: Fifty-four patients (38 males, mean age 66+/-13 years) received a ventricular pacemaker model Regency SC+ with low polarization bipolar lead for high-grade atrioventricular block (n=42) and sick sinus syndrome (n=12). Evoked response and polarization signal were assessed initially at 24 hours postimplant, and follow-up measurements were systematically conducted at week 1 and months 1, 3 and 6. Further evaluation of eligible patients was performed at 6-monthly intervals. Lead implantation parameters were optimum in all patients. At 6 months, the algorithm was functional in 51 patients. The pacing threshold increased to 0.89+/-0.36 V (p<0.001) in the first month and stabilized thereafter. Significant saving of energy was accomplished by a constant output safety margin of 0.3 V instead of the traditional 100%. While the evoked response signal remained stable throughout the study period, the potential signal increased significantly from 0.6+/-0.7 mV to 1.0+/-0.6 mV (p<0.001) in the first month and remained steady subsequently. Back-up pacing in the event of exit block was confirmed in all 25 patients who underwent a 24-hour Holter test. Based on the suggested sense margins, ventricular undersensing was observed in 7 (28%) patients, the majority of whom had competitive cardiac rhythms. An elderly patient with pneumonic illness succumbed to pulmonary embolism at 6 months. CONCLUSIONS: This large single-center experience on AutoCapture demonstrates the success of this algorithm in low-energy ventricular pacing without compromising the patient's safety.

Flutter auricular crónico: una manifestación infrecuente de enfermedad del nódulo sinusal: caso clínico / Chronic atrial flutter as an infrequent manifestation of sick sinus syndrome: report of 1 case

We report a 41 years old female, previously operated of an atrial septal defect, presenting with a persisting atrial flutter. Sinus node dysfunction became evident during an electrophysiological study at the moment of interrupting the flutter with electrical stimulation. The patient was treated with his bundle ablation and implantation of a definitive pacemaker. After one year of follow up, she is devoid of symptoms

Carbamazepine-induced sinus node dysfunction

Carbamazepine, a drug used for the treatment of epilepsy and neuralgias, may exert hazardous effects on the cardiac conduction system. We report such a case of symptomatic brady-arrhythmia occurring in a 43-years-old male while on therapy with carbamazepine. Additionally, a literature review is made of previous cases of carbamazepine-induced sinus mode, AV node and His-Purkinje conduction disturbances

Comparative evaluation of left ventricular function in sick sinus syndrome on different long-term pacing modes.

Single-chamber ventricular pacing has been implicated in the development or progression of congestive heart failure in patients with sick sinus syndrome (SSS). To define the exact role of pacing modality in causation of congestive heart failure, quantitative two-dimensional echocardiographic examination was performed in 51 consecutive patients with SSS who received an initial pacemaker from January 1979 to September 1989 and were free of any structural heart disease at the time of implant. Atrial or dual chamber pacemakers were implanted in 21 patients (Group I) and ventricular pacemakers in 30 (Group II). The two groups were matched for age, gender, paced rate, blood pressure and duration of pacing. After a mean follow-up of 64 +/- 34 months, congestive heart failure developed in one patient in group I and 3 in Group II. Patients in group II, had larger left atrium (41 +/- 5 vs 37 +/- 6 mm, p < 0.05) and left ventricular end-diastolic volume (64 +/- 18 vs 54 +/- 12 ml/m2, p < 0.01) but similar left ventricular end-systolic volume (27 +/- 12 vs 24 +/- 9 ml/m2, p = NS), ejection fraction (59 +/- 10 vs 57 +/- 8%, p = NS), left ventricular mass (84.8 +/- 31 vs 85.6 +/- 29.2 gm/m2, p = NS), meridian end-systolic wall stress (48.3 +/- 22.1 vs 49.8 +/- 25 Kdynes/cm2, p = NS) and wall stress/end-systolic volume ratio (1.27 +/- 0.94 vs 1.42 +/- 0.59, p = NS). Pacing mode does not appear to influence left ventricular systolic function in patients with SSS.

Electrocardiographic features of atrial depolarization during pacing of right atrial appendage.

Identification of atrial capture during pacing from right atrial appendage is frequently difficult. Electrocardiograms of forty five patients implanted with AAI/DDD pacemakers (thirty unipolar, fifteen bipolar) were analysed to characterize the specific morphology of paced P waves. Compared to sinus P waves, atrial pacing resulted in atrial depolarization of lower amplitude (0.16 +/- 0.05 mv vs 0.11 +/- 0.032 mv, P less than 0.005) but increased duration (0.07 +/- 0.009 sec vs 0.08 +/- 0.017 sec, P less than 0.005). P wave morphology was similar in unipolar and bipolar pacing units. It was positive in lead I (80%), II (71.11%), III (80%) and aVF (75.55%). In lead aVL, paced P waves were usually diphasic with an initial negative deflection (35.55%). Precordial leads showed paced atrial depolarization of small amplitude and did not help in identification of atrial capture. In unipolar pacing P waves were best seen in lead III because of small pacing spike in this lead. Lead II was suitable for identification of paced P waves in bipolar pacing. Thus careful examination of standard ECG leads for paced P waves of low amplitude, prolonged duration and specific morphology can help in confirming atrial capture following pacing stimulus from right atrial appendage.

Extrasistolia supraventricular con intervalo post-extrasistólico prolongado: su importancia para el diagnóstico de la enfermedad del nódulo sinusal / Supraventricular extrasystole with prolonged post-extrasystolic interval: its importance for the diagnostic of sick sinus

Se presentan 5 (cinco) pacientes estudiados mediante monitoreo electrocardiográfico contínuo (sistema Holter), se mostraron en sus respectivos registros extrasístoles supraventriculares con pausas post-extrasistólicas de más de 2.000 milisegundos (Ms) y PRs normal. Se correlaciona este dato con aumento significativo del Tiempo de recuperación del Nódulo Sinusal corregido (TRNSo), determinado por medio de estudios electrofisiológicos. De la relación directa y permanente observada entre ambos datos, siempre coincidentes, se infiere la importancia que adquiere la medición de la pausa post-extrasistólica auricular en el ECG de Holter para el diagnóstico de la Enfermedad del Nódulo Sinusal (ENS)