Classification of sinus node dysfunction

A case report of sinoatrial arrest caused by temporal lobe epilepsy in subclinical glioblastoma

Background

Atrial fibrillation with symptomatic bradycardia, higher grade atrioventricular block, and sinus node disease are all common indications for permanent pacemaker implantation. The most frequent causes of sinus node disease treated with pacemaker implantation involve degenerative structural changes of the sinus node; less often, extrinsic causes (such as damage due to myocardial infarction or heightened parasympathetic nervous system activity) lead to pacemaker implantation.

Case presentation

A 50-year-old patient with syncope and documented sinoatrial arrest was referred. Neurologic exams (including CT and EEG) revealed no pathologies, so a pacemaker was implanted. Postoperatively, syncope occurred again due to a focal seizure during which sinus rhythm transitioned to atrial pacing by the device. Further neurologic testing revealed focal epilepsy. Six months later, stage IV glioblastoma was diagnosed and the patient was treated surgically.

Conclusion

Intracerebral tumors should be considered in the differential diagnosis for patients with unexplained sinoatrial block, as well as in patients with repeat syncope after pacemaker implantation. Cranial MRI could aid the diagnostic workup of such cases.

Two methods for modeling of sick sinus syndrome in rats: Ischemia reperfusion and sodium hydroxide induced injury

The Sick Sinus Syndrome (SSS) is a serious life-threatening heart disease. It is important to establish a credible and stable sinus node damage model. In this study, we use two methods to construct an SSS damage model in rats. One is to inject sodium hydroxide to the SSS area through internal jugular vein. Another is to cause ischemia-reperfusion injury on the SSS area. 43 healthy SD rats were randomly divided into 4 groups, namely ischemia-reperfusion injury group (IRIG), inject sodium hydroxide group (ISHG), and propranolol group (PG) and the control group (CG). The achievement ratio of modeling was 67% in the IRIG and 83% in the ISHG. The HR significantly decreased after operation in the IRIG and ISHG compared with pre-operation (P＜0.01). The HR was reduced by above 30% in these 2 groups after modeling, while the reduction was better maintained in IRIG. Additionally, the sinoatrial node recovery time (SNRT) and sinoatrial conduction time (SACT) were significantly prolonged compared with pre-modeling in 2 groups (P < 0.01). Morphology results showed blurry in structure and boundaries with pale cytoplasm. It is speculated that IRIG and ISHG modeling might influence the calcium concentration and damage the sinus node function by decrease the expression of HCN4 and SCN5A, which impaired the driving ability of sinus node and leading to apoptosis. Ischemia reperfusion injury and sodium hydroxide injury could construct stable SSS models which could represent clinic pathological damage. Thus, both methods could be used for further studies of the SSS mechanisms and drugs.

Sick sinus syndrome

Sinus-node dysfunction is common in the elderly and, in most cases, does not cause any symptoms. Despite the high number of laboratory investigations, most diagnoses of sinus-node dysfunction are made by 12-lead electrocardiography, which shows severe sinus bradycardia, sinus arrest, or sinoatrial block. Continuous electrocardiographic monitoring, exercise testing, and electrophysiologic investigations (including pharmacologic interventions to cause complete autonomic blockade) are sometimes useful in detecting transient or latent sinus-node abnormalities. The term sick sinus syndrome should be reserved for patients with symptomatic sinus-node dysfunction. Sick sinus syndrome has a protean presentation with variable degrees of clinical severity. Symptoms are often intermittent, changeable, and unpredictable. Because these symptoms can be observed in several other diseases, none are specific to sick sinus syndrome. Owing to the nonspecific nature of its symptoms, sick sinus syndrome can be diagnosed only when clear electrocardiographic signs corroborate symptoms. In the absence of a demonstrable link between signs and symptoms, a diagnosis can be presumed only when signs of severe sinus dysfunction are present and when every other possible cause of symptoms has been excluded carefully. Sinus-node dysfunction frequently is associated with diseases of the autonomic nervous system, and autonomic reflexes play a major role in the genesis of syncope. Survival does not seem to be affected by sick sinus syndrome. Atrioventricular block, chronic atrial fibrillation, and systemic embolism are major pathologic conditions that affect the outcome of the syndrome. Treatment should be aimed at controlling morbidity and relieving symptoms. Cardiac pacing is the most powerful therapy; physiologic pacing (atrial or dual-chamber) has been shown definitively to be superior to ventricular pacing.

Sinus node function and protamine sulfate

This report analyzes the effects of protamine sulfate (PS) on the heart rate and sinoatrial node function in dogs anesthetized with diazepam, fentanyl, and pancuronium bromide, and subjected to different modalities of extracorporeal circulation (ECC). All groups were given 3 mg/kg of heparin sodium and 5 mg/kg of PS. The sinus node function was evaluated by means of sinoatrial conduction time (SACT), absolute sinus node recovery time (SNRTa), and corrected sinus node recovery time (SNRTc). The spontaneous heart rate (HR) of the animals was also analyzed. Under the experimental conditions established in this study, the intravenous administration of a bolus of PS produced a decrease in the HR in all the groups, regardless of the type of ECC used. The modifications in the conduction and recovery times of the sinus node by PS did not correlate with those of the heart rate; the sinoatrial conduction time increased in groups subjected to ECC, while the absolute and corrected recovery times of the sinus node were prolonged only in the group that underwent rapid rewarming.

Sinus node suppression in acute strokes--case reports

The authors report on 5 patients, 4 of them observed over a period of only two months in one community hospital, who developed profound sinus node suppression in the early phase following acute strokes. This complication resulted in the death of 2; in the remaining 3, it was controlled by electrical cardiac pacing or intravenous atropine. In 3 patients, the strokes were due to subarachnoid hemorrhage, and in 2, they were secondary to vascular occlusion. In at least 4 patients, the prognosis seemed favorable from a neurologic standpoint. Vagally mediated sinus node arrest may, therefore, represent a potentially fatal complication of strokes and may be more frequent than currently appreciated. Continuous monitoring in the early phase of acute strokes and pacemaker therapy may be lifesaving in some patients. This and the general phenomenon of functional failure of the sinus node due to a variety of causes are discussed.

The mammalian sinoatrial node

The sinoatrial node (SAN) was discovered in 1906 by Keith and Flack. The relation between its ultrastructure and function was first studied by Trautwein and Uchizono in 1963, whereas this relation was definitely established by Taylor and coworkers in 1978. The impulse originates from cells with a relatively low percentage of myofilaments. Earliest discharge is restricted to one site only in rabbit, guinea pig, cat, and pig and presumably also in larger animals. From this primary pacemaker area, the impulse is preferentially conducted towards the crista terminalis. The amount of cells in the primary pacemaker area may vary from a few hundred to a few thousand. In rabbit, guinea pig, cat, and pig, the amount of collagen is considerable. Normal SAN function was observed in the cat although the SAN volume occupied by myocytes was less than 5%. Changes in ionic composition of the perfusion fluid and the addition of autonomic substances may cause pacemaker shifts and altered activation patterns.

Bedside evaluation of sinus bradycardia: usefulness of atropine test in discriminating organic from autonomic involvement of sinus automaticity

In 55 patients with persistent sinus bradycardia who underwent an electrophysiologic study of sinus node, both in the basal state and after autonomic blockade (propranolol, 0.2 mg/kg, and atropine, 0.04 mg/kg), an atropine test (0.02 mg/kg) was performed the following day. The 49 patients in whom sinus rate could be evaluated after atropine were subdivided into two groups--group I, 24 patients (age: 54 +/- 13 years) with normal intrinsic sinus automaticity (normal intrinsic heart rate and intrinsic corrected sinus node recovery time) and group II, 25 patients (age: 62 +/- 9 years) with abnormal intrinsic sinus automaticity. In group I, atropine increased sinus rate from 53.7 +/- 4 to 87.9 +/- 17 bpm (delta %: 65.5 +/- 33) and in group II from 51.6 +/- 5 to 73.9 +/- 14 bpm (delta %: 43.1 +/- 26). The discriminant threshold of sinus rate after atropine and its percent increase, obtained by discriminant analysis, was 80 bpm and +52%, respectively, with a misleading classification of 32% and 36%, respectively. The overall predictive accuracy of sinus rate after atropine was higher than the percent change in sinus rate (73% and 65%, respectively). These data evidence that the atropine test is not very helpful in discriminating between an organic and an autonomic involvement of sinus automaticity in patients with sinus bradycardia.