Sinoatrial Block Research Articles

Guidelines for Cardiac Pacing

ABSTRACT Cardiac pacing has enjoyed rapid growth since it became technically available about 25 years ago. Its indications since then have broadened to include virtually every known arrhythmia. Criteria for pacing, published by the American College of Cardiology and the American Heart Association in 1983, and since then adapted with modification by Medicare, divide indications for implantation of pacemakers into the following three classes: (1) pacing clearly required, (2) some disagreement about necessity, and (3) contraindicated.Guidelines for Cardiac Pacing is a videotape moderated by William C. Roberts, MD, editor in chief, American Journal of Cardiology. Panel members are Drs Leonard S. Dreifus, Seymour Furman, Paul C. Gillette, Jerry C. Griffin, David L. Hayes, and Paul A. Levine. Intermedics has produced Guidelines for Cardiac Pacing to clarify certain controversial gray areas concerning the use of pacemakers in patients with congenital heart block, acquired heart block, sinoatrial block, and hypersensitive carotid sinus

Direct and reflex cardiovascular effects of trichothecene mycotoxins

Intravenous injection of T-2 toxin or roridin-A (2 mg/kg) into pentobarbital-anesthetized (30 mg/kg) dogs produced, respectively, decreased systolic pressure within 30 min and atrio-ventricular block within 60 min. Within 45 ± 15 min after injection of each toxin heart rate increased and remained elevated for at least 4 hr. The increase in sinus rate was reduced by 50% when dogs were pretreated with i.v. propranolol—HCI (5 mg/kg); pretreatment with atropine sulphate (5 mg/kg) did not alter the effect of the trichothecenes. Upon administration of T-2 toxin or roridin-A (30 mg/1) to isolated arterially perfused canine right atria, sinus rate decreased by 12% and 28%, respectively, and sinus node cell diastolic potentials became more negative by 7% and 10%, respectively. Sino-atrial block observed in 50% of the isolated atrial preparations perfused with roridin-A disappeared when toxin perfusion was discontinued. Perfusion with T-2 toxin or roridin-A produced no significant effects on atrial muscle cell action potentials. The cardiovascular response to systemic trichothecenes was hypotension followed by propranonol-sensitive tachycardia. The direct effects on conduction system cells may contribute to the overall deleterious action on the cardiovascular system.

Sinus arrest with intravenous amiodarone

Amiodarone is a benzofuran derivative with potent electrophysiologic effects on the impulse generation and conduction system of the heart. 1 The effects of amiodarone on the sinus node, in particular, are well described. 2,3 Sinus arrest 4 and sinoatrial block(5) with oral therapy have been demonstrated; we describe a patient with acute sinus arrest after intravenous amiodarone therapy.

The human sinus nodal electrogram: Techniques and clinical results of intra-atrial recordings in patients with and without sick sinus syndrome

An intra-atrial recording technique previously employed in animal experiments was successfully used to record SNP from the anatomic sinus nodal region of the high right atrium in 29 out of 41 patients (71%) thus examined. Due to the low amplitudes (microvolt range, 40 to 120 μV, mean 79 ± 20 μV), these potentials were discernible only on high amplification (A = 10 4 to 10 6), but with a conventional electrode catheter. Against the background of a gradual diastolic depolarization (0.6 to 3.5 μV/msec, mean 1.9 ± 0.71 msec), SNP stood out distinctly from the subsequent abrupt atrial depolarization. In four patients with SSS, first- and second-degree sinoatrial blocks, respectively, were recorded. SACT were measured both directly and indirectly, and the results were compared in all 18 patients without SSS and in 11 patients with SSS. Although the recordings were not made simultaneously, the paired values for the patients without SSS correlated well ( r = 0.890, p < 0.001), whereas no correlation was found in the patients with SSS ( r = 0.163, p = 0.316). In spite of unresolved questions, direct recording of SNP appears to be of potential value in evaluating patients with SSS.

Experimental study on the relationship between cardiac arrhythmias and sleep states by ambulatory ECG-EEC monitoring.

The relationship between cardiac arrhythmias and sleep states was investigated in rats using the ambulatory ECG-EEG monitoring system under the 14/10 light-dark illumination schedule. Records of 14 rats obtained over 94 days were analyzed. Bradyarrhythmias (SA block and AV block) and ventricular arrhythmias [ventricular premature contraction (VPC) and short run of VPCs (ventricular tachycardia, VT)] were observed. Average number of episodes of bradyarrhythmia per day was 7.5, and the ratio of SA block to AV block was 34.9% to 65.1%. Average VPC or VT occurrence per day was 0.9 or 0.1 times, respectively. Sleep states were divided into alertness, slow-wave sleep, and paradoxical sleep, and the relationship between sleep states and arrhythmias was investigated. Bradyarrhythmias appeared predominantly during paradoxical sleep, while ventricular arrhythmias appeared during alertness as well as paradoxical sleep. Bradyarrhythmic episodes decreased by right or left vagotomy 78% or 70%, respectively. Sinus bradyarrhythmias disappeared almost completely by the right vagotomy, while the occurrence of AV block decreased by the right or left vagotomy. Circadian rhythms in arrhythmias were also analyzed by the cosine-fitting technique, and significant circadian rhythms were demonstrated in both bradyarrhythmias and ventricular arrhythmias. Acrophases were 9:56 A.M. and 1:47 A.M., respectively. Occurrence of VT was rare, but the most frequent incidental time zone was immediately following transition from light effects (rest) to dark (activity). This knowledge of circadian rhythm effects in arrhythmias must be incorporated into improved treatment of arrhythmias.

Xylazine hydrochloride-ketamine hydrochloride immobilization of wolves and its antagonism by tolazoline hydrochloride.

Fourteen wolves (Canis lupus L.) were singularly or repeatedly immobilized with 30 mg xylazine hydrochloride (HCl) and 400 mg ketamine HCl. Mean induction time was 5.3 +/- 4.6 min (mean +/- SD). Administration of 8.0 mg/kg tolazoline HCl as an antagonist significantly reduced immobilization times from 148.0 +/- 52.7 to 47.9 +/- 8.9 min (F = 63.69, df = 1,17, P less than 0.05). The average times from injection to ambulation for 2.0, 4.0, and 8.0 mg/kg tolazoline HCl were 35.2 +/- 31.8, 18.5 +/- 11.7, and 10.2 +/- 9.1 min. Tolazoline HCl increased heart rates significantly (P less than 0.001) from 75 +/- 14 to 120 +/- 23 beats/min, reversing a xylazine HCl-induced bradycardia. Respiratory rates also increased significantly (P less than 0.01) after tolazoline HCl injection from 19 +/- 7 to 28 +/- 8 breaths/min. Immobilization resulted in an initial hypertension which was normalized after tolazoline HCl administration. One female wolf had a single sinoatrial block within 1 min of receiving tolazoline HCl. Tolazoline HCl appears to be an effective antagonist for xylazine HCl-ketamine HCl immobilization of wolves.

Congenital Swallowing‐induced Symptomatic Heart Block: A Case Report of a Probably Hereditary Disorder

A 15-year-old girl had had syncope induced by swallowing since infancy. An ECG recorded during food intake revealed SA block with very slow junctional and ventricular escape rhythms. No symptoms or signs of other cardiac disorders or gastrointestinal diseases were present. Activation of a strong vagal reflex, able to inhibit impulse formation and propagation in an otherwise normal heart, is the most likely explanation of the disorder in this patient. Furthermore, ECGs of her close relatives which were recorded during food intake as compared with the findings in a reference group (n = 20), indicated that a genetic factor could be involved.

Dynamic interactions and mutual synchronization of sinoatrial node pacemaker cells. A mathematical model.

Dynamic interactions and mutual entrainment of coupled sinoatrial pacemaker cells with different intrinsic frequencies were investigated using a computerized mathematical model. Transmembrane potentials were simulated using equations of individual membrane currents based on voltage clamp data for the sinoatrial node. The intrinsic frequency of a given cell was altered by applying bias hyperpolarizing current, or by changing the amount of slow inward current. Cells were coupled through simple ohmic resistances to form linear arrays of two or more cells. Simulations closely reproduced previous experimental work showing that the mutual interactions between pacemakers are mediated electrotonically and show phase dependence. Results from the present simulations provide an explanation for the ionic basis of these phase-dependent interactions. In addition, it is demonstrated that the mutual entrainment of coupled pacemakers can lead to their coordinated behavior (synchronization). Two pacemaker cells can synchronize at simple harmonic (i.e., 1:1, 2:1, etc.) or more complex ratios (3:2, 5:3, etc.), depending on the differences in intrinsic frequencies and the degree of electrical coupling between cells. Simulations using larger numbers of linearly connected cells yielded various patterns of pacemaker activity including 2:1 sinoatrial block and complex dysrhythmic activity. The overall results may be used to predict higher order interactions of thousands of cells comprising the sinus node. Under such a scheme, synchronization occurs not by the conducted influence of a dominant pacemaker cell, but by the mutual "democratic" interaction of individual pacemaker cells.

Competence, persistence and motivation: Relationships in structured and unstructured assessments of high social risk 13 month olos

A case of a 29 year old female patient with sinoatrial block, first degree A-V heart block and Adams-Stokes seizures since the age of 11 is reported. The mechanism of the syncopal attacks was established by continuous radioelectrocardiographic monitoring as episodes of sinoatrial heart block or arrest, or both. There was no evidence of inflammatory, degenerative or congenital heart disease, and the patient had never received drugs assocated with the production of Adams-Stokes seizures. From the etiologic standpoint exaggerated vagal effects undoubtedly played a role; the existence of a congenital abnormality of the conduction system must, however, be taken into consideration. Treatment with artificial pacemaker stimulation proved effective and prevented further Adams-Stokes attacks.

Role of the suprachiasmatic nuclei of the hypothalamus on diurnal rhythm in cardiac arrhythmias.

Ambulatory EGG and EEG recordings were recorded under a 14/10-h light-dark illumination schedule using rats. The rats consisted of two groups: a suprachiasmatic (Sch) lesioned group (n = 5) and a normal control group (n = 5). Bilateral Sch nuclei were lesioned electrically (DC, 2.5 mA, 30 s for each) using a pair of platinum electrodes 0.3 mm in diameter. After recovery from surgery, recordings of ECGs (leads I, II, and III) and EEGs from the cortex and the left dorsal hippocampus were continued for 6 days. Diurnal periodicity in bradyarrhythmia (sinoatrial block, atrioventricular block) and heart rate was analyzed by the least square fit of 24-h cosines. Significant diurnal rhythm was observed in control rats, whereas Sch-lesioned rats showed no significant diurnal rhythm. The integrity of the Sch nuclei, therefore, is necessary for the generation and/or the expression of diurnal periodicity in bradyarrhythmia in rats.

“Escape-Reentry-Capture” Trigeminy: A Rare Electrocardiographic Sequence

en a long pause follows sinoatrial block or atrioventnicular block, A-V junctional escape beat ensues. The same holds true for marked sinus bradycardia. Thus, it is natural that escape beats are encountered frequently in sick sinus syndrome. Ifsinus impulse resumes control ofthe ventricles, ie, “captures” the ventricles, and “escape-capture” occurs in succession, then “escape-capture” bigemmny is the result. Alternatively, mfthe next sinus beat is further detamed, junctional impulse can be conducted retrogradely to the atria and then back to the ventricles, eliciting a reciprocal beat. The underlying mechanism is reentry. Occurring in pairs and in succession, the phenomenon is “escape-reentry” bigeminy. Both “escape-capture” and “escape-reentry” bigemmny are common in sick sinus syndrome; however, the sequence of “escape-reentry-capture” trigeminy is a rarity. Recently, we encountered a case of bradycardiatachycardia syndrome displaying an ECG pattern of “escape-reentry-capture” during 24-hour telemetric ECG on the second day of hospitalization.

Cardiac involvement in congenital myopathy

We examined cardiac changes in 8 patients (4 men and 4 women, age 21–43 years) with congenital myopathy proven by skeletal muscle biopsy. Of 8 patients, 4 showed cardiac changes, including 1 with cytoplasmic body myopathy (patient 1), 2 with minimal change myopathy (patients 2 and 3) and 1 with nemaline myopathy (patient 4). Patients 1 and 2 showed left ventricular dilatation with severe global hypokinesis of left ventricular wall. These clinical features were quite similar to those of dilated cardiomyopathy and the patients were in NYHA class 3 or 4. Patient 3 had severe mitral regurgitation with mitral valve prolapse. This patient also had a persistent left superior vena cava and hypoplasia of the aorta, and her cardiac function was in NYHA class 3. Patient 4 showed moderate global left ventricular hypokinesis but the left ventricle was not dilated. This patient also had sino-atrial block and type A Wolff-Parkinson-White syndrome. His cardiac function was NYHA class 1. In conclusion, various types of congenital myopathy are associated with cardiac changes which can result in severe congestive heart failure.

Amiodarone-induced sinoatrial block

We observed sinoatrial block due to chronic amiodarone administration in a 5-year-old boy with primary cardiomyopathy, Wolff-Parkinson-White syndrome and supraventricular tachycardia. Reduction in the dosage of amiodarone resulted in the disappearance of the sinoatrial block and the persistence of asymptomatic sinus bradycardia.

Sinus node electrogram in patients with the hypersensitive carotid sinus syndrome

Sinus node electrograms were obtained in two patients with unexplained syncope and the cardioinhibitory form of the hypersensitive carotid sinus syndrome. Direct recordings of sinus node potentials were obtained using a transvenous electrode catheter. Sinus node function was normal in both patients during standard electrophysiologic evaluation. Carotid sinus massage was performed in both patients and the sinus node electrogram was continuously recorded. After the onset of carotid sinus massage, prolongation of sinoatrial time, slowing of sinus rate of depolarization, sinoatrial exit block and finally sinus node arrest were recorded. After termination of carotid sinus massage, sinus node potentials did not precede the first atrial impulse; subsequent beats showed markedly prolonged sinoatrial times as well as changes in the P wave on the surface electrocardiogram. Sinus rate and sinoatrial time returned to control values gradually, as did the P wave configuration. Intravenous atropine (1.0 mg) abolished the abnormal response to carotid sinus massage. It is concluded that the application of carotid sinus massage in patients with the hypersensitive carotid sinus syndrome produces profound changes in sinoatrial conduction including sinoatrial exit block, as well as shifts in primary pacemaker site and sinus node arrest. These alterations in conduction and automaticity are reversible with atropine and may be secondary to denervation sensitivity to acetylcholine.

Sinoatrial Block with Complicating Sinoatrial Reciprocation

This presentation reflects an atypical manifestation of sinoatrial block in a patient with chronic renal failure and hyperkalemia (7.8 mEq/L). An allorhythmic distribution of P-P intervals permits the interpretation of sinoatrial block complicated by sinoatrial reciprocation.

Ambulatory 24 hour ECG in patients with a history of syncope. A retrospective follow-up study over 2 years.

174 patients referred to a general hospital for unexplained syncope were examined by ambulatory 24 hour ECG (AECG) and a follow-up by questionnaire after 2 years. The AECG demonstrated sinus rhythm in 113 patients, atrial fibrillation in 15 (in 2 of these there were occasional RR intervals of more than 3 seconds), atrioventricular (AV) block in 10, sinoatrial (SA) block in 14, tachycardia or frequent ventricular extrasystoles (VES) in 21, and no recording (technical failure) in one. Ten patients got a permanent pacemaker due to these findings, and 7 were given antiarrhythmic drug therapy. 121 patients responded to the questionnaire, 37 were dead and 16 lost to follow-up. Of the 121 responders, 36 reported multiple syncopes in the follow-up period, and another 17 one syncope. Eleven patients had received a permanent pacemaker during the follow-up period.

Cardiopathology of sinoatrial block in horses.

Six horses consisting of 3 cases with sinoatrial (S-A) block and other 3 without any arrhythmias, were studied for cardiopathology. Histopathologically focal lesions of perinodal myocardial ischemia and/or fibrosis in the S-A node area, were found out in each of the horses exhibiting this arrhythmia. In the 3 horses with sinus rhythm, the postmortem coronary arteriography revealed that the S-A node artery arose from both the left and right coronary arteries, and that the inter-arterial coronary anastomoses were located in a part of the S-A node area with the anterolateral region of the right atrium. The angiographic observation led to the suggestion that occurrence of the ischemic and/or fibrotic lesions of the S-A node area in the animals with S-A block seemed to correspond to localization of the inter-arterial coronary anastomoses. Multifocal lesions in the cardiac nerves of both the sympathetic and parasympathetic (vagal) systems, were also pointed out in the cases with arrhythmia. It seemed probable, therefore, that the pathological changes of the S-A node area, their localization and the cardiac nervous disturbances in both the systems were associated with a genesis of S-A block in the horse.

Sinus node echoes and concealed concealed conduction: Additional sinus node phenomena confirmed in man by direct sinus node electrography

Direct sinus node electrography has been previously used to assess several aspects of sinus node physiology: sinus node pauses, overdrive suppression, sinoatrial entrance block. This report presents data in which sinus node electrograms confirm two additional physiologic phenomena in man: concealed conduction in the sinoatrial junction and sinus node reentry. These findings verify the presence of previously suspected phenomena by careful deductive analysis of electrocardiographic and electrographic tracings.

Cigarette smoking and ventricular arrhythmia in coronary heart disease

With use of 24-hour ambulatory electrocardiographic monitoring, the effect of 1 hour of cigarette smoking on cardiac rhythm in 73 patients with coronary heart disease was studied. Fifteen subjects had no arrhythmia; 37 subjects had fewer than 2 atrial or ventricular premature complexes (APCs or VPCs)/hour, with APCs possibly related to smoking in 2 and VPCs related to smoking in 1. Nineteen subjects had more than 2 VPCs/hour (range 4 to 368) and had 16 ± 29 VPCs/hour (± standard deviation) less during than before smoking (p <0.05), associated with an increase in heart rate of 4.6 ±6.8 beats/ min (p <0.01). In none of the 9 subjects with unifocal VPCs did multiform beats develop during or after smoking, whereas 3 of 10 subjects with multiform VPCs had only unifocal beats during and immediately after smoking. In 1 of these 19 subjects, frequent APCs developed during smoking. One other subject had frequent APCs unaffected by smoking and another had sinoatrial block, which disappeared during smoking on 1 of 3 monitorings. In conclusion, no sustained or high-grade ventricular arrhythmia was provoked by smoking; although APCs may have been related to smoking in a few persons, the frequency and complexity of VPCs tended to be reduced in these subjects with coronary artery disease.

Chronic paroxysmal hemicrania: heart rate changes and ECG rhythm disturbances. A computerized analysis of 24 h ambulatory ECG recordings.

Ambulatory ECG recordings have been carried out in five patients suffering from CPH. During the study a total of 105 attacks occurred. Contrary to findings in cluster headache, no typical pattern of heart rate change was found in association with attacks of CPH. A striking finding in all patients, however, was that there were often large and rapid variations in heart rate which could be observed "before", "during" or "after" the attacks. One patient developed bradycardia and sino-atrial block and another bundle branch block together with episodes of atrial fibrillation in association with attacks.