Sinus Node Area Research Articles

Excitation-contraction mechanisms of the quail heart are functional at temperatures near freezing point

1. 1.Both subcellular contractile waves and the electrically triggered twitches of the isolated cardiac myocytes of the quail ( Coturnix coturnix japonica) could be observed down to 0°C, where contractions ceased but recovered if the temperature was raised before freezing took place. 2. 2.The threshold for excitation to the electrical field stimulus increased steeply in single myocytes at temperatures below 20°C. Energy of activation E a) as calculated from Arrhenius plot for the rheobase values were 24 kJ above and 49 kJ below 20°C. 3. 3.Electrical activity as well as visible contractions of the whole heart preparation stopped between 16 and 18°C, but could be triggered by electrical stimulus down to 6°C. However, irregular, spontaneous local contractions could still be observed in the sinus node area at 4°C. 4. 4.Below 17°C the rheobase for the whole heart excitation increased more steeply than that of the single myocyte. 5. 5.The results suggest that the excitation-contraction processes of the quail myocardial cells can function down to the freezing point. Because of a failure in propagation of excitation in the syncytial structure the limit for the spontaneous beat of the whole heart lies between 16–18°C.

Direct Entrainment‐Guided Catheter Fulguration of Atrial Flutter in Man

Direct catheter fulguration of the reentrant circuit of atrial flutter was performed in a 63‐year‐old patient referred for His bundle ablation. Careful right atrial mapping was performed using standard catheter electrodes. Two zones of fragmented potentials were recorded: one in the low posterior right atrial septum and the other one in the sinus node area. Entrainment of the tachycardia was attempted and achieved, while at the same moment the electrograms of the sinus node area dissociated, thereby excluding it as part of the reentrant circuit. Two shocks of100 and 150 J respectively were delivered in the low postero‐septal area without complication. Seventy weeks of follow‐up were uneventful despite persistence of inducibility of a rapid (non clinical) atrial flutter at late control (day 90). Direct catheter ablation in human atrial flutter seems to be a promising procedure if further studies confirm its efficiency.

A Clinical Angiographic Study of the Arterial Blood Supply to the Sinus Node

We studied the arterial blood supply to the sinus node area in 309 consecutive patients undergoing coronary arteriography. Seventy-nine had had a previous myocardial infarction. In two who developed temporary sinus node dysfunction, the sinus node artery arose from the distal portion of a severely stenotic left circumflex coronary artery, but in 307 of the 309 patients the sinus node arteries themselves were free of atheroma. The sinus node artery arose from the right coronary artery in 182 patients, from the proximal 3 cm in 179, near the origin of the acute marginal in one, and left of the crux in two. In 119 patients it arose from the left circumflex coronary artery, proximally in 87, and in 32 from anywhere throughout its length, running posteriorly as the posterior sinus node artery. Finally, eight patients had two sinus node arteries, one arising from the right coronary artery and one from the left circumflex.

Sinus node function after selective elimination of sympathetic influences on the sinus node area of the dog.

Six-hydroxydopamine (6OHDA) was injected directly into the subepicardium of the sinus node area in an attempt to damage sympathetic nerve terminals in the sinus node. The changes in sinus node function were observed for 4 weeks. The predominant rhythm was of sinus origin throughout the observation period. The sinus rate progressively decreased from 145.1 +/- 14.2 to 76.2 +/- 12.1 beats/min during the first week after injection of 6OHDA. The sinus rate remained at this level for 2 weeks, followed by a gradual increase to 89.3 +/- 18.2 beats/min 4 weeks after injection of 6OHDA. These sinus rates were only significantly different from control dogs through the 14th postoperative day. The sinus rate was considerably increased by intravenous atropine injections 5 to 7 days after the injection of 6OHDA into the sinus node area. The sinus node recovery time was much longer in dogs with an injection of 6OHDA than that in the control dogs throughout the observed period. These results suggest that elimination of the sympathetic influences on the sinus node can be achieved by direct injection of 6OHDA into the sinus node area in the dog, and that sinus node function can be depressed by decreasing sympathetic tone alone, in the absence of an intrinsic dysfunction of the sinus node.

Dysrhythmias after atrial surgery in children

A retrospective study was done in 50 patients after Mustard's operation (group A) and in 204 patients after closure of a secundum atrial septal defect (group B) to analyze the postoperative dysrhythmias and to relate them to surgical factors. Forty-two percent of the patients in group A had dysrhythmias at the end of the follow-up, compared to 23% of group B patients. There was a high late mortality in group A (16%) significantly related to AF and AVJ. In group A a significant correlation was found between dysrhythmias and age at operation, use of cardioplegia, perfusion time, and the type of cannulation. In group B there was a significant relation between the location of the defect and the presence of abnormal pulmonary venous drainage. After ASD closure using hypothermia instead of cardiopulmonary bypass, the incidence of dysrhythmias was significant lower. Damage to the sinus node by cannulation and by suturing in the sinus node area is the main cause of the high incidence of dysrhythmias after atrial surgery. This high incidence should be a factor in the consideration of new types of operations.

Tachycardia and apparent sino-atrial block due to concealed sinus node re-entry.

The role of the middle intercaval area ("internodal pathway") in the genesis of atrial re-entry was studied using microelectrode techniques and the extrastimulus method in the rabbit heart. Following surgical interruption of the anterior and posterior internodal tracts, two patterns of re-entry were observed using the middle internodal pathway manifesting alternatively as tachy- and brady-arrhythmias. Re-entry which was produced by critically timed extrastimulation at the septal branch of the crista terminalis (CT) caused tachycardia reciprocating between the sinus node (SN) and intercaval area. Spontaneous re-entrant impulses were also observed, particularly following the addition of cedilanid (0.04 mg/L). In addition, in association with critical prolongation of conduction in the sino-septal area, premature discharge of the dominant pacemaker fibers was observed and resulted in the appearance of bradyarrhythmias. These were commonly manifest as bigeminy and trigeminy on the surface septal electrogram. Hence concealed sinus node re-entry could manifest itself as apparent sino-atrial block or sino-atrial re-entry tachycardia.

Sinus node coronary arteries studied with angiography

Coronary angiograms of 309 consecutive patients undergoing coronary angiography were reviewed to investigate the blood supply to the sinus node area. Blood was supplied from the right coronary artery in 59% of cases, from the left coronary artery in 38%, and from both coronary arteries in 3%. The posterior sinus node artery was demonstrated in 32 patients (27% of the 119 patients with the sinus node artery originating from the left circumflex and 10.5% of all patients).

The cellular electrophysiologic mechanism of the dual actions of disopyramide on rabbit sinus node function.

To determine the contribution of disopyramide's suggested opposing direct depressant and indirect acceleratory actions on sinus node function, we studied the effects of disopyramide, 1 x 10(-7) to 1 x 10(-4) M, on isolated rabbit sinus node preparations using standard microelectrode techniques. Transmembrane potentials were recorded simultaneously from the sinus node and adjoining crista terminalis area. Disopyramide, as much as 1 x 10(-5) M, had no effects on the sinus cycle length. At a concentration of 1 x 10(-4) M, sinus cycle length was significantly prolonged due to prolongation of the sinus nodal action potential duration. During cholinergic blockade with atropine, 1 x 10(-6) M, disopyramide, 1 x 10(-7) to 1 x 10(-4) M, significantly prolonged sinus cycle length as a result of a prolongation of the sinus nodal action potential duration and a decrease of the slope of phase 4 depolarization. During cholinergic stimulation with carbamyl choline, 1 x 10(-9) M, disopyramide, 1 x 10(-7) to 1 x 10(-6) M, tended to reverse carbamyl choline-induced prolongation of the sinus cycle length (NS). This acceleratory action of disopyramide was caused by a significant increase of the slope of phase 4 depolarization. Disopyramide, 1 x 10(-7) to 1 x 10(-4) M, had no significant effects on corrected sinus node recovery time or on sinoatrial conduction time under any conditions studied. We conclude that disopyramide has a direct depressant action on normal sinus node cells at the upper therapeutic and toxic levels, which is enhanced during cholinergic blockade, and that disopyramide's acceleratory action appears only at much lower concentrations and only during cholinergic stimulation.

The sinus node electrogram in patients with and without sick sinus syndrome: techniques and correlation between directly measured and indirectly estimated sinoatrial conduction time.

SUMMARY Sinus node electrograms (SNEs) were recorded in 44 patients using a standard quadripolar electrode catheter (USCI #6) with 10-mm interelectrode distance. In 23 patients, the catheter was positioned at the junction of the superior vena cava (SVC) and right atrial (RA) wall so that the concave curve of the catheter was facing the concave surface of the RA wall. The distal poles of the catheter were close to but not in direct contact with the RA endocardium underlying the anatomic location of the sinus node (method 1). In 21 patients, the catheter was looped in the RA and advanced to the junction of the SVC-RA wall so that the distal poles of the catheter were in direct contact with the RA endocardium underlying the area of the sinus node (method 2). Stable SNEs could be obtained in 10 of 23 patients (43%) by method 1 and in 18 of 21 (86%) by method 2. SNEs by both methods showed two negatively directed deflections (diastolic and upstroke slope of the sinus node) of low frequency and amplitude occurring after the deflections of the T and U waves but before the P wave and intraatrial electrograms from various atrial sites. Unlike method 1, atrial activation by method 2 was characterized by an atrial injury potential. SNEs by method 2 were more stable and less prone to baseline drifts. Carotid sinus massage performed in 10 patients resulted in prolongation of the onset of the upstroke slope to atrial activation. In one patient, it resulted in marked first-degree sinoatrial block. SNEs were recorded in one patient during and after a run of spontaneous atrial flutter. After termination of atrial flutter, sinoatrial conduction time (SACT) prolonged for the first postflutter sinus beat and normalized by the third sinus beat. Direct SACTwas assessed on the SNE in all 28 patients, 12 of whom had sick sinus syndrome (SSS). SACT was also estimated indirectly by continuous pacing in 28 patients and by premature stimulation in 20 patients. Direct SACT was significantly (p < 0.001) longer in patients with SSS (135 30 msec, mean SD) than in patients without SSS (87 12 msec).There was a good correlation between direct SACT and SACT by continuous pacing (r = 0.843, n = 28) and direct SACT and SACT by premature stimulation (r = 0.778, n = 18). However, in certain patients, there were appreciable differences and direct SACTwas longer than estimated SACT by continuous pacing or premature stimulation. We conclude that (1) the success rate of stable SNEs with no appreciable baseline drift is increased with direct contact of the catheter with atrial endocardium underlying the sinus node area (method 2); (2) carotid sinus massage results in depression of sinus node automaticity and prolongation of SACT; (3) direct SACT is significantly longer in patients with SSS and can separate most patients with from those without SSS; and (4) there is a good correlation between direct SACT and indirectly estimated SACT, although the latter underestimates the actual SACT.

Sympathetic neural effects on regional atrial recovery properties and cardiac rhythm

The functional distribution of the cardiac sympathetic nerves to the atria and their arrhythmiogenic effects were determined in 16 open-chest pentobarbital-anesthetized dogs. Shortening of refractory periods at four right and two left atrial sites during stimulation of the nerves was taken as a criterion of their distribution. Stimulation of right stellate ganglion, craniovagal, and right stellate cardiac nerves produced localized shortening on the right atrium, particularly at the sinus node area, and invariably induced sinus tachycardia. The recurrent cardiac nerve produced little shortening at all sites and less arrhythmiogenic effect. The left stellate ganglion and ventrolateral cardiac nerve affected only left atrial sites and induced atrioventricular junctional rhythm. The ventromedial cardiac nerve affected all sites and had no consistent arrhythmiogenic effect. The innominate nerve had no substantial effect. We concluded that the functional distribution of the cardiac sympathetic nerves is localized, and that rate, rhythm, and refractory period changes induced by stimulation of these nerves are characteristic of the area of distribution.

An S-Shaped Atrial Artery Supplying the Sinus Node Area: An Anatomical Study

An S-shaped sinus node artery (SSNA), originating in the posterolateral part of the left circumflex artery (LCir) below or behind the left auricle, is described in detail. The coronary vessels were studied in 300 human hearts by x-ray films or by casting of the vessels, and the SSNA was found in 24 (21.5 percent) of the 111 cases where the sinus node artery (SNA) arose from the LCir, (ie, 8 percent of all the hearts). The SSNA constituted a branch of the LCir in 15 cases, the upper part of a divided LCir in 6 cases, and the main continuation of this artery in 3 cases, always following basically the same route to the sinus node (SN) area. It was larger than the normal SNA, supplying the SN and surrounding area, almost the whole left atrium, a large part of the interatrial septum and right atrium, and partially supplying the atrioventricular node area.

Sustained intra-atrial reentrant tachycardia. Electrophysiologic study of 20 cases.

Twenty cases of sustained tachycardia due to intra-atrial reentry were investigated in patients aged 17 to 80 years (mean 47). The average frequency of the tachycardia was 128.6/min (extremes 95 and 180). Three modes of onset of the tachycardia were observed: atrial extra-stimulus (19 times), progressively accelerated atrial pacing (9 times) and atrial escape beat (10 times). The tachycardia was stopped in all cases by a premature stimulation. When spontaneous, the termination was either sudden (10 times) or preceded by a progressive slowing (9 times) or an alternating phenomenon of long-short cycle (13 times). Precise atrial mapping allowed to localize the first atrial depolarization less frequently in the sinus node area (1 case) than in the mean right atrium (21 cases), the low right atrium (2 cases), the interatrial septum (2 cases), and the left atrium (4 cases). The macroscopic size of the reentry circuit was demonstrated in only 3 cases. A junctional reentry was accurately ruled out in all cases thanks to the existence of a second or third-degree AV or VA black, or by studying the sequence of retrograde atrial activation. A true junctional reciprocating tachycardia was associated with the intra-atrial reentry in 2 cases.

Irrigação do nó sinu-atrial em carneiros da raça Merino

The arterial blood supply to the sinus node district has been studied, by dissections (64) and clearing technique after injection of opaque solution (11), in the heart of 75 sheep. The AA found that this district is vascularized exclusively by the ramus proximalis atrii dextri and ramus intermedius atrii dextri, branches of the right coronary artery, in 57.3% ± 5.7 of the cases. In 33.3% ± 5.4 of the sheep the sinus node area is prevalently supplied by the ramus proximalis atrii sinistri, originating from the left coronary artery, and partially by the ramus intermedius atrii dextri. In 5.3% ± 2.5 of the subjects examined the vascularization of the sinus node district is provided simultaneously by the ramus proximalis atrii dextri, ramus proximalis atrii sinistri andramus intermedius atrii dextri; in the remaining 4.0% ± 2.2 the contribution of the ramus proximalis atrii sinistri is doubtful.

Contribuição ao estudo da irrigação arterial do nó sinu-atrial em coelhos de raça Nova Zelândia

The arterial blood-supply of the sinuatrial node has been studied in 50 rabbits (26 females and 24 males). In 26 (52.0% ± 7.0) hearts examined, the sinus node received only the ramus proximalis atrii sinistri collateral of the a. coronaria sinistra. In 22 (44-0% ± 7.0) animals, the sinus node was exclusively nourished by collaterals of the a. coronaria dextra; in 20 cases (40.0% ± 6.9) only by the ramus proximalis atrii dextri and in 2 cases (4.0% ± 2.7) by the latter and the ramus intermedius atrii dextri. In the remaining 2 cases (4.0% ± 2.7) both the rami proximalis atrii sinistri and proximalis atrii dextri respectively originated from the a. coronaria sinistra and, a. coronaria dextra nourished the sinus node area. The AA. did not observe arterial anastomosis among the vessels involved in the sinus node arterial vascularization.