Left atrial rhythm. Experimental production in man

Low Atrial Rhythm in a Large Cohort of Children from Transylvania, Romania

Low atrial rhythm (LAR) is an ectopic rhythm originating in the lower part of the right or left atrium. Prior observational studies attempted to quantify the prevalence of low atrial rhythm in the pediatric population, but the observed prevalence was highly variable with relatively small sample sizes. We aimed to characterize low atrial rhythm and determine its prevalence in a large population of 24,316 asymptomatic children from northwestern Transylvania. We found a prevalence of 0.6% (145 children) for low atrial rhythm. Children with LAR had a significantly lower heart rate (mean 78.6 ± 8.3 bpm), than the control sinus rhythm group (85.02 ± 4.5 bpm). Furthermore, a shorter PR interval was seen in children with LAR (132.7 ± 12.7 ms) than in the children from the control group (141.7 ± 5.4; p = 0.0001).There was no significant association between gender and the presence of left LAR (LLAR) or right LAR (RLAR) (p = 0.5876). The heart rate of children with LLAR was significantly higher (81.7 ± 11.6 bpm) than that of the children with LRAR (77.6 ± 11.1 bpm) (p = 0.037). Pediatric cardiologists should recognize low atrial rhythm and be aware that asymptomatic, healthy children can exhibit this pattern, which does not require therapeutic intervention.

Non-invasive localization of atrial ectopic beats by using simulated body surface P-wave integral maps

Non-invasive localization of continuous atrial ectopic beats remains a cornerstone for the treatment of atrial arrhythmias. The lack of accurate tools to guide electrophysiologists leads to an increase in the recurrence rate of ablation procedures. Existing approaches are based on the analysis of the P-waves main characteristics and the forward body surface potential maps (BSPMs) or on the inverse estimation of the electric activity of the heart from those BSPMs. These methods have not provided an efficient and systematic tool to localize ectopic triggers. In this work, we propose the use of machine learning techniques to spatially cluster and classify ectopic atrial foci into clearly differentiated atrial regions by using the body surface P-wave integral map (BSPiM) as a biomarker. Our simulated results show that ectopic foci with similar BSPiM naturally cluster into differentiated non-intersected atrial regions and that new patterns could be correctly classified with an accuracy of 97% when considering 2 clusters and 96% for 4 clusters. Our results also suggest that an increase in the number of clusters is feasible at the cost of decreasing accuracy.

P wave morphology during atrial pacing along the atrioventricular ring. ECG localization of the site of origin of retrograde atrial activation

P wave morphology during atrial pacing along the atrioventricular (AV) ring was evaluated to develop electrocardiographic (ECG) criteria for identifying the site of origin of the atrial activation wave during reentrant supraventricular tachycardia. Because P wave morphology changes as the pattern of atrial activation changes, the P wave should show characteristic morphologies during reentrant supraventricular tachycardia with use of either accessory AV pathways or the AV node for retrograde atrial activation. In 14 patients, 12-lead ECGs were recorded during bipolar atrial pacing at sites in the coronary sinus vein (along the mitral annulus) and along the atrial endocardium of the tricuspid annulus. P wave morphology was graded for each lead at each site. Sensitivity, specificity, and predictive value of ECG criteria for left versus right and anterior versus posterior atrial pacing sites were evaluated. Data were obtained from 14 sites along the AV ring, including 71 recordings at 6 sites in the coronary sinus vein and 94 recordings at 8 sites along the tricuspid annulus. These recordings were further divided into 54 anterior sites and 80 posterior sites, as well as 62 recordings along the right free wall and 32 recordings along the right atrial septum. The predictive value of a positive P wave in lead I indicating right atrial site of origin was 98.9%, and that for a negative or isoelectric P wave in lead I indicating a left atrial site of origin was 94.6%. Negative P wave in leads II, III, and aVF indicated a posterior site of origin, with a predictive value of 91.2%. The predictive value of a negative or isoelectric P wave in lead V1 indicating a right atrial free wall site was 87.5%. Thus, P wave morphology can be used to localize the site of origin of the atrial depolarization wave to a region along the AV ring.

Atrial flutter--update on the mechanism and treatment

Atrial flutter is a common and usually benign but symptomatic supraventricular tachycardia. There is a striking similarity between patients with atrial flutter suggesting a common substrate despite the presence or absence of underlying heart disease. In man, the mechanism is a single reentrant circuit originating in the right atrium whose center appears to be functional within the anatomical constraints of the right atrium. The reentrant circuit of atrial flutter contains an area of slow conduction in the inferior right atrium but the size and exact location is uncertain. Drug therapy directed at terminating and preventing atrial flutter has been available for many years. The efficacy and safety of this therapy is not as well tested as is the same therapy for atrial fibrillation. The most effective way to terminate atrial flutter is a nonpharmacological approach. Several nonpharmacological methods provide new treatment options in the management of patients with drug resistant or hemodynamically unstable atrial flutter. The use of anticoagulation for this disorder is still evolving. There is a risk of clinically apparent thromboemboli in some patients with atrial flutter although the risk appears less than that for atrial fibrillation. In the future, refinements and improvements in therapy for atrial flutter will likely be derived from a better understanding of its mechanism.

Morphology of the region of the coronary sinus in respect to coronary sinus rhythm

The arterial supply to the region of the coronary sinus and the interatrial septum was examined in 18 normal canine hearts. In 13 of a further 18 dogs, coronary sinus rhythm was evoked by the ligation of atrial arteries, subsequent to which the arteries were visualized by injection of latex. A stable coronary sinus rhythm is evoked by producing ischaemia in an extensive area of the right atrium, including the sinus node, the interatrial septum and Bachmann's bundle, but preserving from ischaemia the posteroinferior part of the right atrium. Microscopical examination of the hearts with coronary sinus rhythm, and comparison with 9 control hearts, failed to demonstrate any morphological centre, in the form of nodal cells, which might have been responsible for the abnormal rhythm. In the posterior part of the right atrium, the ischaemic changes failed to affect the approaches of the atrioventricular node. The approaches were predominantly composed of cells poor in myofibrils mixed to a variable degree with cells of the working myocardium. We discuss the possibilities of the development of coronary sinus rhythm and "circus movement" with regard to the participation of the approaches to the atrioventricular node.

Body surface maps of ectopic P waves originating in the left atrium in the dog

Body surface maps of the P wave in dogs stimulated at various sites on the atria were prepared to find diagnostic signs to detect the origin of left atrial rhythm. Body surface electrograms from 87 points on the thorax and 8-12 points on the epicardial surface of both atria were simultaneously recorded. The body surface P maps disclosed characteristic findings according to whether the site of the stimulation was at the lower right atrium (RA) or the upper, middle, or lower left atrium (LA). In the LA rhythm, the maximum of the P maps moves from the left to the right chest during the later phase of atrial excitation, while it goes from the right to the left in the sinus or the RA rhythm. In the P maps of the rhythm originating in the upper LA, the minimum always stays at a position on the chest above the location of the maximum, while the negative potential areas are above the positive ones. The maps of the middle LA rhythm show that the maximum and the minimum are located horizontally to each other on the chest. The positive and negative areas cover both sides of the chest, separated by zero lines running vertically. In the low LA rhythm, the maximum is always located at a position on the chest above the minimum, and the positive areas are above the negative ones. These results indicate that mapping of the body surface P waves is a valuable method for diagnosing left atrial rhythm and for detecting the approximate location of its origin.

Clinical confirmation of ECG criteria for left atrial rhythm

Controversy exists as to which of several ECG criteria are necessary for the diagnosis of left atrial (LA) rhythm. We performed invasive electrophysiologic study in five patients (6 to 15 years-of-age) who had symptomatic supraventricular tachycardia (SVT) that could not be controlled by aggressive pharmacologic treatment. All patients were found to have automatic atrial tachycardia with the earliest site of activation during SVT in the LA. The ECG of each patient demonstrated negative P waves in lead I. The frontal plane P wave axis ranged between +90 to +270 degrees in each of our patients. Spontaneous "dome-and-dart" P waves occurred in lead V1 in two of our patients. We conclude that the necessary criterion for the diagnosis of LA rhythm should be negative P waves in lead I. The finding of "dome-and-dart" P waves in V1 is an additional useful and definitive criterion but is not present in each case.

Current management of patients after cardiopulmonary bypass

The postoperative management of cardiac surgical patients is reviewed with particular reference to some of the recent advances and current controversies. It is emphasised that there has been a marked decrease in the incidence of many of the major problems associated with cardiopulmonary bypass and that, in the majority of cases, cardiac surgery is now a routine procedure associated with a very low morbidity and mortality.

Left atrial rhythm in man: an experimental study

Ten patients with atrial septal defect of the secondum variety undergoing diagnostic haemodynamic study were subjected to electrical stimulation of the endocardium of the left atrium using a bipolar pacing electrode catheter. The polarity, frontal plane P wave axis and P wave configuration were analysed from ten scalar 12 lead electrocardiogram (ECG), recorded at 25-50 mm/sec during sinus rhythm and left atrial stimulation. While four patients demonstrated the "dome and dart" appearance of P waves in V1, nine out of ten patients revealed upright P waves in V1 during left atrial pacing; one patient showed inverted P waves in V1-V6. Four patients had negative "P" waves in L1 and only five of ten patients had inverted "P" waves in L1 and V6. All the criteria of left atrial rhythm were present in only one patient. It appears that the "P" waves change during left atrial pacing are variable and that the typical findings of left atrial rhythm are not obtained in all cases. This study was planned because trans-septal left atrial stimulation in the genesis of left atrial rhythm has not been widely reported.

Electrophysiologic characteristics of concealed bypass tracts: clinical and electrocardiographic correlates

Twelve of 60 consecutively studied patients undergoing electrophysiologic study for paroxysmal supraventricular tachycardia had atrioventricular (A-V) bypass tracts functioning as the retrograde limb of the reentrant circuit. None had evidence of preexcitation in the surface electrocardiogram, but in two patients anterograde preexcitation could be produced by pacing from the coronary sinus. In all 12 patients with concealed bypass tracts the retrograde atrial activation sequence or effect of left bundle branch block aberration during the tachycardia, or both, confirmed the left-sided bypass tract. A negative P wave in lead I during the tachycardia was also diagnostic of a left-sided bypass tract. Dual A-V nodal pathways were found in five patients with concealed bypass tracts but were unrelated to the development of the tachycardia. When compared with supraventricular tachycardia due to A-V nodal reentry, clinical findings suggestive of a concealed bypass tract included: (1) P wave following the QRS complex (12 of 12 versus 12 of 40), (2) negative P wave in lead I during the tachycardia, and (3) bundle branch block aberration during the tachycardia (8 of 12 versus 3 of 40). Other characteristics of patients with concealed bypass tracts that were of less value in individual cases were shorter cycle lengths of tachycardia, younger patient age and lesser incidence of organic heart disease.

Overdrive pacing for supraventricular tachycardia: a review of theoretical implications and therapeutic techniques

Rapid atrial pacing for treatment of supraventricular arrhythmias has been demonstrated to be safe and effective. Virtually any supraventricular tachycardia with the exception of atrial fibrillation, Type II atrial flutter, and probably sinus tachycardia can be treated successfully with pacing techniques. The recognition of the advantages of cardiac pacing over drug therapy or DC cardioversion has resulted in its widespread use, especially after open-heart surgery. Although the response to overdrive pacing may not reliably identify the underlying mechanism of supraventricular tachycardia, the response of the arrhythmia to pacing (i.e., whether it is interruptable or noninterruptable), is most useful in the approach to management of the individual patient.

Entrainment and interruption of atrial flutter with atrial pacing: studies in man following open heart surgery

To examine the question of why the pacing rate and duration of atrial pacing are crucial factors in the successful interruption of atrial flutter, studies were performed on 30 patients in the period following open heart surgery. In each patient the diagnosis of atrial flutter was made using a pair of wire electrodes placed on the right atrial epicardium at the time of operation and brought out through the anterior chest wall. The same electrodes were used for atrial pacing. Pacing faster than the spontaneous rate of the atrial flutter which failed to interrupt the atrial flutter was associated with transient entrainment of the atrial flutter up to the atrial pacing rate. Atrial flutter was interrupted successfully when the atria were paced at a rate which was too fast for the atrial flutter to follow. This was heralded by the conversion of previously negative flutter waves to positive atrial complexes in ECG lead II. When pacing the atria at a constant rate, 2-22 seconds with a mean of 10 seconds were required to interrupt the atrial flutter.

Changing P wave polarity. Intermittent posterior internodal conduction

Spontaneous changes of P-wave polarity without change in heart rate were noted on the resting electrocardiogram of a patient admitted because of chest pain. Intracardiac and His bundle electrograms were compatible with a sequence of activation from high to low right atrium with both positive and negative P waves in lead aVR. The decrease in the P-His interval with positive P waves in lead aVR is consistent with selective conduction via the posterior internodal pathway.

Repetitive paroxysmal tachycardia originating in the left atrium

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Electrophysiological properties of cardiac muscle in the anterior mitral valve leaflet and the adjacent atrium in the dog. Possible implications for the genesis of atrial dysrhythmias

Transmembrane action potentials were recorded from multiple sites in isolated canine anteromedial left atrial wall preparations with the anterior mitral valve leaflet attached. The preparations were superfused with Tyrode's solution. When the left atrial wall was electrically stimulated, activity propagated into the mitral valve leaflet. Typical atrial action potentials occurred in atrial wall fibers. However, maximum diastolic potential, total action potential amplitude, and rate of depolarization decreased markedly in the atrium overlying the fibrous annulus (junctional region), and repolarization characteristics were altered in this region. Mitral valve muscle fibers demonstrated still lower maximum diastolic potential, action potential amplitude, and rate of depolarization. Electrical excitation of single discrete regions in the mitral valve leaflet did not result in conduction to the atrium; conduction block occurred in the junctional region. However, simultaneous excitation of several mitral valve sites did cause an impulse to propagate to the atrium, but transmembrane action potentials of junctional fibers were characteristically different from those recorded from the same junctional fibers during activation from the atrium. Muscle fibers in the mitral valve leaflet were capable of developing spontaneous diastolic depolarization, which resulted in automatic impulse initiation, when they were exposed to epinephrine or norepinephrine (1 x 10 -7 to 1 x 10 -5 M) or when they were stretched. Spontaneous diastolic depolarization and automaticity also occurred occasionally without pharmacological or other experimental interventions; moreover, spontaneous activity originating in the mitral valve leaflet could propagate into and activate the atrial wall. Acetylcholine abolished spontaneous activity. These data suggest that the mitral valve could act as a site of ectopic impulse initiation in the left atrium.

AV junctional versus left atrial rhythm

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Studies on left atrial automaticity in dogs

The site of origin and the sequence of atrial activation were studied in 21 open-chested dogs anesthetized with sodium pentobarbital. Bipolar plunge electrodes were used to record atrial electrograms simultaneously with surface lead II and His bundle electrogram. In sinus rhythm the sinus node was activated first, followed sequentially by Bachmann's bundle, right atrial appendix, left atrial appendix, posterior left atrium, and the proximal portion of the coronary sinus. In 15 dogs left atrial beats and rhythms of various rate were recorded, including instances of left atrial exit block and of rapid left atrial rhythms. In such beats one of the left atrial electrodes was activated first and was followed by Bachmann's bundle, sinus node, proximal portion of the coronary sinus, and by right atrial appendix. Left atrial beats were observed occurring (1) spontaneously; (2) as a result of vagal stimulation; (3) after destruction of the sinus node; (4) during ventricular pacing. Left atrial pacing through the electrode recording initial activity reproduced the sequence and configuration of atrial electrogram similar to that seen in the ectopic left atrial beats. These results demonstrate that in dogs ectopic activity frequently originates in the left atrium.