Use of machine learning and Poincaré density grid in the diagnosis of sinus node dysfunction caused by sinoatrial conduction block in dogs

BACKGROUND

Sinus node dysfunction because of abnormal impulse generation or sinoatrial conduction block causes bradycardia that can be difficult to differentiate from high parasympathetic/low sympathetic modulation (HP/LSM).

HYPOTHESIS

Beat-to-beat relationships of sinus node dysfunction are quantifiably distinguishable by Poincaré plots, machine learning, and 3-dimensional density grid analysis. Moreover, computer modeling establishes sinoatrial conduction block as a mechanism.

ANIMALS

Three groups of dogs were studied with a diagnosis of: (1) balanced autonomic modulation (n = 26), (2) HP/LSM (n = 26), and (3) sinus node dysfunction (n = 21).

METHODS

Heart rate parameters and Poincaré plot data were determined [median (25%-75%)]. Recordings were randomly assigned to training or testing. Supervised machine learning of the training data was evaluated with the testing data. The computer model included impulse rate, exit block probability, and HP/LSM.

RESULTS

Confusion matrices illustrated the effectiveness in diagnosing by both machine learning and Poincaré density grid. Sinus pauses >2 s differentiated (P < .0001) HP/LSM (2340; 583-3947 s) from sinus node dysfunction (8503; 7078-10 050 s), but average heart rate did not. The shortest linear intervals were longer with sinus node dysfunction (315; 278-323 ms) vs HP/LSM (260; 251-292 ms; P = .008), but the longest linear intervals were shorter with sinus node dysfunction (620; 565-698 ms) vs HP/LSM (843; 799-888 ms; P < .0001).

CONCLUSIONS

Number and duration of pauses, not heart rate, differentiated sinus node dysfunction from HP/LSM. Machine learning and Poincaré density grid can accurately identify sinus node dysfunction. Computer modeling supports sinoatrial conduction block as a mechanism of sinus node dysfunction.

Non-invasive beat-to-beat analysis of stroke volume and digital pulse volume in patients with complete heart block and artificial pacing

This study presents a beat-to-beat analysis of digital arterial pulse volume (DAPA), left ventricular end-diastolic diameter (LVEDD), and stroke volume (SV) and their correlation to PQ interval in ten patients with complete heart block and artificial cardiac pacing. DAPA was measured by strain-gauge plethysmography and LVEDD/SV by echocardiography. A close relationship was found between SV and DAPA (R = 0.83-0.97) in seven patients, who all drew considerable benefit from atrial contraction as regards SV and DAPA (increase with 35-94%). The optimal PQ interval was calculated to approximately 240 msec for DAPA and 180 msec for LVEDD and SV. It may be concluded that the present study demonstrates a close relationship between beat-to-beat variations of SV measured by echocardiography and plethysmographically recorded digital arterial pulse volume. These variables may be useful in clinical practice for assessing the hemodynamic effect of atrial contribution in patients with various forms of cardiac conduction disturbances. The two methods may, for instance, be useful for screening in order to pick out patients who may benefit from AV synchronous rather than ventricular pacing.

Sinus node dysfunction in 128 patients. A retrospective study with follow-up

A retrospective study covering all admissions during a 6-year period revealed 128 patients with sinus node dysfunction (SND). The patients were grouped according to the ECG criteria chosen: group I 33 patients with sinus bradycardia, group II 37 with sinoatrial block/sinus arrest, group III 58 with brady-tachy syndrome. Additional heart disease, predominantly ischaemic, was found in 56%. The frequency and severity of symptoms increased from group I to group III. Pacemaker treatment was given to 40% of the cases, while medical treatment alone was successful in 17%. A follow-up including 104 patients was carried out after a mean observation period of approximately three years. Sixteen patients had died. The cause of death may have been SND per se in only one case. Five patients died of apoplectic insults or complications to such. In total, nine possible or proven systemic embolic events were found--all occurring in patients with brady-tachy syndrome. A progression of the ECG abnormality from a lower to a higher group took place in nine patients during the observation period. It is concluded that SND is a condition with a broad clinical spectrum and a stationary or slowly progressive course. In general, it carries a good prognosis. A substantial number of deaths of disabilities in patients with brady-tachy syndrome may be ascribed to systemic embolism. Long-term anticoagulant therapy is proposed in this subgroup of patients with SND.

The sick sinus syndrome

Clinical and electrophysiological characteristics have been investigated in a group of 30 patients with a sick sinus syndrome. No predictable response to exercise or drugs was observed, although a poor response of the sinus rate to atropine was present. Distal conduction abnormalities were found in seven of 14 patients, in whom detailed electrophysiological measurements were made, and sinus node recovery time was abnormal in all except one. Treatment with permanent pacing not only relieved syncope and dizziness, but made drug treatment of associated tachyarrhythmias feasible. The elusive and intermittent nature of the syndrome is stressed. The pathological findings in one case are described at length.

Prospective evaluation of atrial tachyarrhythmias in patients with interatrial block

INTRODUCTION

Interatrial block (P-wave> or =110 ms) is clinically associated with left atrial enlargement and electromechanical dysfunction as well as atrial tachyarrhythmias. We prospectively evaluated the incidence of such arrhythmias, especially atrial fibrillation among patients with interatrial block over the course of 1 year.

METHODS

118 patients (aged 48 to 104 years; female 56.6%) who had been hospitalized between December 15, 2004 and January 14, 2005 were identified and divided into 3 groups based on their respective baseline electrocardiogram (interatrial block=41 patients, sinus non-interatrial block=51 patients and atrial tachyarrhythmia=24 patients). Patients were subsequently followed for 12 months for pertinent cardiovascular events (heart failure, peripheral embolism, transient ischemic attacks and stroke), atrial tachyarrhythmias (atrial fibrillation and atrial flutter) and death as endpoints.

RESULTS

19 patients (17.9%) had atrial fibrillation during the 12-month follow-up (sinus non-interatrial block group=4 [9.1%], interatrial block group=12 [29.3%] and atrial tachyarrhythmia group=3 [14.3%]). Coronary artery disease, hypertension, pre-existing atrial fibrillation history, dilated cardiomyopathy, atrioventricular valvular disease and interatrial block (age- and sex-adjusted hazard ratio=4.2; 95% confidence interval 1.2-14.4; p=0.02) were significantly associated with future events of atrial fibrillation. However, logistic regression analysis indicated that interatrial block was not an independent predictor of future atrial fibrillation whereas only history of pre-existing atrial tachyarrhythmias was (hazard ratio=23.6; 95% confidence interval 4.5-121.7; p=0.0002).

CONCLUSION

Interatrial block may be associated with atrial fibrillation but in a 12-month period, does not appear to be an independent predictor of future atrial fibrillation. Continued prospective investigation of such a relationship is certainly warranted given its already known consequences.

The scoring of cardiac events during sleep

Standardized guidelines for polysomnography (PSG) have not specified methods for acquiring or interpreting electrocardiographic (ECG) data. The practice of single lead ECG monitoring during PSG may allow identification of simple measures of cardiac rhythm but reduces the ability to detect myocardial ischemia and to define cardiac intervals. Although simple measures of cardiac rhythm such as heart rate and cardiac pauses are inherently reliable, there is limited data regarding outcome measures relative to sleep related heart rates and cardiac events during sleep. Several observational and cross-sectional studies demonstrate that average heart rate drops nearly 50% from infancy through young adulthood and that the average heart rate slows during sleep compared with wakefulness; the definitions of sinus bradycardia and sinus tachycardia should therefore be lower during sleep than wakefulness. Asystoles of up to 2 seconds are seen in normal populations during sleep. Although there may be an increased risk of certain arrhythmias at night, particularly in sleep disordered breathing, there is no evidence that supports different definitions for these arrhythmias during sleep compared with wakefulness. When the quality of tracings permits, the standard definitions of narrow- and wide-complex tachycardias and atrial fibrillation may be employed. In the future, expansion to multiple ECG leads and the use of alternative tools may provide better definition of heart rates and cardiac events during sleep.

Bradydysrhythmias and atrioventricular conduction blocks

Bradydysrhythimas include sinus bradycardia, junctional brady-cardia, and idioventricular rhythm, which can be distinguished by examining the tracing for the presence or absence of P waves,noting the morphology of these P waves, and determining the width of the QRS complex. Sinoatrial blocks may occur in either first, second, or third degree varieties. Only second degree sinoatrial block can be detected on the 12-lead ECG. Sinus pause and sinus arrest may mimic second degree sinoatrial block, but their periodicity is irregular. The cyclic variability of sinus arrhythmia is unique; as with the other bradydysrhythmias, it may be innocent or pathologic depending upon clinical circumstances. Atrioventricular blocks may occur, and, similar to sinoatrial blocks, they are also categorized as first-, second-, or third degree. These are of greater clinical relevance than their sinoatrial counterparts.

[The ECG-phenomenon of ST segment elevation: the reasons for it and its clinical significance]

The authors adduce a detailed analysis of the reasons for ST segment elevation, which is found in patients with various pathologic conditions and in some normal individuals, basing this analysis on their own experience and literature data. The authors pay special attention to differential ECG-diagnostics of ST elevation, which plays the most significant part in practice.

Confirmation of the prevalence and importance of a 12-lead investigation for diagnosis of interatrial block [corrected]

We investigated 500 consecutive, unselected electrocardiograms of outpatients for interatrial block (IAB) using all 12 leads rather than the usual recommendation in the literature, which is lead II, sometimes with another lead. IAB had been reported in 2 widely separated large general hospitals in >40% of 1,000 patients in sinus rhythm in each. Because the P waves in IAB (duration > or =110 ms) generally have low amplitude despite their excessive width, we used magnifying graticules and, for greater specificity, a minimal duration of > or =120 ms. Four hundred sixty-nine patients remained after excluding those with atrial arrhythmias or technically poor tracing. Two hundred three of these patients (40.6%) had IAB. Had we used lead II alone, only 110 cases would have been identified, which would have meant overlooking almost 1/2 the cases with this lesion, which is important (1) as a predictor of atrial fibrillation and other arrhythmias, and (2) represents a large, dysfunctional left atrium. Leads V3 and V4 yielded larger numbers of IAB than lead II. (The slightly smaller prevalence than in the 2 cited studies may be due to our using 1/2 the number of patients.) Electrocardiographic interpreters should seek IAB in all 12 leads and consider its anatomic functional and predictive correlates.

Atrial activation mapping in sinus rhythm in the clinical electrophysiology laboratory: observations during Bachmann's bundle block

INTRODUCTION

The high posterolateral right atrium (RA) is considered the "sinus node area," but we lack information on endocardial atrial activation in sinus rhythm. We studied RA and left atrial (LA) endocardial activation in the electrophysiology laboratory.

METHODS AND RESULTS

Thirty-five patients (21 men) aged 47 +/- 16.4 years (mean +/- SD) underwent RA mapping (22.2 +/- 3.8 points). In 21 patients, LA activation was mapped (11.1 +/- 3.9 points) through the coronary sinus (CS), right pulmonary artery, and/or a patent oval foramen. Fourteen patients had atrial arrhythmias, and 3 an ECG pattern of Bachmann's bundle block. Endocardial RA activation preceded P wave in 5 (-14 +/- 4.2 ms), coincided in 11, and followed P onset in 18 (16.7 +/- 6.6 ms). Location of the zero point varied from the superior vena cava to the low RA and from lateral to paraseptal RA. In 19 patients, activation started simultaneously in 2 to 5 points located >or=1 cm apart. RA activation was descending in most, but in 3 with low onset there was collision in the anterior and septal walls. In 15 of 21 patients, descending LA activation dominated, ending in the mid CS in 12, proximal CS in 1, and simultaneously throughout the CS in 2. In 3 with Bachmann's bundle block, CS activation was ascending and in 2 double potentials were recorded from the LA roof.

CONCLUSION

During stable sinus rhythm, RA activation can start in different areas or simultaneously over large areas resulting in different activation patterns, both in the RA and the LA. LA activation is predominantly descending, but in Bachmann's bundle block it becomes ascending, and double potentials suggest a location of block in the LA roof.

[Lyme carditis and symptomatic sinus node dysfunction]

Lyme carditis is typically associated with AV nodal conduction abnormalities. We describe the case of a 66 year old female patient, who experienced a series of syncopal attacks after several tick bites two weeks earlier. ECG monitoring revealed recurrent sinus arrest with a maximum pause duration of 8 seconds. After institution of antibiotic therapy for Lyme carditis, sinus node dysfunction resolved rapidly and the patient had no further syncopes. Pacemaker implantation was not necessary. We therefore have to assume that in this patient Lyme carditis was the cause of symptomatic sinus node dysfunction.

[Early invasive strategy in acute coronary syndromes without persistent ST-segment elevation. Baseline characteristics and in-hospital outcome: Zabrze Registry]

Acute coronary syndromes (ACS) without ST elevation (which include unstable angina [UA] and non ST elevation MI [NSTEMI]) are caused by dynamic changes in the atherosclerotic plaque and coronary blood flow. To determine characteristics, in-hospital outcome and management of patients with ACS without ST elevation. The total of 502 patients were enrolled. Inclusion criteria were: rest angina within the last 24 hours, ST-segment deviation (>0,05 mV), T-wave inversion (>0,1 mV) in at least two leads, positive serum cardiac markers. There were 63,3% of patients with Braunwald's IIIB UA and 6,8% with IIIC UA, 29,9% of patients were diagnosed with NSTEMI. All patients were diagnosed invasively with subsequent revascularization (PCI-73,1% or CABG-16,7%) if apprioppriate. 1,6% of patients underwent PCI and elective CABG and 16,7% of patients were treated conservatively. Overall mortality was 2,98%--PCI subgroup (N = 367) 1,36%, CABG subgroup (N = 84) 8,33% and conservative subgroup (N = 43) 6,07%. Non-fatal myocardial infarction (MI) complicated the hospital course in 0,99%, 0,27%, 3,57%, and 2,32% of patients respectively. 1,4%, 0,54%, 6% and 0% of patients respectively had fatal MI. Early invasive strategy in patients with ACS without ST elevation is efficacious method of treatment.

Atrial escape-capture bigeminy in dominant atrial rhythm with 2:1 exit block

A 27-year-old woman with atrial bigeminy is reported in whom long PP intervals alternate with short PP intervals. All P waves are negative in lead II and all PR intervals measure 0.12 s. In the 12-lead electrocardiogram, however, these P waves were definitely different in configuration from each other, and were divided into two groups. Namely, these negative P waves are divided into those of dominant atrial rhythm J1 with 2:1 exit block, and those of atrial escape J2. Long J1-J2 intervals alternate with short J2-J1 intervals. These electrocardiographic findings show the presence of atrial escape-capture bigeminy. Such atrial escape-capture bigeminy in dominant atrial rhythm with 2:1 exit block has never been reported before.

Apparent bradycardia-dependent sinoatrial block associated with respiration

In our previous patients, apparent bradycardia-dependent block has been shown in the atrioventricular (AV) junction and in the accessory pathway. It was suggested that these previous cases were not of true bradycardia-dependent block; namely, that, as a result of periodic increases in vagal tone associated with respiration, conductivity in the AV junction or in the accessory pathway was depressed to a greater degree than automaticity in the sinus node. In the present article, 3 patients with frequent sinoatrial (SA) block were reported. In 1 patient, sinus escape-capture bigeminy caused by SA block was found. In these present patients, when the sinus cycle lengthened, SA block occurred. The purpose of the present article is to show that the patients have apparent bradycardia-dependent SA block, namely, not true bradycardia-dependent SA block. In all patients, the respiration curve was recorded simultaneously with the electrocardiogram. In all patients, during inspiration, the sinus cycle gradually shortened; on the other hand, during expiration, the sinus cycle gradually lengthened, and then a sinus impulse was blocked in the SA junction. These findings suggested that increased vagal tone during expiration depressed conductivity in the SA junction to a greater degree than automaticity in the sinus node.

Sinus escape-capture bigeminy and sinus extrasystolic bigeminy

Blocking conduction between the sinus node and the atria (SA block) can be responsible for symptomatic rhythm problems. However, in atrial escape-capture bigeminy with SA block, when atrial escape P waves originate in a site within or close to the sinus node, the diagnosis of SA block is not easy. Electrocardiograms were selected from 7 people with atrial bigeminy because (1) all atrial deflections (P waves) were almost the same in shape and in length of PR intervals, (2) comparatively long PP intervals alternated with comparatively short PP intervals, and (3) occasionally the atrial bigeminy changed to normal regular sinus rhythm in which 2 or more sinus P waves were found in succession. An attempt is made to clarify the mechanism for these cases. When regular sinus rhythm changed to bigeminal rhythm, the long PP interval introduced the bigeminy in 3 cases, indicating the presence of "sinus" escape-capture bigeminy; whereas the short PP interval introduced the bigeminy in the other 4 cases, indicating the presence of "sinus" extrasystolic bigeminy. In cases of sinus escape-capture bigeminy associated with SA block, the cases may occasionally be diagnosed wrongly as ordinary sinus arrhythmia not associated with SA block. Therefore, it seems that sinus escape-capture bigeminy is not so rare as is generally believed. Patients with SA block often require implantation of the artificial pacemaker. Thus, the authors believe that differentiation of sinus escape-capture bigeminy from other forms of "sinus" bigeminy is clinically important.

[Implantation of atrial pacemaker in patients with sinoatrial failure]

From 1990 to 1997 a total of 42 atrial pacemakers (41 of them rate responsive) were implanted in patients with sick sinus syndrome at Aust-Agder Central Hospital, Arendal, Norway. 22 women and 20 men aged 42-86 years (average 69 years) were treated. Follow-up time was from 1-80 months (average 26 months). Sinusbradycardia and sinoatrial block were diagnosed in 17 patients, whereas 25 patients suffered from tachybrady syndrome. It was not necessary to change the pacemaker in any of the patients. One patient developed a second degree atrioventricular, Wenckebach type block, two patients developed permanent atrial fibrillation after seven and 43 months, respectively, and five patients were treated for paroxysmal atrial fibrillation. Thus, 34 patients had no need of antiarrhythmic treatment in the follow-up period. Although over 30% of patients who need a pacemaker in Norway suffer from sick sinus syndrome, only 8-12% of them are treated with atrial pacemakers. Recent studies have demonstrated that in patients with sick sinus syndrome there is greater improvement in prognosis and quality of life with physiological pacing than with ventricular pacing. Therefore, more patients should be considered for implantation of atrial pacemakers.

Mechanism of atrial escape-capture bigeminy: second-degree sinoatrial exit and entrance block

Two women with atrial escape-capture bigeminy were reported in whom sinus P waves and escape P waves alternated with each other. Their electrocardiographic findings showed that, during the bigeminal rhythm, 2:1 exit block of sinus impulses associated with entrance block of escape impulses occurred in the sinoatrial junction. Three phenomena are suggested to explain the observations. (1) Seeming bradycardia-dependent sinoatrial exit block may have occurred, probably as a result of phasic changes in vagal tone due to respiration, with decreased vagal tone depressing conductivity in the sinoatrial junction to a greater degree than automaticity in the sinus node. (2) In case 1, type II second-degree entrance block in the sinoatrial junction may have occurred, reflecting the presence of sinus parasystole with incomplete entrance block. (3) Sinus escape also may have occurred, especially in case 2. These phenomena have never been reported before.

Irreversible sinus node dysfunction induced by resumption of lithium therapy

We present the case of a 56-year-old woman with syncope and sinus node dysfunction after long-term lithium therapy. Following lithium discontinuation, sinus node function recovered completely. After resuming low doses of lithium, however, severe sinus node dysfunction recurred. Thereafter, sinus node function did not recover after lithium was discontinued, and a permanent pacemaker was implanted. These findings suggest that irreversible sinus node dysfunction should be recognized as a potentially fatal, albeit rare, risk of lithium therapy, and that previous recovery from sinus node dysfunction after long-term lithium treatment cannot always guarantee the reversible nature of this abnormality after resumption of lithium therapy.

[Sinoatrial block caused by gastroesophageal reflux. The role of simultaneous 24 hr. esophageal pH-metry and Holter-ECG in the differential diagnosis of angina pectoris]

The authors report on a 61-year-old female patient, who has suffered from recurrent angina-like chest pain for 30 years. The patient's complaints became intolerable, in spite of therapy with nitroglycerin, H2 receptor blockers and sedative medication. The echocardiography, the ECG exercise testing and Thallium scintigraphy were normal, the upper gastrointestinal endoscopy did not prove oesophagitis either macroscopically or microscopically. The simultaneous 24-hr Holter ECG monitoring and esophageal pH-metry demonstrated pathological acid gastro-oesophageal reflux and frequent sinoatrial blocks (Mobitz I) in painful periods. After monotherapy with proton pump inhibitor (omeprazole) the patient became complaint-free. Repeated combined 24-hr oesophageal pH-metry and Holter ECG monitoring indicated nonpathological acid reflux and insignificant number of sinoatrial blocks. During the course of 19 months the patient was asymptomatic. The acid pump inhibitor was stopped for a 10 day-period, while the chest pain returned. The combined 24-hr Holter ECG and esophageal pH-metry proved pathological acid gastro-oesophageal reflux and frequent sinoatrial blocks during chest pain period. After treatment with acid pump inhibitor the patient became asymptomatic again.

CONCLUSIONS

1. The acid gastro-oesophageal reflux may be a provocative factor of sinoatrial blocks and it can be influenced by proton pump inhibitor successfully. 2. Simultaneous 24-hr oesophageal pH-metry and Holter ECG monitoring can be contribute to the differentiation among causes of atypical chest pain.

Reversal of sinus arrest and atrioventricular conduction block in patients with sleep apnea during nasal continuous positive airway pressure

Sinus arrest and atrioventricular (AV) block have been demonstrated in as much as 30% of patients with sleep apnea (SA). The reversal of heart block after tracheostomy has been shown. Nasal continuous positive airway pressure (nCPAP) now is widely used as the treatment of SA, but little data are available on the effect of nCPAP on heart block in patients with SA. During a 17-mo period 239 patients were found to have SA in an ambulatory study. Heart block was identified in 17 (16 male, one female) of these patients. Standard polysomnography and two-channel long-term ECG before and during nCPAP therapy were performed in order to assess the effect of nCPAP on SA and heart block. Mean age of the 17 patients was 50.7 yr (range, 27 to 78 yr), mean respiratory disturbance index (RDI) was 90/h (SD +/- 36.1) before nCPAP and 6/h (SD +/- 6.2) on the second treatment night. The number of episodes of heart block during sleep decreased significantly (p < 0.001) from 1,575 before therapy to 165 during nCPAP. In 12 patients (70.6%) heart block was totally prevented by nCPAP. In another three patients, there was a 71 to 97% reduction in the number of episodes of heart block on the second treatment night, and in two of them a complete reversal occurred thereafter. Two patients exhibited an increase in block frequency during nCPAP, which was reversed after 4 wk of nCPAP in one but persisted in the other.(ABSTRACT TRUNCATED AT 250 WORDS)

Infra-His blocked premature atrial contractions simulating 2:1 sinoatrial block in a patient with an atrio-His bypass tract

Blocked atrial premature contractions simulated 2:1 sinoatrial block because those were superimposed on the T wave of the preceding sinus beats and were not visible on the surface electrocardiogram of our patient. Additionally, His bundle recordings and premature atrial stimulation demonstrated the presence of an atrio-His anomalous pathway. The premature atrial contractions traveled anterograde via the anomalous pathway and were blocked distally to the His bundle. The term, pseudosinoatrial block, is used to describe the arrhythmia because there was no evidence of an intrinsic abnormality of sinus node function and sinoatrial conduction.

Sinoatrial and atrioventricular block caused by intracoronary infusion of adenosine early after heart transplantation

Intracoronary adenosine was infused in 22 patients early (less than 2 months) after heart transplantation to study coronary flow reserve in the left anterior descending artery. Potentially serious bradycardia requiring discontinuation of the infusion occurred in three patients. This complication had not been noted when adenosine was given to 84 patients with at least 1 year after transplantation. Newly transplanted hearts may therefore have increased susceptibility to the bradycardic action of adenosine, which should be used with caution in this population.

The therapeutic and diagnostic cardiac electrophysiological uses of adenosine

Adenosine is a purine nucleoside with a rapid onset and brief duration of action after intravenous bolus administration. Its most prominent cardiac effect is impairment or blockade of atrioventricular nodal conduction, but other effects are depression of automaticity of the sinus node and attenuation of catecholamine-related ventricular after-depolarizations. The cardiac cell surface receptor is the A1 purinoceptor. The therapeutic value of adenosine is predominantly in those arrhythmias in which the atrioventricular node forms part of a reentry circuit, as clearly demonstrated by the high success rate for termination of atrioventricular nodal reentry tachycardia and of atrioventricular reentry tachycardia involving an accessory pathway in the Wolff-Parkinson-White syndrome. Ventricular tachycardias are generally unresponsive, with the exception of right ventricular outflow tract tachycardia. A diagnostic role has emerged for adenosine. The transient blockade of the atrioventricular node that it causes can reveal important electrocardiographic features in arrhythmias, such as atrial flutter, or can unmask latent preexcitation. In wide-QRS tachycardias, adenosine can help to distinguish ventricular tachycardia from supraventricular tachycardia with QRS aberration. Unlike verapamil, adenosine is safe in ventricular tachycardia. A suggested dosing scheme is to give incremental doses at 1-minute intervals, starting at 0.05 mg/kg and continuing until complete atrioventricular block is induced or a maximum of 0.25 mg/kg is reached. Side effects are transient, sometimes uncomfortable, and not hazardous; dyspnea and chest discomfort are most frequent. A history of asthma is a relative contraindication. Aminophylline antagonizes and dipyridamole potentiates the effects of adenosine.

Sinus node disease. Current concepts in diagnosis and therapy

Sinus node disease (SND) encompasses a number of abnormalities of sinus impulse generation and transmission within the atria and may lead to both bradyarrhythmias and tachycardias. Such abnormalities may be due to primary atrial electrophysiological abnormalities, or be secondary to drugs or abnormal autonomic control. The diagnosis may be readily established from the surface ECG or Holter recordings in many cases, but invasive electrophysiological study or assessment of the effects of autonomic blockade may be required in symptomatic patients in whom the diagnosis is suspected but not confirmed by simple electrocardiographic monitoring. Treatment should be restricted to those patients in whom clear correlation between symptoms and electrocardiographic or electrophysiological abnormalities has been established. Although a number of pharmacological agents have been assessed, the treatment of bradyarrhythmias should be permanent pacing. There is now substantial evidence that physiological (atrial or dual chamber) pacing reduces atrial arrhythmias, systemic embolisation, progression to heart failure and mortality, compared to single chamber ventricular pacing. Antiarrhythmic therapy may be required to control atrial tachyarrhythmias if they persist following pacing. In patients with uncontrolled atrial arrhythmias, especially those with ventricular pacemakers, long term oral anticoagulation should be considered to reduce the risk of systemic embolisation which is a common complication in patients with the bradycardia/tachycardia syndrome.

Early atrial arrhythmias in acute myocardial infarction. Role of the sinus node artery

We studied atrial arrhythmias during the first 12 h of admission to the hospital in 266 consecutive patients with acute myocardial infarction who subsequently underwent coronary angiography. Ten patients developed atrial fibrillation, one atrial flutter, and one supraventricular tachycardia. Another five developed sinus dysrhythmias. All of the above patients had an acute inferior myocardial infarction, and in 10 of the 12 patients with supraventricular arrhythmias and in four of five with sinus dysrhythmias, the origin of the sinus node artery started just after an occluded right coronary or left circumflex artery or was involved in the occlusion. Thus, ischemia of the sinus node due to coronary occlusion proximal to the origin of the sinus node artery was a likely cause of these arrhythmias.

Postextrasystolic sinoatrial exit block in human sick sinus syndrome: demonstration by direct recording of sinus node electrograms

Ten patients with sick sinus syndrome having repetitive sinus node electrograms during long postpacing pauses were studied during programmed atrial stimulation. Sinus node activity was recorded using a percutaneous catheter electrode. A sinus node electrogram was recorded before the return atrial beat in seven patients; it was similar to the sinus node electrogram observed during postpacing pauses and is clearly identified because sinoatrial conduction time was markedly prolonged following the atrial extra beat. Complete sinoatrial exit block occurred in four patients. (1) Sinus node electrograms were thus validated both during postpacing pauses and during programmed atrial stimulation in most patients with sick sinus syndrome. (2) Sinoatrial conduction time was markedly prolonged after one extrasystole, accounting for supracompensatory atrial return cycles. (3) If it were cumulative following multiple extrasystoles, this effect could constitute the electrophysiologic link between an abnormal response during programmed atrial stimulation and the complete sinoatrial block recorded during the pauses that follow rapid atrial pacing.

Active vs passive rhythms as an explanation of bigeminal rhythm with similar P waves

We describe the criteria for differential diagnosis between 3:2 sinoatrial block from atrial bigeminy due to an ectopic focus in the sinus or parasinus zone. In the 3:2 sinoatrial block the RR interval of the basic rhythm is similar to the short R-R interval of the paired rhythm. In atrial bigeminy, the R-R interval of the basic rhythm is similar to the long R-R interval of the paired rhythm.

Sino-atrial arrest due to temporal lobe epilepsy

A case of sino-atrial arrest due to temporal lobe epilepsy is described and compared with previously documented such cases in the literature. The rarity of bradycardias and sinus arrest due to arrhythmogenic seizures is discussed, as is the role of prospective ambulatory electroencephalographic and electrocardiographic studies in evaluating this association.

Reliability of transesophageal pacing in the assessment of sinus node function in patients with sick sinus syndrome

The purpose of this study was to find out whether transesophageal pacing could be utilized for assessment of sinus node function in patients with sick sinus syndrome (SSS). In 17 patients with SSS (study group) we compared the results of sinus node tests obtained both in the basal state and after pharmacological autonomic blockade by endocavitary stimulation and, 24 hours later, by transesophageal pacing. In another group of 17 patients with SSS (control group), we compared the results obtained by two endocavitary studies. In "study group", sinus cycle length (SCL) and corrected sinus node recovery time (CSRT) did not show significant differences between the two studies both in the basal state and after autonomic blockade, whereas sinoatrial conduction time (SACT) was more prolonged during esophageal pacing (P less than 0.01). In "control group", sinus node measures did not show significant differences between the two studies. In the "study group," the following coefficients of correlation were obtained in the basal state; SCL, r = 0.65, CSRT, r = 0.57, SACT, r = 0.52 and after autonomic blockade: SCL, r = 0.95, CSRT, r = 0.62 and SACT, r = 0.53. In the basal state, the correlation for SCL and CSRT between the two studies was lower in the "study group" than in the "control group" (P less than 0.05), whereas after autonomic blockade the correlation for sinus node measures did not show significant differences between the two groups of patients. These data suggest that transesophageal study influences the autonomic tone regulating the sinus node; however, it is not responsible for important variations in sinus node measures.(ABSTRACT TRUNCATED AT 250 WORDS)