Neurally-mediated sincope.

Syncope is a syndrome characterized by a relatively sudden, temporary and self-terminating loss of consciousness; the causes may vary, but they have in common a temporary inadequacy of cerebral nutrient flow, usually due to a fall in systemic arterial pressure. However, while syncope is a common problem, it is only one explanation for episodic transient loss of consciousness (TLOC). Consequently, diagnostic evaluation should start with a broad consideration of real or seemingly real TLOC. Among those patients in whom TLOC is deemed to be due to ''true syncope'', the focus may then reasonably turn to assessing the various possible causes; in this regard, the neurally-mediated syncope syndromes are among the most frequently encountered. There are three common variations: vasovagal syncope (often termed the ''common'' faint), carotid sinus syndrome, and the so-called ''situational faints''. Defining whether the cause is due to a neurally-mediated reflex relies heavily on careful history taking and selected testing (e.g., tilt-test, carotid massage). These steps are important. Despite the fact that neurally-mediated faints are usually relatively benign from a mortality perspective, they are nevertheless only infrequently an isolated event; neurally-mediated syncope tends to recur, and physical injury resulting from falls or accidents, diminished quality-of-life, and possible restriction from employment or avocation are real concerns. Consequently, defining the specific form and developing an effective treatment strategy are crucial. In every case the goal should be to determine the cause of syncope with sufficient confidence to provide patients and family members with a reliable assessment of prognosis, recurrence risk, and treatment options.

Pharmacotherapy of neurally mediated syncope.

A wide variety of pharmacological agents are currently used for prevention of recurrent neurally mediated syncope, especially the vasovagal faint. None, however, have unequivocally proven long-term effectiveness based on adequate randomized clinical trials. At the present time, beta-adrenergic receptor blockade, along with agents that increase central volume (eg, fludrocortisone, electrolyte-containing beverages), appear to be favored treatment options. The antiarrhythmic agent disopyramide and various serotonin reuptake blockers have also been reported to be beneficial. Finally, vasoconstrictor agents such as midodrine offer promise and remain the subject of clinical study. Ultimately, though, detailed study of the pathophysiology of these syncopal disorders and more aggressive pursuit of carefully designed placebo-controlled treatment studies are essential if pharmacological prevention of recurrent neurally mediated syncope is to be placed on a firm foundation.

Living anatomy of the atrioventricular junctions. A guide to electrophysiologic mapping. A Consensus Statement from the Cardiac Nomenclature Study Group, Working Group of Arrhythmias, European Society of Cardiology, and the Task Force on Cardiac Nomenclature from NASPE.

Current nomenclature for the atrioventricular (AV) junctions derives from a surgically distorted view, placing the valvar rings and the triangle of Koch in a single plane with antero-posterior and right-left lateral coordinates. Within this convention, the aorta is considered to occupy an anterior position, although the mouth of the coronary sinus is shown as being posterior. Although this nomenclature has served its purpose for the description and treatment of arrhythmias dependent on accessory pathways and atrioventricular nodal reentry, it is less than satisfactory for the description of atrial and ventricular mapping. To correct these deficiencies, a consensus document has been prepared by experts from the Working Group of Arrhythmias of the European Society of Cardiology and the North American Society of Pacing and Electrophysiology. It proposes a new anatomically sound nomenclature that will be applicable to all chambers of the heart. In this report, we discuss its value for description of the AV junctions, establishing the principles of this new nomenclature.

Characterization of subcutaneous microvascular blood flow during tilt table-induced neurally mediated syncope.

OBJECTIVES: This study aimed to characterize subcutaneous blood flow changes during neurally mediated syncope and to determine whether microvasculature oscillation (vasomotion) is characteristically altered in conjunction with syncopal events. BACKGROUND: Marked pallor is commonly associated with neurally mediated syncope. However, little attention has been paid to the evaluation of subcutaneous blood flow and vasomotion in this setting. METHODS: This study utilized laser Doppler flowmetry to assess changes in subcutaneous microvascular blood flow during head-up tilt table testing in 13 patients with syncope and 6 control subjects. Blood flow and vasomotion frequency were measured continuously before, during and after completion of 80 degrees head-up tilt testing (< or = 25-min duration). RESULTS: Among the 13 patients with syncope, tilt testing reproduced syncopal symptoms in 9 (tilt-positive group) but not in 4 (tilt-negative group). None of the six control subjects developed symptoms during testing. Baseline mean subcutaneous blood flow did not differ significantly among the three groups. However, during upright tilt, blood flow gradually diminished in the tilt-positive group, reaching a nadir of 0.8 +/- 0.33 ml/min per 100 g of tissue (mean +/- SD), but remained relatively constant in the tilt-negative group and control subjects. The difference in mean blood flow response to tilt was statistically significant when the tilt-positive group was compared with either the tilt-negative group or control subjects (p < 0.001). Similarly, baseline blood flow oscillation frequency did not differ significantly in the three subgroups (tilt-positive group 0.2 +/- 0.11 Hz; tilt-negative group 0.2 +/- 0.02 Hz; control subjects 0.2 +/- 0.11 Hz). Subsequently, during tilt testing only the tilt-positive group exhibited increased oscillation frequency; oscillation frequency remained essentially constant throughout the tilt test in the tilt-negative group and control subjects (p < 0.001, tilt-positive group vs. either the tilt-negative group or control subjects). CONCLUSIONS: These findings document an expected diminution of subcutaneous blood flow in association with neurally mediated syncope and indicate that characteristic changes in microvasculature oscillation frequency occur in conjunction with syncopal symptoms. To the extent that microvasculature vasomotion is influenced by neural control, the changes in vasomotion frequency are consistent with relative diminution of peripheral sympathetic neural influence during neurally mediated syncopal episodes.

Electromagnetic interference from welding and motors on implantable cardioverter-defibrillators as tested in the electrically hostile work site.

OBJECTIVES: This study was designed to determine the susceptibility of an implanted cardioverter-defibrillator to electromagnetic interference in an electrically hostile work site environment, with the ultimate goal of allowing the patient to return to work. BACKGROUND: Normal operation of an implanted cardioverter-defibrillator depends on reliable sensing of the heart's electrical activity. Consequently, there is concern that external electromagnetic interference from external sources in the work place, especially welding equipment or motor-generator systems, may be sensed and produce inappropriate shocks or abnormal reed switch operation, temporarily suspending detection of ventricular tachycardia or ventricular fibrillation. METHODS: The effects of electromagnetic interference on the operation of one type of implantable cardioverter-defibrillator (Medtronic models 7217 and 7219) was measured by using internal event counter monitoring in 10 patients operating arc welders at up to 900 A or working near 200-hp motors and 1 patient close to a locomotive starter drawing up to 400 A. RESULTS: The electromagnetic interference produced two sources of potential interference on the sensing circuit or reed switch operation, respectively: 1) electrical fields with measured frequencies up to 50 MHz produced by the high currents during welding electrode activation, and 2) magnetic fields produced by the current in the welding electrode and cable. The defibrillator sensitivity was programmed to the highest (most sensitive) value: 0.15 mV (model 7219) or 0.3 mV (model 7217). The ventricular tachycardia and ventricular fibrillation therapies were temporarily turned off but the detection circuits left on. CONCLUSIONS: None of the implanted defibrillators tested were affected by oversensing of the electric field as verified by telemetry from the detection circuits. The magnetic field from 225-A welding current produced a flux density of 1.2 G; this density was not adequate to close the reed switch, which requires approximately 10 G. Our testing at the work site revealed no electrical interference with this type of defibrillator. Patients were allowed to return to work. The following precautions should be observed by the patient: 1) maintain a minimal distance of 2 ft (61 cm) from the welding arc and cables or large motors, 2) do not exceed tested currents with the welding equipment, 3) wear insulated gloves while operating electrical equipment, 4) verify that electrical equipment is properly grounded, and 5) stop welding and leave the work area immediately if a therapy is delivered or a feeling of lightheadedness is experienced.

Digital cellular telephone interaction with implantable cardioverter-defibrillators.

OBJECTIVES: This study sought to determine, in vivo, whether electromagnetic interference (EMI), generated by North American Digital Communications (NADC)/Time Division Multiple Access-50-Hz (TDMA-50) mobile cellular digital telephone model AT&T 6650, disturbs normal implantable cardioverter-defibrillator (ICD) operation and to verify these observations in vitro by testing a selection of telephones representing worldwide systems. METHODS: The effects of cellular phone interference on the operation of various models of market-released ICDs from a single manufacturer, Medtronic, Inc., were tested. The in vivo clinical test was undertaken in 41 patients using the AT&T 6650 digital telephone with the NADC/TDMA-50 technology. The in vitro component of the study was examined twofold: 1) antenna generated far field; and 2) analog/digital cellular telephone near field. RESULTS: None of the ICDs tested in 41 patients were affected by oversensing of the EMI field of the cellular telephones during the in vivo study. Therefore, the binomial upper 95% confidence limit for the failure rate of 0% is 7%. The in vitro antenna-generated field testing showed that telephone modulation frequencies used in the international Global System Mobile and TDMA-50 cellular telephone technologies did not result in ICD sensing interference at the predicted electric field intensity. The in vitro near field tests were performed using both analog and digital cellular telephones in service, or in the test mode, and indicated no interaction with normal operation. However, the static magnetic field generated by the cellular telephone placed over the ICD at a distance < or = 0.5 cm will activate the internal reed switch, resulting in temporary suspension of ventricular tachycardia and fibrillation detection. CONCLUSIONS: We conclude that TDMA-50 cellular telephones did not interfere with these types of ICDs. However, we recommend that the patient not carry or place the digital cellular telephone within 15 cm (6 in.) of the ICD.

Indications for modification of coexisting dual atrioventricular node pathways in patients undergoing surgical ablation of accessory atrioventricular connections.

Concomitant susceptibility to atrioventricular (AV) node reentrant tachycardia has been demonstrated in certain patients having reentrant tachycardia utilizing accessory AV connections. For those patients undergoing accessory connection ablation, AV node surgical modification may be warranted during the same operative procedure. To assess indications for a combined operative procedure, this study evaluated potential predictors of subsequent spontaneous AV node reentrant tachycardia in patients undergoing ablation of accessory AV connections. Among 62 consecutive patients undergoing surgical ablation of an accessory AV connection, 13 (21%) manifested dual AV node pathways. The latter were identified preoperatively in five patients (four with concealed and one with bidirectional accessory connections) and postoperatively in seven (all seven with bidirectional accessory connections). In one patient with a bidirectional accessory connection, dual AV node pathways could not be demonstrated preoperatively, but AV node reentrant tachycardia was induced. Operative ablation of an accessory connection was successful in all patients. However, postoperatively, 2 of the 13 patients had inducible AV node reentrant tachycardia, 5 had AV node "echo" beats and 6 had no inducible arrhythmia. During 26 +/- 7 months of follow-up study, the two patients with inducible AV node reentrant tachycardia postoperatively had symptomatic AV node reentrant tachycardia. In addition, the one patient with inducible AV node reentrant tachycardia preoperatively had recurrence of this tachycardia 4 months after attempted surgical modification of the AV node. Consequently, although dual AV node pathways appear to be common in patients undergoing surgical ablation of an accessory AV connection (21%), only a small group (3 of 13) of these patients are at risk for subsequent clinical AV node reentrant tachycardia.(ABSTRACT TRUNCATED AT 250 WORDS)

Intracavitary electrode catheter cardioversion of atrial tachyarrhythmias in the dog.

This study examined factors determining efficacy of intracavitary cardioversion of atrial tachyarrhythmias in closed chest, anesthetized dogs with talc pericarditis. Electrode catheters were positioned transvenously with the cathode in the right atrial appendage. In Group 1 dogs (n = 6), three anode sites (superior and inferior venae cavae ostia and mid-right atrium) were tested with graded energy shocks to determine the lowest effective cardioversion energy at each anode position. In Group 2 dogs (n = 9), multiple cardioversion attempts with energy levels of 0.01 to 5.0 J were used to evaluate reproducibility of energy thresholds. In Group 3 dogs (n = 6) without talc-induced pericarditis, atrial pathologic study was done after five intracavitary shocks (0.5 or 5.0 J). In Group 1, cardioversion was achieved with 0.75 J or less with no significant difference in minimal effective cardioversion energies among the three anode positions tested. In Group 2, 98 (26%) of 372 cardioversion attempts were successful. Intra-animal minimal effective cardioversion energies varied widely, and timing of shocks relative to atrial electrograms did not influence efficacy. Complications were infrequent and included delayed sinus rhythm recovery, transient atrioventricular block and ventricular fibrillation. Ventricular fibrillation occurred in 9 (2.4%) of 372 shocks, and was associated with higher delivered energies (6 of 9 with greater than or equal to 1.0 J) and with shocks delivered 116 to 180 ms after onset of the QRS complex. In Group 3, two dogs had no histologic damage, three dogs had multiple small foci of subendocardial necrosis and in one dog these foci coalesced to involve half the atrial wall thickness. Thus, low energy cardioversion of atrial tachyarrhythmias is feasible using intracavitary electrodes. Synchronization of energy delivery to the QRS complex is important to minimize risk of ventricular fibrillation.

Cardiac asystole: a manifestation of neurally mediated hypotension-bradycardia.

It has been proposed that prolonged cardiac asystole mimicking an episode of sudden cardiac death may occur as a manifestation of neurally mediated hypotension-bradycardia syndrome. To assess this possibility, electrocardiographic and hemodynamic findings during upright tilt testing were evaluated in six survivors of suspected asystolic sudden cardiac arrest with normal conventional electrophysiologic evaluation (Group I). These observations were compared with findings in two control groups: six patients with syncope but without evident asystole and with normal conventional electrophysiologic evaluation but demonstrable neurally mediated hypotension-bradycardia (Group II), and six patients with syncope in whom conventional electrophysiologic evaluation provided a presumptive diagnosis (Group III). Patients in all three groups ranged in age from 16 to 59 years. During head-up tilt testing (either alone or with isoproterenol infusion), patients in both Groups I and II developed syncope in less than or equal to 5 min, whereas patients in Group III remained asymptomatic. Patients in Groups I and II exhibited a similar tilt-induced decrease in mean arterial pressure (-46 +/- 9 and -40 +/- 9 mm Hg, respectively, p = NS) and heart rate (-44 +/- 28 and -49 +/- 12 beats/min, respectively, p = NS). In contrast, patients in Group III manifested only a moderate decrease in mean arterial pressure (-14 +/- 5 mm Hg) and had an increase in heart rate (+14 +/- 8 beats/min). Both mean arterial pressure and heart rate changes in Group I and Group II patients differed significantly (p less than 0.001) from values in Group III patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Cardiac and skeletal muscle abnormalities in cardiomyopathy: comparison of patients with ventricular tachycardia or congestive heart failure.

Results of cardiac muscle and skeletal muscle biopsies were compared in 22 patients with cardiomyopathy; 11 patients presented with symptoms secondary to ventricular tachycardia (Group 1) and 11 had symptoms of severe congestive heart failure (Group 2). No patient had structural or ischemic cardiac disease. In Group 1 patients, hemodynamic abnormalities were subtle, but invasive study demonstrated dilated cardiomyopathy in two patients and restrictive cardiomyopathy in nine. In Group 2, eight patients had dilated cardiomyopathy and three had restrictive cardiomyopathy. Cardiac biopsy results were abnormal in all 22 patients and the abnormalities were similar for the two groups. Cardiac histologic study revealed a spectrum of abnormalities including fibrosis, dilated sarcoplasmic reticulum, increased numbers of intercalated discs and mitochondrial abnormalities. Histologic abnormalities of skeletal muscle were similar in each group, consisting of endomysial fibrosis and increased lipid deposits. Slightly more than half of the Group 1 and Group 2 patients also had a low concentration of skeletal muscle long chain acylcarnitine. These data demonstrate that abnormalities of both cardiac and skeletal muscle are common in patients with cardiomyopathy; abnormalities are similar whether initial symptoms are due to ventricular tachycardia or congestive heart failure. It is suggested that these patients with cardiomyopathy may have a generalized myopathy.

Prevention of recurrent sudden cardiac arrest: role of provocative electropharmacologic testing.

This study evaluates the usefulness of serial provocative electropharmacologic testing for predicting the efficacy of prophylactic antiarrhythmic treatment regimens in patients resuscitated from sudden cardiac arrest in the absence of acute myocardial infarction. Testing was carried out in 34 consecutive patients (28 men and 6 women) who required cardiopulmonary resuscitation and direct current countershock for treatment of primary ventricular fibrillation (28 patients), ventricular tachycardia (5 patients) or excessively rapid heart rate during atrial fibrillation with preexcitation (1 patient). In 8 (24%) of the 34 patients, drug testing either was not feasible because of absence of inducible arrhythmia or was incomplete because of patient withdrawal from study; and 3 of these 8 patients had recurrent sudden cardiac arrest within 10 to 19 months. In an additional five patients, treatment regimens failed to prevent initiation of sustained ventricular tachyarrhythmias in the catheterization laboratory, and two of these five patients had cardiac arrest recurrences within 2 weeks to 25 months of follow-up. In the remaining 21 (62%) of the 34 patients, including 3 patients with preexcitation syndrome, a drug regimen or surgical treatment, or both, was found that prevented inducible life-threatening tachyarrhythmias in the laboratory. Subsequently, only 1 (5%) of these 21 patients died suddenly within a 7 to 38 month (mean +/- standard deviation, 18 +/- 8.3) follow-up period. Thus, provocative electropharmacologic testing appears to be useful in predicting response to therapy in survivors of sudden cardiac arrest.

Bromocriptine treatment of digitalis-induced ventricular tachyarrhythmias: studies in a canine model.

Ventricular tachyarrhythmias associated with digitalis toxicity are believed to be due, in part, to cardiac glycoside-mediated increased central sympathetic neural activity. Because dopaminergic receptor agonists reduce sympathetic outflow, this study assessed effectiveness of the available dopaminergic agonist, bromocriptine, in slowing or terminating ouabain-induced ventricular tachycardia in anesthetized dogs. In all experiments, ouabain was administered intravenously (20 micrograms/kg body weight bolus injection, followed by 2.5 micrograms/kg per min infusion) until the onset of stable ventricular tachycardia. Of seven untreated dogs (Group 1), ouabain-induced ventricular tachyarrhythmias resulted in ventricular fibrillation in three, while in four dogs tachycardia persisted without significant change in rate until the study was terminated. Fourteen dogs (Group 2) received bromocriptine, either 30 micrograms/kg (Group 2A) or 50 micrograms/kg (Group 2B), after the onset of ventricular tachycardia. Tachycardia slowed in all 14 dogs and terminated with resumption of sinus rhythm in 8 of the 14. In all six dogs pretreated with the peripheral dopaminergic antagonist domperidone (Group 3), bromocriptine, 50 micrograms/kg, slowed ventricular tachycardia and in three of the six, tachycardia terminated. In contrast, of five dogs pretreated with haloperidol, a central and peripheral dopaminergic receptor antagonist (Group 4), bromocriptine, 50 micrograms/kg, failed to slow ventricular tachycardia in three, and two of the three developed ventricular fibrillation. In summary, the dopaminergic receptor agonist, bromocriptine, presumably acting at central dopaminergic receptor sites, consistently slowed and in most cases reversed ouabain-induced ventricular tachycardia in a canine model.

Clinical investigation of antiarrhythmic devices. A statement for healthcare professionals from a joint task force of the North American Society of Pacing and Electrophysiology, the American College of Cardiology, the American Heart Association, and the Working Groups on Arrhythmias and Cardiac Pacing of the European Society of Cardiology.

The goal of radiofrequency catheter ablation and the criterion for efficacy is the elimination of arrhythmogenic myocardium. The application of radiofrequency current in the heart clearly results in lower morbidity and mortality rates than thoracic and cardiac surgical procedures in general, and comparisons of therapy with radiofrequency catheter ablation and therapy with thoracic and cardiac surgical procedures in randomized clinical trials is unwarranted. Trials of radiofrequency catheter ablation versus medical or implantable cardioverter-defibrillator therapy may be indicated in certain conditions, such as ventricular tachycardia associated with coronary artery disease. Randomized trials are recommended for new and radical departures in technology that aim to accomplish the same goals as radiofrequency catheter ablation. Surveillance using registries and/or databases is necessary in the assessment of long-term safety and efficacy.

Inducible ventricular arrhythmias in a naturally occurring model of cardiomyopathy.

This study examined inducibility of ventricular tachyarrhythmias in turkeys with and without naturally occurring dilated cardiomyopathy. Using a transvenously positioned electrode catheter, 32 cardiomyopathy and 12 control unsedated turkeys aged 2 to 4 months were studied by right ventricular endocardial extrastimulus testing at basic pacing cycle lengths of 200 and 170 ms with both 1 and 2 extrastimuli and burst pacing at progressively shorter cycle lengths (200 to 100 ms). Following study, a dilatation index (determined as the ratio of left ventricular endocardial and epicardial diameter at level of the apex-base midpoint) was utilized to assess the functional severity of cardiomyopathy. All control turkeys had a dilatation index less than 0.3. In cardiomyopathic turkeys, dilatation index was normal (less than 0.3) in 3/32, showed mild to moderate dilatation in 25/32 (0.3 to 0.6), and severe dilatation in 4/32 (greater than 0.6). Results showed no difference in right ventricular effective or functional refractory periods between control and cardiomyopathic turkeys. Control turkeys had no inducible ventricular tachyarrhythmias, but 16/32 cardiomyopathic turkeys (p less than 0.005) had inducible ventricular tachyarrhythmias, consisting most frequently of two beats of rapid ventricular tachycardia supervened by ventricular fibrillation. In the cardiomyopathic turkeys, inducible tachyarrhythmias occurred in 1/3 with normal dilatation index, in 11/25 with mild to moderate dilatation, and in 4/4 with severe dilatation. Thus, inducibility of ventricular tachyarrhythmias in cardiomyopathic turkeys is closely associated with increasing ventricular dilatation, but does not correlate with altered right ventricular refractoriness. This model may be suitable for studying the relationship between ventricular tachyarrhythmias and cardiomyopathy.

Calcium uptake by cardiac sarcoplasmic reticulum in human dilated cardiomyopathy.

To determine the biochemical basis of abnormal diastolic properties in human dilated cardiomyopathy calcium uptake by the sarcoplasmic reticulum in ventricular homogenates of biopsy specimens from 21 patients with dilated cardiomyopathy was compared with that in nine normal controls. As a group, patients with cardiomyopathy had considerably lower calcium uptake rates (3.3(0.6) nmol.mg-1.min-1 vs 6.5(0.5) nmol.mg-1.min-1, p less than 0.01). Calcium uptake rates correlated modestly with resting haemodynamic values and significantly with plasma noradrenaline concentrations but not with plasma renin activity. These results show that sarcoplasmic reticulum function is impaired in human dilated cardiomyopathy and that this impairment is related both to the severity of haemodynamic dysfunction and to the extent of sympathetic nervous system activation.

Cellular electrophysiological changes in "round heart disease" of turkeys: a potential basis for dysrhythmias in myopathic ventricles.

Arrhythmias are commonly recorded in "round heart disease", a presumed viral, congestive cardiomyopathy of turkeys. To assess whether cellular electrophysiological changes may be associated with arrhythmia susceptibility, we compared transmembrane action potential characteristics in left and right ventricular endocardial muscle fibres from 19 inbred myopathic turkeys with findings in 13 normal control turkeys (age 1 to 74 days). In left ventricular tissue, as a group, action potential duration at 50% repolarisation (APD50) was reduced in myopathic hearts (201+/-6(SEM) vs 228+/-9 ms in controls. P less than 0.01), while the maximum rate of phase 0 (dV/dtmax) action potential amplitude, diastolic resting membrane potential and action potential duration at 90% repolarisation (APD90) did not differ from control turkeys. By contrast, in myopathic right ventricular tissue, as a group, both APD50 (186+/-5 vs 206+/-4 ms in controls) and APD90 (208+/-4 vs 228+/-3 ms in controls) were shorter (P less than 0.01). The plateau potential in both right and left ventricular tissue was significantly higher in inbred turkeys. Since a spectrum of cardiac dilatation and hypertrophy is present in myopathic turkeys, we examined the effect of hypertrophy on action potential characteristics. In "round heart disease" turkeys, left ventricular hypertrophy was characterised by reduced dV/dtmax (98+/- vs 274+/-26 V.s-1, P less than 0.01) and right ventricular hypertrophy by further shortening of both APD50 (174+/-7 vs 202+/-6 ms, P less than 0.01) and APD90 (193+/- vs 224+/-5 ms, P less than 0.01), but no change in dV/dtmax (105+/-13 vs 120+/-9 V.s-1, P = NS). These results indicate that certain electrophysiological differences (eg reduced action potential duration), may, in part, contribute to dysrhythmia susceptibility in this presumed viral cardiomyopathy model.

Atrial flutter in infancy: diagnosis, clinical features, and treatment.

The clinical features and treatment of atrial flutter in eight infants (four male and four female) less than 2 months of age are presented. Atrial flutter was noted during the first week of life in six of the infants and between 6 and 8 weeks of life in the other two infants. Four of the eight infants had associated structural or functional cardiovascular disease, and in three infants a central venous pressure catheter was present in the atrium at the time atrial flutter was diagnosed. Classic flutter waves were apparent on 12-lead ECGs in only two infants. In six infants, flutter waves were not obvious on standard ECGs, but transesophageal electrogram recordings demonstrated the presence of atrial flutter with second degree atrioventricular block. The atrial cycle length during flutter ranged from 135 to 180 ms (mean 149 ms; mean atrial rate 403 beats per minute); there was a 2:1 ventricular response to atrial flutter. Successful termination of atrial flutter was accomplished using three modes of electrical cardioversion in seven of the eight infants: direct current cardioversion in one, transvenous atrial pacing in one, and transesophageal atrial pacing in five. One asymptomatic infant converted to normal sinus rhythm 24 hours following digoxin administration. One infant had multiple atrial flutter recurrences and required chronic procainamide therapy. In seven of the eight infants, no recurrences have been noted in 6 months to 3 1/2 years of follow-up. These results demonstrate that atrial flutter may be difficult to diagnose in infants with tachycardia unless transesophageal electrogram recording is utilized for evaluation.(ABSTRACT TRUNCATED AT 250 WORDS)

Prediction of digoxin treatment failure in infants with supraventricular tachycardia: role of transesophageal pacing.

Transesophageal atrial pacing was used to initiate and terminate tachycardia in 24 infants (seven female and 17 male, aged 1 to 34 days) with ECG documentation of supraventricular tachycardia. Six infants received no chronic treatment, and chronic oral digoxin prophylaxis was administered to 18 infants in an effort to prevent recurrences of tachycardia. In these 18 infants, the effectiveness of digoxin therapy in preventing the initiation of tachycardia by transesophageal pacing was compared with its ability to prevent spontaneous recurrences of supraventricular tachycardia. While receiving chronic oral digoxin therapy, tachycardia could be reinitiated in 15/18 (83%) infants. In these infants, the cycle length of tachycardia and the atrioventricular interval were the same before and during chronic digoxin treatment. Three infants in whom tachycardia could not be initiated during chronic digoxin therapy had no spontaneous recurrences during 6 months of follow-up, whereas 10/15 (67%) infants in whom tachycardia could be reinitiated had clinically significant recurrences in spite of chronic digoxin therapy. Six infants who received no chronic drug treatment had no documented recurrences during 6 months of follow-up. This study demonstrates that digoxin was effective in preventing significant spontaneous recurrences of supraventricular tachycardia in only 8/18 (44%) infants treated with digoxin. The ability to initiate supraventricular tachycardia with transesophageal pacing may be useful in determining which digoxin-treated infants are at risk for recurrence. Finally, not all infants with supraventricular tachycardia require chronic prophylaxis; six of the untreated infants had no documented recurrences.

Antiarrhythmic, antifibrillatory, and hemodynamic actions of bethanidine sulfate: an orally effective analog of bretylium for suppression of ventricular tachyarrhythmias.

Bethanidine sulfate is a chemical and pharmacologic analog of bretylium tosylate that has virtually identical antifibrillatory and inotropic actions on the heart. Bretylium is the only drug approved by the Food and Drug Administration specifically for the "prophylaxis and treatment of ventricular fibrillation." Unlike bretylium, which is poorly absorbed from the gut and limited to parenteral use, oral bethanidine is absorbed rapidly. Bethanidine was given to 23 patients with recurrent multiple drug refractory ventricular tachycardia and fibrillation. Eighteen patients (78%) had complete suppression of spontaneous or electrophysiologically inducible tachyarrhythmias; 3 were improved and 2 had no benefit. In 6 of a 9 patient subgroup studied by programmed electrophysiologic drug testing, bethanidine completely prevented previously inducible ventricular tachyarrhythmias at the maximal stimulus tested (including 4 extrastimuli and burst-pacing at 10 times threshold). Cardiac output measured in 6 patients 1 to 2 hours after bethanidine was increased in 4, unchanged in 2, and decreased in 1. Ten patients on long-term therapy with bethanidine and protriptylene (to prevent orthostatic hypotension) have been free of arrhythmias from 2 to 26 (average 13) months.

Modes of onset ("initiating events") for paroxysmal atrial tachycardia in infants and children.

Observations of spontaneous onset of paroxysmal atrial tachycardia (PAT) in infants and children have been infrequently reported. This study reports on modes of spontaneous onset of PAT in 22 infants and 8 children in whom onset of PAT was recorded during continuous electrocardiographic recording. During PAT, all 30 patients used the normal specialized atrioventricular conduction system for ventricular activation, with atrial activation occurring through an accessory atrioventricular connection (orthodromic reciprocating tachycardia). Wolff-Parkinson-White syndrome was present in 7 patients. Analysis of the mode of onset of PAT revealed that infants initiated PAT with atrial extrasystoles or sinus acceleration (a gradual shortening of the P-P interval). In 10 infants more than 10 PAT onsets were recorded, and in these infants the mode of onset was sinus acceleration. In 7 infants, both atrial extrasystole and sinus acceleration were observed to initiate PAT. In the older children, onset of PAT followed atrial extrasystole (3 patients), ventricular extrasystole (2 patients), and sinus pause with junctional escape (3 patients). It has been previously recognized that the natural history of these "initiating events" varies with patient age. Variations in frequency of spontaneous episodes of PAT may relate to chronologic variations in frequency and type of initiating events.