Magnetocardiographic rhythm patterns at initiation and termination of fetal supraventricular tachycardia.

BACKGROUND: Using fetal magnetocardiography (fMCG), we characterize for the first time the electrophysiological patterns of initiation and termination of reentrant fetal supraventricular tachycardia (SVT), the most common form of life-threatening fetal arrhythmia. METHODS AND RESULTS: In contrast to the expectation that reentrant SVT is initiated by spontaneous premature atrial contractions (PACs) and is terminated by spontaneous block, 5 distinct patterns of initiation and 4 patterns of termination were documented, with the most common patterns of initiation involving reentrant PACs. Waveform morphology and timing, including QRS and ventriculoatrial interval, were assessed. This enabled detection of such phenomena as Wolff-Parkinson-White syndrome, QRS aberrancy, and multiple reentrant pathways that were crucial for defining the rhythm patterns. In addition, fMCG actocardiography revealed an unexpectedly strong association between fetal trunk movement and the initiation and termination of SVT, suggesting that autonomic influences play a key role. CONCLUSIONS: This study demonstrates that the patterns of initiation and termination of fetal SVT are more diverse than is generally believed and that the most common patterns of initiation involve reentrant PACs. The ability to discern such patterns can help elucidate the underlying mechanisms and guide antiarrhythmic drug therapy. fMCG provides a noninvasive means of analyzing complex tachyarrhythmia in utero, with efficacy approaching that of postnatal electrocardiographic rhythm monitoring.

Wolff-Parkinson-White syndrome and supraventricular tachycardia during infancy: management and follow-up.

The records of 90 patients with Wolff-Parkinson-White syndrome who presented with supraventricular tachycardia in the first 4 months of life were reviewed. Among these, 63% were male. Structural heart disease was present in 20%, most commonly Ebstein's anomaly. All patients presented with a regular narrow QRS tachycardia, and pre-excitation became evident only when normal sinus rhythm was established. Only one infant had atrial flutter and none had atrial fibrillation. Type A Wolff-Parkinson-White syndrome was most common (49%), with heart disease occurring in only 5% of these patients. In contrast, heart disease was identified in 45% of those with type B syndrome. Initially, normal sinus rhythm was achieved in 88% of the 66 infants treated with digoxin with no deaths. Normal sinus rhythm resumed after electrical countershock in 87% of the 15 infants so treated. Maintenance digoxin therapy was used in 85 patients. The Wolff-Parkinson-White pattern disappeared in 36% of the patients. Four infants died of cardiac causes during the mean follow-up period of 6.5 years. Two of these four infants had congenital heart disease; the third, with a normal heart initially, developed ventricular fibrillation and died from a cardiomyopathy considered related to resuscitation. The remaining infant, with a normal heart, died suddenly at 1 month of age. All were receiving digoxin. A wide QRS tachycardia later appeared in three patients, all with heart disease, one of whom died.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of transesophageal and intracardiac electrophysiologic studies in characterization of supraventricular tachycardia in pediatric patients.

OBJECTIVES: This study sought to determine the accuracy of transesophageal electrophysiologic studies in diagnosing and characterizing various mechanisms of supraventricular tachycardia in pediatric patients. BACKGROUND: Transesophageal electrophysiologic studies are a relatively noninvasive means of characterizing supraventricular tachycardia. Although widely used, to our knowledge no data exist that directly compare information obtained from transesophageal electrophysiologic studies with that from intracardiac electrophysiologic studies. METHODS: We reviewed the records of 57 pediatric patients undergoing both transesophageal and intracardiac electrophysiologic studies at our institution. The results of these studies were compared with respect to mechanism of tachycardia, localization of accessory atrioventricular (AV) connections (if present) and characterization of anterograde accessory connection conduction properties. RESULTS: Tachycardia mechanisms were concordant in 56 of 57 patients: orthodromic reciprocating tachycardia in 43, antidromic reciprocating tachycardia in 1, both orthodromic and antidromic tachycardia in 2, AV node reentrant tachycardia in 5, atrial reentrant tachycardia in 4 and ectopic atrial tachycardia in 2. Of 29 patients with orthodromic reciprocating tachycardia using a concealed accessory connection, transesophageal study predicted the accessory connection site through changes induced by transient bundle branch block in 12. By the Bland-Altman method in 14 patients with pre-excitation, the anterograde accessory connection effective refractory period determined by transesophageal study compared favorably with that determined by intracardiac study (mean difference 5.0 ms, limits of agreement -55 and 65 ms). CONCLUSIONS: Transesophageal electrophysiologic studies are a highly accurate means of diagnosing and characterizing various mechanisms of supraventricular tachycardia in pediatric patients.

Fetal tachycardia: mechanisms and predictors of hydrops fetalis.

OBJECTIVES: This study had three objectives: 1) to determine the electrophysiologic mechanisms of fetal supraventricular tachycardia at presentation and postnatally; 2) to identify the clinical and electrophysiologic predictors of hydrops fetalis; and 3) to describe the medium-term follow-up (1 to 7 years) of patients with fetal supraventricular tachycardia. BACKGROUND: Fetal supraventricular tachycardia causes significant fetal and neonatal morbidity and mortality. Prenatal analysis and postnatal confirmation of fetal supraventricular tachycardia mechanisms have been limited. METHODS: Supraventricular tachycardia mechanisms were evaluated by prenatal Doppler/M-mode echocardiography, immediate neonatal surface electrocardiography and postnatal transesophageal electrophysiologic procedures in 30 consecutive patients presenting with fetal supraventricular tachycardia (17 managed prenatally, 13 first managed postnatally). RESULTS: The fetal supraventricular tachycardia mechanism was 1:1 atrioventricular conduction in 22 patients and supraventricular tachycardia with atrioventricular block (atrial flutter) in 8. At the postnatal transesophageal electrophysiologic procedure, tachycardia was induced in 27 of 30 patients; atrioventricular reentrant tachycardia in 25 (93%) of 27 and intraatrial reentrant tachycardia in only 2 (7%) of 27. Hydrops was present in 12 of 30 fetuses. Sustained supraventricular tachycardia (> 12 h) and lower gestation at presentation correlated with hydrops (p < 0.02, p < 0.05), but mechanism of tachycardia and heart rate did not. Gestational age at delivery was significantly greater in those who received intrauterine management (39 +/- 1.3 vs. 37 +/- 2.9 weeks, p = 0.04) despite earlier presentation (32.6 vs. 37.1 weeks). Cesarean section deliveries were reduced in the same group (3 of 17 vs. 11 of 13, p = 0.0006). CONCLUSIONS: Atrioventricular reentrant tachycardia was the predominant mechanism of supraventricular tachycardia in the fetus. There was a high association of supraventricular tachycardia with atrioventricular block in utero and accessory atrioventricular connections. Outcome at 1 to 7 years was excellent regardless of severity of illness at clinical presentation.

Congenital aneurysm of the left sinus of Valsalva with an aortopulmonary tunnel.

Aneurysm of the left sinus of Valsalva is rare, and there is only one previous report of rupture into the pulmonary artery. This report describes a patient with valvular pulmonary atresia and ventricular septal defect in whom a portion of his pulmonary blood flow was supplied by an aortopulmonary tunnel arising from a left sinus of Valsalva aneurysm. The surgical implications of precise definition of the type of aortopulmonary communication are discussed.

Use of amiodarone for short-term and adjuvant therapy in young patients.

Limited data are available defining the safety of amiodarone for short-term use or as part of combination antiarrhythmic therapy in pediatric patients. Results of amiodarone in 47 young patients for an average treatment duration of 12 months were examined. There were 21 male and 26 female patients (age range of 23 weeks gestation to 29 years). Patients were divided into 4 groups: group 1--electrocardiographic documented ventricular tachycardia (n = 7); group 2--syncope of unknown cause (n = 16); group 3--primary atrial tachycardia (n = 11); and group 4--supraventricular tachycardia (n = 13). Amiodarone was clinically useful in 32 (68%) patients. Amiodarone was considered effective as a sole antiarrhythmic agent in 21 (45%) patients. Treatment was ineffective but was continued in 11 (23%) patients; in 10 of these 11 patients amiodarone was adjuvant to other antiarrhythmic drugs. Amiodarone was considered ineffective and was withdrawn in 15 (32%) patients. No patient required cardiac pacemaker implant during therapy. Torsades de pointes and cardiac arrest occurred in 1 patient each after 9 and 14 days of therapy, respectively. Two patients underwent successful cardiac transplant after 2 and 14 months of amiodarone administration, respectively. Amiodarone was used as short-term treatment (less than 18 months) in 7 infants (age less than 18 months), and after cessation of treatment there was no recurrence of tachycardia for 4 to 24 months. Results of this study confirm reports of successful amiodarone use in pediatric patients with a variety of rhythm disturbances.(ABSTRACT TRUNCATED AT 250 WORDS)

Usefulness of metoprolol for unexplained syncope and positive response to tilt testing in young persons.

The efficacy of intravenous metoprolol in preventing symptoms during a repeat tilt test was compared with the outcome of chronic oral treatment in 21 patients (14 female, 7 male), age 8 to 20 years (mean 13 +/- 3) with unexplained syncope (> or = 1 episode) and a positive response to tilt testing. A positive response was defined as the development of either syncope or presyncope. During the initial tilt test, a positive response occurred during baseline (14 patients) or isoproterenol (0.03 to 0.1 microgram/kg/min) infusion (7 patients) with a cardioinhibitory (1 patient), vasodepressor (5 patients) or mixed (15 patients) pattern. Metoprolol (0.1 to 0.2 mg/kg) was administered intravenously. During the repeat tilt test, response was negative in 18 patients, including 11 of 14 patients with a positive response in the baseline and 7 of 7 patients with a positive response during isoproterenol infusion. Metoprolol (0.8 to 2.8 mg/kg/day) was administered orally to 15 patients for an average of 10 months. Symptoms were absent (7 patients) or improved (2 patients); metoprolol was discontinued because of adverse effects (3 patients) or recurrence of symptoms (3 patients). In 7 of 12 patients with a negative response and 2 of 3 patients with a positive response after intravenous metoprolol, oral administration of metoprolol prevented or improved symptoms without adverse effects. Many young patients (60%) with recurrent syncope obtained symptomatic improvement from chronic oral metoprolol treatment without adverse effects; repeat tilt testing after intravenous metoprolol did not appear to offer any additional information than would have been obtained from a trial of chronic oral treatment.

Electrophysiologic drug testing in symptomatic ventricular arrhythmias after repair of tetralogy of Fallot.

Nine patients with symptomatic ventricular arrhythmias were evaluated a mean interval of 16 years after surgical repair of tetralogy of Fallot. The clinical arrhythmia was sustained ventricular tachycardia (VT) in 4 patients (group I) and premature ventricular contractions in 5 (group II). All patients underwent cardiac catheterization and electrophysiologic studies. Ventricular tachycardia was induced at electrophysiologic study in all patients in group I and in 3 patients in group II. Six patients with inducible sustained monomorphic VT underwent chronic drug testing based on electrophysiologic study. A mean of 3.3 drugs per patient was tested. Patients with right ventricular systolic hypertension did not respond to any drug tested, and underwent surgery. Five patients received drug treatment based on the results of electrophysiologic study. During a mean follow-up period of 2.2 years, no patient in either group had recurrent episodes of VT or syncope. In the postoperative patient with tetralogy of Fallot with symptomatic ventricular arrhythmias, it is concluded that electrophysiologic study is useful in reproducing clinical episodes of VT and in selecting effective antiarrhythmic medication; a small number of patients with ventricular premature complexes alone will have inducible sustained VT during electrophysiologic study; prognosis of these patients may be improved by treatment that results in prevention of VT induction; and in patients with right ventricular hypertension, VT is likely to be refractory to drug treatment.

Subxiphoid two-dimensional echocardiographic identification of tricuspid valve abnormalities in transposition of the great arteries with ventricular septal defect.

Tricuspid valve morphology was examined using subxiphoid 2-dimensional echocardiography (2-D echo) in 39 infants aged 2 years or younger who had transposition of the great arteries (TGA) and ventricular septal defect (VSD) (group I). Age-matched control groups were 21 patients with simple TGA (group II), 30 patients with VSD and normally related great arteries (group III), and 15 normal patients (group IV). Valve abnormalities, consisting of chordal attachments to the infundibular septum or ventricular septal crest, straddling, overriding or some combination of these, were identified in 25 of 39 patients (64%) in group I, no patients in groups II or IV and 6 of 30 patients (20%) in group III. Intraatrial baffle repair was performed in 27 patients in group I (median age at surgery 3.5 months) and 19 patients in group II (median age 4 months). Preoperative right ventricular angiography, performed in all patients with TGA, demonstrated tricuspid regurgitation (TR) with biventricular dysfunction in 1 patient in group I. After surgery, TR was present in 9 of 17 group I patients and none of the 8 group II patients who underwent catheterization. All patients in whom TR was not present preoperatively had abnormal chordal attachments; 3 required valve replacement. These results demonstrate that tricuspid valve abnormalities are common in patients with TGA and VSD and may be identified preoperatively using 2-D echo. Patients with abnormal chordal attachments are at increased risk for TR after intraatrial baffle repair and should be considered for arterial switch repair.

Supraventricular tachycardia mechanisms and their age distribution in pediatric patients.

To better define the natural history of supraventricular tachycardia (SVT) in young patients, age distribution of SVT mechanisms was examined in 137 infants, children and adolescents. Patients with a history of cardiac surgery or neuromuscular diseases were excluded. An electrophysiologic study was performed in each patient: transesophageal (110 patients) or transvenous (14 patients) or both (13 patients). Mechanisms were classified as SVT using accessory atrioventricular (AV) connection (SVT using accessory connection, including orthodromic and antidromic reciprocating tachycardia), primary atrial tachycardia (including chaotic, automatic and reentrant atrial tachycardia), and tachycardia due to reentry within the AV node. SVT using accessory connection occurred in 100 of 137 patients (73%) and was the most prevalent mechanism. Primary atrial tachycardia and reentry within the AV node were present in 19 of 137 (14%) and 18 of 137 (13%) patients, respectively. Using a multinomial logit model, relative probabilities for tachycardia mechanisms for 5 age groups--prenatal, less than 1, 1 to 5, 6 to 10 and greater than 10 years--were determined. Primary atrial tachycardia (11 to 16%) and SVT using accessory connection (58 to 84%) appeared throughout infancy, childhood and adolescence. On the other hand, tachycardia due to reentry within the AV node (0 to 31%) rarely appeared before age 2 years. Mechanisms of SVT appear to have age-dependent distributions. SVT using accessory connection is the most common mechanism in young patients. We speculate that the propensity to tachycardia due to reentry within the AV node occurs during postnatal development.

Impact of arrhythmia circuit cryoablation during Fontan conversion for refractory atrial tachycardia.

Refractory atrial arrhythmias in late postoperative Fontan patients are usually associated with residual hemodynamic abnormalities and result in significant morbidity and mortality. Surgical revision of the Fontan anastomosis may improve hemodynamics without eliminating tachycardia. This study sought to assess the impact of surgical cryoablation of the arrhythmia circuit at the time of Fontan conversion on the clinical recurrence of tachycardia. Sixteen consecutive atriopulmonary Fontan patients with refractory atrial arrhythmias underwent surgical conversion to lateral tunnel total cavopulmonary anastomosis (15) or Fontan revision (1 patient). The initial 4 patients underwent Fontan conversions alone, without specific arrhythmia surgery. The subsequent 12 patients underwent electrophysiologically guided cryoablation of the tachycardia circuits at the time of surgical conversion. The mean age at Fontan revision was 15.6 +/- 3.8 years. Cryoablation was directed to 3 identified major tachycardia circuits: the inferomedial right atrium, the superior rim of the prior atrial septal defect patch, and along the lateral right atrial wall. Transmural antitachycardia pacemakers were implanted in 11 of the 16 patients. There was no surgical mortality in either group, and all patients improved in functional classification. All patients not undergoing cryoablation experienced recurrent symptomatic tachycardia requiring antiarrhythmic therapy (median follow-up, 54 months) versus 2 of 12 patients receiving cryoablation (median follow-up, 25 months; p <0.02). Thus, surgical cryoablation of the arrhythmia circuit at the time of Fontan conversion is highly effective in the management of refractory atrial arrhythmias, and is superior to Fontan conversion alone.

Randomized comparison of atenolol and fludrocortisone acetate in the treatment of pediatric neurally mediated syncope.

Overall, these results indicate that oral treatment of neurally mediated syncope is safe and efficacious. Further randomized trials in children will be required to determine the significance of a placebo effect, as well as potential differences in results related to the mechanism of syncope.

Ventricular arrhythmias in postoperative tetralogy of Fallot.

Ventricular arrhythmias in patients after total surgical repair of tetralogy of Fallot have been associated with late sudden death. In this large multicenter retrospective study of 359 patients with postoperative tetralogy of Fallot, spontaneous ventricular premature complexes (VPCs) on 24-hour ambulatory electrocardiographic monitoring and laboratory-induced ventricular tachycardia (VT) by electrophysiologic stimulation were analyzed. The mean age at surgical repair was 5 years and the mean follow-up duration after repair was 7 years. Spontaneous VPCs on ambulatory monitoring were found in 48% and induced VT on electrophysiologic stimulation was found in 17% of patients. Both spontaneous VPCs and induced VT were significantly related to delayed age at repair, longer follow-up interval, symptoms of syncope or presyncope and right ventricular systolic hypertension (greater than 60 mm Hg) (p less than 0.05), but not to right ventricular diastolic pressure greater than 8 mm Hg. The VPCs on ambulatory monitoring were more complex with increasing age at repair and follow-up duration. Induction of VT on electrophysiologic stimulation correlated with spontaneous VPCs including VT on 24-hour ambulatory electrocardiographic monitoring. The electrophysiologic stimulation protocol varied and the induction of VT increased with a more aggressive stimulation protocol. While induced sustained monomorphic VT was related to all forms of spontaneous VPCs, induced nonsustained polymorphic VT was related to more complex forms of VPCs on ambulatory monitoring. VT was not induced in asymptomatic patients who had normal 24-hour ambulatory electrocardiographic monitoring and normal right ventricular systolic pressure. (ABSTRACT TRUNCATED AT 250 WORDS)

Fontan conversion to cavopulmonary connection and arrhythmia circuit cryoblation.

OBJECTIVES: We review our surgical experience patients with atriopulmonary Fontan operations who had obstructive or arrhythmia indications for conversion to total cavopulmonary artery connections, arrhythmia circuit cryoablation, and placement of atrial antitachycardia pacemaker. METHODS: Fourteen patients (mean age 14 +/- 4 years) had conversion to total cavopulmonary artery connection 8 +/- 3 years after the original atriopulmonary Fontan operation primarily for atrial arrhythmias in 11, obstructive lesions in 2, and bradycardia with cyanosis in 1. Arrhythmia circuit cryoablation was performed on 11 patients and 10 had atrial antitachycardia pacemakers. Preoperative functional New York Heart Association class was IV in 9, III in 4, and II in 1. RESULTS: One patient had brain death (7%) presumably caused by resternotomy complications despite an excellent hemodynamic result. Another required reoperation for a maldeployed clamshell device after attempted fenestration closure. Average length of stay was 10 +/- 3 days; chest tubes were removed on day 7 +/- 3. There were no long-term deaths (mean follow-up 1.7 years, range 5 months to 5 years). Postoperative arrhythmias occurred in five patients, three of whom had successful termination by antitachycardia pacemaker and two who had pharmacologic control of their respective junctional ectopic and slow atrial tachycardia. All patients have improved to New York Heart Association class I or II. CONCLUSIONS: Total cavopulmonary artery conversion in association with arrhythmia circuit cryoablation and atrial antitachycardia pacemaker placement can be accomplished with low morbidity and mortality, oftentimes resulting in dramatic increases in functional class and control of life-threatening arrhythmias.

Total cavopulmonary conversion and maze procedure for patients with failure of the Fontan operation.

OBJECTIVES: Hemodynamic abnormalities and refractory atrial arrhythmias in patients late after the Fontan operation result in significant morbidity and mortality. We review our experience with conversion to total cavopulmonary artery connections and arrhythmia surgery. METHODS: Between 1994 and 2001, 40 patients underwent Fontan conversion and arrhythmia surgery. Significant hemodynamic lesions such as aortic aneurysm (n = 1), atrioventricular valve insufficiency (n = 8), and pulmonary arterioplasty (n = 9) were repaired concomitantly. Thirty-four patients were in New York Heart Association class III or IV. Mean age at the original Fontan operation was 7.5 +/- 6.5 years and mean age at Fontan conversion was 18.7 +/- 9.0 years. Arrhythmia surgery has evolved from isthmus cryoablation in 10 patients to right-sided maze in 16 patients for atrial reentry tachycardia. The maze-Cox III operation was used for 14 patients with atrial fibrillation. Atrial (n = 33) and dual-chamber (n = 5) pacemakers were placed. RESULTS: There has been no early mortality. Chest tubes were removed on postoperative day 9.0 +/- 6.0. Hospital stay was 11.8 +/- 6.6 days. Three patients required cardiac transplantation at 8 days, 9 months, and 33 months postoperatively. There was 1 death 2 years postoperatively from acute myocardial infarction. For the entire series, arrhythmia recurrence is 12.5%, with only 10% of patients receiving long-term antiarrhythmic medications; these patients were among the first 8 patients in our series. Most patients are in New York Heart Association class I or II. Bruce protocol in 12 patients showed increased tolerance (P <.05). CONCLUSIONS: Fontan conversion to total cavopulmonary connection with concomitant arrhythmia surgery is excellent therapy for patients whose Fontan repair has failed. Fontan conversion is safe, improves New York Heart Association class, improves exercise tolerance, and has a low incidence of recurrent arrhythmias.

Congenital Heart Surgery Nomenclature and Database Project: arrhythmias.

This discussion of arrhythmia terminology attempts to classify rhythm disorders for which surgical therapy may be necessary. The subject was debated and reviewed by members of the STS-Congenital Heart Surgery Database Committee and representatives from the European Association for Cardiothoracic Surgery, for the purpose of establishing a unified reporting system. Efforts were made to include all relevant nomenclature categories, using synonyms where appropriate. Extant surgical ablative procedures, detailed methods of pacemaker insertion, and AICD technology are discussed. A comprehensive database set is presented that is based on a hierarchical scheme. Data are entered at various levels of complexity and detail, which can be determined by the clinician. These data can lay the foundation for comprehensive risk stratification analyses. A minimum database set is also presented, which will allow for data sharing and will lend itself to basic interpretation of trends. Outcome tables relating diagnoses, procedures, and various risk factors are presented.

Bidirectional Glenn shunt in association with congenital heart repairs: the 1(1/2) ventricular repair.

BACKGROUND: The bidirectional Glenn shunt has been used to incorporate a smaller tripartite ventricle into the circulation and create pulsatile pulmonary artery flow. We reviewed our operative experience and assessed hemodynamics of the bidirectional Glenn shunt in 1(1/2) ventricular repair or in conjunction with other repairs of congenital heart defects. METHODS: Between 1992 and 1998, 15 patients (mean age, 8.1+/-7.9 years) had bidirectional Glenn shunt in association with repair of congenital heart defects. Eighty-seven percent had at least one previous operation. All patients had simultaneous or previous intracardiac repair and had bidirectional Glenn shunt to volume unload the small right ventricle (group A, n = 7), to unload the poorly functioning right ventricle (group B, n = 2), to redirect superior vena cava-pulmonary venous atrial connection to treat cyanosis (group C, n = 2), or to unload the pulmonary left ventricle for residual intracavitary hypertension in patients with L-transposition of the great arteries, ventricular septal defect, and pulmonary stenosis (group D, n = 4). Intraoperative hemodynamic assessment was done in 2 patients in group A by selective use of inflow occlusion and flow probes. RESULTS: All patients survived. Four patients had successful, concurrent arrhythmia circuit cryoablation for Wolf-Parkinson-White syndrome (n = 1) or atrial reentry tachycardia (n = 3). Superior and inferior vena caval flow averaged 36% and 64% of cardiac output, respectively. Postoperative superior vena caval pressure (n = 13) was 13.7+/-4.0 mm Hg with pulmonary arterial flow pattern contributed by the ventricle in systole (pulsatile) and the superior vena cava in diastole (laminar). CONCLUSIONS: The bidirectional Glenn shunt is an effective adjunct to congenital heart repair to treat pulmonary ventricular pressure-volume problems and anomalous superior vena caval to left atrial connections.

Arrhythmias in the tiny, premature infant.

In contrast to the older infant or child in whom arrhythmias are usually secondary to congenital heart disease, arrhythmias in the small, preterm infant are most commonly secondary to central nervous system immaturity or extrinsic causes. Bradycardia is the most common arrhythmia observed in this population. The staff involved in the care of these extremely fragile and usually complicated patients have to be aware of the possibility of other rhythm disturbances occurring in such patients; this will help recognition and appropriate management of the individual cases.