FIG 22.6 Rhythm strip demonstrating functional 2 : 1 atrioventricular block in the presence of QT prolongation (prolonged ventricular refractoriness) Patients with significant and persistent bradycardia and sinus node or AV block who do not undergo antibradycardia pacing require ongoing follow-up with serial ECGs, Holter monitors, and echocardiograms The frequency of such testing should be based on the clinical status of the patient after discussions with the medical team caring for him or her There are few data on the use of serial echocardiograms in establishing definitive recommendations for a pacemaker, but it is generally helpful to assess ventricular size and function, the degree of AV valve regurgitation, and atrial size Postoperative Atrioventricular Block Postoperative AV block occurs in 1% to 3% of cardiac operations, with the greatest risk occurring following repair of AV canal defects, tetralogy of Fallot, and ventricular septal defects as well as in hearts with AV discordance (Llooped) and heterotaxy syndrome.32–35 Although transient AV block has been reported in nearly 7% of surgical cases, resolution may occur; if so, it will do so in 97% by 10 days following surgery.33,35 As such, the risk of sudden cardiac death following surgical advanced second- or third-degree AV block that is not expected to resolve or persists for at least 7 days after cardiac surgery is a class I indication for pacemaker implantation.24 In addition, junctional JET may be a concomitant observation in patients with complete AV block.35 Patients in whom postoperative advanced second- or third-degree AV block has resolved and in whom conduction returns to normal have a good prognosis, and pacing is not indicated If there is incomplete recovery with new residual bifascicular block (complete right-bundle-branch block [RBBB] and left axis deviation), uncertainty remains (class IIB in the American College of Cardiology/American Heart Association recommendations and class IIa in the European Society of Cardiology) Postoperative AV interval determination may help to assess the risk of late-onset AV block in patients with residual conduction disorders (bifascicular block and PR prolongation); however, this is not always practical.36 If epicardial wires are available and there is concern about the stability of the residual conduction abnormality, it may be worth evaluating the AV node's Wenkebach cycle length Discussions with the cardiac intensive care unit and surgical teams regarding leaving epicardial wires in place to assess AV nodal conduction should occur Long-term instability of the conduction system has been postulated in patients with transient postoperative heart block and is thought to contribute to late sudden death in some patients Thus patients should be monitored for any recurrence of heart block or evidence of arrhythmia with regular ambulatory monitors Syncope Syncope (transient loss of consciousness) is a result of cerebral hypoperfusion and is most commonly a result of autonomic nervous system dysfunction Neurally mediated (or vasovagal) syncope results in loss of consciousness typically after being in an upright posture (for more than 30 seconds) or with emotional stress or pain, often with associated symptoms of vision changes, warmth, diaphoresis, and nausea Hypotension and bradycardia may exist and patients are often profoundly fatigued following the event The frequency of syncope peaks at 11 years of age, with a lesser peak between 6 and 18 months of age in the form of pallid breath-holding events.37–39 Guidelines for the evaluation and treatment for vasovagal syncope and postural orthostatic hypotension syndrome were recently published by the American Heart Association, American College of Cardiology, and Heart Rhythm Society.40,41 Cardiologists are frequently asked to evaluate a child with syncope in both the acute and outpatient settings Each evaluation should begin with a detailed personal history surrounding the event from the individual as well as from any witnesses, a thorough physical examination, and a carefully constructed family history concerning unexplained syncope, seizures, or sudden cardiac death in the young Although current guidelines support an initial routine ECG examination in patients presenting with syncope, the yield in those with clinically suspected vasovagal syncope is low, and efforts should be made to reduce false positives.42 It is of utmost importance to be aware of any potential red flags that warrant additional testing (Table 22.1) In a retrospective study of 60 patients with exertional syncope, 53% were identified as having a cardiac etiology Syncope that occurs during exertion should be differentiated from postexertional syncope, which tends to be more aligned with neutrally mediated syncope.43 A pediatric cardiologist or adult congenital heart disease specialist should urgently evaluate patients with syncope in the setting of repaired or palliated congenital heart disease Detailed evaluation for the possibility of bradyarrhythmias or tachyarrhythmias should be sought in this high-risk cohort The Heart Rhythm Society along with pediatric and adult specialists from North America and Europe recently published guidelines on the evaluation and management of the adult patient with congenital heart disease and syncope.44 ... hypotension syndrome were recently published by the American Heart Association, American College of Cardiology, and Heart Rhythm Society.40,41 Cardiologists are frequently asked to evaluate a child with syncope in both the... that occurs during exertion should be differentiated from postexertional syncope, which tends to be more aligned with neutrally mediated syncope.43 A pediatric cardiologist or adult congenital heart disease specialist should urgently evaluate patients with syncope in the setting of repaired or palliated congenital heart... tachyarrhythmias should be sought in this high-risk cohort The Heart Rhythm Society along with pediatric and adult specialists from North America and Europe recently published guidelines on the evaluation and management of the