Use of Single Lead VDD Pacing in Children

The development of transvenous ventricular pacing leads with proximal electrodes capable of atrial sensing and the recent availability of smaller generators has created the opportunity to treat children with complete AV block and normal sinus node function with a transvenous single lead VDD pacing system. Studies in adults have demonstrated this system to be efficacious with low complication rates. Transvenous single lead VDD pacemakers were implanted in ten children, aged 5–15 years, between December 1993 and April 1996, in our institution. The indications were complete AV block with severe bradycardia in 5 patients, second-degree or complete A V block following congenital heart surgery in 3, complete A V block with long QT syndrome in 1, and second-degree AV block and syncope in 1. There were no complications related to the procedure in any case. P and R wave amplitudes were measured and thresholds were determined intraoperatively on all patients. Amplitudes and thresholds were remeasured on seven patients with a mean follow-up of 17 months; Holter monitors were performed on seven patients with a mean follow-up of 16 months. P and H wave amplitudes were generally diminished at follow-up compared to initial values but remained within an acceptable range for all patients. Four patients required reprogramming after pacemaker insertion, 1 received an atrial lead for dual chamber pacing, 1 required repositioning for lead dislodgment. and 1 patient required a new lead for an inadequate ventricular pacing threshold. No patient had evidence of failure to sense or capture as evaluated by Halter monitoring at last follow-up. Single lead VDD pacing systems can be successfully used in properly selected children with high degree or complete AV block with normal sinus node function.     

Ectopic atrial rhythm with exit block following catheter ablation for focal atrial tachycardias in a patient with prior surgery for atrial septal defect

The patient was a 40-year-old woman with a history of surgery for atrial septal defect and catheter ablation for typical atrial flutter. An electrophysiological study was performed because she had palpitation and syncope. She had ectopic atrial rhythm originating from low lateral RA. Two focal atrial tachycardias ([1] superior vena cava-RA junction and [2] a lowposteroseptal RA) were successfully ablated. Following catheter ablation for the second atrial tachycardia, she developed junctional rhythm because ectopic atrial rhythm showed exit block. However, atrial activation of junctional rhythm could conduct into the ectopic atrial rhythm focus and reset the rhythm when atrial activation of junctional rhythm reached the blocked line after atrial refractoriness by preceding ectopic atrial rhythm.     

Atrioventricular Electrotonic Interaction in Complete Atrioventricular Block: An Experimental Model Using Radiofrequency Energy in the Rabbit Heart

Provided the conditions for electrotonic transmission exist, an automatic focus surrounded by a block zone may be externally modulated. The atrioventricular (AV) electrotonic interaction was studied in 16 perfused rabbit hearts with supra-Hisian complete AV block induced using low radiofrequency energy doses (2.5 watts; 10 seconds). In nine experiments the sinus node was preserved (group I), whereas in seven it was removed maintaining an AV nodal rhythm (group II). The V-V (ventricular cycle length) and V-A (coupling of the intervening atrial beat) in both groups, and also the A-A (atrial cycle length) and A-V (coupling of the intervening ventricular beat) intervals in group II, were measured beat by beat after current delivery. The phase response curves V-V versus V-A, and A-A versus A-V showed AV interaction in five experiments from group I, and in four from group II, as follows: (1) accelerating phase response curve, characterized by a pacemaker acceleration (V-V or A-A abbreviation) at a critical V-A or A-V coupling interval; maximum acceleration could be progressively (phase response curve without rapid cross-over) or briskly (phase response curve with rapid crossover) reached; from this point onwards acceleration decreased with a further increase in V-A or A-V coupling interval (acceleration slope). (2) Biphasic phase response curve, characterized by initial delaying and late accelerating phases. Maximum acceleration and the acceleration slope were both smaller in accelerating phase response curves without rapid cross-over. On reverting complete block in two experiments, a progressive increase in maximum acceleration and acceleration slope was observed. Conclusions: (1) AV interaction in complete AV block can be manifested as accelerating or biphasic phase response curves; (2) transition from electrotonic interaction to conduction seems to be a continuum.     

Atrioventricular Block in Situs Ambiguus and Left Isomerism (Polysplenia Syndrome)

Three patients are described who had situs ambiguus and left isomerism (polysplenia syndrome) and advanced atrioventricuiar block. One presented with a complex bradyarrhythmia with Wenckebach block. The other two had congenital atrioventricular block with a narrow QRS at a ventricular rate of 80 per minute, an atrial rate of 150' per minute, and both had a P wave axis directed superiorly and to the right in one, and superiorly to the left in the other. This ECG pattern was not observed in more than 400 adult patients with complete A-V block treated in our service. It is our opinion that in infants and children with heart disease the presence of complete A-V block with narrow QRS and an unusual P waves axis directed superiorly is strongly suggestive of left isomerism. The incidence rate of complete A-V block in left isomerism is nearly twenty percent of the cases described.     

Prospective Evaluation of Infrahisal Second-Degree AV Block Induced by Atrial Pacing in the Presence of Chronic Bundle Branch Block and Syncope

The value of nonfunctional infrahisal second-degree atrioventricular (AV) block induced by incremental atrial pacing was prospectively examined in 192 patients with chronic bundle branch block (BBB) and syncope. We compared 174 (91 %) patients with normal response to atrial pacing (Group I) to 18 (9%) patients with atrial pacing induced nonfunctional infrahisal second-degree AV block (Group II). Patients in group I had higher incidence of organic heart disease, ventricular tachycardia induction, and retrograde ventriculoatrial conduction (P < 0.001, P < 0.05, P < 0.01, respectively), while patients in group II had higher incidence of primary conduction disease and prolonged H-V intervals (P < 0.001, P < 0.01, and P < 0.001). During mean follow-up period of 65 ± 34 months for group I, and 68 ± 35 months for group II, a development of spontaneous second- or third-degree AV block was higher in group II (14/18 [78%]), than in group I (15/174 [9%]) (P < 0.001). The site of AV block was infrahisal in all patients in group II, and in 10 of 15 patients in group I. Because of the prophylactic pacing in all patients in group II, the incidence of sudden death was similar among the two groups, but patients in group I had higher incidence of cardiac death (P < 0.05). Conclusion: In patients with chronic BBB and syncope, a nonfunctional infrahisal AV block induced by incremental atrial pacing identified patients with particularly high risk of development of spontaneous infrahisal AV block. Therefore, permanent cardiac pacing is absolutely indicated in these patients.     

Second and Third Degree Atrioventricular Block with Graves' Disease: A Case Report and Review of the Literature

A previously healthy woman experienced Adams-Stokes attacks ten weeks after the initiation of antithyroid medication for Graves' disease. The patient manifested advanced atrioventricular (A-V) block requiring a temporary transvenous pacemaker. The site of heart block was localized to the A-V node by utilizing a His bundle electrogram. With control of the hyperthyroid state, normal A-V conduction was restored. Review of the literature identified twenty-five additional cases of second or third degree A-V block associated with Graves' disease, ten of whom had Adams-Stokes syncope or convulsive seizures. The A-V nodal block was reversible with cure of the primary endocrine disease. It is postulated that excessive thyroid hormone has a direct effect on the cardiac conduction system, specifically, the region of the A-V node and bundle of His. Recommendations are made regarding the recognition and management of patients at risk for developing heart block associated with Graves' disease.     

Severe Conduction Disturbances and Ventricular Arrhythmias Complicating Mediastinal Irradiation for Hodgkin''s Disease: A Case Report

A 27-year-old male had undergone mediastinal and retroperitoneal irradiation for stage IIIA Hodgkin's disease at age 19. When he was admitted to the hospital, because of lightheadedness and syncope, trifascicular bundle branch block was noted and the patient underwent a clinical electrophysiological investigation. AH and HV intervals were prolonged and ventricular fibrillation was induced during programmed right ventricular stimulation. Serial electrophysiological studies allowed us to prescribe effective antiarrhythmic drug therapy with no recurrence of symptoms during a follow-up period of 12 months.     

双腔起搏对三度房室传导阻滞病人左心房收缩功能的影响

目的评价三度房室传导阻滞病人植入双腔起搏器后对左心房收缩功能的影响。方法筛选20例三度房室传导阻滞病人,分别于双腔起搏器植入术前及术后1、3个月应用应变率成像（SRI）技术评价左心房的收缩功能。结果与术前比较,术后1个月左心房排空分数（LAEF）、左心房收缩期峰值应变率（SRa）、左心室射血分数（LVEF）和E／A显著升高;术后3个月,上述指标变化更为显著,差异均有统计学意义（F=6．798～25．763,P〈0．05）。术后1个月和3个月LVEF变化率与SRa变化率呈正相关（r=0．500、0．525,P〈0．01）。结论双腔起搏器植入术可改善三度房室传导阻滞病人左心房的收缩功能,表现为辅泵功能增加,同时改善病人的心功能。     

A retrospective case study to assess the value of the implantable loop recorder for the investigation of undiagnosed syncope

If not diagnosed by history, examination, or ECG, the diagnosis of syncope can be difficult with a low yield from echocardiography, ambulatory ECG recording, electrophysiological study, and tilt table testing. During 2 years, 48 patients with unexplained syncope or presyncope from three hospitals in one city underwent the implantation of a Medtronic Reveal implantable loop recorder capable of cardiac monitoring for 14 months. All patients had at least two prior episodes of syncope or presyncope. Fifty-two percent of patients had electrophysiological studies, all of which were negative. The implantable loop recorder remained implanted until a diagnostic event was recorded, or until the end of the battery life. After a mean follow-up of 5.6 +/- 5.7 months, symptoms reoccurred in 25 (52.1%) patients at a mean of 2.8 +/- 2.1 months after insertion of an implantable loop recorder. No further symptoms occurred in 23 (47.9%) patients. Of the 25 patients who had a symptom and recorded an event, an arrhythmia was seen in 10 (40%) patients. Seven patients had bradycardia; 4 with profound sinus bradycardia/sinus arrest, 1 with complete heart block, and 2 in association with the cardioinhibitory component of vasovagal syncope. Three patients had tachycardias; two with supraventricular tachycardia and one with atrialflutter. Fifteen (60%) of the 25 patients who activated their device due to syncope or presyncope were in sinus rhythm during the event. The implantable loop recorder was effective in making a cardiological or noncardiological diagnosis for unexplained syncope or presyncope in 52.1% of the patients.     

Possible Risks of General Anesthesia in Patients with Intraventricular Conduction Disturbances

In order to assess the risk of complete AV bloek in patients, with intraventricular conduction disturbances who undergo general anesthesia, 20 patients with various conduction defects (7 LBBB, 1 RBBB and 1st degree AV block, 1 incomplete RBBB, 9 RBBB+LAH and 2 RBBB+LPH) were studied by means of His bundle recording and corrected sinus node recovery time (CSNRT) before and after the subministration of thiopental (0.2 g. I.V.), succinylcholine (1 mg/kg I.V.), Eluothane (l%) and Ethrane (1.6%). Nineteen patients displayed signs of dizziness or syncope; both the sinus rate and the CSNRT, did not undergo significant variations. A slight and not significant variation of intranodal conduction during sinus rhythm was observed after Fluothane administration (AH was prolonged by 8%). A less evident negative dromotropic action of thiopental and Ethrane was only revealed by atrial pacing. No significant variations were demonstrated in His-ventricular conduction after administration of the various drugs. The maximum average increase (1.5%) of the H-V interval was observed after administration of succinylcholine. Acute AV block distal to the His bundle appeared in three patients after succinylcholine administration.     

Atrioventricular block following overdose of decongestant cold medication

A 24-year-old man developed high-degree atrioventricular (A-V) block with a pulse rate of 40 beats per minute and hypertension following an overdose of a combination decongestant cold medication that contained phenylpropanolamine, phenylephrine, chlorpheniramine, and phenyltoloxamine. The patient was treated with ipecac, activated charcoal, and cathartics in the emergency department (ED). After his admission to the coronary care unit, the A-V block gradually resolved to sinus rhythm with periods of second-degree block, Mobitz types I and II. No treatment was required. The patient had a normal sinus rhythm and normal blood pressure prior to discharge.     

Evaluation of Patients with Bundle Branch Block and "Unexplained" Syncope: A Study Based on Comprehensive Electrophysiologic Testing and Ajmaline Stress

Thirty-five patients with bundle branch block (BBB) and unexplained syncope underwent electrophysiologic study (EPS) including programmed ventricular stimulation and ajmaline administration (1 mg/kg, IV) to induce infra-His block. A prolonged HV interval (greater than 55 ms) was present in 16 of the 35 patients. Ajmaline-induced HV block occurred in 12 patients (complete HV block in 10, and 2:1 HV block in two). Monomorphic ventricular tachycardia (VT) was inducible in nine (25.7%) and polymorphic VT in two patients (5.7%). Left ventricular ejection fraction (LVEF) was less than 40% in five patients (45.5%) with inducible VT. Two patients had an unexpected co-existence of inducible HV block and VT. The remaining 14 patients (40%) had no detectable abnormality. The incidence of inducible VT was higher (45% vs 13.3%), and the presence of negative studies was lower (30% vs 53.3%) in patients with structural heart disease (n = 20), when compared to those with no significant heart disease (n = 15) (differences not significant [NS]). During a mean follow-up period of 16.5 +/- 9.2 months, all the patients with inducible HV block have been asymptomatic after having received permanent pacemakers. Patients with inducible monomorphic VT (except one with poor left ventricular function who died suddenly) have also been asymptomatic on antiarrhythmic drugs. Of the remaining patients, seven with normal EPS, two with prolonged HV intervals but no inducible HV block (despite being given permanent pacemakers) and one patient with polymorphic VT on antiarrhythmic drugs continue to have recurrent syncope. Approximately 60% of patients with BBB and unexplained syncope have clinically significant electrophysiologic abnormalities.(ABSTRACT TRUNCATED AT 250 WORDS)     

Slow junctional rhythm during catheter ablation of right posteroseptal accessory pathway causing transient atrioventricular block

A male patient with palpitations and syncope during an episode of atrial fibrillation was evaluated. After DC cardioversion, the ECG showed a pattern of pre-excitation compatible with right posteroseptal bypass tract. The patient was submitted to RF. During energy application a slow junctional rhythm without AV block was noted. Twenty-four hours after the procedure AV block was observed. The AV conduction was resumed spontaneously 48 hours later with unremarkable outcome up to 1 year. We postulated that the edema caused by RF application damaged the compact AV node, causing transient AV block. The AV node lesion has been manifested by a fast junctional rhythm, but in this case we observed that even a slow junctional rhythm could do it.     

The Effect of Exogenous Adenosine in Patients with Neurally-Mediated Syncope and Sick Sinus Syndrome

The effects of a 20-mg IV, bolus of adenosine 5'triphosphate (ATP) on the heart rhythm was studied in 79 patients affected by neurally-mediated syncope (26 cases) or sick sinus syndrome (22 cases) or both syndromes (31 cases) and in 31 healthy control subjects in order to examine the sensitivity of cardiac purinoceptors in such circumstances. During ATP infusion, the sinus cycle lengthened to > 2 seconds in no control, in 1 (4%) patient with neurally-mediated syncope, in 5 (23%) patients with sick sinus syndrome, and in 13 (42%) patients with both neurally-mediated and sick sinus syndromes (P = 0.01). Atrioventricular block occurred in 14 (45%) of controls, in 10 (38%) patients with neurally-mediated syncope, in 4 (18%) patients with sick sinus syndrome, and in 13 (42%) patients with both neurally-mediated syncope and sick sinus syndrome (n.s.). Thus, exogenous ATP exerts different effects on patients with neurally-mediated syncope and patients with sick sinus syndrome. In fact, intrisic disease of the sinus node is necessary to modulate an abnormal adenosine-mediated sinus arrest, whereas patients affected by neurally-mediated syncope alone show a normal sensitivity to the drug administration. The effect of ATP on atrioventricular conduction is greater than that on sinus node and is of similar magnitude in patients and controls; thus the clinical meaning of ATP induced atrioventricular block remains uncertain.     

The Development of Sinoatrial Dysfunction in Pacemaker Patients with Isolated Atrioventricular Block

The purpose of this paper is the assessment of sinus node competence over time in patients with isolated atrioventricular block (AV block). Patients implanted with AV synchronous pacemakers for isolated A V block between December 1993 and June 1995 were prospectively evaluated at predischarge, 6 weeks, and subsequent 6 months follow-up with respect to atrial rate monitors/24-hour Holter and modified exercise test. Patients unable to maintain AV synchronous pacing or complete a modified exercise test were excluded. Sinus node competency is interpreted as: (1) absence of atrial brady- or tach-yarrhythmia, (2) ability to achieve a minimum heart rate of 100 beats/min with modified exercise test or during daily activities. There were 58 patients (22 women), mean age 71.0 ± 13.8 with an average follow-up of 30.4 months (11–40). Three patients did not complete a modified exercise test, 4 patients were lost to follow-up, and 2 patients were unable to maintain AV synchronous pacing. Of the remaining 49 patients, 3 developed chronic or paroxysmal atrial fibrillation. No patient developed significant bradyarrhythmias. All patients achieved a heart rate of ≥ 100 beats/min modified exercise test. In our group of patients with isolated AV block within a moderate follow-up period, development of Sinoatrial dysfunction was rare (6%). A longer follow-up is required to delineate the natural history of Sinoatrial dysfunction in patients with isolated AV block.     

Effects of Propafenone on Induction and Maintenance of Atrioventricular Nodal Reentrant Tachycardia

Electrophysiologic studies were performed in 10 patients with atrioventricular (A-V) nodal reentrant paroxysmal supraventricular tachycardias (PSVT), before and after intravenous administration of propafenone (1.5 mg/kg). All patients utilized an A-V nodal slow pathway for anterograde conduction and an A-V nodal fast pathway for retrograde conduction of the reentrant impulse. Propafenone depressed retrograde fast pathway conduction which was manifested by: 1) complete V-A block at all ventricular paced cycle lengths after propafenone in 3 cases; 2) increase in mean +/- SD of ventricular paced cycle length producing V-A block from less than 308 +/- 37 ms to 432 +/- 63 ms in the remaining 7 patients. Nine of the 10 patients had induction of sustained PSVT before propafenone. In 7 of the 9, PSVT could not be induced or sustained after propafenone, reflecting depression of the retrograde fast pathway conduction with either absence of atrial echoes (5 patients) or induction of nonsustained PSVT, with termination occurring after the QRS (2 patients). In 1 patient, single atrial echoes were induced before propafenone but none were noted after the drug. In only 2 patients was a sustained PSVT inducible after propafenone. In conclusion, propafenone inhibited induction of sustained A-V nodal reentrant PSVT in most patients, reflecting depression of retrograde A-V nodal fast pathway conduction.     

Catheter-induced A-V Nodal Block Occurring during Electrophysiologic Study

We describe a patienl who underwent electrophysiologic study for evaluation of recurrent syncope. No abnormalities were found but high-grade A-V block proximal to the A-V bundle depolarization developed abruptly as the coronary sinus electrode catheter was being withdrawn. The A-V block disappeared gradually over a 12-hour period, progressing to type I second-degree A-V block, and then to first-degree A-V block (due to prolonged A-V nodal conduction), prior to resuming normal conduction. We postulate that A-V block was induced by direct contact between the electrode catheter and the A-V node or very proximal His bundle. Catheter-induced A-V block at this site has been described only rarely, possibly because of the relatively protected location and the configuration of the A-V node.     

Single Pass VDD Pacing in Children and Adolescents

Use of a single pass lead for VDD pacing in complete heart block is well described in adults, but there are only brief reports of its use in children. We have used standard adult size single pass leads in 13 children and adolescents aged 3.7–17.2 years (mean 10.1 years) and weighing 13.5–76 kg (mean 34.8 kg). Congenital complete heart block was present in 7 patients, surgical complete heart block in 5 patients and 2:1 AV block of unknown cause in 1 patient. In four patients, the VDD system was their first pacing system. In nine of the patients, 1–6 previous systems had been used and simultaneous extraction of ventricular leads and/or atrial leads was performed. Leads of four different types were used: Brilliant IMPl5Q, Brilliant + IMR15Q, CapSure 5032, and Unipass 425–13 with 4 different generators: Saphir 600, SaphirII620, Thera VDD 8948, and Unity 292–07. At implantation, via a subclavian vein puncture, excess lead was advanced into the right atrium to allow both atrial sensing and slack for further growth. Ventricular thresholds ranged from 0.2–0.7 V. The minimal atrial amplitude was 0.7–4 mV and the maximum amplitude was 2.5–8 mV. There were no complications. Ail patients have maintained adequate atrial signals for reliable pacing with follow up of 3–36 months (mean 17.6 months) during which time some have undergone considerable growth. Beliable atrial synchronous ventricular pacing is possible in growing children with complete heart block using a standard adult single pass lead.     

Atrial fibrillation in the Wolff-Parkinson-White syndrome: ECG recognition and treatment in the ED

Estimated to occur in 0.1% to 0.3% of the population, Wolff-Parkinson-White syndrome (WPW) is a condition where atrial impulses bypass the atrioventricular node and activate the ventricular myocardium directly via an accessory pathway. Clinical clues to the diagnosis include a young patient with previous episodes of palpitations, rapid heart rate, or syncope. Although several different rhythm presentations are possible, atrial fibrillation is a not infrequent dysrhythmia seen in the WPW patient. Electrocardiographic features suggestive of WPW atrial fibrillation include irregularity of the rhythm; a very rapid ventricular response; presence of a delta wave; and a wide, bizarre QRS complex. Stable patients suspected of having this condition should not receive agents that predominantly block atrioventricular conduction, but they may be treated with procainamide or ibutilide. If instability is present, electrical cardioversion is required.     

Paroxysmal Atrial Fibrillation and High Degree AV Block: Use of Single-Lead VDDR Pacing with Mode Switching

Dual chamber rate responsive pacing incorporating a mode switching option is increasingly listed in patients with chronic paroxysmal atrial fibrillation and high degree AV block. Single-lead VDDR pacemakers have been rarely used for this indication. The purpose of this study was to determine thnir reliability of atrial sensing during atrial fibrillation, the percentage of at rial synchronous ventricular pacing, and the behavior of the sinus rate outside the phases of atrial fibrillation. We studied ten patients with a single-lead VDDR pacemaker implanted for this indication. Follow-up visits were performed at predischarge and after 1, 3, 6, 12. 18, and 24 months. During the mean follow-up period of 18.9 ± 6.9 months, the atrial sensing thresholds in sinus rhythm remained stable. Atrial synchronous ventricular stimulation was achieved in 68,7 ±31.2% (median 82.5%) of the whole follow-up time. All patients showed an adequate atrial rate response during sin us rhfthm. Atrial fibrillation was detected by the pacemakers in 24.0 ± 29.8% of time. In 3 of 10 patients the duration of atrial fibrillation showed a steady increase from visit to visit. The sensed amplitudes of atrial fibrillation ranged from 0.1–1.0 mV. A programmed atrial sensitivity of 0.1 mV was necessary to achieve complete sensing of atrial fibrillation. None of the patients experienced tachycardias with optimized pacemaker programming. Single-lead VDDR pacing incorporating a mode-switching option is useful in patients with high degree AV block and paroxysmal atrial fibrillation, since it provides atrial synchronous ventricular pacing in more than two-thirds of follow-up time. In a subgroup of patients, a progressive increase of the time during atrial fibrillation was demonstrated. A reliable detection of paroxysmal atrial fibrillation requires the programming of the atrial sensitivity to its most sensitive value.