Episodes Of Complete Heart Block Research Articles

Abstract 10047: A Case of Recurrent Miscarriages Due to Malignant Situational Cardioinhibitory Nerurocardiogenic Syncope Treated With Pacemaker Placement

Case Presentation: A 29- year-old G5A4 woman with history of seizure disorder presented with severe nausea and vomiting (N&V) with transient loss of consciousness with twitching motor activity at 7-weeks' gestation. She had no post-ictal state, but a brief period of nausea and lethargy with a rapid return to baseline. Her medical history only included a diagnosis of seizure disorder since childhood treated with different anti-epileptic agents. She reported 4 first-trimester abortions secondary to reported intractable recurrent seizures during pregnancy accompanied by significant morning sickness. Her physical examination, laboratory tests, brain CT, EEG, EKG, and a trans-thoracic echocardiogram were unremarkable. Levetiracetam was started. While monitored in telemetry she had an episode of complete heart block for 8-seconds with ventricular standstill triggered by a bout of severe N&V resulting in convulsive syncope. The diagnosis of situational cardioinhibitory malignant Neurocardiogenic Syncope (NS) was made. She underwent dual-chamber pacemaker implantation with complete resolution of her symptoms. After 6-months Levetiracetam was discontinued. Her pregnancy progressed to term delivering a healthy newborn. She remains asymptomatic 4 years after her pacemaker implantation. Discussion: Malignant NS is a type of neurally-mediated syncope that can lead to significant morbidity and occasional mortality. Situational syncope occurs when a vaso-vagal reflex occurs in response to a specific trigger, in the present case straining is associated with N&V and has not been described with miscarriages. In this case, the pronounced vagal response to N&V resulted in ventricular stand-still causing brain hypoperfusion and seizures, which are associated with miscarriage due to slower fetal heart rate, fetal hypoxia, fetal injury, placental hypoperfusion, placental abruption or trauma. To the best of our knowledge, this is the first case reported in the literature of recurrent miscarriages due to NS successfully treated with a pacemaker. Conclusions: Convulsive syncope can result in miscarriages and should remain in the differential diagnosis in patients presenting with suspected seizures associated with vaso-vagal triggers during pregnancy.

0854 A case of complete heart block in a patient with severe obstructive sleep apnea

Abstract Introduction Obstructive sleep apnea (OSA) has been associated with bradycardic arrythmias and cases of transient heart block. Heart block occurring during sleep has been described in up to 10% of patients with obstructive sleep apnea, most commonly during stage R sleep and through a mechanism known as vagal activation. Stage R sleep is associated with desynchronization of respiratory and cardiovascular functions, and the excessive autonomic response (vagal activation) occurs due to the stronger stimulation of chemoreceptors and baroreceptors induced by hypoxemia, intrathoracic pressure swings, and hemodynamic alterations. Treatment of the underlying sleep-disordered breathing will typically treat the bradycardic arrythmia as well. Report of Cases: A 49-year-old male with a BMI of 30 kg/m , neck circumference of 16 inches, and obstructive sleep apnea presented to the sleep center to establish care for management of his preexisting OSA. He was previously diagnosed with moderate OSA in 2007 but had discontinued therapy shortly after due to Continuous Positive Airway Pressure (CPAP) intolerance. The patient complained of snoring, nocturia, and excessive daytime sleepiness (18/24 on Epworth Sleepiness Scale). During the split night study, the patient was noted to have 2:1 second degree heart block followed by a transient episode of complete heart block, manifested by 4 non-conducted p-waves. The patient remained asymptomatic throughout the night. Upon study completion, the patient denied any prior chest pain, presyncope, syncope, or medications that might cause heart block. Conclusion Bradyarrythmias can be seen in severe obstructive sleep apnea in the setting of excessive vagal stimulation through increased stimulation of chemoreceptors and baroreceptors. Treatment with PAP therapy can lead to prevention of heart block in 80-90% of these patients. Support (If Any)

Very low event rate and few device implants in drug-induced brugada. A seven-year experience of ajmaline challenge at a district general hospital

Abstract Funding Acknowledgements Type of funding sources: None. Background Patients with a drug-induced Brugada electrocardiogram (ECG) are thought to have a lower risk of sudden cardiac death than those with a spontaneous type 1 ECG. Despite having a Brugada ECG, most patients do not need an implantable cardioverter defibrillator (ICD). Purpose To report a district general hospital experience on referral and outcomes of ajmaline challenge (AC) with medium term follow up. Methods 92 consecutive patients (50 males, mean age 41 ±17) had an AC in a single centre from 2014-2021. High ventricular leads were used from 2015. Ajmaline (1m/kg) was administered intravenously over 10-minutes. Data were collected from the electronic health record. Results The AC was positive in 18 (20%) patients. The yield from high leads was higher (7% vs 22%) p=0.28) but not statistically significant. There were no deaths or documented ventricular arrhythmias (VA) in AC positive patients during a median follow up of 3.2 years (1.7-4.9). The resting ECG was normal in 46.7%. A type 1 pattern had been provoked by fever or electrolyte derangements in 3.3%, type 2 pattern in 8.7% and a type 3 pattern in 5.4%. An RSR pattern (not in keeping with a BrS ECG) was seen in 26.4%. The test was stopped prematurely due to QRS widening >150ms in 1 patient. No adverse arrhythmic events occurred (table 1). In our cohort, positive AC patients were older (48y vs 37y p= 0.05) and more likely to have a type 2 (28% vs 4% p=0.007) or type 3 ECG (17% vs 3% p=0.05). Asymptomatic patients were more likely to have a normal ECG (22% vs 78% p=0.05) Of those with a positive AC, nine patients had symptoms of palpitations or syncope (table 2). A subcutaneous ICD (S-ICD) was implanted for syncope in two patients. No device therapies have occurred during a follow up of 2.5 years and 3.9 years respectively. Of those with a positive AC but asymptomatic, one S-ICD was initially implanted due to patient preference. A second S-ICD was implanted in a patient who experienced a collapse and brief seizure in the context of modest alcohol consumption. In seven positive patients (39%) and 18 negative patients (23%) an ILR was implanted. 1 episode of complete heart block was detected in an ajmaline negative patient during a median follow up of 2.7 years (1.7-3.9). There were no device related complications or adverse events. Conclusion AC is safe with a low number of device implants and ICD shocks. The yield from ILR implants was very low. A single patient had a potentially adverse outcome after consuming alcohol, a known trigger for VA in BrS. Our findings are in keeping with contemporary evidence that suggests the risk of adverse cardiac events in drug-induced BrS is low. However, time to first ICD shock may occur after ten years or more from diagnosis so long term follow up is required.

C8. An Extremely Rare Case: Cardiac Contusion Presenting with an Atrioventricular Block, An Unfortunate Fall

Abstract Background Blunt cardiac injury (BCI), also referred to cardiac contusion, is a known cause of myocardial injury. It is often challenging to diagnose in the absence of clear diagnostic criteria. The clinical manifestation ranges from none to fatal arrhythmias to cardiac wall rupture seen on post-mortem examination. Cardiac biomarkers and electrocardiograms are usually helpful in identifying cardiac trauma but are not necessarily abnormal in all cases. Case Illustration A 55-year-old male with no history of cardiac disease was brought to the emergency department after a motor vehicle collision resulted in chest wall injury. The patient was found to have left clavicle fracture, left costae II-VII fractures, and hematothorax followed by chest tube insertion. The patient had multiple episodes of complete heart block with junctional escape rhythm alternate with high degree 2:1 AV conduction, and sometimes became a normal sinus rhythm. A temporary pacemaker was inserted. After the patient underwent the ORIF procedure, cardiac rhythm revealed normal sinus rhythm and temporary pacemaker is removed. Discussion High-degree AV block has been reported in human studies following BCI, secondary to necrosis, inflammation, or fibrotic changes in the subendocardial tissue. 50% of patients reviewed in the literature had a recurrence or permanent complete heart block requiring pacemaker implantation and complete heart block secondary to BCI which was associated with a 20% mortality in the post-traumatic period. Our patient developed a fatal heart block in the early period which could have easily been missed.

C8. An Extremely Rare Case: Cardiac Contusion Presenting with an Atrioventricular Block, An Unfortunate Fall

Abstract Background Blunt cardiac injury (BCI), also referred to cardiac contusion, is a known cause of myocardial injury. It is often challenging to diagnose in the absence of clear diagnostic criteria. The clinical manifestation ranges from none to fatal arrhythmias to cardiac wall rupture seen on post-mortem examination. Cardiac biomarkers and electrocardiograms are usually helpful in identifying cardiac trauma but are not necessarily abnormal in all cases. Case Illustration A 55-year-old male with no history of cardiac disease was brought to the emergency department after a motor vehicle collision resulted in chest wall injury. The patient was found to have left clavicle fracture, left costae II-VII fractures, and hematothorax followed by chest tube insertion. The patient had multiple episodes of complete heart block with junctional escape rhythm alternate with high degree 2:1 AV conduction, and sometimes became a normal sinus rhythm. A temporary pacemaker was inserted. After the patient underwent the ORIF procedure, cardiac rhythm revealed normal sinus rhythm and temporary pacemaker is removed. Discussion High-degree AV block has been reported in human studies following BCI, secondary to necrosis, inflammation, or fibrotic changes in the subendocardial tissue. 50% of patients reviewed in the literature had a recurrence or permanent complete heart block requiring pacemaker implantation and complete heart block secondary to BCI which was associated with a 20% mortality in the post-traumatic period. Our patient developed a fatal heart block in the early period which could have easily been missed.

B-PO03-139 AN EVALUATION OF FUNCTIONAL MAPPING TECHNIQUES FOR AVNRT

Identification of the correct ablation site for treatment of AV-nodal re-entrant tachycardia (AVNRT) has historically been determined by local electrogram appearance. We investigated whether activation mapping of the triangle of Koch improves identification of the correct ablation site for slow pathway modification. To determine if Ripple or isochronal activation mapping can accurately identify successful sites of slow pathway modification. We performed a retrospective analysis of all adult patients at our center who underwent an electrophysiology study and ablation with CARTO electroanatomic mapping for management of AVNRT from January 1, 2015 to October 31, 2019. Ripple (Biosense Webster) and isochronal mapping was applied to each map. The region of critical slowing was then identified on each map without knowledge of the successful ablation sites. We then measured the distance and orientation between the sites on the Ripple and isochronal maps with the successful ablation site. Sixty-seven patients underwent AVNRT ablation with CARTO, of which 18 cases had maps with sufficient point density for activation mapping. Mean age was 51y (20-76) with 72% typical AVNRT, 17% atypical, and 11% with dual features. All included cases used radiofrequency ablation as opposed to cryoablation. There were no episodes of complete heart block or acute damage to the AV node. The area of slowing on Ripple mapping was within an average of 5.7 mm (range 1.8-10.9, SD 2.5) of the successful ablation site, with 5 cases within 4 mm. Slowed conduction identified with isochronal mapping was on average 6.4 mm (range 2.7-12.5, SD 2.6) from the successful ablation site, with 5 cases within 4 mm. There was no statistical difference between the two methods (p-value = 0.51). There was no tendency towards any one direction for these measurements. Both Ripple and isochronal mapping accurately localized to the previously identified sites of successful ablation in the vast majority of cases, with a small range of error. There was no statistical difference between the accuracy of these two techniques. Prospective, multicenter trials are necessary to confirm whether activation mapping can enhance ablation in patients with AVNRT.

Late Complete Heart Block after Surgical Repair of an Atrial Septal Defect

ABSTRACT Atrial septal defects (ASD) are among the most common forms of congenital heart disease. Although surgical correction was the only available therapy for decades, its long-term complications remain unknown and many patients do not have structured medical follow-up in later life. However, increasing evidences suggest that late-onset cardiac problems, such as complete heart block (CHB), can arise after surgery and therefore, long-term follow-up should be advised in these patients. We hereby present an interesting case of CHB occurring in a 30-year-old patient who had undergone surgical secundum ASD closure approximately 21 years prior to this event and now presented with episodes of dizziness and pre-syncope. Seven-day Holter reported seven episodes of CHB, corresponding to the presenting complaints. The patient was successfully managed with conduction system pacing and he remained asymptomatic on further follow-up. The case description is followed by a brief overview of the available literature.

Transient Third-degree Heart Block Secondary to Asymptomatic COVID-19 Infection

COVID-19 predominantly affects the lungs manifesting as respiratory illnesses including pneumonia and acute respiratory distress syndrome. Cardiac manifestations are also being increasingly reported such as pericardial disease, myocardial injury and dysfunction, arrhythmias and conduction abnormalities. A 70-year-old male with asymptomatic COVID-19 infection developed a transient episode of complete heart block just prior to his planned discharge from hospital. There are only few case reports purporting the development of a transient complete heart block in patients with moderate to severe COVID-19 infection. However, to date, this is the first report of incidentally detected, asymptomatic COVID-19 infection manifesting as third degree heart block.

Chest palpitations in a teenager as an unusual presentation of Lyme disease: case report

BackgroundThe incidence of Lyme disease (LD) in North America has increased substantially in the past two decades. Concomitant with the increased incidence of infection has been an enhancement in the recognition of LD complications. Here, we report a case of Lyme carditis complicated by heart block in a pediatric patient admitted to our children’s hospital. What is unique about this case is that the complaint of chest palpitations is an infrequent presentation of LD, and what it adds to the scientific literature is an improved understanding of LD in the pediatric population.Case presentationThe patient was a 16-year-old male who presented with the main concerns of acute onset of palpitations and chest pain. An important clinical finding was Erythema migrans (EM) on physical exam. The primary diagnoses were LD with associated Lyme carditis, based on the finding of 1st degree atrioventricular heart block (AVB) and positive IgM and IgG antibodies to Borrelia burgdorferi. Interventions included echocardiography, electrocardiography (EKG), and intravenous antibiotics. The hospital course was further remarkable for transition to 2nd degree heart block and transient episodes of complete heart block. A normal sinus rhythm and PR interval were restored after antibiotic therapy and the primary outcome was that of an uneventful recovery.ConclusionsLyme carditis occurs in < 5% of LD cases, but the “take-away” lesson of this case is that carditis can be the presenting manifestation of B. burgdorferi infection in pediatric patients. Any patient with suspected Lyme carditis manifesting cardiac symptoms such as syncope, chest pain, or EKG changes should be admitted for parenteral antibiotic therapy and cardiac monitoring. The most common manifestation of Lyme carditis is AVB. AVB may manifest as first-degree block, or may present as high-grade second or third-degree block. Other manifestations of Lyme carditis may include myopericarditis, left ventricular dysfunction, and cardiomegaly. Resolution of carditis is typically achieved through antibiotic administration, although pacemaker placement should be considered if the PR interval fails to normalize or if higher degrees of heart block, with accompanying symptoms, are encountered. With the rising incidence of LD, providers must maintain a high level of suspicion in order to promptly diagnose and treat Lyme carditis.

Beta-blockers for congestive heart failure in children.

Beta-blockers are an essential part of standard therapy in adult congestive heart failure and therefore, are expected to be beneficial in children. However, congestive heart failure in children differs from that in adults in terms of characteristics, aetiology, and drug clearance. Therefore, paediatric needs must be specifically investigated. This is an update of a Cochrane review previously published in 2009. To assess the effect of beta-adrenoceptor-blockers (beta-blockers) in children with congestive heart failure. We searched the Cochrane Central Register of Controlled Trials (CENTRAL) in The Cochrane Library, MEDLINE, EMBASE, and LILACS up to November 2015. Bibliographies of identified studies were checked. No language restrictions were applied. Randomised, controlled, clinical trials investigating the effect of beta-blocker therapy on paediatric congestive heart failure. Two review authors independently extracted and assessed data from the included trials. We identified four new studies for the review update; the review now includes seven studies with 420 participants. Four small studies with 20 to 30 children each, and two larger studies of 80 children each, showed an improvement of congestive heart failure with beta-blocker therapy. A larger study with 161 participants showed no evidence of benefit over placebo in a composite measure of heart failure outcomes. The included studies showed no significant difference in mortality or heart transplantation rates between the beta-blocker and control groups. No significant adverse events were reported with beta-blockers, apart from one episode of complete heart block. A meta-analysis of left ventricular ejection fraction (LVEF) and fractional shortening (LVFS) data showed a very small improvement with beta-blockers. However, there were vast differences in the age, age range, and health of the participants (aetiology and severity of heart failure; heterogeneity of diagnoses and co-morbidities); there was a range of treatments across studies (choice of beta-blocker, dosing, duration of treatment); and a lack of standardised methods and outcome measures. Therefore, the primary outcomes could not be pooled in meta-analyses. There is not enough evidence to support or discourage the use of beta-blockers in children with congestive heart failure, or to propose a paediatric dosing scheme. However, the sparse data available suggested that children with congestive heart failure might benefit from beta-blocker treatment. Further investigations in clearly defined populations with standardised methodology are required to establish guidelines for therapy. Pharmacokinetic investigations of beta-blockers in children are also required to provide effective dosing in future trials.

Update on a no-cost epilepsy gene panel for seizure onset between 2 and 4 years of age: Results from 682 tests

A young child presented with severe ventricular dysfunction and troponin leak in the setting of coronavirus disease-2019. He developed intermittent, self-resolving, and hemodynamically insignificant episodes of complete heart block that were diagnosed on telemetry and managed conservatively. This report is the first description of coronavirus disease-2019–induced transient complete heart block in a child. (Level of Difficulty: Intermediate.)

Intermittent complete heart block presenting as recurrent pulmonary edema

A middle-aged female presented with recurrent flash pulmonary edema. On evaluation, the patient had apparently stable 2:1 atrioventricular block and a good left ventricular systolic function. Holter recordings revealed intermittent episodes of complete heart block (CHB) precipitating pulmonary edema. The patient underwent permanent pacemaker implantation with complete resolution of symptoms. Isolated recurrent pulmonary edema in CHB is a rare manifestation and has never been reported before.

Pregnancy and Electroconvulsive Therapy: A Multidisciplinary Approach.

To scrutinize a series of pregnant women treated with electroconvulsive therapy (ECT) at a tertiary treatment center and combine these data with a literature review to refine the treatment guidelines for ECT during pregnancy. A retrospective chart review of mentally ill pregnant patients treated with ECT since the establishment of a formal women's mental health program. A total of 8 pregnant women treated with ECT were identified from January 2012 to August 2014. Information was extracted from the medical records of a total of 30 ECT treatments across this group. Subjects received an average of 3.75 ECT treatments (range, 1-7). All women were diagnosed as having a mood disorder (either unipolar or bipolar), and 5 of the 8 women had suicidal ideation. The treatment team for ECT was consistent across all treatments. Two women experienced significant complications after the initial treatment: 1) an acute episode of complete heart block; and 2) acute onset of mania after ECT. Obstetrical complications included 2 women with preterm delivery-one secondary to premature rupture of membranes. No other complications or adverse outcomes were recorded. The 5 women with suicidal ideation had symptom resolution, and significant symptom improvement was noted in 6 of the 8 women. Electroconvulsive therapy is a safe and effective treatment during pregnancy and of particular benefit in the acute treatment of suicidal ideation.

Beta-blockers for congestive heart failure in children.

Beta-blockers are an essential part of standard therapy in adult congestive heart failure and therefore, are expected to be beneficial in children. However, congestive heart failure in children differs from that in adults in terms of characteristics, aetiology, and drug clearance. Therefore, paediatric needs must be specifically investigated. This is an update of a Cochrane review previously published in 2009. To assess the effect of beta-adrenoceptor-blockers (beta-blockers) in children with congestive heart failure. We searched the Cochrane Central Register of Controlled Trials (CENTRAL) in The Cochrane Library, MEDLINE, EMBASE, and LILACS up to November 2015. Bibliographies of identified studies were checked. No language restrictions were applied. Randomised, controlled, clinical trials investigating the effect of beta-blocker therapy on paediatric congestive heart failure. Two review authors independently extracted and assessed data from the included trials. We identified four new studies for the review update; the review now includes seven studies with 420 participants. Four small studies with 20 to 30 children each, and two larger studies of 80 children each, showed an improvement of congestive heart failure with beta-blocker therapy. A larger study with 161 participants showed no evidence of benefit over placebo in a composite measure of heart failure outcomes. The included studies showed no significant difference in mortality or heart transplantation rates between the beta-blocker and control groups. No significant adverse events were reported with beta-blockers, apart from one episode of complete heart block. A meta-analysis of left ventricular ejection fraction (LVEF) and fractional shortening (LVFS) data showed a very small improvement with beta-blockers.However, there were vast differences in the age, age range, and health of the participants (aetiology and severity of heart failure; heterogeneity of diagnoses and co-morbidities); there was a range of treatments across studies (choice of beta-blocker, dosing, duration of treatment); and a lack of standardised methods and outcome measures. Therefore, the primary outcomes could not be pooled in meta-analyses. There is not enough evidence to support or discourage the use of beta-blockers in children with congestive heart failure, or to propose a paediatric dosing scheme. However, the sparse data available suggested that children with congestive heart failure might benefit from beta-blocker treatment. Further investigations in clearly defined populations with standardised methodology are required to establish guidelines for therapy. Pharmacokinetic investigations of beta-blockers in children are also required to provide effective dosing in future trials.

Ropivacaine plasma levels following local infiltration analgesia for primary total hip arthroplasty

We measured total and free plasma concentrations of ropivacaine following high-volume, high-dose local infiltration analgesia in 19 patients aged 65 years or over undergoing unilateral total hip arthroplasty. The patients received 180 ml ropivacaine 0.2% (360 mg), which was injected into the deep and peri-capsular tissues, the gluteal muscles and fascia lata, and the subcutaneous tissues and skin. Patients were monitored for clinical symptoms and signs of systemic local anaesthetic toxicity. Total levels of plasma ropivacaine varied from 0.081 to 1.707 μg.ml(-1) (mean (SD) 0.953 (0.323) μg.ml(-1) ). Free levels of plasma ropivacaine varied from 0.000 to 0.053 μg.ml(-1) (mean (SD) 0.024 (0.011) μg.ml(-1) ). No samples reached the toxic threshold for venous ropivacaine concentration, although four patients exhibited mild symptoms consistent with local anaesthetic toxicity. One patient had episodes of complete heart block on ECG monitoring, but plasma ropivacaine levels were below toxic levels. We conclude that plasma levels for ropivacaine associated with toxicity in a volunteer population (total 2.2 μg.ml(-1) , free 0.15 μg.ml(-1) ) are not reached during local infiltration analgesia for hip arthroplasty in elderly patients.

Risk of Developing Complete Heart Block During Bedside Pulmonary Artery Catheterization in Patients With Left Bundle-Branch Block

We examined the incidence of complete heart block (CHB) as a complication of pulmonary artery catheterization with balloon-tipped, flow-directed catheters in patients with left bundle-branch block (LBBB). The study group included 47 consecutive critically ill patients with LBBB in the medical intensive care and coronary care units, who underwent a total of 82 pulmonary artery catheterizations. Twenty-six patients had an acute myocardial infarction, 34 patients had severe congestive heart failure (Killip class III or class IV), and 15 patients died during their hospitalization. Thirty patients had an old LBBB (more than one month in age), nine patients had a new LBBB, and the age of the LBBB was indeterminate in eight patients. There were five episodes of CHB in the group of patients with old LBBB. However, none of these episodes were related to the pulmonary artery catheterization, since CHB occurred either prior to catheterization (one case) or from one to 16 days after the pulmonary artery catheter had been removed (four cases). There were no episodes of CHB related to the pulmonary artery catheterization procedure in the patients with either old LBBB or indeterminate-aged LBBB. There were two episodes of CHB in patients with new LBBB. In both patients, the CHB occurred one day after the pulmonary artery catheter had been inserted. In both patients, CHB developed after episodes of ventricular tachycardia that eventually resulted in their deaths. Although it is unlikely, we could not rule out the possibility that the CHB was related to the presence of the pulmonary artery catheter. We conclude that the incidence of CHB complicating pulmonary artery catheterization with balloon-tipped, flow-directed catheters in critically ill patients with old or indeterminate-aged LBBB is extremely low. Therefore, we do not recommend the routine placement of a temporary transvenous pacemaker in all patients with LBBB prior to pulmonary artery catheterization.

His bundle recording in progressive external ophthalmoplegia

A teen-age girl with a 5 year history of PEO was noted to have a progressive disturbance of atrioventricular conduction with LAD, RBBB, and intermittent second degree heart block of Mobitz type II. His bundle recordings revealed a prolongation of the H-V conduction time interval and the development of Mobitz type II second degree block following atropine administration. A permanent demand cardiac pacemaker was implanted and successfully paced the patient during episodes of complete heart block which subsequently developed. A teen-age girl with a 5 year history of PEO was noted to have a progressive disturbance of atrioventricular conduction with LAD, RBBB, and intermittent second degree heart block of Mobitz type II. His bundle recordings revealed a prolongation of the H-V conduction time interval and the development of Mobitz type II second degree block following atropine administration. A permanent demand cardiac pacemaker was implanted and successfully paced the patient during episodes of complete heart block which subsequently developed.

Electrophysiologic studies in Mobitz type II second degree heart block

The electrophysiologic basis for Mobitz type II second degree heart block was studied in a patient with documented episodes of complete heart block and Stokes-Adams seizures. Recording of His bundle electrograms demonstrated that all atrial impulses were conducted through the atrioventricular (A-V) node to the bundle of His. Nonconducted P waves were blocked distal to the bundle of His. The frequency of blocked beats increased when the rate was accelerated by atrial pacing. Administration of atropine caused more frequent blocked beats, reaffirming the concept that the block occurred beyond the node. It is concluded that Mobitz type II second degree heart block is a manifestation of bilateral bundle branch block. Testing with atropine in this case was useful in distinguishing block in the bundle branches from that in the A-V node.