Atypical Wenckebach periodicity simulating Mobitz II AV block

Mobitz type II second-degree atrioventricular block: a commonly overdiagnosed and misinterpreted arrhythmia

Mobitz type II second-degree atrioventricular block (AVB) is an electrocardiographic pattern that describes what appears to be an all-or-none conduction without visible changes in the AV conduction time or PR intervals before and after a single non-conducted P wave. An unchanged PR interval after the block is a sine qua non of Mobitz type II block. A 2:1 AVB cannot be classified in terms of type I or type II AVB. The diagnosis of Mobitz type II block AVB requires a stable sinus rate, which is an important criterion because a vagal surge (generally benign) can cause simultaneous sinus slowing and AV nodal block, which can resemble Mobitz type II AVB. Atypical forms of Wenckebach AVB may be misinterpreted as Mobitz type II AVB when a series of PR intervals are constant before the block. Concealed His bundle or ventricular extrasystoles may mimic both Wenckebach and/or type II AVB (pseudo-AVB). Correctly identified Mobitz type II AVB is invariably at the level of the His-Purkinje system and is an indication for a pacemaker.

Definitions and Pitfalls in the Diagnosis of Atrioventricular Block

The widespread use of disparate definitions of atrioventricular block has created important diagnostic problems. Adherence to the correct definitions provides a logical and simple framework for clinical evaluation. This review focuses on the clinical importance of the definitions in the diagnosis of the various types of atrioventricular (AV) block and the associated diagnostic pitfalls.

Mobitz type II second-degree atrioventricular block during sleep: true or false?

A number of publications have claimed that Mobitz type II second-degree atrioventricular (AV) block can occur during sleep apnea. None has provided a definition of type II block used in the articles, and representative electrocardiograms have been generally missing. Despite these reports, the existence of type II AV block during sleep must remain questionable.

Problematic definitions of Mobitz type II second degree AV block: Historical aspects

Problems with the definition of type II second degree AV block are best understood by reviewing the historical aspects that include Mobitz's original description, the contributions of the Chicago Arrhythmia School and the growing importance of excluding slowing of the sinus rhythm.

Self-Resolving Mobitz Type II Second-Degree Heart Block (Atypical Wenckebach Block) After Cesarean Section Under Subarachnoid Block: A Case Report

The majority of the perioperative arrhythmias in patients undergoing cesarean section under spinal anesthesia are benign. We report a case of a 30-year-old full-term parturient with a history of an uneventful previous cesarean section. She had no preexisting comorbidities. She subsequently underwent another emergency cesarean section three years later due to abdominal pain and scar tenderness indicative of impending rupture. Two hours after an uneventful surgery, the patient developed epigastric pain with a prolonged PR interval (280 ms) and intermittent second-degree AV block with two consecutive blocked P waves, which was consistent with Mobitz type II second-degree heart block (atypical Wenckebach block). However, she remained hemodynamically stable throughout. Serial electrocardiogram (ECG) did not demonstrate any evidence of ST-T wave changes, and normal troponin I and echocardiography excluded myocardial ischemia as a potential cause for the arrhythmia. Normal serum electrolytes and the resolution of the sensorimotor block caused by the spinal anesthesia excluded other known causes for such ECG changes. The PR interval gradually decreased to 240 ms on the second postoperative day and normalized to 200 ms on the fifth postoperative day. Such patients, especially those with a wide QRS complex, are susceptible to developing dangerous ventricular arrhythmias that can adversely affect circulatory function. Close vigil is the key to avoiding adverse perioperative outcomes.

Second-degree atrioventricular block revisited

Type I second-degree atrioventricular (AV) block describes visible, differing, and generally decremental AV conduction. The literature contains numerous differing definitions of second-degree AV block, especially Mobitz type II second-degree AV block. The widespread use of numerous disparate definitions of type II block appears primarily responsible for many of the diagnostic problems surrounding second-degree AV block. Adherence to the correct definitions provides a logical and simple framework for clinical evaluation. Type II second-degree AV block describes what appears to be an all-or-none conduction without visible changes in the AV conduction time before and after the blocked impulse. Although the diagnosis of type II block requires a stable sinus rate, absence of sinus slowing is an important criterion of type II block because a vagal surge (generally a benign condition) can cause simultaneous sinus slowing and AV nodal block, which can superficially resemble type II block. Furthermore, type II block has not yet been reported in inferior myocardial infarction (MI) and in young athletes where type I block may be misinterpreted as type II block. The diagnosis of type II block cannot be established if the first postblock P wave is followed by a shortened PR interval or the P wave is not discernible. A narrow QRS type I block is almost always AV nodal, whereas a type I block with bundle branch block barring acute MI is infranodal in 60-70 % of cases. A 2:1 AV block cannot be classified in terms of type I or type II block, but it can be nodal or infranodal. A pattern resembling a narrow QRS type II block in association with an obvious type I structure in the same recording (e.g., Holter) effectively rules out type II block because the coexistence of both types of narrow QRS block is exceedingly rare. Concealed (nonpropagated) His bundle or ventricular extrasystoles may mimic both type I and/or type II block (pseudo AV block). All correctly defined type II blocks are infranodal. Infranodal block presenting with either type I or II manifestations requires pacing regardless of QRS duration or symptoms.

Reappraisal of the traditional Wenckebach phenomenon with a modified ladder diagram

Understanding of the traditional Wenckebach phenomenon is enhanced by using a modified ladder diagram where AV conduction in any cycle is represented by a slanted line in the AV bar together with similar AV conduction lines of all the preceding cycles. The diagram facilitates calculation of the duration of RR intervals (equal to the basic PP or sinus interval minus the PR or AV increment applied to this particular cycle) and the duration of the pause (equal to 2 × PP or sinus interval minus the sum of all the increments applied to the AV delay). The modified Wenckebach diagram should help students understand the mysterious clustering of QRS complexes or "paradoxical" increase of the ventricular rate that occurs during a Wenckebach sequence.

Arrhythmias following spinal anesthesia for cesarean delivery - Is Wenckebach common?

Arrhythmias in pregnancy are common and may cause concern for the well-being of both mother and fetus. Generally, no previous history of heart disease is elicited and majority of the arrhythmias are benign. Bradycardia is commonly seen following subarachnoid block for cesarean section. However, the incidence of subsequent heart block is low. This case report highlights the occurrence of perioperative arrhythmias following sympathetic blockade in pregnant patients and their early detection by vigilant monitoring.

Asymptomatic rhythm and conduction abnormalities in children with acute rheumatic fever: 24-hour electrocardiography study

Some rhythm and conduction abnormalities can occur in children with acute rheumatic fever. These abnormalities have been defined based on standard electrocardiography; however, the real prevalence of these abnormalities has not been investigated previously by the evaluation of long-term electrocardiographic recordings. In this study, we evaluated the asymptomatic rhythm and conduction abnormalities in children with acute rheumatic fever by evaluating the 24-hour electrocardiography. We evaluated the standard electrocardiography and the 24-hour electrocardiography of 64 children with acute rheumatic fever. On standard electrocardiography, the frequency of the first-degree atrioventricular block was found to be 21.9%. Electrocardiography at 24 hours detected three additional and separate patients with a long PR interval. Mobitz type I block and atypical Wenckebach periodicity were determined in one patient (1.56%) on 24-hour electrocardiography. While accelerated junctional rhythm was detected in three patients on standard electrocardiography, it was present in nine patients according to 24-hour electrocardiography. Premature contractions were present in 1.7% of standard electrocardiography, but in 29.7% of 24-hour electrocardiography. Absence of carditis was found to be related to the presence of accelerated junctional rhythm (p > 0.05), and the presence of carditis was found to be related to the presence of premature contractions (p = 0.000). In conclusion, our results suggest that in children with acute rheumatic fever, the prevalence of rhythm and conduction abnormalities may be much higher than determined on standard electrocardiography. Further studies are needed to clarify whether or not these abnormalities are specific to acute rheumatic fever.

Atrioventricular block revisited

AV blocks, their definitions and significance, are discussed. Type II, second-degree AV block is infranodal, whereas 2/3 of Type I with BBB are infranodal, 2:1 AV block is neither Type I nor II block. Infranodal blocks require pacing regardless of symptoms.

Second-degree atrioventricular block: a reappraisal

In this review, we discuss the various forms and causes of second-degree atrioventricular (AV) block and the reasons they remain poorly understood. Both type I and type II block characterize block of a single sinus P wave. Type I block describes visible, differing, and generally decremental AV conduction. Type II block describes what appears to be an all-or-none conduction without visible changes in the AV conduction time before and after the blocked impulse. Although the diagnosis of type II block is possible with an increasing sinus rate, absence of sinus slowing is an important criterion of type II block because a vagal surge (generally a benign condition) can cause simultaneous sinus slowing and AV nodal block, which can superficially resemble type II block. The diagnosis of type II block cannot be established if the first postblock P wave is followed by a shortened PR interval or is not discernible. A pattern resembling a narrow QRS type II block in association with an obvious type I structure in the same recording (e.g., Holter) effectively rules out type II block because the coexistence of both types of narrow QRS block is exceedingly rare. Concealed His bundle or ventricular extrasystoles confined to the specialized conduction system without myocardial penetration and depolarization can produce electrocardiographic patterns that mimic type I and/or type II block (pseudo-AV block). All correctly defined type II blocks are infranodal. A narrow QRS type I block is almost always AV nodal, whereas a type I block with bundle branch block barring acute myocardial infarction is infranodal in 60% to 70% of cases. A 2:1 AV block cannot be classified in terms of type I or type II block, but it can be nodal or infranodal. Infranodal blocks require pacing regardless of form or symptoms. The widespread use of numerous disparate definitions of type II block appears primarily responsible for many of the problems surrounding second-degree AV block. Adherence to the correct definitions provides a logical and simple framework for clinical evaluation.

Case report: type I second-degree AV block masquerading as Type II block

This report describes a patient with type I second-degree atrioventricular block and sequences consistent with type II block according to widely accepted criteria. The electrocardiograms illustrate the importance of deductive reasoning and the clinical context in the diagnostic evaluation of perplexing forms of second-degree AV block.

Arrhythmias during spinal anesthesia for Cesarean section

PURPOSE

Spinal block has long been considered a safe anesthesia technique for surgery. However, severe bradycardia, cardiac arrest, and other arrhythmias during spinal anesthesia have been reported and the incidence of intraoperative arrhythmias is not well established. In this study the incidence of arrhythmias during spinal anesthesia was determined.

METHODS

We studied 254 healthy women undergoing Cesarean section under spinal anesthesia prospectively. Spinal anesthesia with 10 mg bupivacaine mixed with 0.2 mg morphine was performed at the L3-4 interspace. Intraoperative arrhythmias were recorded and verified later by a cardiologist.

RESULTS

First degree atrioventricular block developed in nine patients (3.5%), second degree atrioventricular block in nine (3.5%), severe bradycardia (heart rate < 50 beats x min(-1)) in seventeen (6.7%), multiple VPC in three (1.2%). The height and weight of patients with severe bradycardia, multiple VPCs, or atrioventricular block were not different from those of the other patients. However, the age of patients in the potentially dangerous arrhythmias group was greater than that in the other group (P = 0.006).

CONCLUSION

The incidence of arrhythmias as well as hypotension during spinal anesthesia for Cesarean section was higher than expected. Although most of these arrhythmias were transient and recovered spontaneously, they might unexpectedly occur and sometimes need immediate and prompt treatment. It is necessary to remain vigilant during spinal anesthesia for Cesarean section and careful monitoring of these patients is warranted, especially in older parturients.

A generalized description of Wenckebach behavior with analysis of determinants of ventricular cycle-length variation during ambulatory electrocardiography

Although variation in ventricular cycle length during Wenckebach-type second-degree atrioventricular block traditionally has been explained by the direction of incremental change in PR lengthening preceding the blocked complex, changing PP intervals can also affect Wenckebach periodicity. A generalized algebraic solution was derived to define changing ventricular cycle length as a function of both changing PP and changing incremental PR interval behavior in Wenckebach block. Based on this solution, the determinants of cycle-length variation were examined for 65 episodes of Wenckebach block detected by ambulatory electrocardiography in 51 patients. As previously demonstrated, only 20% (13 of 65) of Wenckebach episodes were characterized by the "classic" shortening of RR intervals; in contrast, ventricular cycle length increased in 57% (37 of 65) and remained constant in 23% (15 of 65) of cases. Algebraic analysis of these episodes revealed that the direction of ventricular cycle-length change preceding the blocked complex was primarily determined by the direction of change of incremental PR intervals in only 35% (23 of 65) of Wenckebach episodes; RR change was governed by the direction of change of preceding PP intervals in 34% (22 of 65) and by equal change of PP and incremental PR intervals in 31% (20 of 65) of these episodes. Both inverse and concordant relationships between changing RP and PR intervals were primarily determined by the direction of PP variation during in vivo Wenckebach block. These data confirm that classic Wenckebach block is less common than "atypical" Wenckebach periodicity and demonstrate that RR variation in Wenckebach block is governed by the changing PP interval as often as by the changing incremental PR interval.

Prevalence and clinical correlates of non-Wenckebach, narrow-complex second-degree atrioventricular block detected by ambulatory ECG

Among 113 patients with transient, narrow-complex second-degree atrioventricular (AV) block detected by ambulatory ECG, there were 20 with non-Wenckebach behavior. Based on the presence or absence of PR interval shortening after single blocked complexes, patients with narrow-complex non-Wenckebach patterns could be separated into a pseudo-Mobitz II group of 16 patients (greater than or equal to 20 msec of PR shortening after the blocked complex) and a classic Mobitz II group of four patients (constant PR interval). These groups had additional distinct ECG and clinical features. Patients with the pseudo-Mobitz II pattern had a 44% prevalence of associated Wenckebach block during the same ambulatory recording, whereas Wenckebach behavior did not occur in patients with classic Mobitz II block. Pseudo-Mobitz II block occurred at significantly longer cycle lengths (876 vs 585 msec) and with significantly longer PR intervals (225 vs 165 msec) preceding the blocked complex than did classic Mobitz II block. Syncope was the presenting symptom in 38% of patients with pseudo-Mobitz II block and in all patients with classic Mobitz II block. Patients with pseudo-Mobitz II block had a 56% prevalence of associated coronary disease and a 44% prevalence of congestive heart failure; the mortality rate was 38% in this group over 4 years of follow-up, but in all instances death was due to associated disease rather than to conduction itself. In contrast, patients with classic Mobitz II block had hypertensive or valvular disease but no evidence of coronary disease or congestive failure; all are alive with pacemakers after 3 years of follow-up.(ABSTRACT TRUNCATED AT 250 WORDS)

The Wenckebach phenomenon

The Wenckebach phenomenon, or type I AV block, refers to a progressive lengthening of impulse conduction time, followed by a nonconducted impulse, or dropped beat. It can occur in a variety of pathologic settings, especially inferior myocardial infarction. Although a temporary pacemaker may be required, full spontaneous recovery is the rule.

Atrioventricular block. Mechanism, clinical presentation, and therapy

The mechanism of AV block and bifascicular block and the role of His bundle electrocardiography in localizing the site of AV block are reviewed. The clinical presentation and therapy of the different types of AV block and the indications for permanent pacing are discussed.

Multiple electrophysiologic manifestations and clinical implications of vagally mediated AV block

Clinical, surface ECG, and intracardiac findings were analyzed in 20 patients with spontaneous conduction disturbances in whom vagally mediated AV block could be induced by carotid sinus pressure during electrophysiologic evaluation. The latter demonstrated that the surface ECG pattern attributed to bradycardia-dependent (phase 4), and paroxysmal block within the His bundle and bundle branches could reflect vagally mediated, bradycardia-associated (rather than bradycardia-dependent), and paroxysmal AV nodal (AH) block. The decision regarding the use of pacemakers was not based on QRS duration or on patterns (or site) of block but on the underlying clinical settings and the correlation of symptoms with maximal ventricular (R-R) pauses. However, more studies are required to extend our findings, especially to other subgroups of patients (or normal individuals) in whom vagally mediated block occurs.

Direct Wenckebach periods in the left bundle branch during bradycardia-dependent left bundle branch block in a patient with sick sinus syndrome

Direct Wenckebach periods in the left bundle branch with periods of 4:3 and 5:4 conduction alternating with 2:1 left bundle branch block (LBBB) were observed in a patient who was admitted because of congestive heart failure. There was no previous documented LBBB and serial electrocardiographic (ECG) mainfestations afterwards were indicative of sick sinus syndrome. This is probably the first report to describe direct Wenckebach periods in the left bundle branch during bradycardia-dependent (phase-4) LBBB in a patient with sick sinus syndrome.

Second-degree atrioventricular block

1) While it is possible only one type of second-degree AV block exists electrophysiologically, the available data do not justify such a conclusion and it would seem more appropriate to remain a "splitter," and advocate separation and definition of multiple mechanisms, than to be a "lumper," and embrace a unitary concept. 2) The clinical classification of type I and type II AV block, based on present scalar electrocardiographic criteria, for the most part accurately differentiates clinically important categories of patients. Such a classification is descriptive, but serves a useful function and should be preserved, taking into account the caveats mentioned above. The site of block generally determines the clinical course for the patient. For most examples of AV block, the type I and type II classification in present use is based on the site of block. Because block in the His-Purkinje system is preceded by small or nonmeasurable increments, it is called type II AV block; but the very fact that it is preceded by small increments is because it occurs in the His-Purkinje system. Similar logic can be applied to type I AV block in the AV node. Exceptions do occur. If the site of AV block cannot be distinguished with certainity from the scalar ECG, an electrophysiologic study will generally reveal the answer.