Observations on second degree atrioventricular block, including new criteria for the differential diagnosis between type I and type II block

Atrioventricular block can be used as a risk predictor of clinical atrial fibrillation

Background

Atrial fibrillation (AF) is the most common cardiac arrhythmia, with its incidence making up nearly one‐third of all hospital admissions. Atrioventricular block (AVB) is a conduction abnormality along the atrioventricular node or the His‐Purkinje system. The relationship between atrioventricular conduction block and AF is controversial.

Hypothesis

This study is designed to observe whether there is a correlation between AVB and AF, and which type of AVB has the most obvious correlation with AF.

Methods

This study retrospectively reviewed 1345 patients. We classified the AVB according to the AVB classification criteria. One hundred and two patients were excluded, and the final total sample size was 1243 patients, including 679 patients in the AF group (378, 55.7% males) and 564 patients in the non‐AF group (287, 50.8% males). AF group and non‐AF group were compared to observe the relationship between AVB and AF.

Results

The I AVB have a relative statistical risk of 1.927 (95% confidence interval [CI]: 1.160‐3.203, P < 0.05) with the occurrence of AF. II AVB occupied the largest proportion, accounting for 67 cases (9.87%), and the statistical risk of II AVB in AF is 16.845 (95% CI: 6.099‐46.524, P < 0.000). III AVB has a comparative statistical risk of 17.599 (95% CI: 4.212‐73.541, P < 0.000).

Conclusions

The three types of AVB in the AF group were significantly higher than that in the non‐AF group. II AVB has the highest incidence rate compared with other types of AVB in the AF group. AVB can be used as a risk factor for AF occurrence.

Dynamic Electrocardiography is Useful in the Diagnosis of Persistent Atrial Fibrillation Accompanied with Second-Degree Atrioventricular Block

BACKGROUND

Periodic electrocardiography (ECG) at every clinical visit is generally performed for heart rhythm surveillance, and 24-h Holter ECG is usually used as the gold standard. We aimed to investigate the electrocardiographic features of persistent atrial fibrillation (AF) accompanied with second-degree atrioventricular block (AVB).

METHODS

From October 2012 to November 2015, 204 patients with an RR interval > 2.0 s before radiofrequency ablation were included. Dynamic ECG (DCG) was performed before and after the radiofrequency ablation. The patients were divided into two groups based on changes in DCG after radiofrequency ablation: group A (non-second-degree AVB group) and group B (second-degree AVB group). An RR interval > 2.0 s, the distribution of escape rhythm, mean heart rate and the long RR interval in the two groups were analyzed.

RESULTS

After radiofrequency ablation, all 204 patients who had persistent AF converted to sinus rhythm successfully. In group A (n = 193), the distribution of an RR interval > 2.0 s and escape rhythm were significantly correlated with sleep or rest, while no correlation was observed in group B (n = 11). The average RR interval prolongation and escape rhythm were significantly higher in group B than in group A (p < 0.05). The average number of long RR intervals > 3.0 s and average number of escape rhythm episodes (< 35 bpm) were significant predictive factors of second-degree AVB after radiofrequency ablation.

CONCLUSIONS

DCG is a useful tool for the diagnosis of persistent AF accompanied with second-degree AVB.

Human His-Purkinje System: Abnormalities of Conduction, Rhythm Disorders and Case Studies

This review covers many of the arrhythmias and conduction abnormalities related to His-Purkinje System. These include junctional premature complexes, junctional and fascicular tachycardias, bundle branch reentry (BBR), and the role of apparent conduction in various forms of supraventricular tachycardias (SVT) with or without involvement of accessory pathways (AP).

Management and outcome of topical beta-blocker-induced atrioventricular block

BACKGROUND

Topical beta-blockers have a well-established role in the treatment of glaucoma. We aimed to investigate the outcome of patients who developed symptomatic atrioventricular (AV) block induced by topical beta-blockers.

METHODS

All patients admitted or discharged from our institution, the Siyami Ersek Training and Research Hospital, between January 2009 and January 2013 with a diagnosis of AV block were included in the study. Subjects using ophthalmic beta-blockers were recruited and followed for permanent pacemaker requirement during hospitalisation and for three months after discontinuation of the drug. A permanent pacemaker was implanted in patients in whom AV block persisted beyond 72 hours or recurred during the follow-up period.

RESULTS

A total of 1 122 patients were hospitalised with a diagnosis of AV block and a permanent pacemaker was implanted in 946 cases (84.3%) during the study period. Thirteen patients using ophthalmic beta-blockers for the treatment of glaucoma and no other rate-limiting drugs were included in the study. On electrocardiography, eight patients had complete AV block and five had high-degree AV block. The ophthalmic beta-blockers used were timolol in seven patients (55%), betaxolol in four (30%), and cartelol in two cases (15%). The mean duration of ophthalmic beta-blocker treatment was 30.1 ± 15.9 months. After drug discontinuation, in 10 patients the block persisted and a permanent pacemaker was implanted. During follow up, one more patient required pacemaker implantation. Therefore in total, pacemakers were implanted in 11 out of 13 patients (84.6%). The pacemaker implantation rate did not differ according to the type of topical beta-blocker used (p = 0.37). The presence of infra-nodal block on electrocardiography was associated with higher rates of pacemaker implantation.

CONCLUSION

Our results indicate that topical beta-blockers for the treatment of glaucoma may cause severe conduction abnormalities and when AV block occurs, pacemaker implantation is required in a high percentage of the patients.

Management of patients with drug-induced atrioventricular block

OBJECTIVE

To identify the frequency of atrioventricular (AV) conduction improvement after discontinuation of the culprit drug in patients with AV block.

BACKGROUND

AV blockers are considered as reversible causes of AV block that do not require pacemaker (PM) implantation. However, controversial reports declared that a major part of these drug-induced AV blocks are persistent or recurrent.

METHODS

Of 668 consecutive patients with symptomatic type II second- or third-degree AV block, 2:1 AV block, atrial fibrillation, and bradyarrhythmia, 108 patients (62 patients enrolled prospectively) using AV blockers without myocardial infarction, electrolyte abnormalities, digitalis toxicity, and vasovagal syncope were enrolled into the present study. The level of AV block (AV-nodal or infranodal) was defined according to electrocardiographic characteristics.

RESULTS

The most frequent culprit medications were β-blockers followed by digoxin. Drug discontinuation was followed by resolution of AV block in 72% of cases, whereas spontaneous resolution of AV block occurred in only 6.6% of patients who had AV block in the absence of medications. However, 27% of patients with improved AV conduction experienced a recurrence of AV block despite discontinuation of the culprit drug. Twenty-one of 24 carvedilol-induced AV blocks resolved after discontinuation of the drug and never recurred, whereas 24 of 36 metoprolol-induced AV blocks persisted or recurred. A digoxin-induced AV block usually improved (28 of 39) after withdrawal of the drug. Roughly half of the patients with drug-induced AV block underwent permanent PM implantation.

CONCLUSION

Drug-induced AV block is a serious disease that requires a permanent PM for almost half of the patients.

Drug-induced atrioventricular block: prognosis after discontinuation of the culprit drug

OBJECTIVES

The goal of this study was to determine how often atrioventricular (AV) block is really caused by medications.

BACKGROUND

Beta-blockers, verapamil, and diltiazem are considered a cause of AV block for which pacemaker implantation is not indicated. However, it is not known if such patients can expect a benign course after discontinuation of the culprit medication.

METHODS

Consecutive patients with II or III degree AV block not related to acute myocardial infarction, digitalis toxicity, or vasovagal syncope were studied. The level of AV block (AV-nodal or infranodal) was defined by electrocardiographic criteria. The cause and effect relation between AV block and drugs was defined according to the response to drug discontinuation.

RESULTS

Of 169 patients with AV block, 92 (54%) were receiving beta-blockers and/or verapamil or diltiazem. Patients receiving medications had similar clinical and electrocardiographic characteristics with patients who had AV block in the absence of drugs. Drug discontinuation was followed by resolution of AV block in 41% of cases, whereas spontaneous improvement of AV conduction occurred in 23% of patients who had AV block in the absence of drugs. However, 56% of the patients for whom drug discontinuation led to resolution of AV block had recurrence of AV block in the absence of therapy. Atrioventricular block that was "truly caused by drugs" was found in only 15% of patients who had II or III degree AV block during therapy with beta-blockers, verapamil, or diltiazem.

CONCLUSIONS

Atrioventricular block is commonly "related to drugs" but is rarely "caused by drugs."

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.

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)

Clinical and electrocardiographic features and long-term results of electrical therapy in patients with isolated His bundle disease

The clinical, ECG, and electrophysiologic findings of 35 consecutive patients with second- and third-degree intra-His block with normal QRS complexes were examined. The follow-up period varied between 12 and 120 months (mean 45). Seventy-seven per cent of the patients were women. Underlying heart disease was present in 43% of the patients. ECGs were characterized by both second-degree type I and type II atrioventricular block, normal or slightly prolonged PR interval of the conducted beats or of the first conducted beat of a Wenckebach sequence, and by subtle changes in the initial forces of the QRS complexes of the escape beats. Electrophysiologic study showed normal sinus and atrioventricular node function and normal infra-His conduction in all patients. In four patients repetitive bradycardia-dependent intra-His block was induced. Thirty-two patients were permanently paced soon after the initial evaluation and three during the follow-up period. Total long-term mortality rate was 23%. None of the patients developed bundle branch block.

Antiarrhythmic treatment: an overview

Atrial and ventricular arrhythmias cause significant morbidity and mortality. Abnormalities of impulse generation, e.g., abnormal automaticity or triggered activity, or abnormalities of impulse conduction, e.g., atrioventricular block or reentry, are the prime mechanisms of atrial or ventricular arrhythmias. The ventricular arrhythmias are of special interest because they are a key element in sudden cardiac death, the number 1 public health problem in the U.S. Electrocardiographic recording or provocative testing, e.g., exercise or programmed ventricular stimulation, are used to detect and classify ventricular arrhythmias. Drugs with different mechanisms of action are being rapidly developed to combat cardiac arrhythmias. Ventricular arrhythmias can be defined as benign, potentially malignant or malignant. Benign ventricular arrhythmias require no drug treatment; potentially malignant arrhythmias are subject to drug prophylaxis; and the malignant ventricular arrhythmias require aggressive therapy with drugs, surgery or electronic devices. The management of the malignant ventricular arrhythmias should be evaluated by 1 of 2 programmatic approaches: electrophysiologic or Holter/exercise. Both are complex, costly and inconvenient, but both are excellent for identifying effective treatment for malignant ventricular arrhythmias.

Bedside evaluation of atrioventricular block with narrow QRS complexes: usefulness of carotid sinus massage and atropine administration

Second-degree intra-His bundle block is frequently of type I (Wenckebach periods) or 2:1. In this situation, the surface electrocardiogram does not permit distinction between intranodal (atrioventricular [A-V] and subnodal (intra-His) block. This study examined the value of bedside carotid sinus massage and atropine administration in diagnosing the site of block from the standard electrocardiogram in subjects with chronic A-V block and narrow QRS complexes. Fifteen patients had intra-His bundle block and 10 had intranodal block. The combination of two tests correctly located the site of block in 22 subjects, and was noncontributory in 3. Thirteen of the 15 intra-His bundle blocks and 9 of the 10 intranodal blocks were properly identified; in three cases the results were nondiagnostic, but no wrong diagnoses were made. The noninvasive bedside method of carotid sinus massage and the use of atropine permit both the localization and the determination of the type of block in the majority of cases of second degree A-V block and narrow QRS complexes. In a proper clinical context they can obviate the need for invasive electrophysiologic studies.

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.

Clinical and electrophysiologic findings in patients with paroxysmal slowing of the sinus rate and apparent Mobitz type II atrioventricular block

Over five years, 13 patients with episodic apparent type II atrioventricular (AV) block associated with sinus slowing were seen. This phenomenon occurred only transiently during an acute illness in eight patients (group I) but recurred chronically in five (groupII). For the group as a whole, the mean spontaneous cycle length was 42% longer during the period of AV block compared with periods of 1:1 AV conduction (800 +/- 116 msec to 1138 +/- 489 msec) (P less than 0.05). Electrophysiologic studies in four group I patients showed no abnormalities, whereas abnormalities in AV nodal conduction and refractoriness or provocation of intranodal Mobitz type II AV block (during carotid massage) were observed in three patients in group II and were totally abolished by atropine. In group I patients, apparent type II AV block was self-limited. In the chronic group, recurrent symptoms required insertion of permanent pacemakers in two patients. Simultaneous type II block and sinus slowing appeared to be related to the effects of increased vagal tone on both nodal structures. Intracardiac pacing is not indicated for patients with transient episodes associated with an acute illness, but may be required for symptomatic patients with recurrent episodes.

An unusual form of the bradycardia-tachycardia syndrome: paroxysmal A-V block and ventricular tachycardia

An unusual case of alternating bradycardia-tachycardia, paroxysmal Mobitz II A-V block and ventricular tachycardia is described. The patient presented with a normal resting (control) electrocardiogram and intracardiac conduction times (A-H and H-V intervals). The clinical evaluation, electrophysiology, and importance of defining the cause of serious rhythm disturbances prior to therapy are discussed.

Chronic bilateral bundle-branch block. Long-term observations in ambulatory patients

During a period of 28 months, all patients (79) who presented with bilateral bundle-branch block were selected for study from a private practice outpatient population. They were followed prospectively from the date of entry into the study and their charts were reviewed retrospectively. The average age of the participants was 73-3 years and they were observed clinically for a cumulative period of 4237 months (353-08 years). A high incidence of severe heart disease and death was noted among the study group. Twenty-four (30-3%) had a New York Heart Association functional classification of 3 or 4. Eight (10-1%) died. Only one patient died suddenly and he had had a stable electrocardiographic pattern of bilateral bundle-branch block for a period of 118 months (9 years 10 months). Seven patients required permanent pacemakers. In 6 instances death resulted from pump failure; in one it was the result of lung cancer. In none of these 7 individuals did rhythm disturbances contribute to death. In most cases vertigo was not of cardiac origin (88-2%). Eight patients had 11 major surgical procedures with no significant cardiac sequelae. Our observations suggest that elderly patients with chronic bilateral bundle-branch block should be managed conservatively. The prognosis in these patients appears primarily to be related to the degree of myocardial disease rather than to the conduction disorder.

Concealed intraventricular conduction in the His bundle electrogram

Multiple areas of concealed intraventricular conduction are deduced on the basis of aftereffects observed in His bundle recordings. Electrocardiograms and His bundle recordings are presented from two patients with unstable bilateral bundle branch block, the instability of which depended on the interval at which ventricular depolarization was initiated by sinus or paced impulses. This circumstance allows postulation of 1) concealed transseptal retrograde penetration of the left bundle branch system; 2) concealed transseptal retrograde penetration of the right bundle branch system; 3) alternate beat Wenckebach phenomenon with two areas of block in the bundle branch system with concealed penetration of the proximal area; 4) concealed re-entry in the right bundle branch system during an H-V Wenckebach cycle with resetting of the sequence of 2:1 H-V block and return of the re-entry wave to the A-V node causing subsequent A-H block; 5) proximal 2:1 block and distal Wenckebach block producing only two consecutively blocked beats; and 6) infrahisian Wenckebach block with changes both in A-V conduction and QRS contour.

[Clinical value of His bundle electrography (author's transl)]

Methodical problems, indication and clinical implication of His bundle electrography are discussed. In 200 successive patients undergoing His bundle electrography and atrial stimulation the indication was as follows: Intraventricular conduction defects in 24%, A-V block in 21%, sick sinus syndrome in 20%, preexcitation in 17%, and complex arrhythmias in the remaining cases. In 38% of the patients did the HBE prove to be of help by providing information not available after analysis of the surface ECG. In 22% this technique contributed essentially to the management of these patients. In spite of dificiencies of our knowledge of the basic mechanisms, specific therapy, and prognosis of various arrhythmias His bundle electrography is clinically useful in selected patients. Therefore, this method has become a routinely used clinical tool.

Pathophysiology of second degree atrioventricular block: a unified hypothesis

An in vivo and in vitro correlative study of second degree atrioventricular (A-V) block in the canine proximal His-Purkinje system after ligation of the anterior septal artery is reported. Evidence is presented to suggest that Mobitz type II and the Wenckebach ypte of conduction represent different degrees of the same disorder rather than two distinct electrophysiologic processes. The in vivo study showed that an increment of conduction delay almost always preceded the blocked impulse in second degree A-V block. The increment, as 1 or 2 msec at the early stage of block, often increased gradually up to 180 msec. The in vitro study consistently showed an increment of conduction delay preceding the blocked impulse. The same experiments revealed a greater increment in conduction delay early after excision that, on recovery during superfusion, gradually decreased to a few milliseconds (the reverse order of the in vivo observation). Characteristic changes in duration and configuration of action potentials in the ischemic proximal His-Purkinje system were observed depending on the state of transmission and the temporal relation of the impaled cell to areas of slow propagation and block. The study revealed a remarkable similarity between characteristics of conduction in the ischemic His-Purkinje system and conduction in both the normal A-V doe and Purkinje fibers subjected to various pathophysiologic interventions. It is suggested that in the pathologic situation--exemplified in this study by acute myocardial ischemia--the normal His-Purkinje system may gradually lose the characteristics of the fast response and start showing properties of the slow response. At an early stage of departure from normal, the proximal His-Purkinje system may show second degree A-V block with no perceptible to a few milliseconds' increment of conduction delay (the equivalent of Mobitz type II block). On further departure from normal, the His-Purkinje system resembles the A-V node in showing a significant increment of conduction delay prior to the blocked impulse (the equivalent of Wenckebach periodicity). Both the in vivo and in vitro observations demonstrated a clear propensity of the ischemic proximal His-Purkinje system to develop paroxysmal A-V block during the stage of second degree A-V block when there is no perceptible to a few milliseconds' increment of conduction delay. A new classification of second degree A-V block is presented based on the suggested electrophysiologic mechanism.

Wenckebach periods of alternate beats. Clinical and experimental observations

Wenckebach periods of alternate beats (AW) can be described as a 2:1 atrioventricular (A-V) block in which the conducted P waves show progressive prolongation of the P-R interval of the Wenckebach type. However, while classical Wenckebach periods terminate with a single blocked P wave, AW necessarily ends with (or begins from) two consecutive blocked P waves. Five clinical cases and several experimental examples of AW are reported. Recovery curves of A-V conduction were constructed, and it was demonstrated that AW is related to a marked prolongation of both the absolute and relative refractory periods. All the cases were associated with intraventricular block. In addition, recording of His bundle potentials in one case, histological study of the conduction system in another, and the experimental observations, support the view that AW tends to occur below the A-V node, in one of the main ventricular conducting fascicles. Four of the five patients developed complete heart block and Adams-Stokes seizures.