2:1 Atrioventricular block: order from chaos

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.

Paradoxical worsening of bradycardia following atropine administration

Introduction

Bradyarrhythmias are a common entity in both emergency and out-of-hospital (OOH) medicine. In unstable bradycardic patients, paramedics will often initiate life-saving therapies in the OOH setting. Clinical guidelines for bradyarrhythmias are largely consistent across the globe, with intravenous (IV) atropine recommended as a first-line therapy, escalating to IV adrenaline or isoprenaline and transcutaneous pacing where atropine is unsuccessful. In this case report, we describe a case in the OOH setting of ventricular standstill following the administration of atropine to a patient with bradycardia and 2:1 heart block.

Case presentation

The patient was a 77-year-old female presenting with a symptomatic 2:1 heart block. Following a single dose of 600 micrograms IV atropine, the patient deteriorated into ventricular standstill with a loss of consciousness and decorticate posturing. The patient was successfully managed with an IV infusion of adrenaline and subsequently received an implanted pacemaker in hospital.

Conclusion

The paradoxical worsening of this patient's bradycardia following atropine administration may have been related to the location of the heart block. It has been shown that patients with atrioventricular blocks at the level of the His-Purkinje fibres (infranodal) are at an increased risk of adverse events following atropine administration, while those at the nodal level or secondary to increased vagal tone are more likely to respond favourably. Paramedics should be prepared to manage unexpected adverse events secondary to atropine administration in patients with heart block.

Expert-enhanced machine learning for cardiac arrhythmia classification

We propose a new method for the classification task of distinguishing atrial fibrillation (AFib) from regular atrial tachycardias including atrial flutter (AFlu) based on a surface electrocardiogram (ECG). Recently, many approaches for an automatic classification of cardiac arrhythmia were proposed and to our knowledge none of them can distinguish between these two. We discuss reasons why deep learning may not yield satisfactory results for this task. We generate new and clinically interpretable features using mathematical optimization for subsequent use within a machine learning (ML) model. These features are generated from the same input data by solving an additional regression problem with complicated combinatorial substructures. The resultant can be seen as a novel machine learning model that incorporates expert knowledge on the pathophysiology of atrial flutter. Our approach achieves an unprecedented accuracy of 82.84% and an area under the receiver operating characteristic (ROC) curve of 0.9, which classifies as "excellent" according to the classification indicator of diagnostic tests. One additional advantage of our approach is the inherent interpretability of the classification results. Our features give insight into a possibly occurring multilevel atrioventricular blocking mechanism, which may improve treatment decisions beyond the classification itself. Our research ideally complements existing textbook cardiac arrhythmia classification methods, which cannot provide a classification for the important case of AFib↔AFlu. The main contribution is the successful use of a novel mathematical model for multilevel atrioventricular block and optimization-driven inverse simulation to enhance machine learning for classification of the arguably most difficult cases in cardiac arrhythmia. A tailored Branch-and-Bound algorithm was implemented for the domain knowledge part, while standard algorithms such as Adam could be used for training.

General anesthesia in a patient with asymptomatic second-degree two-to-one atrioventricular block

Background

The major perioperative concern in patients with second-degree atrioventricular (AV) block is the progression to complete AV block. Therefore, the prophylactic implantation of a temporary pacemaker prior to surgery is recommended, especially in symptomatic patients. However, as no quantitative preoperative risk assessment from progression to complete AV block is available, there is currently no established indication for preoperative prophylactic pacemaker implantation. Here, we present a case of progression from asymptomatic second-degree two-to-one (2:1) AV block to complete AV block following the induction of general anesthesia.

Case presentation

A 69-year-old female with degenerative spinal stenosis was scheduled for transforaminal lumbar interbody fusion surgery under general anesthesia. She had no cardiac symptoms, but routine preoperative resting 12-lead electrocardiogram revealed second-degree 2:1 AV block. After discussion with the surgeon and referring cardiologist, we scheduled the surgery without implantation of a temporary pacemaker before surgery for the following reasons: (1) asymptomatic, (2) no evidence of underlying cardiac disease, and (3) a narrow QRS complex. On the day of surgery, general anesthesia was induced with 150 mg of intravenous thiamylal and 25 μg of fentanyl, followed by intravenous administration of 50 mg of rocuronium to facilitate endotracheal intubation. Sevoflurane (1.0–2.0%) was used to maintain anesthesia. A few minutes after induction, the 2:1 AV block progressively converted to complete AV block, and the surgery was postponed. During emergence from anesthesia, the third-degree AV block recovered to 2:1 AV block, similar with the preoperative pattern. The patient was monitored in the intensive care unit for 2 days and then transferred to the normal orthopedic ward uneventfully. One month later, the surgery was rescheduled with preoperative implantation of a temporary pacemaker. A slow mask induction using sevoflurane with oxygen was started. Upon loss of consciousness during the inhalation of initial sevoflurane, complete AV block developed and temporary pacing was immediately initiated. Subsequent anesthesia and surgery were uneventful. The patient made an uncomplicated recovery from surgery with stable hemodynamics. The temporary pacemaker was not required after surgery, and the pacemaker catheter was removed 1 day after surgery.

Conclusions

The present case indicates that a prophylactic pacemaker should be implanted preoperatively in patients who have 2:1 AV block even without symptoms.

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.

Particulate matter inhalation exacerbates cardiopulmonary injury in a rat model of isoproterenol-induced cardiomyopathy

Ambient particulate matter (PM) exposure is linked to cardiovascular events and death, especially among individuals with heart disease. A model of toxic cardiomyopathy was developed in Spontaneously Hypertensive Heart Failure (SHHF) rats to explore potential mechanisms. Rats were infused with isoproterenol (ISO; 2.5 mg/kg/day subcutaneous [sc]), a beta-adrenergic agonist, for 28 days and subsequently exposed to PM by inhalation. ISO induced tachycardia and hypotension throughout treatment followed by postinfusion decrements in heart rate, contractility, and blood pressures (systolic, diastolic, pulse), and fibrotic cardiomyopathy. Changes in heart rate and heart rate variability (HRV) 17 days after ISO cessation indicated parasympathetic dominance with concomitantly altered ventilation. Rats were subsequently exposed to filtered air or Harvard Particle 12 (HP12) (12 mg/m(3))--a metal-rich oil combustion-derived PM--at 18 and 19 days (4 h/day) after ISO infusion via nose-only inhalation to determine if cardio-impaired rats were more responsive to the effects of PM exposure. Inhalation of PM among ISO-pretreated rats significantly increased pulmonary lactate dehydrogenase, serum high-density lipoprotein (HDL) cholesterol, and heart-to-body mass ratio. PM exposure increased the number of ISO-pretreated rats that experienced bradyarrhythmic events, which occurred concomitantly with acute alterations of HRV. PM, however, did not significantly affect mean HRV in the ISO- or saline-pretreated groups. In summary, subchronic ISO treatment elicited some pathophysiologic and histopathological features of heart failure, including cardiomyopathy. The enhanced sensitivity to PM exposure in SHHF rats with ISO-accelerated cardiomyopathy suggests that this model may be useful for elucidating the mechanisms by which PM exposure exacerbates heart disease.

Peri-operative atrioventricular block as a result of chemotherapy with epirubicin and paclitaxel

A 47-year-old woman presented for mastectomy and immediate latissimus dorsi flap reconstruction having been diagnosed with carcinoma of the breast 6 months previously. In the preceding months she had received neo-adjuvant chemotherapy with epirubicin, paclitaxel (Taxol) and cyclophosphamide. This had been apparently uncomplicated and she had maintained a remarkably high level of physical activity. She was found to be bradycardic at pre-operative assessment but had no cardiac symptoms. Second degree Mobitz type II atrioventricular block was diagnosed on electrocardiogram, and temporary transvenous ventricular pacing instituted in the peri-operative period. We discuss how evidence-based guidelines would not have been helpful in this case, and how chemotherapy can exhibit substantial cardiotoxicity that may develop over many years. We suggest that patients who have received chemotherapy at any time should have a pre-operative electrocardiogram even if they are asymptomatic.

ATROPINE OFTEN RESULTS IN COMPLETE ATRIOVENTRICULAR BLOCK OR SINUS ARREST AFTER CARDIAC TRANSPLANTATION: AN UNPREDICTABLE AND DOSE-INDEPENDENT PHENOMENON

BACKGROUND

A paradoxic response to atropine with development of atrioventricular (AV) block has been described in patients after heart transplantation (HTx). We investigated further the incidence and dose-response relationship of this paradoxic atropine response and explored predictive factors.

METHODS

We investigated 25 clinically stable patients (age 55 +/- 2 years) 18 to 126 months after HTx. After endomyocardial biopsy, a temporary pacemaker was introduced and patients were monitored. Atropine was given in ascending doses (0.004 mg/kg body weight initially, total cumulative dose 0.035 mg/kg body weight). Physiologic tests were performed to evaluate the presence of reinnervation.

RESULTS

In 20% of the patients (5/25), a paradoxic response to atropine was observed. Four patients exhibited third degree AV block, one of whom also demonstrated sinus arrest. A fifth patient showed sinus arrest only. In all patients but one, there was no ventricular escape rhythm before ventricular pacing was commenced (10 sec after block). The observed adverse effect was not correlated with the applied atropine dosage, and predisposing factors could not be identified, apart from a slightly lower resting heart rate (80 +/- 5 vs. 90 +/- 2 beats/min, P = 0.07).

CONCLUSION

A significant proportion of patients respond paradoxically to atropine after HTx, leading to asystole as the result of sinus arrest or AV block. Although a plausible explanation for this effect remains speculative, our data indicate that the use of atropine or other anticholinergic drugs in patients after HTx is contraindicated.

Electrocardiographic manifestations: diagnosis of atrioventricular block in the Emergency Department

Patients with bradycardia are commonly encountered by the Emergency Physician. Of the possible bradydysrhythmias, atrioventricular blocks (AVB) represent a significant portion of these presentations. In this article, we provide four illustrative cases of patients presenting to the Emergency Department (ED) with AVB. We review the various types of AV block dysrhythmias (1st, 2nd, and 3rd degrees) and their underlying etiologies. This discussion also focuses on the presentation, clinical considerations, management and acute treatment of AVB dysrhythmias in the emergent setting.

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.