Mobitz II Second-Degree Heart Block During Total Hip Arthroplasty: ACase Report

Abstract

Spontaneous intraoperative development of Mobitz II second-degree atrioventricular block is a rare event which requires decisive action on the part of anesthesiologists and anesthetists. Given that this arrhythmia can be fatal if not properly managed, it is imperative that every practitioner know how it should be managed. Currently, there is a lack of literature discussing what to expect when a patient develops this complication and what the best management strategies are. This case report describes the unexpected development of Mobitz II second-degree atrioventricular block in an elderly patient with no prior history of conduction abnormalities undergoing total hip arthroplasty and how it was managed during the perioperative period to avoid morbidity or mortality. It includes a proposed management algorithm as an easy to use guide in the management of similar clinical scenarios. While this algorithm should be familiar to anesthesiologists and experienced anesthetists, it can serve as a reference in critical situations, and may help in educating trainees.

1. Introduction

Mobitz II second-degree atrioventricular (AV) block is an uncommon perioperative arrhythmia that is rarely seen, particularly without a history of first-degree or type I (Wenckebach) second-degree AV block. Mobitz II is a significant and ominous finding, as it can progress to complete heart block (CHB) and Stokes-Adams cardiac arrest [[1], [2], [3]].

Second-degree AV block is a form of impaired conduction of atrial beats to the ventricles. Type I (Wenckebach) second-degree AV block is characterized by a delay in the electrical impulse of the atrio-ventricular (AV) node with progressively increasing PR interval until a dropped P wave occurs on electrocardiogram (ECG), while in type II the PR interval is constant with occasional blocked electrical signals resulting in dropped QRS complexes. When vagally mediated, it is known as paroxysmal AV block with slowing of the sinus node functional rate and consequently the AV nodal conduction.

While first degree AV block and type 1 second-degree AV block are both considered benign, persistent Mobitz II can lead to syncope or even cardiac arrest and must be managed with full monitoring and ultimately pacemaker implantation [[4], [5], [6]]. The presentation of a previously undiagnosed type II necessitates timely and decisive management. Therefore, we present this incidental case during an elective total hip surgery to keep anesthesiologists aware of its clinical significance and help guide them in management.

2. Case report

A 91-year-old female with a past medical history of osteoarthritis of the right hip, hyperlipidemia, schizophrenia, mild to moderate aortic stenosis, and diminished exercise tolerance presented for elective total hip arthroplasty. Her preoperative medication list included quetiapine 50 mg daily, atorvastatin 10 mg daily, celecoxib 200 mg daily, vitamin D 50,000 units weekly, perphenazine 4 mg 4 times per day, risperidone 4 mg daily, and zolpidem 5 mg nightly. The latter two medications may influence cardiac repolarization but not QRS propagation. The patient's exercise tolerance was limited due to the arthritis within the hip joint. The patient's Her family history was negative for any congenital disease or genetic predispositions to cardiac or systemic disease. The patient She was evaluated 7 days prior to surgery in a pre-surgical evaluation and was observed to not have any acute symptoms, including cardiac symptoms. The patient's preoperative ECG (Fig. 1) demonstrated normal sinus rhythm and preoperative complete blood count and basic metabolic panel were within normal limits without any electrolyte abnormalities.

Fig. 1.

Preoperative ECG showing no AV block.

The anesthetic plan for this case was general anesthesia with endotracheal tube. Neuraxial anesthesia was eschewed due to her history of mild to moderate aortic stenosis. For this reason, a pre-induction arterial line was also placed and 20 mg of esmolol was administered just prior to induction. The patient was induced with 10 mg etomidate, 100 mcg fentanyl, and 60 mg lidocaine. 40 mg of rocuronium was used for paralysis and 200 mcg of phenylephrine was given on induction to avoid hypotension. Isoflurane at approximately 1 minimum alveolar concentration was utilized for maintenance of anesthesia. Adjunctive agents included 10 mg dexamethasone, 4 mg ondansetron, and 1 g of tranexamic acid.

Approximately 45 minutes into the case, the patient had several episodes of severe bradycardia with a heart rate as low as 29, each lasting less than 1 minute. Intraoperative 5 lead ECG demonstrated sinus rhythm with dropped QRS complexes and no prolongation in PR interval (Fig. 2), consistent with Mobitz II second degree AV block. At this point, external pacing pads were immediately placed on the patient. Continuous hemodynamic monitoring was possible due to the existing arterial line placed prior to induction. The management plan included immediate external pacing in the event of bradycardia-induced hypotension and avoidance of any additional AV nodal blocking agents. Anticholinergic agents were not utilized, as high degree AV blocks are often resistant to their effects. Additionally, coronary perfusion pressure was maximized by increasing afterload in case the development of AV block was due to ischemia. The patient never became hypotensive secondary to their her bradycardia (mean arterial pressures >80 during transient AV block) and never progressed to CHB. She was thus extubated at the conclusion of the procedure and was taken to the post-anesthesia care unit (PACU) monitored and in stable condition. Dropped QRS's were again noted on a 12-lead ECG in PACU (Fig. 3). Postoperative basic metabolic panel (BMP) again demonstrated no electrolyte abnormalities and a high sensitivity troponin was negative.

Fig. 2.

Intraoperative rhythm strip showing Mobitz II second-degree AV block without the presence of Mobitz I.

Fig. 3.

Postoperative ECG showing dropped QRS complex.

The cardiac electrophysiology (EP) team was consulted postoperatively, and the patient was admitted for observation on a telemetry floor. Telemetry did not show a recurrence of Mobitz rhythms or a progression to CHB and instead demonstrated intermittent Wenckebach rhythms followed by junctional escape beats thought to be due to increased vagal tone. A 2D transthoracic echocardiogram (TTE) was ordered and performed the day after surgery showing normal cardiac function with calcification of the aortic valve, as was known preoperatively. Given the determination of vagally mediated heart block, a permanent pacemaker was not indicated, and the patient was discharged home with follow up as needed.

3. Discussion

Mobitz II second-degree AV block is a rare and ominous arrhythmia with a variety of causes that can be encountered in any patient and without warning. The causes of Mobitz II second degree AV block can be transient such as with vagal overstimulation or drug toxicities, or they may be chronic such as from ischemic cardiomyopathy or infiltrative diseases [7]. The most important steps to take if encountered intraoperatively are to quickly recognize the arrhythmia, identify/remove any reversible causes, and protect the patient from decompensation. It is key to identify any potential vagal stimulation which can be quickly removed such as manipulation of the carotid sinus during neck surgeries or abdominal insufflation during laparoscopic procedures. If an ultrasound is available, it could be useful to perform a bedside TTE to evaluate for evidence of ischemia such as regional wall motion abnormalities or right heart strain.

What makes Mobitz II AV block a more significant clinical finding than a first-degree or a Mobitz I (Wenckebach) AV block is that it has the potential to progress to CHB, which can be fatal if untreated. Therefore, placing external pacing pads on the patient as soon as possible is the most important preparatory step in management. The patient should also have continuous invasive blood pressure monitoring if it has not already been placed so that you can quickly identify if the patient is unstable and external pacing is required.

Caution should be exercised initially with the administration of positive chronotropic medications to patients in new onset Mobitz II heart block due to the possibility that the inciting cause is cardiac ischemia. Mobitz II is commonly caused by damage to the bundle branches in the septum from anterior myocardial infarction [8], which could worsen with increased stress on the heart. Since it may be difficult to identify the source of the heart block intraoperatively, it would be safest to use chronotropic medications as a last resort if unable to use external pacing effectively or if resources are limited initially. Additionally, high degree AV blocks are often resistant to the effects of positive chronotropes such as anticholinergic agents.

The process of determining the cause of the patient's heart block can often begin in the operating room (OR) with lab work and ECG findings, but it will usually require a more thorough workup with the help of cardiologists and electrophysiologists. Therefore, new onset Mobitz II AV block noted intraoperatively should prompt the anesthesia provider to consult the electrophysiology team for a detailed workup. Additionally, the patient should be monitored on a telemetry-capable floor for the duration of their hospitalization. While this patient was fortunate and did not require further interventions, it is important that any underlying pathology be addressed to minimize the risk of unstable arrhythmia after the patient is discharged.

Mobitz type II AV block is an arrhythmia that is rarely encountered in the OR. Furthermore, There is currently a lack of research discussing the identification and management of Mobitz II in the OR setting during non-cardiac surgery. which may lead to distress when faced with such a situation. There have been cases reported of Mobitz type II developing postoperatively and with the preoperative management of known Mobitz type II [9,10], but few cases were found which discussed the intraoperative development of Mobitz type II [[11], [12], [13]]. These cases involved intense sympatholytic medications (remifentanil) or anesthetic techniques (subarachnoid block). However, no article discussed in any detail the considerations for intraoperative and postoperative management of this rare uncommon and ominous worrisome arrhythmia as this case report aims to do. As such, we present a simple algorithm for management of intraoperative Mobitz II (Fig. 4). The vital steps include confirming the diagnosis, communicating the diagnosis, preventing, and preparing for deterioration, and ensuring appropriate postoperative care. This algorithm may serve as a reference in what can be a challenging and tense situation.

Fig. 4.

Proposed algorithm for management of intraoperative Mobitz II.

The findings within this case may be limited. Though the patient had a preoperative ECG showing normal cardiac function, an inevitable error of the ECG is that the cardiac rhythm and rate is only recorded for those few seconds that the machine is on. It can miss various cardiac rhythms or rates that may occur outside that window of time. Notably, most ECGs are not performed on sleeping patients preoperatively, meaning vagally mediated arrhythmias are less likely to be detected. Had the dropped QRS complexes been seen preoperatively, the case may have been cancelled or the patient would have been managed differently perioperatively.

An ECG can also present as normal within various patients who have a known cardiac disease. This is particularly true of the cardiac monitor we utilize intraoperatively which usually only shows select leads (leads II and V5). This may cause the disease to go undiagnosed and improperly managed.

4. Conclusion

The recording of intraoperative Mobitz II arrythmia without the presence of prolonged PR intervals as seen in Mobitz I is a unique and ominous finding. Though rare, it is important to know how to diagnose Mobitz II and the rapid steps needed to ensure safe care of the patient intraoperatively and postoperatively. The use of a management algorithm, such as presented here, can assist in this stressful circumstance.

Consent form and IRB approval

The patient signed a consent form, and a copy was given to her. The original file is kept in file for our records. IRB approval is not needed for this case report.

Funding statement

This project was supported in part by the Clinical and Translational Science Collaborative (CTSC) of Cleveland which is funded by the National Institutes of Health (NIH), National Center for Advancing Translational Science (NCATS), Clinical and Translational Science Award (CTSA) grant, UL1TR002548. The content is solely the responsibility of the authors and does not necessarily represent the official views of the NIH.

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CRediT authorship contribution statement

Robert M. Owen: Writing – review & editing, Writing – original draft, Validation, Supervision, Investigation, Data curation, Conceptualization. Christopher Eppel: Writing – review & editing, Writing – original draft, Data curation. Michael Platten: Writing – review & editing, Writing – original draft, Investigation, Data curation. Marianne Tanios: Writing – review & editing, Writing – original draft, Funding acquisition, Data curation. Luis Tollinche: Writing – review & editing, Supervision.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.