Congenital complete atrioventricular heart block is a rare and heterogeneous disorder. The estimated incidence is 1 in 20,000 live births.1 A subset of these patients are asymptomatic until reaching adulthood, at which time they may become symptomatic on exposure to anesthetic agents. Our patient knew of her condition, but did not know of the risks associated with anesthetic exposure.
Our patient consented to the publication of this report.
The patient was a 25-year-old active duty military servicewoman whose preoperative interview was only significant for atrial septal defect (ASD) repair. She recently had seen a cardiologist before being stationed in Japan to get medical clearance because of her prior heart surgery. The cardiologist report was not available during preoperative questioning. She stated that she had a normal echocardiogram and was fit for duty per her cardiologist. She denied any complications with anesthesia during her open ASD repair. On the basis of this information, no further investigation was done. Her medical chart was not available, nor was a preoperative electrocardiogram. She was exceptionally fit, having recently competed in a triathlon. On the basis of her asymptomatic status, normal vital signs, and exceptional level of fitness, her anesthesia provider decided to proceed with the elective septorhinoplasty.
Before induction, the anesthesiologist noted junctional bradycardia in the rhythm strip, which was attributed to her level of fitness. After receiving 100 mg lidocaine, 100 mcg fentanyl, and 200 mg propofol, she became severely bradycardic (approximately 20 bpm), and then nearly asystolic. After several doses of atropine with a delayed response, chest compressions and transcutaneous pacing were almost initiated. Her bradycardia changed to a junctional escape rhythm with varying degrees of atrioventricular (AV) block (Fig. 1). The case was aborted. She emerged uneventfully from anesthesia, without neurological deficit.
Her complete medical record was retrieved. The record revealed a thorough investigation after her screening electrocardiogram (initial military medical screening) showing a junctional escape rhythm. A follow-up echocardiogram showed mild decreased left ventricular systolic function and possible biventricular noncompaction. On the basis of these findings, she was referred to a tertiary cardiac center to evaluate the possibility of noncompaction cardiomyopathy. This rare disorder results from the failure of myocardial ventricular development to fully mature during embryogenesis.2 Further cardiac magnetic resonance imaging and transesophageal echocardiography excluded this condition but showed a secundum ASD with normal systolic function. Right heart catheterization demonstrated normal filling pressures and cardiac output. Yet, the ratio of pulmonary to systemic flow was elevated.
On the basis of the increase of left to right flow with no signs of increased pulmonary pressures, a percutaneous route to repair the ASD was undertaken. The procedure was aborted due to temporary complete AV block with asystole. The resuscitation was successful and a follow-up electrophysiological (EP) study revealed complete AV block (probably congenital) with an escape rhythm at the level of the bundle of His. It also indicated that her AV block was reversible with vagal input withdrawal or catecholamine exposure. Due to her asymptomatic status and stable escape rhythm, a pacemaker (PM) was deemed unnecessary at the time. The patient was cleared for active duty with restrictions on job selection after an uneventful open ASD repair.
None of this was gleaned before proceeding to the operating room. The patient was extensively counseled on her condition and anesthetic risk. She was given a letter highlighting her unique anesthetic implications for future anesthesia providers.
This patient most likely had congenital complete AV heart block. When diagnosed early in life, this condition is associated with passively acquired autoimmune disease of the fetus. If diagnosed later in life, the causes are unknown. Our patient was diagnosed in her early 20s. This condition may be isolated or associated with structural cardiac disease.3 The latter is associated with greater morbidity, but occurs less frequently.4 It was difficult to determine whether our patient had structural heart disease, other than the minor ASD. The initial diagnosis of biventricular noncompaction was excluded after further studies. It was difficult to categorize her risk status since she had minor structural abnormalities but was otherwise asymptomatic.
The level of the block also plays a key role in the severity of the disease. When the block is located high in the septum between the AV node and bundle of His, patients tend to be asymptomatic. The electrocardiogram shows normal QRS complexes.5 Exercise, atropine, and sympathomimetic drugs will increase the resting heart rate. When the block is located distal to the bundle of His, patients are symptomatic. Their QRS complexes are wide and there is no response to exercise or medications. These patients are usually diagnosed early and require pacemakers.4
Current controversy revolves on timing of PM insertion for asymptomatic patients with congenital complete AV heart block. All eventually need a PM.6 At this time, pacing is only recommended for patients with associated heart failure symptoms, ventricular pauses ≥ 3 seconds, or a resting heart rate < 40 beats/min while awake, and have a Class I indication.7 Previously, the prognosis of congenital complete AV heart block in asymptomatic adults was favorable, but 1 prospective study warns of the frequent incidence of cardiac complications in these patients.6 Their recommendation favors early PM implantation in asymptomatic patients.
Anesthetic implications are not considered in current PM requirement guidelines.7 Upon further discussion with our patient’s cardiologist, his recommendations (based on the EP study) for future anesthetics was the use of atropine before induction and the potential need for pharmacological pacing. This requirement can present significant challenges during the perioperative period. Steward and Izukawa advise preoperative PM insertion in all patients with congenital complete AV heart block receiving general anesthesia. They recommend transvenous pacing since the risk is less than the undetermined arrhythmia risk in these patients. If a PM is not inserted, one should be readily available for emergency intraoperative use.8 This is an older recommendation, but considering the inconsistencies of transcutaneous pacing, the advice is prudent. Another option would be for esophageal pacing, whether the equipment and experience were availabe.9
Most of our anesthetics alter conduction to some degree. There are numerous case reports and studies highlighting anesthesia catastrophes associated with rhythm and our drugs.5,10–13 These occurrences mostly occur during induction. Heart rhythm disorders are predictive of perioperative cardiac arrest.14 They are independent risk factors during any type of anesthetic. The anesthesiologist must have a clear understanding of the underlying rhythm, whether or not the patient is asymptomatic.
Patients with congenital complete AV heart block can be prone to severe bradycardia or other arrhythmias when exposed to anesthetic drugs. Volatile anesthetics in the presence of preexisting conduction abnormalities can enhance AV nodal blocking. They can prolong cardiac conduction and significantly prolong the QT interval by inhibition of voltage gated sodium and L-type calcium channels.15 Propofol can similarly diminish voltage-dependent L-type calcium channels, which play an important role in the PM activity in nodal cells.16 Amide local anesthetics are sodium channel blockers as well, and if needed, should be used with caution. Paralytics and several other drugs have been implicated in enhancing AV blocks as well.10–13 Most of our drugs can enhance preexisting conduction defects. Other well-known AV nodal blocking drugs such as adenosine, beta-blockers, calcium channel blockers, and digoxin should be avoided. A few cases document the safety and risks associated with regional/neuraxial anesthesia in these patients.10,11
On the basis of this experience, we propose several considerations for patients with congenital complete AV heart block who require surgery. First, there should be a thorough preoperative evaluation with particular focus on their cardiovascular history. Any history of syncope may indicate need for a pacemaker. If asymptomatic, determine block location. If the block is between AV node and bundle of His, the patient will most likely be asymptomatic with narrow QRS complexes and a junctional rhythm. If there is no electrocardiogram, then one should be obtained to evaluate the QRS. Second, at the time of induction, pay close attention to the rhythm strip, which may show varying degrees of AV block (Fig. 2). Any rhythm other than normal sinus rhythm mandates a gradual exposure to anesthetic drugs if the case is elective.
Third, consider deferring surgery until an EP study has determined the site of AV block. Current recommendations do not require patients with asymptomatic congenital complete AV heart block to get an EP study.7 Current evidence indicates that most undiagnosed cases have higher AV blocks, hence, they are asymptomatic.5
Fourth, patients should receive atropine before induction. Dopamine or isoproterenol may also be needed. Transcutaneous, transvenous, or esophageal pacing should be available.
In this patient, induction with lidocaine, fentanyl, and propofol led to a transient complete block with minimal escape. It is difficult to determine the offending drug, or whether they all contributed.
This case highlights the importance of a comprehensive preoperative interview. A recent study indicates that one of the biggest reasons for anesthesia lawsuits are from incomplete preoperative interviews.17 Red flags in her interview were not addressed. The patient’s incomplete disclosure along with her exceptional level of physical fitness falsely reassured her provider.
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