Pre-anesthesia evaluation leading to a diagnosis of long QT syndrome – a case study
Abstract
Long QT Syndrome is a rare disorder characterized by prolongation of QT interval on an ECG. Patients with this disorder have an increased risk of developing life-threatening arrhythmias such as torsades de pointes, and occasionally sudden cardiac arrest.
We present this case of undiagnosed Long QT Syndrome in a 7 years old boy, who presented to our service for incision and drainage of an abscess in the left axilla under general anesthesia. This case highlights the importance of proper and meticulous pre-anesthesia evaluation, even in low risk patients, so that potentially harmful medical conditions are diagnosed well in time and managed accordingly.
Key word: Long QT Syndrome; Anesthesia; Pediatrics; Torsades de Pointes
Citation: Ashfaq M, Yousef SM, Chandrashekaraiah MM, Adeel S. Pre-anesthesia evaluation leading to a diagnosis of long QT syndrome – a case study. Anaesth Pain & Intensive Care 2017;21(2):263-267
Received: 28 Mar 2017, Reviewed: 28 Mar, 10 Apr 2017, Accepted: 28 May 2017
INTRODUCTION
Long QT Syndrome (LQTS) is an inherited or acquired disorder resulting from cardiac ions channel disorders. During repolarization, potassium enters the myocardial cells through both the rapid (IKR) and slow (IKS) potassium channels. Genetic mutations, medical conditions or drugs that alter the activities of these channels cause abnormalities in repolarization of the myocardium that results in long QT interval as seen on an ECG.1
The continuous advances in health care management have led to a relatively increased number of diagnoses of long QT syndrome in recent years. The prevalence of LQTS has been reported to be around 1 in 2000 in the general population.2
The QT interval is measured on ECG trace from the beginning of the QRS complex to the end of T wave. This interval depicts the ventricular depolarization and repolarization. Long QT is described as a QTc of more than 0.44 seconds in both genders from birth until adolescence, and as more than 0.45 sec in adult males and more than 0.47 in adult females.3 Since QT interval is inversely related to heart rate, a correction of heart rate to 60 bpm is made in calculation.4 In this case, we use the widely popular Bazetts formula (QTc = QT√ RR) for calculation of the corrected QT interval.5
Presentation in patients with long QT is either based on the symptoms of syndromes associated with long QT such as congenital deafness in Jervell and Lange-Nielsen syndrome, or symptomatology due to the QT interval such as syncope.6 This makes it a challenge to investigate and diagnose asymptomatic individuals who are found to have an incidental finding of long QT interval on ECG, and so a full list of investigations may be warranted.
We present a case of a young child who was incidentally found out to be suffering from this syndrome.
CASE REPORT
A 7-year-old boy (Weight: 19 kg, Height: 116 cm) got admitted from the emergency department for incision and drainage of left axillary abscess. On history taking, there was no significant past medical or surgical history. He had a positive family history of sudden death of his mother at the age of 24 years, preceded by an episode of syncope.
During routine pre-anesthesia evaluation, it was noticed that the patient was having episodes of bradycardia in the range of 50-60 bpm during sleep and a regular heart rate of 70-80 bpm when awake. A subsequent ECG was requested that showed normal sinus rhythm, heart rate of 65 and a QTc of 447 ms. Patient was referred to pediatrics department for evaluation and was provisionally diagnosed to have LQTS after thorough investigations including ruling out electrolyte abnormalities and scoring as per the Schwartz Criteria. The patient had no new active complaints and was asymptomatic from a cardiac standpoint.
The anesthesia team reviewed the patient again before the surgery and a high-risk consent was obtained because of the increased risk of sudden cardiac arrest among these patients. Repeat lab investigations were reviewed before the surgery to rule out any correctable abnormalities.
A calm and comfortable environment was provided before induction of anesthesia to minimize anxiety factor. All precautionary measures were taken before the start of the surgery, including preparation of an emergency trolley inside the theatre with the availability of a defibrillator. ECG leads were applied to the patient for continuous observation. Upon arrival in the operating room, standard monitoring was applied as per AAGBI Guidelines.7 Chest pads were applied, in case defibrillation was required intra operatively. Patient was induced with fentanyl 25 µg and propofol 80 mg IV. Airway was secured with size 2.5 LMA, maintenance of anesthesia was achieved using sevoflurane in oxygen and air mixture to reach MAC 1.0. Patient remained stable during the surgery with normal variability in his heart rate ranging from 80 -110 bpm. It was a short surgical procedure and surgical time was about 10 min. Child woke up smoothly, and postoperatively he was shifted to the pediatric ICU for standard monitoring for 24 hours.
Continuous monitoring and repeat ECG postop showed QT interval to be 460 ms. Patient remained asymptomatic and was discharged from the hospital in good health after recovering completely from the surgery with a follow up appointment in the outpatient clinics with pediatrics services. Serial repeat ECGs were obtained in the OPD that showed the QTc ranging from 450 ms to 480 ms, all of which are higher than what is acceptable for his age.7 Diagnosis of LQTS was confirmed, and the patient was referred to pediatric cardiology department for further evaluation and management.
DISCUSSION
Routine monitoring in asymptomatic patients, if carefully observed may help in the early diagnosis of potentially fatal medical conditions. This case presented here highlights the importance of proper and scrupulous evaluation in these asymptomatic patients who are undergoing anesthesia. Timely diagnosis in these patients may lead to early intervention in the disease process and a better long term outcome.
LQTS is a rare genetic or acquired cardiac channel disorder that renders the individual more susceptible to developing fatal arrhythmias such as torsades de pointes and ventricular fibrillation, which may result in sudden death. It may either present with very vague symptoms or may be an incidental finding in asymptomatic individuals, as was the case with our patient. A normal variation exists in QT interval due to different physiological factor, as it is inversely correlated to the heart rate. All these factors make it very challenging to diagnose and establish a clinical pathway for patients who are not in any acute cardiac distress.8
After ruling out reversible causes of prolonged QT, the best initial test that helps in establishing a diagnosis is repeat ECGs that show consistently prolonged long QT intervals. This initial suspicion is then complemented by the use of the Schwartz score (Table 1) that gives points based on ECG findings, clinical findings and family history to help establish the diagnosis of long QT syndrome.5
