Anesthesia for a Patient with Catecholaminergic Polymorphic Ventricular Tachycardia

Catecholaminergic polymorphic ventricular tachycardia (CPVT) is a rare genetic disease affecting cardiac conduction. Fewer than 100 cases have been reported. Clinically, syncope—especially in association with exercise or emotional stress—is the most often described symptom. Electrophysiologically, it is characterized by stress or exercise-induced bi-directional ventricular tachycardia (VT), which may degenerate to cardiac arrest. There is no description of anesthesia for such patients in the literature. This report describes the uneventful anesthesia of an 18-yr-old patient with the condition and discusses the anesthetic issues relevant to CPVT and its treatment. Case Report A morphologically normal 18-yr-old woman, who was mildly learning-disabled, presented for insertion of an automatic implantable defibrillator. She presented at age five with a history of exercise syncope and was initially treated with sodium valproate. Further investigation demonstrated polymorphic ventricular premature beats and VT on 24-h Holter monitoring. Until the age of 15, she was treated with twice-daily sotalol, aiming for a blood level of 2 mg/L and a corrected QT interval of <500 ms. At levels higher than this, sotalol-associated prolongation of the QT interval may provoke dysrhythmias, including torsades de pointes. At the age of 15, she was converted to nadolol. Treatment with β-adrenergic blockers successfully controlled her dysrhythmias on both routine annual exercise testing and Holter monitoring and terminated her exercise-induced syncopal attacks. At age 18, though symptom free in daily life, her exercise test demonstrated atrial fibrillation and self-limiting runs of VT (see Fig. 1, electrocardiogram [ECG] on exercise). She was currently taking nadolol 80 mg twice daily and was unable to tolerate further dose increases. Her maximal nadolol dose was limited by the onset of shortness of breath, orthostatic hypotension, and bradycardia. The decision was made to insert an implantable defibrillator. Of note, at age 11, while asymptomatic on sotalol, she underwent uneventful general anesthesia for a fractured radius.Figure 1: Exercise electrocardiogram (ECG) demonstrating sinus tachycardia and polymorphic ventricular ectopic beats.The patient was formally instructed by both letter and phone to take her usual morning dose of β-adrenergic blocker. Because dysrhythmias have occurred in some patients in response to the stress of imminent venipuncture (1), IV access was only obtained after premedication with 30 mg of temazepam and application of routine monitoring. The patient was drowsy and clinically well β blocked with a sinus bradycardia of 42 bpm and a noninvasive blood pressure of 92/52 bpm on arrival in the operating room. Target controlled infusion of propofol 1.5–2.5 mg/mL (Diprifusor) together with a remifentanil infusion of 0.02–0.08 μg · kg−1 · min−1 were used to allow rapid alteration in the level of analgesia and anesthesia in anticipation of the expected short episodes of profound stimulation associated with testing the device. The drug infusions were titrated to maintain the systolic blood pressure within ± 10% of the preinduction blood pressure. Induction with the target-controlled infusion of propofol occurred over 5 min, with the target blood level increased in 0.5 mg/mL increments from 1.0 mg/mL to 2.5 mg/mL (when loss of lash reflex occurred). Except when testing the device, the cardiac rhythm remained sinus bradycardia (from 38 to 49 bpm). A size 3 laryngeal mask airway (Laryngeal Mask Company, Henley-on-Thames, United Kingdom) was inserted, and the patient spontaneously breathed oxygen-enriched air. End-tidal CO2 remained <4.8 kPa throughout the procedure. Insertion and testing of the device were uneventful. Tramadol 100 mg IV and ondansetron 4 mg IV were given for postoperative analgesia and antiemesis, respectively. At the end of the procedure, the wound was infiltrated with 20 mL of plain bupivacaine 0.5%. The patient made an uneventful recovery and went home the next day. Discussion In the United States, dysrhythmogenic cardiac death may account for 5% of all nontraumatic sudden deaths in the young (2). CPVT usually presents in childhood or young adulthood with a history of syncope or sudden cardiac death (3). Two patients presented at age 30 (1,4). It has also been prospectively diagnosed in blood relatives of an index case. Syncope, especially in association with exercise or emotional stress, is the most often described symptom. Approximately 35% of patients will have a family history of juvenile syncope or sudden cardiac death (5). In those patients without a family history, misdiagnosis as either epilepsy or vagal hyper-reactivity is common. The mean time to correct diagnosis is between 24 and 38 months (4,5). Though first described in the early 1970s (6), CPVT was only fully characterized in 1995 (7). Diagnosis requires the demonstration of stress-related bi-directional VT in a patient with a structurally normal heart on cardiac echocardiography, magnetic resonance imaging, and angiography. Tilt table testing is negative. There is a normal QT interval on both resting and exercising ECG. Features of the resting ECG are otherwise unremarkable. During exercise testing, VT/fibrillation most often develops when the heart rate exceeds 130 bpm. One fourth of patients may also exhibit runs of atrial fibrillation. The dysrhythmias will worsen as the workload increases. Dysrhythmias are not induced on programmed electrical stimulation, but they can be elicited by isoproterenol infusions. The bi-directional VT observed resembles the pattern seen with digitalis toxicity and calcium overload and is distinct from the pattern seen with long QT syndrome (see Table 1). Unlike the long QT syndromes, CPVT is linked to chromosome Lq42-q43 (8). The human cardiac ryanodine receptor gene (hRyR2) also maps to Lq42-q43. There is speculation that CPVT is secondary to a dysfunction in the cardiac muscle ryanodine receptor, which is responsible for calcium release from the sarcoplasmic reticulum. The bi-directional VT may be triggered by delayed afterdepolarizations secondary to calcium overload. In isolated canine myocytes, α-adrenergic stimulation failed to induce delayed afterdepolarizations, whereas β-adrenergic stimulation elicited delayed afterdepolarizations that in turn initiated and maintained sustained triggered rhythms (9).Table 1: Comparison of CPVT and Long QT syndromeBeta-adrenergic blockers control syncopal attacks and dysrhythmias on serial electrophysiologic-pharmacologic testing and are the treatment of choice. Nadolol is the preferred option because of its prolonged half-life and the possibility of once daily dosing. Dosages can be difficult to establish and must be adjusted as the child grows. Overdose may be associated with treatment-induced bradycardia and hypotension. Without treatment, sudden death may occur in 50% of affected individuals before the age of 20 (5). There is a report of sudden death after one missed dose (4). Success of treatment is assessed by the disappearance of symptoms and the absence of VT on Holter monitoring and exercise testing. Because implantable cardioverter defibrillators are increasingly easy to implant and are effective, the indications for implantable cardiac defibrillators may be expanding. The anesthetic goals in a patient with CPVT include the avoidance of endogenous catecholamine surges secondary to fear or inadequate levels of anesthesia, the avoidance of extrinsic catecholamines, especially β-adrenergic agonists, the maintenance of therapeutic levels of β-adrenergic blockade, the treatment of dysrhythmias should they occur, and the management of any undesirable effects of β-adrenergic blockade. Dysrhythmias may in theory be more common or more persistent in the presence of hypernatremia, hypomagnesemia, or hypokalemia, all of which should be avoided. Whereas implantable defibrillators are frequently placed under local anesthesia and sedation, the problem of achieving a genuinely calm patient and the contraindication to epinephrine supplementation of the local anesthetic may make this course less attractive than general anesthesia. General anesthesia may rarely cause severe hypotension in the presence of large dose β-adrenergic blockade. Positive-pressure ventilation may exacerbate hypotension by reducing venous return. Treatment includes Trendelenburg positioning and judicious fluid challenge. IV glucagon has been used to treat resistant β-adrenergic blocker overdose (10). The administration of a pure α-adrenergic agonist, e.g., IV phenylephrine, may be safe in CPVT. Hypotension secondary to bradycardia should be treated with atropine or pacing. Intraoperative tachycardia should be avoided, and the patient’s usual β-adrenergic blockade may require supplementation. IV esmolol has the advantage of rapid onset, especially if initial loading doses are used. The calculated dose may need to be reduced in the presence of underlying β-adrenergic blockade. Dysrhythmias that have not self-terminated during exercise testing have been treated with IV esmolol, IV magnesium, and defibrillation. In summary, CPVT is a rare genetic condition. Patients without a family history may initially be misdiagnosed, and anesthesiologists should remain wary of the patient diagnosed with “epilepsy” but without a completed diagnostic workup. In patients who have a documented diagnosis, β-adrenergic blockers must be continued. Importantly, tachycardia, emotional distress, and β agonist drugs should be avoided.