The process of diagnosis and acute management of WCT in the pediatric patient is similar to the adult patient. Diagnostically, age-related differences in rate and QRS complex duration must be considered. Therapeutically, the primary differences between the two populations includes alterations in the drug dosages of anti-arrhythmic drugs and energy required for synchronized cardioversion (0.51 joules/kg) or, if pulseless, defibrillation (24 joules/kg).63
Acute management of WCT in a pediatric patient depends on the patient's age and hemodynamic status.64 When faced with shock or cardiovascular collapse, immediate synchronized cardioversion with 0.51 joule/kg is necessary. In more stable situations and if a diagnosis of SVT is made, 0.10.2 mg/kg of adenosine can be given in rapid boluses to induce transient AV block.63 If VT is the diagnosis, amiodarone, procainamide, or lidocaine are all acceptable therapeutic agents.
The Adult Patient With Congenital Heart Disease
The evaluation and management of WCT in patients with simple' adult congenital heart diseases, such as atrial septal defects and un-operated small ventricular septal defects, are not significantly different from the standard approach. Complex adult congenital heart disease, however, does merit additional consideration. The largest body of information is available for postoperative tetralogy of Fallot.
Supraventricular arrhythmias are a frequent complication in patients who have a surgical correction of their tetralogy of Fallot.65 The supraventricular rhythms in these patients are typically RBBB in morphology.65 Therefore, if a post-operative tetralogy of Fallot patient has a WCT with an LBBB morphology, the dysrhythmia is likely VT.65
The Pregnant Patient With Wide Complex Tachycardia
The major concern regarding anti-arrhythmic drug therapy during pregnancy is the potential adverse effects on the fetus.66None of the anti-arrhythmic drugs available are FDA category A for use in pregnancy. Among the anti-arrhythmics commonly used, only lidocaine and sotalol are category B. Of note, amiodarone, which is the most commonly used antiarrhythmic in the treatment of WCT in non-pregnant patients, is a category D drug in pregnancy. Other than phenytoin (FDA category X), the vast majority of the remaining anti-arrhythmics are FDA category C.
SVT and VT can arise for the first time during pregnancy or become more frequent during this period.67At least two groups of investigators have noted an increased incidence of arrhythmias associated with an accessory pathway during pregnancy.68,69Similar to non-pregnant patients, the 12-lead ECG is an important tool in the diagnosis of WCT. The diagnostic strategies used to discriminate between the different etiologies of WCT are similar to the non-pregnant patient. When a pregnant patient presents with new onset WCT in the last few weeks of pregnancy or within 6 months of delivery, the possibility of peripartum cardiomyopathy should be considered.
Regardless of the etiology, if a pregnancyassociated WCT becomes hemodynamically unstable, DC cardioversion of 50100 J should be considered. If unsuccessful, higher energies should be used (100360 J). DC cardioversion is considered safe in all stages of pregnancy with no significant fetal complication.70-72 As with other pregnancy-associated disease processes, "stabilize the mother and you will stabilize the fetus." It is necessary, however, to monitor the fetal rhythm if possible, because transient fetal arrhythmia has been reported during DC cardioversion in pregnancy.73 As fetal monitoring is not possible in most EDs, specialty consultation is advised, but management decisions should not be delayed if the patient becomes unstable. When necessary, cardiopulmonary resuscitation (CPR) should be performed with the pregnant patient tilted on her side, with either a wedge or another rescuer's knees for support.74
In the hemodynamically stable pregnant patient with undifferentiated monomorphic WCT, diagnosed VT, or preexcited tachycardia, initial therapy should be intravenous procainamide (FDA category C).75,76 Procainamide has been used with no evidence of teratogenicity.77 The next drug of choice is lidocaine (FDA category B) in patients with VT or undifferentiated WCT (it is not effective in preexcited achycardias). Given the category B status of lidocaine, one could consider using lidocaine before procainamide in a pregnant patient with VT. Data from non-pregnant patients, however, does demonstrate a marked superiority of procainamide over lidocaine in the acute termination of hemodynamically stable VT (80% vs. 21%).51 Use of lidocaine in the early stages of pregnancy is not teratogenic.75 Amiodarone (FDA category D) is of limited value in pregnancy; it is associated with many serious side effects for the fetus, including hypothyroidism, growth retardation, and premature delivery.78 Hence, it should be reserved for lifethreatening and refractory conditions.79
In the pregnant patient with polymorphic VT, intravenous magnesium can be very useful, similar to its use in the non-pregnant patient. It is particularly effective in patients with torsades de pointes. The dosage is 2 g intravenously with supplemental doses and an infusion as needed. Adverse impacts are rare and include maternal hypothermia, fetal bradycardia, respiratory depression, and hypotonia in the newborn which may require aggressive measures.80 Initial treatment of the stable patient with SVT with AVC should start with vagal maneuvers to terminate the arrhythmia. If this fails, adenosine (FDA category C) should be used. It is not known to be teratogenic and it is as effective in terminating SVT (> 90% successful) in pregnant patients as it is in those not pregnant.76,82 While information about the use of diltiazem (FDA category C) in pregnancy is limited, verapamil (FDA category C) has a history of safe use in pregnancy.103 One retrospective analysis suggested a risk of birth defects associated with its use in the first trimester.83 Beta blockers have been widely used in pregnancy for a variety of indications. Propranolol (FDA category C) has been extensively used but has been associated with a small risk to the fetus.73 Labetolol and metoprolol are also frequently used, but both are category C. While atenolol is category D, two new beta blockers (pindolol and acebutelol) are category B.103
Stable pregnant patients with AF with AVC should be managed with beta-blockers, diltiazem, or verapamil to achieve rate control similar to nonpregnant patients. Early DC cardioversion or chemical cardioversion should be considered (within 48 hours) to avoid the need for anticoagulation.103 While quinidine (FDA category C) has a long history of safe use in pregnancy, chemical cardioversion with other anti-arrhythmic drugs (e.g., flecainide, propafenone, ibutilide, procainamide) has also been reported in pregnancy patients.81,103