CURRENT Essentials of Critical Care.pdf

Chapter 9 Cardiology 127Supraventricular Tachycardia■ Essentials of Diagnosis• Tachycardia (heart rate 100) with origin of electrical rhythmwithin atria or atrioventricular (AV) node resulting in narrowQRS complex (120 msec)• Palpitations, dyspnea, chest pain• ECG and rhythm strip essential for diagnosis• Constant rate as clue to arrhythmia: 150 consider atrial flutterwith 2:1 block; 180 consider AV nodal reentry• Regularity can guide differential diagnosis: regular (ST, AVNRT,AVRT, AT, JT), irregular (MFAT, A-fib), either (A-flut)• MFAT often associated with severe lung disease• Suspect accessory tract if PR interval shortened and ventricularrate 200; examine rhythm strip for delta waves■ Differential Diagnosis• Sinus tachycardia (ST)• AV nodal reentry tachycardia (AVNRT)• Atrioventricular reentry via accessory pathway (AVRT)• Ectopic atrial tachycardia (AT)• Multifocal atrial tachycardia (MFAT)• Junctional tachycardia (JT)• Atrial flutter (A-flut)• Atrial fibrillation (A-fib)■ Treatment• Adenosine to evaluate underlying rhythm; often terminatesAVNRT; uncovers fibrillatory and flutter waves• AV nodal blockade and rate control• Urgent electrical cardioversion when hemodynamically unstable• Reverse potential precipitating factors: electrolytes, hypoxemia,alkalosis, ischemia• Antiarrhythmics useful in A-fib, A-flut, AT• Overdrive atrial pacing can be attempted• Electrophysiological study in refractory cases with or withoutablation■ PearlIn patients with supraventricular tachycardia and evidence of an accessorybypass tract (Wolff-Parkinson-White syndrome), the use of AVnodal blocking agents should be avoided as they can promote antegradeaccessory pathway conduction and worsen tachycardia. Procainamideis the agent of choice.ReferenceBlomstrom-Lundquist C et al: ACC/AHA/ESC guidelines for the managementof patients with supraventricular arrhythmias. J Am Coll Cardiol 2003 Oct15;42:1493. [PMID: 14563598]