A confounding factor in diagnosing SVT is the need to differen- tiate symptoms of SVT from symptoms of panic and anxiety disorders or any condition of heightened awareness of sinus tachycardia (such as postural orthostatic tachycardia syndrome). In 1 study, the criteria for panic disorder were fulfilled in 67% of patients with SVT that remained unrecognized after their ini- tial evaluation. Physicians attributed symptoms of SVT to panic, anxiety, or stress in 54% of patients, with women more likely to be mislabeled with panic disorder than men.61 When AVNRT and AVRT are compared, symptoms appear to differ substantially. Patients with AVNRT more frequently describe symptoms of shirt flapping or neck pounding 54,62 that may be related to pulsatile reversed flow when the right atrium contracts against a closed tricuspid valve (cannon a-waves). During 1 invasive study of patients with AVNRT and AVRT, both arrhythmias decreased arterial pressure and increased left atrial pressure, but simulation of SVT mecha- nism by timing the pacing of the atria and ventricles showed significantly higher left atrial pressure in simulated AVNRT than in simulatedAVRT.62 Polyuria is particularly common with AVNRT and is related to higher right atrial pressures and ele- vated levels of atrial natriuretic protein in patients with AVNRT compared with patients who have AVRT or atrial flutter.63 Table 2. 