Potential clinical significance in the use of Lexiscan (regadenoson) in myocardial perfusion imaging (MPI) via treadmill in patients who do not reach their maximum predicted heart rate (MPHR)

Objectives To evaluate the potential clinical significance of Lexiscan for a modified treadmill MPI stress test protocol. In April 2008 the FDA approved Lexiscan, a new stress drug which causes maximum vasodilatation within 30 seconds once given as a bolus injection. MPI treadmill tests in patients who do not reach MPHR can be changed to the Lexiscan protocol immediately; validating their test.

Methods All MPI treadmill tests performed at Evanston Hospital from January to July 2008 were reviewed. Patients with heart rates <85% of the MPHR were considered to have invalid tests. Data was reviewed for these patients to determine if they were candidates for Lexiscan and if further testing was needed for diagnosis.

Results 43 of 216 (20%) MPI treadmill tests had a MPHR of <85%. Reasons for not reaching 85% MPHR include medications, and/or physical limitations: hypertension, dyspnea, leg pain, or inability to walk. Some patients were switched to adenosine per the Cardiologist’s discretion. 9 out of the 43 had asthma, 2^nd or 3^rd degree AV block, or atrial fibrillation (sinus node dysfunction) - contradictions to Lexiscan. 79% could have received Lexiscan during the treadmill study when it was determined that they would not meet the MPHR criteria.18 out of 43 patients (42%) went on to have subsequent cardiac testing within the year: Stress Echo, Echocardiogram, Treadmill stress test, and or Cardiac Catheterization.

Conclusions The data suggests a new protocol using Lexiscan could create a more efficient/effective diagnosis due to more accurate stress testing, better use of patient time, and timely results.