• 7 yr old, 28lb beagle mix presented for preanesthetic exam for a dermal mass removal on the forelimb and dental cleaning.  The heart rate ausculted at 250-300bpm.  
• Echocardiogram shows slightly increased left ventricular wall and left posterior wall at diastole and markedly increased at systole.  Fractional shortening was increased at 55%.  The left atrium measured at the high end of normal but subjectively appeared normal (see cardiac measurments below).  The dog was sedated with butorphanol at 2mg/kg IV to allow for Doppler studies (she was panting excessively during the exam).  Doppler studies showed no evidence of any valvular disease or insufficiencies.  During the intial exam her heart rate would speed up to 250bpm.  After butorphanol sedation it dropped down to 150bpm but could still be seen accelerating from time to time.
• Blood pressure measurements are pending.
• The dog behaves clinically normal at home.
• The dog’s cardiac measurments are as follows: LA=22,AO=16, LA/AO=1.3, MPA=12.7, MPA/AO=0.86, IVSd=11.7, LVIDd= 32.6,LVPWd=12.3, IVSs=20.4, LVIDs=14.8, LVPWs=16.4, FS=55%, HR=150-263 bpm (150 bpm post butorphanol administration)
• I am attaching a few pics from the EKG done by the veterinarian later that day.

I am wondering if this is sinus tachycardia (stress) or supraventricular tachycardia.  It seems a bit high for sinus tachycardia, yet, the dog is asymptomatic.  I guess the big question is whether or not it is ok to proceed with surgery on this dog.  I am also wondering what diseases this asymptomatic middle aged beagle could have that would cause this.