CARDIOMYOPATHY FAQ

 John D. Bonagura DVM, MS, DACVIM
Cardiology

QUESTION

Cali is a 7-year-old spayed female boxer recently diagnosed with boxer cardiomyopathy. She is clinically normal. Holter monitor/Spot ECG's reveal an intermittent arrhythmia. She is on 40 mg sotalol BID. Cali also has a history of multiple mast cell tumors. Recently a  Grade 2 tumor was removed under local anesthesia with clean (but thin) margins. The 0wners are adamant that re-excision be performed. Do you have suggestions for an anesthetic protocol that would be least irritating to the myocardium?

ANSWER

DEC 03, 2002 - VETPLACE VETERINARIANS - We forwarded your question to Dr. John Bonagura. This is his response:

While the presence of a grade I boxer cardiomyopathy (isolated PVC's; no runs leading to collapse or syncope) makes the dog a slightly higher anesthetic risk, we have certainly anesthetized dogs like this, provided the ECG can be monitored throughout the procedure. If the benefit of assuring clean margins is important to the clients and yourself (as a cardiologist, I'm not sure of the best approach to this concern, but it seems reasonable, especially if biopsy reports, palpation of the tissue, or FNA suggests residual tumor), I would consider a brief anesthesia with ECG monitoring throughout. There is no definite rule about the medication approach, but in our practice we would give the sotalol the evening before and perform the procedure the next AM (skipping the AM dose and later giving it when the dog is sufficiently recovered to swallow).

In terms of pre-medication, we have generally had good luck in cardiac patients giving butorphanol alone (0.4 to 0.5 mg/kg, IM) or butorphanol with acepromazine if there is no contraindication to ACP (butorphanol 0.25 to 0.3 mg/kg plus 0.01 mg/kg ACP, mixed, and given IM). The major concern with these premeds is potential slowing of heart rate (because some PVCs worsen with changes in HR since ectopy is often related to cardiac "cycle length" or prior R-R intervals); however, since atropine makes ventricular fibrillation MORE likely, I would not use this as a premed unless the heart rate is very low after induction of general anesthesia.

20 to 30 minutes after the premedication, the dog should be more sedate. The surgical site should be generally prepared at this time (clipping/initial dirty scrub) and an IV should be established. Packs should be prepared to minimize procedural time. ECG leads should be attached and the monitor evaluated. If the rhythm has not deteriorated, you can consider induction with a ketamine-valium or ketamine-midazolam mixture sufficient to allow intubation and general anesthesia with isoflurane in oxygen. This is generally well tolerated in cardiac patients. While propofol is very quick acting, it also depresses cardiac tissues, and after using it about 100 times in heart failure dogs and watching the depressive effects on blood pressure, I'm not much in favor of that drug in dogs with cardiac disease (though admittedly, others still like it).

If there are a number of PVCs evident after sedation, a trial dose of 2-3 mg/kg of lidocaine over 1 minute should be considered prior to inducing general anesthesia. Should runs of PVCs or frequent PVCs develop during general anesthesia, boluses of lidocaine 1-2 mg/kg, IV over 1 minute should be given or a lidocaine infusion (50 to 75 mcg/kg/min) started. Often PVCs will be more obvious initially but once a level plane of GA is established, the rhythm often stabilizes. Controlling pain and sympathetic activity may also reduce the number of PVCs perioperatively as SNS tone can modulate ectopy in this disease. Thus, the use of local anesthesia at the surgical site (for example lidocaine or bupivicaine soaked sponges; irrigation drain for instillation of local anesthesia; or at a minimum irrigation of the wound with local anesthetic) should be considered as well as systemic postoperative pain control, especially if the excision is extensive (opiates; +/- ketoprofen if you use that).

I would monitor the cardiac rhythm post op, and also consider having the dog back the day after for a routine ECG (some VTs are worse the day after GA, perhaps related to reduced coronary blood flow during the procedure?).

I hope these suggestions are helpful. - John Bonagura, DVM, DACIVM (Cardiology, Internal Medicine)