Case 15 — Comparison Case 2

ECG from Tilly, a 6-year-old German shorthaired pointer. Lead II at 25 mm/sec showing sinus beats alternating with bursts of supraventricular tachycardia at approximately 200 bpm.
Baseline ECG from Tilly, a 6-year-old German shorthaired pointer (40 kg). Sinus beats alternate with SVT bursts at ~200 bpm.

Tilly was presented for a swollen mammary gland and cough. An arrhythmia was auscultated. Radiographs showed right heart enlargement typical of heartworm disease (antigen positive). She was treated with thiacetarsemide but treatment was inappropriately discontinued after one dose when ALT increased. Two months later at the VMTH for ovariohysterectomy, the arrhythmia persisted.

Three ECG traces showing diltiazem titration. Top (9 AM after 90 mg): persistent SVT. Middle (10 AM): improving. Bottom (2 PM after additional 30 mg): sinus rhythm with only one premature complex.
Diltiazem titration. Top: persistent SVT. Middle: improving. Bottom: sinus rhythm restored (one premature complex).

Diltiazem was titrated to 120 mg (3 mg/kg) q8h, which maintained sinus rhythm. Surgery was successful. Surprisingly, her heartworm antigen test was now negative and radiographs had improved, so adulticide retreatment was deferred.

At suture removal, the owner had decided not to continue diltiazem unless clinical signs appeared. The arrhythmia was still present at one and three years later, but she had no structural heart disease on echocardiogram at the three-year exam. The owner probably made the right decision.

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