Ventricular tachycardia (VT) is a potentially life-threatening arrhythmia that can result in sudden death. VT can occur in patients with primary cardiac disease such as arrhythmogenic right ventricular cardiomyopathy (common in boxers) or dilated cardiomyopathy (common in Doberman pinschers). Ventricular arrhythmias can also be hereditary and can occur in patients with a structurally normal heart.
The ECG characteristics of VT include wide and bizarre QRS complexes without any associated P waves in addition to tachycardia (heart rate, >180 bpm; Figure 3A).
Although no treatment has been proven to prevent sudden death in patients with VT, antiarrhythmic therapy is used especially if the patient is a breed predisposed to sudden death, the patient is symptomatic, and/or malignant characteristics are present on VT (eg, rapid heart rate [>180 bpm]) or R-on-T or polymorphic QRS complexes are present (Figure 3B). The most common medications used for ventricular arrhythmias include IV lidocaine (acutely administered), sotalol, and PO mexiletine. Sotalol and mexiletine can be compounded into a liquid formulation for titration of doses, if necessary. In cases of significant systolic dysfunction, mexiletine can be used at 4 to 8 mg/kg PO q8h. This same dose can be added to sotalol when ventricular arrhythmias persist despite administration of maximal doses of sotalol. Other medication combinations (amiodarone, flecainide, propafenone, procainamide) may be needed for patients that are refractory to conventional therapy. Implantable defibrillators are occasionally required to treat high-risk patients.
An accelerated idioventricular rhythm should not be confused with VT. Accelerated idioventricular rhythm can also be referred to as slow VT because of the similar appearance on ECG, but the heart rate is generally less than 180 bpm (Figure 3C). Accelerated idioventricular rhythms are often seen in patients with systemic disease (eg, gastric dilatationvolvulus, pancreatitis, hemangiosarcoma, immune-mediated hemolytic anemia) rather than primary cardiac disease. Antiarrhythmic therapy is often unnecessary, as this type of arrhythmia is not typically hemodynamically compromising and is often self-limiting with treatment of the primary disease.