North American Veterinary Licensing Examination (NAVLE) Practice Test

In a middle-aged dog with a rapid and irregular heart rate, what condition is most likely?

1. Dilated cardiomyopathy

2. Mitral regurgitation

3. Wolf Parkinson White syndrome

4. Tricuspid insufficiency

The correct answer is: Dilated cardiomyopathy

In a middle-aged dog presenting with a rapid and irregular heart rate, dilated cardiomyopathy is the most likely condition due to its association with the development of atrial fibrillation. This condition leads to impaired contractility and dilation of the heart chambers, particularly the atria, which in turn can result in irregularities in the electrical conduction system of the heart. The rapid and irregular heart rate often observed is due to the presence of chaotic electrical activity originating from the atria as the condition progresses. Additionally, dilated cardiomyopathy is more prevalent in certain breeds, such as Doberman Pinschers and Boxers, and often occurs in middle-aged dogs. The heart's ability to maintain normal rhythm diminishes as the disease advances, making atrial fibrillation a common arrhythmia associated with this condition. Mitral regurgitation can lead to arrhythmia but typically presents with a different heart rate characteristic and is more often associated with a systolic murmur rather than the pronounced irregularity seen in atrial fibrillation. Wolf Parkinson White syndrome is a congenital arrhythmia condition that is less common and presents earlier in life, while tricuspid insufficiency may also contribute to heart rhythm problems but is less commonly associated with the rapid and