Primary respiratory disease, such as chronic bronchitis, is also common in older small breed dogs. It is important to distinguish between the patient with clinically significant respiratory disease and incidental DMVD from the patient with clinically significant DMVD. Respiratory sinus arrhythmia, indicating vagal influence on heart rate and rhythm, is usually not present in severe cardiac disease. In contrast, sinus arrhythmia is usually preserved or accentuated when respiratory disease is the cause of clinical signs. | Primary respiratory disease, such as chronic bronchitis, is also common in older small breed dogs. It is important to distinguish between the patient with clinically significant respiratory disease and incidental DMVD from the patient with clinically significant DMVD. Respiratory sinus arrhythmia, indicating vagal influence on heart rate and rhythm, is usually not present in severe cardiac disease. In contrast, sinus arrhythmia is usually preserved or accentuated when respiratory disease is the cause of clinical signs. |