In praise of Norman J Holter (part II)

This image is part of the 24 hr Holter study of Millie, the Boxer dog I featured a couple
of days ago. Notice that the heart rate is irregular; it is a rhythm which many people (even vets) often find unsettling, but it is a normal rhythm in healthy dogs; this is sinus arrhythmia in which the heart rate is entrained by the breathing rate - the heart rate increases as the dog breathes in, and decreases as the dog breathes out. The variation in heart rate is due to varying impulses between the heart and the brain carried by the vagus nerve (the 10th cranial nerve).

This image also features 3 consecutive abnormal beats - on the last (bottom) line of the ECG - these are ventricular ectopic beats, of probable left ventricular origin, indicating the presence of myocardial disease.

Missie has a common condition of Boxer dogs, ARVC, or Arrhythmogenic Right Ventricular Cardiomyopathy; the disease is inherited, serious, treatable, but not curable. She has started drug therapy today. We hope she will live a long life, but she has a disease which is often fatal even with treatment.