Sinus tachycardia (ST) is clinically described as a sinus rhythm (heartbeat) with impulses that arise at a faster-than-normal rate: greater than 160 beats per minute (bpm) in standard sized dogs, 140 bpm in giant breeds, 180 bpm in toy breeds, and 220 bpm in puppies. Changes in heart rate usually involve a reciprocal action of the parasympathetic and sympathetic divisions of the autonomic nervous system.
Severe tachycardia can compromise cardiac output, as too rapid rates shorten the diastolic filling time, the point in which the chambers of the heart dilate and fill with blood - which occurs in the space between heart beats. Particularly in diseased hearts, the increased heart rate can fail to compensate for decreased volume, resulting in decreased cardiac output, decreased coronary blood flow and a concurrent increase in oxygen demands. This is the most common benign arrhythmia in dogs. It is also the most common rhythm disturbance in postoperative patients.
Because there are so many things that can cause this condition, it is difficult to diagnose and differentiate from other similar diseases. Your veterinarian will most likely use differential diagnosis. This process is guided by a deeper inspection of the apparent outward symptoms, ruling out each of the more common causes until the correct disorder is settled upon and can be treated appropriately.
Your veterinarian will perform a thorough physical exam on your dog, taking into account the background history of symptoms that you have provided and possible incidents that might have led to this condition. A complete blood profile will be conducted, including a chemical blood profile, a complete blood count, and a urinalysis,which may show infections of the blood or disorders of the organs (e.g., heart, kidneys).
Your doctor may also order chest X-rays to look for possible evidence of primary cardiac disease or tumors. An electrocardiogram (ECG, or EKG) is essential for evaluating the electrical currents in the heart muscles, and may reveal any abnormalities in cardiac electrical conduction (which underlies the heart’s ability to contract/beat), and may show structural cardiac diseases that are affecting the heart. Ultrasound and angiography are also very useful for evaluating adrenal masses. Your doctor may also conduct a thyroid scan to evaluate your dog for hyperthyroidism.
Your veterinarian will develop a treatment plan for your dog once a diagnosis has been confirmed. If there is an underlying cause, that will be the primary focus of treatment.
The care of your dog following diagnosis will depend on the specific disease that is found to be causing the sinus tachycardia. Restricting your dog's activity so that its heart rate does not increase excessively may be called for, but only if your dog is being adversely affected by the increased heart rate.
A medical condition; the contamination of a living thing by a harmful type of bacteria
A cavity within a bone; may also indicate a flow or channel
An in-depth examination of the properties of urine; used to determine the presence or absence of illness
Less oxygen than normal in the blood
A medical condition in which the patient has an abnormally fast heartbeat
To make something wider
The part of the nervous system that contains the nerves that control involuntary movement.
Not being able to cause harm; the opposite of malignant.
The amount of pressure applied by the blood on the arteries.
A condition of the blood in which normal red blood cell counts or hemoglobin are lacking.
A record of the activity of the myocardium