Your Canine Patient Collapsed: Is The Source Cardiac or Neurologic?

A common presentation to any veterinarian is the patient that has "collapsed." It is important to distinguish seizures due to a neurologic cause from cardiogenic syncope so that the appropriate additional diagnostic tests can be performed, or so that the pet can be referred to the appropriate specialist.

A thorough physical examination and a careful history are often starting points to help in this distinction. The history is vitally important. It may be difficult to distinguish a seizure from syncope. Episodes of collapse that are precipitated by exercise, stress, or defecation are more likely to be syncope. If the animal is disoriented and slow to return to consciousness, it is more likely a seizure.

Does the patient have a heart murmur? Are any arrhythmias ausculted? Are there any abnormalities on the neurological examination? What is the signalment?

Answers to the following history questions may be helpful in establishing causation:

• Has the event happened more than once that you have seen and, if so, how often?

• Is there any evidence that something like this might have happened previously that you did not see?

• What was the dog doing immediately before the event? Was the event precipitated by anything? (Exercise, excitement, urination, defecation are commonly seen before cardiogenic syncope. Dogs are often resting before a seizure.)

• How long did the event last? (A description of the episode may help. A prolonged recovery time is more suggestive of a seizure.)

• Did the inside of the mouth (gums) or the tongue look pale (white) or grey? (This suggests a lack of blood flow and is more consistent with cardiogenic issues.)

• Did it look or feel like the heart was beating forcefully through the chest wall? Was the heart rate very fast or very slow? Did you think the heart ever stopped?

• Were there any tonic (stiff) or clonic (shaking) motions of the whole body or parts of the body (e.g. face or jaw twitching)?

• Did the patient do anything before the event to make you think he/she knew something was about to happen (aura)? (Cardiogenic syncope develops quickly and without warning. Patients with seizures may have prodromal signs.)

• Did the patient appear to recover instantaneously or were there residual signs afterward? How long did they last? (Cardiogenic syncope lasts for seconds and there is a fast recovery. Seizures often last for seconds to minutes and the patient is often dazed for a prolonged period afterwards.)

• Did the patient seem to be conscious or unconscious? (Did the patient respond at all?)

• Was there a loss of bladder or bowel control? (Although I have witnessed this with cardiogenic syncope, it is more commonly associated with a seizure.)

• Did the patient have any abnormal eye movements? (This is very suggestive of a seizure.)

Common causes of cardiogenic syncope in dogs include:

• Mechanical or structural cardiac disease (outflow or inflow obstruction due to valve stenosis/dysplasia.)

• Pulmonary hypertension (often due to pulmonary venous hypertension from left sided heart disease or chronic pulmonary disease or heart worm disease.)

• Pericardial effusion

Patients in active heart failure (due to causes such as dilated cardiomyopathy or mitral valve endocardiosis) can appear weak and may appear to have syncope. Arrhythmias such as advanced atrioventricular block, ventricular tachycardias, sick sinus syndrome or very fast supraventricular tachycardias can result in syncope.

Neurocardiogenic syncope (also known as vasodepressor syncope) is an incompletely understood adrenergic-stimulated vagal reflex. One proposed mechanism is that in predisposed patients a sudden drop in preload results in stimulation of the ventricular mechanoreceptors. This mechanical activation results in neural traffic (falsely) mimicking hypertension, and leading to sympathetic withdrawal and parasympathetic activation. The result is a tachycardia in dogs followed by a bradycardia.

If you feel a case is due to a neurological cause, please refer to your local neurologist. If you feel it is due to a cardiac cause, please do not hesitate to contact one of our cardiologists at 480.635.1110 EXT.7.

Diagnostic tests considered in patients with syncope often include chest radiography, a Valley Fever titer in combination with a senior panel, echocardiography, a blood pressure measurement, and evaluation of the heart rhythm (either by an in-hospital ECG or a 24-hour ambulatory Holter monitor). Some patients may need to have the heart rhythm captured during a collapsing episode while wearing an event monitor or an implantable loop recorder.

We welcome your call at 480.635.1110 EXT.7 to learn more, make a referral,
or discuss a case for referral consideration.

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