Collapse in a Dog

Mike Stafford Johnson MVB CertSAM MACVS DVC MRCVS

Mike qualified in 1982 in UCD (Dublin). After many years of mixed practice, mostly in Australia, New Zealand and Canada, Mike settled into small animal practice for 6 years in Manchester before joining the Veterinary Cardiorespiratory Centre in 2001. He completed the Cardiology Diploma examinations in 2004. Together with Mike Martin they have published various articles relating to cardiology and respiratory diseases

This Case Study investigates a 6 year old male Rottweiler with a history of collapsing at exercise. A range of diagnostic tests are used to arrive at the diagnosis.

Case History

A 6 year old male entire Rottweiler presented with a history of collapsing over the previous 8 weeks. Three episodes had occurred in total: 8,6 and 3 weeks prior to referral. All occurred when walking in the park. He was reported to have slowed down somewhat on his walks for several months. Coughing was absent. He was still eating and drinking normally. He had suffered very intermittent diarrhoea for several years but this was infrequent and did not appear to be associated with collapse. No other prior disease had ever been noted.

What is missing from this history? What information is particularly needed at this stage?
- Travel history
- Description of the collapses
- Worm dosing history particularly with regards to lungworm.
- Current medications.
Feedback: All four points should be covered with the client. However, the most important point relates to a detailed discussion surrounding the collapses, so the correct answer is (B) Description of the collapses.

The behaviour shown prior to and during each collapse is of great significance as this can help in differentiating neurological from cardiovascular collapses. Each collapse should be discussed individually.

For example, did excitement or coughing precede collapses, or did these occur at rest? What were the initial signs that a collapse was imminent? What signs were noted during collapse and what was the mucosal colour? What was the duration of collapse? What signs were noted on recovery?
This dog showed no initial signs prior to collapsing. On each occasion he was walking or trotting in the park without being excited. No coughing or other abnormal respiratory signs preceded the events.

On the first occasion, he fell into lateral recumbency. He appeared limp/ flaccid and lay still for 10 minutes. His respiration was shallow. The owners did not note his mucosal colour and were unsure if he was conscious or not. He then began panting but was not dyspnoeic. After 10 minutes he looked around but lay for a further 10 minutes before rising. He seemed slow in his walk with some hind leg weakness for a further 30 minutes but then recovered fully.

On the second occasion he showed brief wobbliness of all 4 legs before collapsing into lateral recumbency. Urination occurred while collapsed. Again he appeared flaccid. He recovered over 5 minutes.

On the final occasion, he showed weakness of his limbs before lying in sternal recumbency where he lay quietly for 30 minutes. He was not unconscious. He then stood up and appeared normal.

What category of collapse seems more likely?
- Metabolic
- Neurological
- Cardiovascular
Feedback: There can be some overlap between all 3 categories of collapse in terms of clinical signs on some occasions. Answer (C) seems the most likely based on the history and presenting signs. Note that urination frequently accompanies cardiovascular related syncope.

The following factors favour a cardiovascular origin rather than a neurological event:
- All events occurred at exercise although this was not severe exertion. Neurological events tend to occur more frequently when relaxed.
- Lack of pre and post ictal signs plus lack of any tonic clonic activity.
Neuromuscular disease such as myasthenia gravis or metabolic collapse (eg anaemia, hypoglycemia, hypoadrenocorticism etc) seem less likely given the sporadic nature of the events. They are not ruled out however at this stage.
Physical Examination

No abnormalities were apparent. The dog was in good body condition and was bright and alert. Mucosae were pink, pulse amplitude normal and heart rate 130/ minute with no evidence of arrhythmias. Respiratory sounds were normal.

Doppler derived systolic blood pressure was normal at 120-140 mmHG.

A full blood profile was unremarkable.

See the above ECG trace. What does this show? Is the cause of collapse apparent at this time?
- Normal sinus rhythm
- Atrial fibrillation
- Ventricular rhythm
- Supraventricular premature beats
Feedback: (A) Normal sinus rhythm. There is a regular rhythm with a P wave for every QRS complex present. None of the beats are premature. The QRS complexes appear of normal conformation.
There is normal sinus rhythm at a rate of 130/minute. Complexes appear normal. No ectopics are present.

What is advised next?
1. Repeat ECG
2. Echocardiography
3. Thoracic radiographs
4. Holter monitoring
- 1 and 2
- 3 and 4
- 2 and 4
- 1 and 3
Feedback: C) Echocardiography is necessary to assess for the presence of structural heart disease. Holter monitoring is useufl in many collapsing dogs where a cardiac cause is suspected, to screen for intermittent arrhythmias which are often not evident on a resting ECG.
A repeat resting ECG is unlikely to detect ectopics if none were present on auscultation or on the initial ECG trace.
Thoracic radiographs are not a priority in the absence of coughing or dyspnoea.
A cardiovascular collapse is still suspected as the normal blood profile means that a metabolic collapse is less likely. Further ECG assessment and echocardiography were next undertaken.

A normal ECG does not rule out collapse due to intermittent arrhythmia. To detect such an arrhythmia would require either prolonged ECG monitoring in the clinic or Holter monitoring. Prolonged in clinic monitoring is time consuming and does not provide the same information as a Holter. The Holter may record over several days if necessary.

A Holter recoding was made. While wearing the Holter there were 2 episodes of weakness but not collapse. What does the Holter recording show?
- Normal sinus rhythm
- Atrial fibrillation
- Sinus rhythm with supraventricular premature beats and supraventricular tachycardia.
- Sinus rhythm with ventricular premature beats and ventricular tachycardia.
Feedback: Answer D) is correct. There is a run of rapid ventricular tachycardia at a rate of 250 beats per minute followed by normal sinus rhythm. This in turn is followed by ventricular premature beats, VPCs, in singles and one couplet. The VPCs averaged 300/ hour. The timing of the 2 episodic weakness events described by the owner corresponded with runs of ventricular tachycardia.
Laboratory Results / Diagnostic Imaging

Echocardiography was performed. Although there are no measurements provided and only selected views are available, what is your opinion of what you see on these images?

right parasternal long axis 4 chamber view

right parasternal long axis 5 chamber view

right parasternal short axis view, at chordae tendinae level

short axis view of the left atrium/ aorta

left parasternal caudal (apical) view
- Enlarged left atrium
- Enlarged left atrium and left ventricle
- Normal heart
- Other abnormality
Feedback: Answer C) is correct. There were no signs of abnormality on a standard echocardiographic examination.

No abnormalities were noted on abdominal ultrasound examination.
At this stage serum troponin was performed. This was normal at 0.12 ng/ ml (normal values less than 0.15 ng/ ml). Troponin is measured to screen for myocarditis which can lead to arrhythmias. Troponin is often significantly elevated in dogs with active myocarditis.

What is the likely diagnosis:
- Mitral valve disease
- Dilated cardiomyopathy
- Non cardiac disease leading to arrhythmias
- Cardiac neoplasia
Feedback: Answer B) is correct. Some breeds which develop dilated cardiomyopathy can present with arrhythmias alone in the absence of structural heart disease on echocardiography. In time however structural changes invariably develop.

Breeds known to develop severe or life threatening arrhythmias, often ventricular arrhythmias, include the boxer and dobermann breeds classically. However rottweilers and weimaraners (and occasionally other large breeds at times) may also present in this way.

Some affected dogs can show sudden death without any other signs developing. Others may show intermittent collapse/ syncope due to the onset of episodic ventricular tachycardia. Collapse or syncope may be prolonged because the ventricular tachycardia may persist for minutes to hours on some occasions. Ventricular tachycardia can revert to normal sinus rhythm with recovery or to ventricular fibrillation and sudden death.
Treatment

What therapy or treatment might be tried in this case?
- Pimobendan, ACEI.
- ACEI and furosemide.
- Digoxin
- Sotalol
Feedback: Answer D) is correct. In this case sotalol was used at 2.5 mg/ kg twice daily. Sotalol is used in dogs with symptomatic or severe supraventricular or ventricular arrhythmias. It can reduce myocardial systolic function so should be used cautiously in dogs with pre existing poor systolic function, for example dogs with a very low fractional shortening. In this case, such a consideration was not relevant.
Outcome

A Holter recording was repeated after 2 weeks of treatment. There was a marked reduction in ectopics (VPCs), which averaged 85/ hour. Several short runs of ventricular tachycardia were documented but these were much less frequent than previously.

It was decided to increase the sotalol to 3 mg/ kg twice daily.

After 2 weeks, a third Holter recording showed VPCs at less 50/ hour with only rare salvos of ventricular tachycardia. These persisted for up to 5 consecutive beats.

Repeat examinations and Holters were scheduled every 3 months.

What is the likely outcome?
- No clinical signs if the sotalol is maintained
- Progression to classical signs of DCM with weakness, exercise intolerance, tachypnoea, coughing or ascites.
- Sudden death
- Development of atrial fibrillation over time.
Feedback: Answer C) is by far the most likely possibility. Answer B) is possible if the dog’s survival is sufficiently prolonged. In this case, sudden death occurred 6 months after diagnosis. There were no premonitory signs.

Anti arrhythmic drugs frequently reduce the numbers of ectopics but although they may delay the time to sudden death, they do not prevent such an outcome. Therefore the prognosis in dogs with suspected DCM which collapse due to severe ventricular arrhythmias is always guarded. Dobermanns are particularly likely to suffer this outcome.