DCM- To treat or not to treat?
Dr Nuala Summerfield and Dr Brigite Pedro
VVS Cardiologists and RCVS and European Specialists in Veterinary Cardiology
Case Study
A 7 year old male Dobermann, Odin, presents for an annual vaccination and health check. He’s up to date on relevant vaccinations, receives a reputable worming and flea treatment, and he is on a good quality commercial diet. His owners have no concerns – as far as they’re aware, he is perfectly healthy.
Based on his signalment, what cardiac condition do you feel he might be at particular risk of? Are there any targeted questions you might like to ask his owners to get a better idea of his current health status? Or any other investigations you might urge them to consider?
Think about it, and then click to see the VVS Cardiologist’s thoughts!
As you’re probably all aware, Dobermanns have an unusually high risk of developing dilated cardiomyopathy, DCM. In fact, in Europe the prevalence is approximately 50%!
The following questions may bring to light subtle signs of preclinical DCM or other important diseases that the owner was not aware of:
1. Have there been any episodes of fainting or weakness?
Syncopal episodes are not uncommon with DCM, although they tend to be more frequent in the more advanced cases.
These episodes are usually associated with ventricular arrhythmias. In fact, DCM in Dobermanns is characterized not only by a dilated heart with reduced systolic function, but it also has an arrhythmogenic component. Having more than 300 ventricular premature contractions (VPCs) in 24 hours is considered diagnostic for DCM in the breed. Atrial fibrillation is another common arrhythmia, which can also lead to syncopal events. This is usually seen in more advanced cases where the left atrium is significantly dilated.
The presence of even one suspected syncopal episode in an at-risk breed of this age should be a red flag for urgent investigations.
Luckily, Odin did not have any history of collapsing episodes or even weakness.
2. Are there any changes in his ability to exercise?
Exercise intolerance can be an early sign of systolic dysfunction or beginning of CHF.
In this case, his owners report that Odin may be slowing down a little on walks but they just assumed it was because he was getting older.
3. Has he lost any weight?
Always be aware of cardiac cachexia!
This tends to be more frequent in more advanced and chronic cases.
Odin’s weight and appetite have been stable.
4. Is his breathing normal?
Resting breathing rates counted by the owner are one of the most sensitive ways to help detect the first onset or recurrence of CHF. Early detection of CHF can limit the emotional and financial impact of any episodes of decompensation. Measuring the resting respiratory rate at home will also empower the owners to be more involved, which is something that the vast majority appreciates. Owners can be instructed how, when, how often and why to count the breathing rates. Breathing rates at home are typically considered increased and thus abnormal if > 30 rpm (when sleeping).
Typically, in dogs with preclinical DCM (no clinical signs of CHF) owners should be instructed to count the respiratory rate at least 1-2 times/week. With clinical DCM (when CHF has already developed) owners should count the respiratory rate on a daily basis.
Odin’s physical exam:
Your physical exam of Odin revealed nothing outside of normal limits – except for the detection of a grade 2/6 left apical systolic murmur. The heart rate was 100 bpm. The respiratory rate was 28 rpm in the clinic. The body weight was 39kg (BCS 5/9).
During the physical examination, emphasis should be on identification of subtle clues that could be consistent with preclinical DCM such as: a soft systolic heart murmur, a gallop heart sound, an arrhythmia that is not thought to be sinus in origin, the presence of an inappropriately fast heart rate, weak femoral pulses, pulse deficits and tachypnoea.
Recommendations to the clients:
Because of the known breed risk for DCM in Dobermanns over the age of 3, recommendation of an annual echocardiography and Holter monitor are appropriate.
Identification of any clues, like the heart murmur found in Odin, further increases the suspicion that he has preclinical disease. Ideally you would perform an echocardiography and Holter monitor, but if owners are reluctant to undertake these diagnostics then other options include: thoracic radiographs, a 5 min ECG and NT-proBNP testing. These simple diagnostics may be used to help ascertain the likelihood of preclinical DCM, which may then help encouraging the owners to agree to an echocardiography and Holter monitor (these are in fact the gold standard tests to investigate DCM in Dobermans).
Odin’s echo results:
Findings: Dilation of the left ventricle in systole and diastole with obvious evidence of systolic dysfunction. There was left atrial dilatation and mild mitral regurgitation. The mitral valve leaflet morphology was normal.
Echocardiographic diagnosis: preclinical DCM.
This is where VVS can really help you to help your patients! Although Odin’s echo findings were relatively obvious, many preclinical DCM patients have only very subtle structural changes. Access to a cardiac specialist for live-guided cardiac workup will help you identifying subtle changes which will be useful in recognizing early stages of the disease and will allow start treatment as soon as possible.
Why is the diagnosis of preclinical DCM important?
The results of the PROTECT study (2012), proved that treatment with pimobendan prolongs symptom-free survival and overall survival in Dobermanns with preclinical DCM, characterized by echocardiographic evidence of left ventricular dilation and systolic dysfunction with or without concurrent ventricular arrhythmias. This was the first time in veterinary cardiology that we knew treatment of the preclinical phase of a disease would change the clinical outcome. This knowledge emphasizes the importance of increased vigilance during routine evaluations of at-risk dogs and planned screening. Early detection of the disease can have a huge impact on survival.
Additional diagnostic tests:
Other diagnostic tests are indicated once the diagnosis of preclinical DCM has been made based on an echocardiography. These adjunctive tests help identify and quantify the severity of concurrent arrhythmias, tailor therapy and offer prognostic insight. Although it is optimal to have the results of all the recommended adjunctive diagnostic tests, they are not all required in order to initiate treatment.
The additional diagnostic tests following echo are:
- ECG to check for any arrhythmias suspected based on physical exam.
If none are suspected and an echocardiographic diagnosis of preclinical DCM has been made, it will be more cost effective to proceed straight to the Holter. If there are significant ventricular arrhythmias present on an ECG then treatment with sotalol can be initiated and a Holter can be delayed i.e. used at a later time to assess response to treatment and guide adjustments.
- Holter to assess the presence and severity of arrhythmias (particularly ventricular arrhythmias).
- Routine blood chemistry to access baseline renal and liver function. Complete blood count +/- urinalysis and systemic blood pressure are indicated as part of a complete database for future reference
- Chest radiographs to be certain there is no early evidence of CHF (pulmonary oedema).
In addition, baseline chest rads can be used for comparison in future to help establish a diagnosis of CHF if/when the dog develops suggestive clinical signs.
Odin’s’s other test results:
Holter findings showed sinus rhythm with 500 VPCs. All VPCs occur as single beats and there are no VPC pairs, VPC triplets or runs of ventricular tachycardia recorded during the Holter monitoring.
These findings are consistent with an arrhythmogenic form of preclinical DCM.
His bloods were within normal limits. His blood pressure was 115 mmHg. No radiographs were performed at this stage.
Diagnosis: Preclinical DCM
Treatment and plan for Odin:
Odin was immediately started on pimobendan.
In Odin’s case, due to lack of arrhythmogenic complexity (no runs of ventricular tachycardia or VPC pairs or VPC triplets) and no history of syncope, treatment of the ventricular arrhythmias was not recommended.
His owners were directed to monitor him for any signs of heart failure (increased resting respiratory rate) or arrhythmias (episodes of weakness or collapse).
Ongoing care:
As long as Odin is doing well at home and the owners are monitoring the respiratory rate closely, a re-check can be booked once every 4-6 months.
These planned rechecks should always emphasise identification of any evidence of CHF and or the development or worsening of arrhythmias. Diagnostic tests such as routine blood chemistry, blood pressure, a Holter monitor and chest radiographs can be considered. Recheck echocardiography is sometimes indicated and can help assess response to pimobendan and identify any signs of disease progression. However these are not required to continue treatment.
A little bit more about DCM:
DCM is the most common form of canine cardiomyopathy and the leading cause of heart failure in mature dogs weighing more than 20kg.
Traditionally, emphasis on diagnosis and treatment has been focused on the symptomatic clinical phase of the disease. However, the clinical phase is merely the ‘tip of the iceberg’ and survival despite optimum treatment in this phase is relatively short.
The PROTECT study proved that the administration of pimobendan to Dobermanns with preclinical or asymptomatic phase of DCM prolongs the time to the onset of clinical signs and extends survival.
It is therefore important to identify the disease while still in the preclinical phase.
The PROTECT study results provide excellent scientific rationale for the use of pimobendan in any Dobermann with an echocardiographic diagnosis of preclinical DCM. Thus, extension of the PROTECT results to other breeds with preclinical DCM should always be considered.
Screening of at high-risk breeds is without any doubts recommended.
Take home message:
- DCM has a poor long-term prognosis once clinical signs of heart failure develop (clinical DCM).
- The use of pimobendan in asymptomatic dogs with DCM (preclinical DCM) will prolong the time to the onset of clinical signs and extend survival.
- Screening dogs at high risk for DCM is essential to identify the disease, start appropriate treatment and monitor these patients over time.
- The clinical findings in dogs with preclinical DCM can be subtle, such as a soft murmur, occasional irregularity of the heart rhythm, a gallop sound or just an increased resting heart rate.
- Although any large of giant breed can get DCM, it is important to know which breeds are particularly at risk of DCM eg. Dobermann, Boxer, Great Dane, Irish Wolfhound.
Cardiology cases can feel overwhelming to deal with in general practice, but VVS’ friendly world-class cardiologists are on hand to support you and to enable you to bring outstanding clinical care to your patients and reassurance to their owners. Bring the specialist to you and your patient with the help of the VVS service. Get in touch to speak to us further about trying this unique service in your practice!
References:
Summerfield NJ, Boswood A, O’Grady MR, Gordon SG, Dukes-McEwan J, Oyama MA, Smith S, Patteson M, French AT, Culshaw GJ, Braz-Ruivo L, Estrada A, O’Sullivan ML, Loureiro J, Willis R, Watson P. Efficacy of pimobendan in the prevention of congestive PROTECT Study). J Vet Intern Med. 2012 Nov-Dec;26(6):1337-49.