AROUND 10% of dogs presenting to primary care veterinary surgeons (PCVs) have canine chronic valvular heart disease (CVHD) and this accounts for 75% of canine heart disease. Diagnosis and treatment of these cases is, therefore, an important matter for vets and one in which there has been recent progress with important clinical research studies and a better understanding of the disease which has advanced our knowledge in recent years. The consensus guidelines are aimed at helping PCVs in what can be a difficult area, updating them on these recent developments. However, there remain a number of areas in which our knowledge is very far from complete. Like the underlying cause of the disease, the factors that determine the progression of the lesions remain unknown, although age, left atrial size and heart rate have been shown to predict outcomes. With respect to treatment, significant controversy remains. A panel was invited by the American College of Veterinary Internal Medicine (ACVIM) to set some guidelines, with a majority of panellists from the USA. The findings were based on evidencebased medicine (EBM) whenever possible. There remain some significant areas in which there is inadequate or contradictory EBM for the panel and in these instances the panel offers interpretative comments, based on other published experimental or anecdotal evidence, clinical experience and expert opinion. This inevitably results in a range of views, some of which may be influenced by different experiences and which, in my opinion, may be influenced by variable drug licensing in different countries. Some regional bias is almost inevitable and is no criticism of the panel or its members, who are acknowledged leaders in the field. The panel recognised that there was considerable variation in the quality of the evidence, but they made no attempt to assign a scientific grade or value to the citations.
Meta-analysis of opinion
The consensus therefore represents a “meta-analysis of opinion” from acknowledged experts, in addition to interpretation of existing data. Where there is disagreement, it is important for vets to know what options different specialists use even if there is no proof as yet that that is a definitive method for diagnosis or especially treatment. In these days where evidence-based medicine (EMB) is king, we like to base our treatment regimens on these data; however, some individual patients can be difficult to fit into specific groups which reflect the (often strict inclusion criteria of the) clinical study, and furthermore each individual case is a little different.
What may work for the majority does not always work for each individual, so vets should start treatment based on the guidelines but should not feel inhibited from tailoring their treatment in individual cases. Nevertheless, general guidelines are useful and are particularly useful for the general practitioner. This article summarises the key issues in the statement. The statement starts by highlighting some of the pathological changes in the disease, which leads to a wide range of gross structural, cellular, matrix and
endothelial changes are well as neurohormonal, inflammatory and other systemic effects. In due course, progressive valvular regurgitation increases cardiac work, leading to ventricular remodelling (eccentric hypertrophy and
intercellular matrix changes), and ventricular dysfunction. We have a great deal further to go before we understand many more of these processes.
In the past few years, however, we have come to understand that many animals with congestive heart failure (CHF) due to CVHD have myocardial
failure and that some also have pulmonary hypertension. This knowledge has put a different light on treatment and changed the consensus for treatment from previously (ISAHC, 1994).
Guidelines for the diagnosis of canine chronic valvular heart disease
The committee clarified the classification of the stages of heart disease and this is summarised in Table 1. This system is an adaptation of the NYHA association human heart failure classification and ISAHC canine system, and attempts to make the classification more objective than the subjective criteria of these previous functional systems. No group system is perfect for a condition which represents a continuum of a range of severity, in animals which are presented at different time points along the course of their disease. However, part treatment is not possible, the PCV has to make a decision, so some form of criteria has to be established which demarcates when treatment should be started or changed. The system is in part based on the human cardiology ACC/AHA consensus statements and also on some
cancer treatment classifications which attempt to identify at-risk groups, those in which intervention might reduce the risk of disease development, identifying asymptomatic disease early in the course of its development, medical, interventional or surgical management of symptomatic patients and palliative management of advanced and refractory patients. Within the groups described by the panel, there remains one group in particular in which the range of severity of the condition is marked. Group B2 covers asymptomatic dogs with mild left atrial enlargement and those with dramatic volume overload in which clinical signs have been inapparent. This presents a problem when interpreting the results of most papers. Existing papers do not clearly distinguish between the outcome in cases with mild versus severe left atrial enlargement in the absence of clinical signs; most studies only enrol dogs in which clinical signs are reported. It is therefore not surprising that opinion on the treatment of these cases differs from clinician to clinician. The panel recommended a series of tests for assessment of all patients. It does not attempt to rank these or to make any judgement as to their value if finances preclude all tests being performed. The list is in some cases long and the lack of distinction between the relative values of each test will frustrate some PCVs who do not have the luxury of completing a complete panel. Of course this does not mean that all the tests are not valuable. In many ways, the biggest issue regarding the test may come in distinguishing cases within B2, when left atrial size is often the key judgement. Whether this is best assessed with radiography or ultrasound may depend on the facilities available to the vet, clinical skills with the different tests, and the patient. In some breeds increased left atrial size is more difficult to judge from radiography, although radiography is key to assessing the onset of congestive heart failure. Clinicians will have to judge which techniques they feel best able to utilise. Clinicians also need to be aware of needing other tests to identify complicating factors due to concomitant disease, which is not uncommon in CVHD patients. The use of tests in stages C and D is less prescriptive because multiple different issues arise and some tests may need to be repeated in managing these more complex cases.
Guidelines for the treatment of canine chronic valvular heart
disease
Drugs can potentially prevent development of disease, slow progression of disease, alleviate clinical signs of disease and prolong the period to death. In fact, the drugs that are used in current clinical practice usually fall into the latter two categories. This is despite a hope that medication might slow the progression of the disease process itself. There are theoretical reasons for action of ACE inhibitors and spironolactone in this respect, but evidence is lacking. There is great scope for new treatment molecules that may slow the
progression of the pathological process, but until our understanding of the process improves, this remains a hope. When considering the decision to recommend a drug, the panel did consider the potential disadvantages of use as well as potential benefits. The panel makes no distinction between different ACE inhibitors, largely referring to enalapril (much more widely used than other ACEi in the US) but the same principles apply to other ACEis.
Salient points of lack of unanimity:
There are many areas in which the panel reached unanimous agreement: for
example, the use of furosemide, pimobendan and ACEi in chronic symptomatic cases (Stage C – chronic) – see Table 3. However, it is where the
panellists disagree that the most interesting points arise. The principle area of controversy remains patients in stage B2. Inevitably, the long-standing controversy in this group has led to competition between drug companies to capture this market. This is in part because there is a wide range of severity of disease within this category, also because EBM is limited, lacking or potentially contradictory, and because there is a lack of agreement on how much a theoretical indication for a drug translates into a clinically significant benefit for the patient. With respect to the advice to use ACEi in dogs with “clinically relevant” left atrial enlargement, no figures for what constitutes clinically relevant are given. Furthermore, there are other drugs, principally beta-blockers, spironolactone and pimobendan that could be useful in those dogs within the group with disease of sufficient severity, but evidence is lacking. Ongoing trials may clarify the situation (we shall need another ACVIM consensus statement in a few years’ time). The panel was divided on the use of beta-blockers, with a minority in favour. Readers should also consider that the risks of use may be greater with some drugs which require considerable experience to titrate to each patient and that beta-blockers may currently be one of these drugs that can be difficult to use, even when the results of an ongoing trial may substantiate or refute
their use in MVD patients. Other drugs which can be difficult to use are also
listed. While the guidelines are useful to help PCVs, they do not highlight the
hazards of use and I would suggest that those without experience in the use of acute action vasodilators such as hydralazine, amplodipine and sodium nitroprusside, intravenous positive inotropes such as dobutamine, multiple
high-dose diuretics, in addition to betablockers, should be cautious. Practical issues which are always part of the decision-making process for a
PCV are costs and owner compliance. The panel did not make any comment as to which drugs should be prioritised should finances preclude the use of multiple drugs. In addition, there are cases in which the introduction of different drugs requires owner management, since compliance and the practicalities of drug administration are factors that need to be considered in addition to the ideal treatment. However, I always say to referring vets that knowing what the ideal treatment would be is the starting point before deciding which if not all are practicable. A thorough explanation of the rationale behind different drugs may help promote owner compliance; too often owners are presented with boxes of different drugs and at best a sheet of when to give them. If the use of the drugs is fully explained, compliance may be better. The consensus does not attempt to draw a line at which further treatment is futile and euthanasia should be recommended. While this is inevitable because euthanasia also requires an owner’s perspective of quality of life, it does give the impression that all cases should receive all possible treatment. Primary care veterinarians know full well that not only will this not be what some owners want, but that a decision on euthanasia can be an essential part of humane veterinary treatment.
Summary
The ACVIM Guidelines for the Diagnosis and Treatment of Canine Chronic Valvular Heart Disease represent a very useful guide for PCVs and one that it would be useful for all to read. Inevitably, they represent a base-line that needs adaptation in each case and full use of the advice will be limited by facilities, finances, owner compliance and attitude and veterinary experience.
