p uppy murmurs: when to worry and what can be done

Blood flow through the heart should be smooth and laminar. turbulent blood occurs with faster rates of flow and describes a chaotic and disorganised flow pathway with formation of eddy currents. When turbulent blood flow is present in the heart, it can be auscultated as a murmur, and this may or may not be associated with underlying heart disease (Spalla 2019). Determining the clinical importance of a murmur can often be the most challenging step in a diagnostic investigation as incidentally detected heart murmurs found during puppy general wellness exams may or may not require further examination (Côté et al. 2015). t he prevalence of congenital cardiac anomalies is low. However misdiagnosing or missing a pathological murmur could prove detrimental for the individual puppy as these may be associated with increased morbidity and mortality and some conditions can be treated and cured if detected early (Côté et al. 2015). t his is why distinguishing between a pathological murmur (from a cardiovascular lesion) and a non-pathological murmur (associated with a structurally normal heart) is important (Côté et al. 2015).

Characteristics of the murmur can help you differentiate between a pathological and non-pathological murmur, including the timing in the cardiac cycle (systolic, diastolic or continuous), point of maximal intensity (left or right sided, apical or basilar), and murmur grade (outlined below). In addition to auscultatory features, the patient’s signalment and physical exam findings can aid in differential diagnoses and formulating an initial case management plan (Côté et al. 2015).

Although there are many ways to grade cardiac murmurs, the most common methods are summarised below using a 6-point scale (Rishniw 2018): l Grade I: A soft murmur that is nearly imperceptible, focal and is not immediately apparent. Both heart sounds (lubdub) are louder than the murmur. l Grade II: A soft murmur that is focal, can be detected immediately and both heart sounds are louder than the murmur. l Grade III: A moderate intensity murmur with heart sounds that are easily heard and are equal to the murmur intensity. typically regional but does not radiate into the lung fields. l Grade IV: A loud murmur that is louder than normal heart sounds and radiates widely into the lung fields. t his means

Contact: you can still hear the murmur while listening to the lungs. No palpable thrill (the ability to feel the murmur with your hands) on the chest wall. l Grade V: A very loud murmur with a palpable precordial thrill. l Grade VI: A very loud murmur that is audible with the stethoscope lifted 1-inch off the chest wall.

Soft cardiac murmurs (grade I–II) are commonly detected in clinically healthy puppies at their first puppy wellness examination (Pugliese et al. 2021). t hese murmurs are most likely to be non-pathological, but a pathological murmur cannot be ruled out (Sewall 2016) (Côté et al. 2015). t herefore, all murmurs identified should be noted on a patient’s medical record to accurately monitor and assess progression or changes over time (van Staveran and Szatmari 2020).

Non-pathological murmurs can also be described as innocent or functional. t hey can be heard in 15–31% of puppies <6 months old and are due to the higher cardiac output relative to cardiac size in young animals (Côté et al. 2015). Furthermore, puppies with innocent cardiac murmurs often have mild, nonpathological anaemia which lowers blood viscosity, leading to turbulent blood flow (Pugliese et al. 2021). t he following characteristics can be used to identify these murmurs: a systolic, soft (grade I or II) murmur on the left side which typically disappears by 6 months of age and which is not associated with clinical signs (Côté et al 2015; Pugliese et al. 2021). Although non-pathological murmurs are common in puppies, they can also occur in adult dogs. t hese murmurs are not caused by structural heart disease but can be seen in athletic dogs, certain breeds (such as Boxers) and are associated with systemic conditions that alter blood viscosity or increase cardiac output, such as anaemia, fever, pregnancy or hyperthyroidism (Côté et al. 2015; Pugliese et al. 2021).

Pathological murmurs in puppies result from congenital heart conditions where there is a structural cardiac abnormality. t hese murmurs can be identified during puppy appointments by specific characteristics of the murmur (covered below), presence of an arrhythmia, or clinical symptoms (Pugliese et al. 2021). Possible clinical signs associated with pathological murmurs include exercise intolerance, increased respiratory rate and effort, cyanosis, ascites, or syncopal events. t hus, attention should be given to related physical exam findings, particularly mucous membrane colour, femoral pulse quality, heart rate and rhythm, and respiratory rate (Côté et al 2015).

so, when should you worry about a heart murmur?

t here are several features of a heart murmur that can give you a clue that it might be pathological. In general, loud murmurs graded III/VI or higher are likely associated with a cardiovascular lesion as these are caused by rapid, turbulent blood flow through an obstructive lesion, leaky valve, or shunt. Any murmur that is heard throughout the entire cardiac cycle (continuous or “machinery-murmur”) or only during diastole is pathological regardless of the grade. t his is also true for a murmur that is loudest on the right-side, as these are typically due to a ventricular septal defect (“hole in the heart”) or tricuspid valve dysplasia. Auscultatory features that should prompt further investigation include ≥ grade III murmurs, continuous or diastolic murmurs, murmurs loudest at right hemithorax, other abnormal heart sounds such as a gallop or arrhythmia, pulse deficits, or if the murmur is accompanied by physical findings of cardiovascular disease (Côté et al. 2015).

Additionally, congenital heart murmurs do not disappear with maturity and some such as those caused by subaortic stenosis, get louder. t herefore, puppies with a murmur during initial vaccination appointments should be re-auscultated at 6 months of age (12 months for giant breeds) (Côté et al. 2015). If a murmur is still present then further diagnostics are warranted, especially if the murmur is noted to increase in grade over time.

you have identified a murmur in a puppy that is concerning for a pathological heart murmur: what are the next steps?

t horacic radiographs can provide information on the presence of cardiac remodelling further indicating a pathological murmur. However, echocardiography (cardiac ultrasound) is the test of choice to identify the cause of the murmur and diagnose the underlying congenital heart disease that is present.

Congenital heart disease can be largely split into diseases that cause obstructions in the heart, diseases that cause a leaky valve and diseases that cause a shunt from one circulation to the other, or a mixture of all three. t he most common congenital cardiac disease in dogs is left-to-right shunting patent ductus arteriosus (PDA) and valvular pulmonic stenosis, both of which are treatable conditions with minimally invasive procedures. Early detection of congenital heart disease allows treatment to be pursued early to prevent clinical signs or improve quality and quantity of life (Rovroy and Szatmari 2021).

Patent Ductus Arteriosus

Patent ductus arteriosus is one of the most common congenital cardiac diseases in dogs, accounting for approximately 21% of congenital heart defects (oliveria et al. 2011).

t he ductus arteriosus is a normal fetal structure that develops to shunt blood away from the pulmonary artery and the deflated lungs, into the aorta. In puppies, the ductus arteriosus functionally closes within a few days after birth as the lungs inflate and requires blood flow. PDA is a failure of the ductus to close allowing blood to flow from the high-pressure aorta to the lower pressure pulmonary artery. t his significantly increases blood flow through the pulmonary circulation leading to volume overload. If left uncorrected a PDA will cause progressive heart enlargement and left-sided congestive heart failure (Saunders et al 2013). Patients with this congenital cardiovascular disorder do not have a normal life expectancy unless the PDA is occluded. Without occlusion, the prognosis is poor with a reported median survival of only 2 years but with occlusion the life expectancy increases by an additional 10 years (i.e., median survival time of 12 years); effectively a normal lifespan (Saunders et al. 2013).

A puppy with a PDA presenting to its first vaccination appointment will likely be asymptomatic, though some present with mild exercise intolerance, stunted growth, or signs of heart failure. A left basilar continuous murmur can be auscultated in these pups (Broaddus and t illson 2010). A continuous heart murmur is distinct and is often described as a “machinery murmur”, importantly there is no break in the cardiac cycle hence the underlying murmur sound is always present. most PDA cases will have a loud murmur and palpable thrill present, but anytime a continuous murmur is heard it should be investigated (Broaddus and t illson 2010) (Israel et al. 2003) (Pugliese et al. 2021). to hear a recording of a continuous murmur please see the university of Washington Department of medicine website: https://depts.washington.edu/ physdx/heart/demo.html occlusion of the PDA either by surgical ligation or minimally invasive techniques is often curative (Bureau et al. 2005) and so should be considered in these cases. minimally invasive techniques for PDA occlusion include transcatheter placement under fluoroscopic guidance of a thrombogenic device into the ductus via a peripheral vessel to promote closure (sometimes the surgical incision is so small a suture is not needed) (Singh et al. 2012). Success of implantation is high with low intraoperative mortality and low post-operative morbidity

Echocardiography is necessary to confirm the diagnosis, evaluate for other concurrent cardiac conditions, and assess whether the patient is a suitable candidate for closure of the PDA.

(Saunders et al. 2013). minimally invasive techniques allow faster patient recovery times and avoid potential adverse complications associated with a thoracotomy to surgically ligate the PDA. With the development of a veterinary specific device, the Amplatz canine ductal occluder, this procedure is generally regarded as the treatment of choice in most cases, with a high success rate of 97% (Saunders et al. 2013; Sewall 2016).

P Ulmonic Stenosis

Along with PDA, pulmonary stenosis is also one of the most common congenital heart diseases in dogs with predisposition in brachycephalic breeds (oliveria et al. 2011). Pulmonic stenosis results from the abnormal development of the pulmonary valve leaflets which thicken and adhere to one-another, creating a physical obstruction to blood flow leaving the right heart. t he disease is classified according to valve morphology and anatomical location of the narrowing into sub valvular stenosis (obstruction in the right ventricular outflow tract), valvular stenosis (pulmonic valve), and supravalvular stenosis (main pulmonary artery), with valvular pulmonary stenosis being by far, the most frequent (macDonald 2006). Compensatory concentric hypertrophy of the right ventricle occurs to normalise the increased wall stress. Severe right ventricular hypertrophy can result in myocardial hypoxia, right-sided congestive heart failure, ventricular arrhythmias, and sudden death (Locatelli et al. 2013).

t he auscultatory findings of a patient with pulmonary stenosis include a left, basilar, systolic murmur. t he intensity of the murmur may vary according to the degree of obstruction, with a louder murmur indicating a more severe disease (Caivano et al. 2018). Possible clinical signs include exercise intolerance, syncope, and right-sided congestive heart failure which could include ascites/ abdominal distention or respiratory effort from pleural effusion (macDonald 2006).

t he definitive diagnosis of pulmonic stenosis is made by echocardiography with visualisation of abnormal and stenotic pulmonary valve leaflets. t he severity of pulmonic stenosis is assessed by measuring the velocity of blood flow through the stenosis and converting this velocity to a pressure gradient. t he faster the velocity – the higher the pressure gradient. Pulmonic stenosis can then be categorised as mild (pressure gradient, < 50 mmHg), moderate (pressure gradient, 50–80 mmHg), or severe (pressure gradient, > 80 mm Hg) (Francis et al. 2011). t he risk of developing clinical signs and/or secondary right ventricular remodelling is highly dependent on the degree of valvular stenosis and pressure gradient across the stenosis (Locatelli et al. 2013).

Prognosis Without Any Intervention

mild pulmonic stenosis is generally associated with a favourable long-term prognosis for a normal lifespan without the need for intervention. Dogs with moderate pulmonic stenosis have a variable outcome but will generally have a cardiac-related death as an older-middle aged dog (Locatelli et al 2013). No clear guidelines have been established regarding the best treatment option for patients affected by moderate pulmonic stenosis and treatment plans are tailored for each patient based on echocardiographic variables and presence/absence of clinical signs (Locatelli et al. 2013; Rovroy and Szatmari 2021). Dogs classified with severe pulmonic stenosis carry a guarded prognosis for long-term survival because of the increased risk of syncope, rightsided congestive heart failure or sudden death (Francis et al. 2011). Retrospective studies show high mortality rates in dogs with severe pulmonic stenosis: 53% mortality within their first year of life and 20% annual mortality after that (Locatelli et al. 2013).

Prognosis With Intervention

Balloon valvuloplasty is the surgical technique of choice for most moderate and all severe pulmonary stenosis cases (Locatelli et al. 2013). t his is a noninvasive procedure via catheterisation of a peripheral vein. With the aid of a guidewire positioned across the pulmonic valve, a balloon dilation catheter is advanced across the valve and is manually and temporarily inflated to tear open the stenotic valve. Success of this procedure is normally defined as a decrease in trans-pulmonic pressure gradient by 50% from pre-procedural measurements and/or reduction in the pressure gradient to < 50 mmHg (Francis et al. 2011; Locatelli et al. 2013).

t he outcome of balloon valvuloplasty has been shown to significantly improve clinical signs in symptomatic dogs and improve survival and overall outcome when compared with dogs not treated by balloon valvuloplasty (Johnson et al 2004; Locatelli et al. 2013).

Other interventional procedures

Interventional cardiology through minimally invasive catheterization has expanded significantly in veterinary medicine (Scansen 2017). In addition to the treatment of patent ductus arteriosus occlusion and pulmonic balloon valvuloplasty for pulmonic stenosis, other interventions that an interventional cardiology service offers include coil, particle, or device occlusion of anomalous vessels/shunts for conditions such as atrial septal defects, intrahepatic shunts, arteriovenous fistulas or other intra or extra-cardiac shunts in addition to balloon angioplasty or stent implantation for a variety of vascular obstructions (Scansen 2017). transvenous artificial pacemaker implantation for bradyarrhythmias is also possible, rounding off the surgical options for various cardiovascular conditions.

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