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Your new puppy has just had his first check-up with your veterinarian and your vet detected a heart murmur on auscultation. What is the significance and can it cause sudden death in puppies?
What is an heart murmur?
Before answering this question, it is important to know what a heart murmur is. It is described as an echo that is heard at the same time or following the jerky noise produced by the closing of the valves during the heartbeat. The echo in question is produced by the turbulence of the blood. Normally, the flow of blood is linear, that is, it moves in a straight line, always in the same direction.
In certain circumstances, the linearity of the blood flow is disturbed and is then projected in several directions. For example, in the presence of anemia where there are fewer red blood cells in the system, the blood is clearer and therefore tends to be turbulent. In contrast, during severe dehydration, the blood is thicker and therefore does not circulate well in the blood vessels which will again cause turbulence.
Another example is when there is a heart valve that is not tight. In this case, the blood will be forced through the defective valve in the previous compartment which will again cause turbulence. The same phenomenon applies when there is a defect in the heart or when the heart muscle does not contract normally.
It is also possible to hear a heart murmur that is not associated with any abnormalities. We then speak of physiological or benign murmur. This one is very common in growing dogs. When the murmur is associated with a functional or structural cardiac abnormality, it is referred to as a pathological murmur.
Gradation of heart murmurs
Heart murmurs are graded from I to VI. Each grade represents the intensity of the breath. Grade I is associated with a very low intensity murmur, heard in one place only. The higher the grade, the more easily the murmur is audible wherever the heart is heard.
In a grade VI murmur, it is audible even with the stethoscope removed from the chest wall. However, it is very important to know that the intensity of the murmur is not associated with the severity of the injury. So a grade VI murmur does not represent a higher risk of sudden death in puppies. This is because a dog with a very serious heart problem may have a grade I / VI murmur while a dog with a grade VI / VI murmur may have a minor injury.
The gradation scale is useful to allow, in some cases, to differentiate between physiological murmurs which are always less than the IV/VI range in intensity and pathological murmurs which can be of any intensity. Veterinarians also use the gradation scale to communicate with each other in a systematic way about a case and also to monitor the evolution of the intensity of a murmur over time.
Benign or pathological murmur
When a murmur is auscultated in a 6 month old dog or younger, it is important to try to determine whether it is a benign or pathological murmur since for this age group a murmur is the first manifestation of most congenital heart abnormalities. Screening such conditions at a young age can allow to correct this defect and thus provide a normal life expectancy while the same lesion, if not detected, can lead to heart failure and sudden death in puppies.
For abnormalities that cannot be corrected and have a poor prognosis, immediate detection may allow the dog owner to understand that a serious problem exists as opposed to discovering it in a an emergency situation where there is possible cardiac decompensation.
There are differences between physiological and pathological murmurs which sometimes allow us to distinguish them, but there is also a large gray area between the two categories, which often makes the cause of the murmur unclear. The diagnostic process can then be tackled in two different ways, either a complete evaluation including ultrasound or a reassessment by auscultation no more than 3 weeks later. If the murmur goes away at that time, it is likely that the cause is physiological and there is no need to further investigate. On the other hand, if it persists, it is strongly advised to perform a full assessment.
Congenital ventricular arrhythmia: another risk of sudden death in puppies
Congenital ventricular arrhythmia, sometimes called congenital ventricular ectopia, is a particular form of inherited heart rhythm disorder which has been observed in breeds suchs as the German Shepherd but the mode of genetic transmission is currently unknown.
Dogs show no clinical signs but die prematurely, typically in his night’s sleep or while resting. Death usually occurs around the age of 4 to 18 months.
Stabilization of arrhythmias
Arrhythmia is rarely present before the age of 12 weeks. It progresses gradually up to 24 to 30 weeks. Depending on the dog’s condition, we can observe the following:
- Worsening of arrhythmias up to sudden death in puppies
- A decrease in arrhythmias which can go until they disappear after 18 months
Congenital ventricular arrhythmia is still poorly understood. When this condition was originally detected in United States, four families of German Shepherds with the same common ancestor were identified. Subsequently, other cases were diagnosed, especially in the US and great Britain.
Diagnosis of congenital ventricular arrhythmia is a challenge
In the absence of clinical signs, the diagnosis is particularly delicate. A suspicion is possible if a cardiac arrhythmia is evidenced by auscultation. But the arrhythmia is most often very intermittent. For the same reasons, the results of a routine EKG are often times not showing anything abnormal and in severe cases, it may show ventricular abnormalities.
A Holter exam is often required to identify the abnormality (but it can also go unnoticed). The biological, radiographic and echocardiographic examinations of these dogs can also return normal results.
Treatment for congenital ventricular arrhythmia
There is currently no satisfactory medical treatment that can be used on a consistent basis. Some treatments can only partially control the situation and allow the dog to pass the 18 month period, beyond which the prognosis is generally more favorable.