How I approach... Heart murmurs in kittens

All clinicians will have been in the position of detecting a heart murmur in a young, apparently healthy kitten presented for vaccination or other routine examination. Meg Sleeper and Camden Rouben discuss a practical approach to such cases and identify which diagnostic tests are best employed.

Meg M. Sleeper
VMD, Dipl. ACVIM (cardiology)
 

Introduction

Young cats (< 1 year of age) frequently present to general practitioners for new patient exams, vaccinations, and breed screening evaluations, only for a heart murmur to be detected. In addition, there are occasions where a heart murmur can be found after clinical signs associated with heart disease are noted. It is important to know how to handle these situations in a confident and efficient manner in order to provide your patient with the best care and your client with the best service. Regardless of whether a heart murmur is present, if a patient is showing clinical signs associated with heart disease, referral to a cardiologist should always be considered.

A heart murmur is a sound wave created by turbulent blood flow moving through the heart or nearby vasculature. Heart murmurs are most notable when blood flows from a chamber of relatively high pressure to one with low pressure (i.e., ventricle to atrium). Movement of blood between two chambers of similar pressure may not create a murmur that is auscultable with a stethoscope, and it is important to note that not all congenital heart defects in cats will cause a murmur (e.g., reversed patent ductus arteriosus [PDA]), although nearly all do. In addition, murmurs frequently occur in cats without structural heart disease; these are termed benign or functional murmurs (1).

Regardless of why the cat is presenting to your exam room it is important to get a thorough history. If a heart murmur is noted on physical exam, specific details to ask the owner include: evidence of lethargy, exercise intolerance, weight of the patient in comparison to its littermates, any increased resting respiratory rate/effort, and any collapsing episodes. It is important to ask the owner about prophylactic deworming (specifically lungworm) and heartworm status. In addition, encourage the owner to ask the breeder if there were any cardiovascular concerns with the pet’s littermates or parents.

Physical examination

Murmur assessment is only a small part of a thorough cardiovascular examination. We personally choose to start a cardiovascular physical exam from the tail and work towards the head, as this is often less threatening for a nervous cat. Femoral pulses should ideally be palpated while listening to the heart to ensure the pulses can be palpated with each heartbeat. Femoral pulses should be assessed for synchronization with the heartbeat and the actual pulse quality. The pulses should be characterized as weak, normal, or increased in strength (also described as hyperdynamic or bounding). Animals with weak pulses have a low systolic pressure or a high diastolic pressure (as with pericardial effusion or dilated cardiomyopathy). Animals with bounding pulses have a low diastolic pressure or a high systolic pressure (as with patent ductus arteriosus or aortic insufficiency).

Heart rate and rhythm should be noted and documented. Often waiting a few moments for the kitten to become acquainted with the new surroundings of the exam room allows for the animal’s initial excitement-induced tachycardia to subside. If the rhythm is irregular, an electrocardiogram should be performed to definitively assess the cardiac rhythm. Mucous membrane color should and can be assessed at the gingival, vulvar, and nail bed areas. A normal, healthy cat should have pink mucous membranes with a capillary refill time of less than two seconds. Pale mucous membranes can occur in young cats with anemia. Cyanosis is caused by arterial hypoxemia due to severe respiratory or cardiac disease, and cyanotic mucous membranes can occur in cats with right to left intracardiac or great vessel shunts. Cyanosis is generalizedwith central venous admixture (i.e., with a Tetralogy of Fallot), or segmental/differential when right to left shunting occurs (i.e., with a reversed patent ductus arteriosus). Differential cyanosis is the term used to describe cyanosis of the lower extremities and vulva/prepuce while the upper extremities and oral mucous membranes appear well oxygenated (i.e., pink). [...]