In the physical examination of cats, heart sound auscultation is essential, and it is also the most meaningful part of clinical animal heart examination. Its importance is no less than that of cardiac imaging examination. A routine heart sound auscultation can provide a lot of information and help diagnose the disease. However, heart auscultation seems very simple, but there is a lot worth exploring.

1. What are heart sounds?

In each cardiac cycle of a healthy cat, two rhythmic alternating sounds, called heart sounds, can be heard. The former is called the first heart sound, and the latter is called the second heart sound. Pet cats will have third and fourth heart sounds under pathological conditions. The third heart sound is after the second heart sound, and the fourth heart sound is before the first heart sound. During the fetal period, fetal heart sounds are present.

The first heart sound occurs during ventricular systole, so it is also called systolic heart sound. The two atrioventricular valves close at the same time, the ventricular muscles contract, and the blood flow impacts the arterial wall. The pitch is low, dull, long in duration, and has a long ending.

The second heart sound occurs during ventricular diastole, so it is also called diastolic heart sound. It is a vibration sound produced by the simultaneous closure of the aortic valve and pulmonary valve. The pitch is high, the duration is short, and the ending is short.

The third heart sound occurs in early diastole of the ventricle. Blood flows from the atrium into the ventricle rapidly, causing the ventricular wall to vibrate. The sound is weak, short and low. For normal cats, the third heart sound cannot be auscultated. If a pathological third heart sound is heard, it is seen in cats with congestive heart failure or ventricular hypertrophy.

The fourth heart sound, also known as atrial sound, is produced by the vibration of atrium contraction. Cats cannot be heard under normal circumstances. If heard, it is a pathological fourth heart sound, which is seen in atrioventricular conduction block, etc.

Fetal-like heart sounds are normally seen in the beating heart of the fetus. Pathologically, it is seen in cats with severe cardiac insufficiency or acute heart failure. Due to the compensatory acceleration of the heartbeat, the diastolic period is shortened. The interval between the first and second heart sounds becomes equal. The intensity and timbre of the two heart sounds also become similar.

2. How to distinguish the first heart sound and the second heart sound?

Under normal conditions, the difference is based on the pitch characteristics of the first and second heart sounds; according to the difference between the pulse, the first heart sound is synchronized with the pulse, and the second heart sound is out of sync; according to the time interval of the heart sounds, the short interval is before the third heart sound. One heart sound, followed by the second heart sound. The long interval is preceded by the second heart sound and followed by the first heart sound. It is not applicable under pathological conditions, such as when premature ventricular contractions occur and the pulse does not match the heart sound. At this time, it can be distinguished based on the ECG waveform.

3. Cat heart auscultation method

Auscultate the animal in a standing position (to keep the heart in a normal anatomical position and avoid murmurs caused by abnormal positions, such as friction between the heart and the chest wall);

Auscultate at points on the chest wall (3 auscultation points on the left chest wall and 1 auscultation point on the right chest wall). All points need to be auscultated (for example, only auscultating the mitral valve position in cats may miss the diagnosis of congenital diseases in young cats. heart disease);

Auscultate the heart and lungs separately (to avoid confusing heart murmurs and breath sounds);

It is difficult to auscultate the heart sounds of cats, and various influences need to be considered comprehensively:

　a. Because the heart is relatively small, the auscultation position can be changed by slightly moving the stethoscope;

b. The heart may “lodging” as age increases, leading to changes in auscultation points;

c. Heart murmurs are usually milder than those in cats;

　d. Faster heart rate;

e. Others. Such as grunting; some heart murmurs can be expressed by accelerating the heart rate. If arrhythmia is found, further examination (ECG) is required.

4. Changes in heart rate frequency

Under normal circumstances, two heart sounds can be heard in each cardiac cycle, and the number of cardiac cycles per minute is the heart rate. Pathological changes in heart rate include tachycardia and bradycardia.

5. Changes in heart sound intensity

The intensity of the heart sound is determined by two factors: the heart sound itself and the heart sound conduction medium. Clinically, there are two changes: heart sound enhancement and heart sound weakening. When determining whether the heart sounds are enhanced, auscultation must be performed at the apex and base of the heart. If both locations are enhanced or weakened, the heart sounds are considered to be enhanced or weakened.

Factors of the heart sound itself: myocardial contractility, heart valve status, circulating blood volume

Factors of the conduction medium: the thickness of the chest wall, the state of the cardiac lobes of the lungs, and the state of the pleural and pericardial cavities.

6. Precautions for auscultation

Before auscultation, you should first touch the heart beat on the surface of the chest wall to find the strongest pulsation site. You can start auscultation from this site and identify its intensity. An experienced veterinarian can tell whether an increased heartbeat is due to excitement or an enlarged heart. Usually an increased heartbeat caused by excitement will weaken as the animal calms down. The membrane-surface listening head of the stethoscope can collect higher-frequency sounds and is suitable for auscultation of normal first and second heart sounds. Abnormal heart sounds can be divided into short heart sounds (such as split heart sounds or gallop S3 or S4) and longer heart sounds (most heart murmurs).

The gallop is a low-frequency diastolic sound that should be listened to with a bell-shaped earpiece. For a single-head stethoscope, close to the chest wall and apply slight pressure to achieve the membrane-surface auscultation effect, while lightly touching the chest wall will result in a bell-shaped stethoscope. Heart murmurs are usually caused by turbulent or high-velocity blood flow within the heart or large blood vessels. Auscultation should be performed in a quiet room, as wheezing can make auscultation more difficult. listenWhen diagnosing a cat, you can try to keep it close to running water or alcohol cotton balls to avoid interference from the cat's wheezing. Sometimes breath sounds may be mistaken for heart murmurs, and it is necessary to observe the animal's breathing process while auscultating for identification. A variety of disturbances can affect auscultation, including tremors, myotremors, hair rubbing against the stethoscope, gastrointestinal peristaltic sounds, and room noise.