Gallop Sound in a Hyperthyroid Cat

Amara Estrada, DVM, DACVIM (Cardiology) University of Florida

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A rapid heart rate, a grade 2/6 systolic ejection murmur (auscultated over the left sternal border), and a gallop sound are heard in this heart sound.

The third and fourth heart sounds occur during diastole and are not typically audible in normal cats; S3 and S4 heart sounds are lower frequency than S1 and S2, and are best appreciated with the stethoscope bell. S3 or S4 sounds may be similar to horse galloping, hence the term gallop heart sounds; however, gallop rhythm should be avoided, as an audible S3 or S4 does not relate to the heart’s underlying electrical rhythm. Rapid ventricular filling generates the S3 (also known as S3, protodiastolic, or ventricular gallop). A presystolic gallop (also called S4 or atrial gallop) is heard just before S1 and occurs just after the P wave on the electrocardiogram.

Protodiastolic gallop sounds in cats are commonly associated with hyperthyroidism, as in this cat’s case. At rapid heart rates (common in cats), ventricular filling and atrial systole transpire very close together, making differentiation between S3 and S4 impossible. The resulting single accentuated sound is referred to as a summation gallop.

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