3.3.4 Arterial pulse
The pulse should be palpated to assess rate, rhythm and quality. Pulses can usually be easily palpated from the facial artery, but pulsation of the transverse facial, median or digital arteries, or arteries in the skin, can also be detected. However, the facial artery is the most reliable because it is less frequently affected by other local factors.
The pulse quality reflects the difference between the systolic and diastolic pressures rather than the absolute or mean arterial pressure. The facial pulse profile usually has a double peak which can be easily detected at resting heart rates. It may be markedly biphasic at normal heart rates in resting animals. Weak pulses can be misleading because the absolute strength of the pulse is quite variable. Pulse quality is stronger in an excited animal. It is well worthwhile palpating arterial pulse quality in as many normal horses as possible, in order to become familiar with the range of normality. One situation in which assessment of the pulse quality is particularly useful is in aortic regurgitation, when it may become strong but short lasting ('water-hammer pulse') if the condition is advanced (see section 6.5.2). 'Pulsus alternans' may occur in animals with myocardial depression. In this situation there is an alternatively strong and weak pulse, despite a regular sinus rhythm. Pulse deficits may occur when there is a premature beat, or a very short R-R interval in an animal with atrial fibrillation. Because the ventricles contract prematurely, they have not have time to fill normally, so the stroke volume is small. In addition, end-diastolic aortic pressure is still relatively high, so the difference between systolic and diastolic pressure is small.