In small animals, palpation of peripheral arterial pulses is most often performed using the femoral arteries. Dorsal pedal arteries may also be used.
The palpable strength of the pulse is determined by:
- the Pulse Width (known as Pulse Pressure), which is = Systolic Pressure – Diastolic Pressure
- the rate of change from systolic to diastolic pressure and back again to systolic pressure
Thus the arterial pulse is affected by (through the effect of systolic and diastolic pressure):
- left ventricular stroke volume
- ejection velocity or systolic function of the left ventricle
- the relative compliance and capacity of the arterial system
- the pressure waves that result from the antegrade flow of blood and reflections of the arterial pulse returning from the peripheral circulation
The arterial pulse strength may be subjectively classified as normal, weak, or strong. Recognize that this is not dependent on absolute blood pressure, because of the formula for pulse width above.
To illustrate, a patient with normal systolic and diastolic blood pressure (120/80 mmHg) has a pulse width of 40 mmHg and a normal peripheral pulse strength. Similarly, a hypertensive patient may have elevated systolic and diastolic blood pressure (160/120 mmHg), yielding still a pulse width of 40 mmHg and a normal pulse strength.
The most exuberant arterial pulses occur with patent ductus arteriosus and aortic valve insufficiency due to diastolic run-off and widening of the pulse width. Strong arterial pulses may occur with enhanced sympathetic tone and conditions such as anemia, hyperthyroidism, and fever, where there is increased stroke volume and/or decreased vascular resistance. Weak arterial pulses may occur with reduced stroke volume due to conditions like hypovolemia, systolic dysfunction (dilated cardiomyopathy) or outflow obstruction like aortic stenosis. However, the arterial pulse can be maintained near normal in the face of a reduced cardiac output, mainly due to the effect of compensatory vasoconstrictor mechanisms.
Pulse deficits are present when the pulse rate is less than the ausculted heart rate. This occurs when a cardiac contraction or several contractions take place prematurely not allowing enough time for ventricular filling (preload). This results in audible heart beats that do not eject enough blood to generate a palpable pulse.
The presence of pulse deficits should alert the clinician to the occurrence of premature ectopic beats. These may be either supraventricular or ventricular in origin, and only the ECG can distinguish these.
Complete absence of peripheral arterial pulses should alert the clinician to systemic arterial thrombosis or thromboembolism in the conscious patient and potential cardiopulmonary arrest in the unconscious patient.
Specific Pulse Patterns
There are few specific pulse patterns that may be recognized in specific underlying conditions.
Pulsus paradoxus refers to an exaggerated decrease in pulse pressure during inspiration and increase during expiration (typically >10 mmHg) that may be appreciated in some cases of cardiac tamponade with pericardial effusion. Irregular or rapid breathing frequently makes this a difficult abnormality to detect in practice.
Pulsus alternans refers to the beat-to-beat alternation of pulse strength (e.g. normal-weak-normal-weak or strong-weak-strong-weak) and is sometimes appreciated in cases with severe myocardial failure or supraventricular tachycardias.
Venous pressures are much lower than arterial pressures, therefore venous pulses are not typically palpated or seen. They may be seen, however, under abnormal conditions. The most common example of this is observing jugular venous pulsation.
Jugular Venous Pulsation and the Hepatojugular Reflux (HJR) Test
Jugular venous distension or pulsation beyond a third of the way up the neck at rest indicates marked elevation of right atrial pressure (assuming there is no obstruction to venous return pre-atrium). The hepatojugular reflux test is an observatory test that attempts to unmask lesser degrees of elevated right atrial pressure. Cranial abdominal pressure is applied in a ventral to dorsal direction with the patient standing or in sternal recumbency. This increases venous return to the right heart by compressing the liver, and the provocation of jugular distension or pulsation indicates moderately elevated right atrial pressure. Patients with a mild elevation in right atrial pressure likely cannot be identified on physical examination.
Jugular distension and pulsation at rest in a miniature Schnauzer indicating elevated right atrial pressure
Jugular pulsation may also be noted in patients with severe tricuspid regurgitation.
On occasion in normal animals, the underlying carotid artery pulse may make the overlying jugular vein “appear” as if it is pulsating, thereby mimicking jugular pulsation. This is rare in dogs and cats since their carotid arteries are reasonably deep relative to the jugular veins. But this imposter may be identified by occluding the jugular vein, in which case the underlying carotid pulse would still be appreciated while a true jugular venous pulse would disappear.