Pulse Rate Monitoring
The distinction between heart rate and pulse rate centers on whether
a given electrical depolarization and systolic contraction of the heart (heart rate)
generates a palpable peripheral arterial pulsation (pulse rate). Pulse deficit describes
the extent to which the pulse rate is less than the heart rate. Such deficit is
typically seen in patients with atrial fibrillation, in which short R-R intervals
compromise cardiac filling during diastole and result in a reduced stroke volume
and imperceptible arterial pulse. The most extreme example of a pulse deficit is
electrical-mechanical dissociation or pulseless electrical activity, seen in patients
with cardiac tamponade, extreme hypovolemia, and other conditions in which cardiac
contraction does not generate a palpable peripheral pulse.
Most monitors report the heart rate and pulse rate separately.
The former is measured from the ECG trace, and the latter is determined from a selectable
pulse source. The pulse oximeter plethysmograph trace provides a suitable pulse
measurement source for most patients except those with severe arterial occlusive
disease or marked peripheral vasoconstriction. In addition to indicating the pulse
rate, this waveform may also provide supplementary diagnostic clues to cardiovascular
function.[21]
Other pulse rate sources include
automatic noninvasive blood pressure devices, which determine the pulse rate from
the pressure oscillations detected by the surrounding cuff, and invasive monitoring
of the direct arterial pressure waveform.
Pulse rate monitoring and heart rate monitoring complement one
another. Although monitoring both may seem redundant, such redundancy is intentional
and being applied to modern computerized monitoring algorithms to reduce measurement
errors and false alarms. In the end, however, as with all numeric information displayed
on the bedside monitor, the clinician must scrutinize the analog ECG tracing and
other waveforms to ensure the veracity of the digital values displayed by the bedside
monitor.
