According to Sonostarss "Sonographers, what are you measuring?" article sonographers are 98% of the time making a wrong fetal echo diagnosis.
M-Mode is the modality we use to obtain a fetal heart rate, but few and far between sonographers even
know what they are really measuring. Unfortunately, sonography schools, though they teach the many facets of OB sonography, are not teaching how to correctly perform, interpret or measure M-mode. This is truly astounding. Why don’t we know this?!! It could make a big difference in a baby’s prognosis and treatment.
When measuring the heart rate, many sonographers are measuring the most pronounced thing they visualize, which is usually the motion of a heart valve. This is NOT the fetal heart rate, and you might be
missing a significant heart dysrhythmia.
It is the sinoatrial (SA) node, located at the roof of the right atrium, that regulates the heart rate. The SA node sends a signal throughout the atrium to contract, and then the signal arrives at the atrioventricular
(AV) node located at the junction of the atrial and ventricular septum. This signal is then transmitted throughout the ventricular fibers causing the ventricles to contract. For every contraction of the atria,
the ventricles should contract immediately after. This is called a sinus rhythm. Think of it as a light switch (the atria) that flips on and immediately sends a signal for the light (the ventricles) to go on.
Sometimes “the wires” do not correctly attach from the light switch to the light, or something impedes the signal. This is called a dysrhythmia.
Understanding this principle is vitally important to understanding when a rhythm is normal or not.
- Detailed information on the downloadable PDF
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