Understanding the ECG
In general terms, lets look at what an ECG is representing and how we’re able to
sense it. The ECG is separated into two basic Intervals, the PR Interval and the
QT Interval, described below.
Note: All information
comes from the Waves
and Intervals section of the ECG
Wikipedia page .
The PR interval is the initial wave generated by an electrical impulse traveling
from the right atrium to the left. The right atrium is the first chamber to see
an electrical impulse. This electrical impulse causes the chambers to “depolarize”.
This forces it to contract and drain deoxygenated blood from both the Superior
and Inferior vena cava into the right ventricle. As the electrical impulse
travels across the top of the heart it then triggers the left atrium to contract.
The left atrium is responsible for receiving newly oxygenated blood from the
lungs into the left ventricle via the left and right pulmonary veins. The
pulmonary veins are
red in the diagram because they are carrying oxygenated blood. They are still
called veins because veins carry blood towards the heart. Science!
The QT Interval is where things get really interesting. The QRS is a complex
process that generates the signature “beep” in cardiac monitors. During QRS both
ventricles begin to pump. The right ventricle begins to pump deoxygenated blood
into the lungs through the left and right pulmonary arteries. The
pulmonary arteries are
blue in the diagram because they are carrying deoxygenated blood. They are still
called arteries because arteries carry blood away the heart. Science, Again! The
left ventricle is also begining to pump freshly oxygenated blood through the
aorta and into the rest of the body. After the initial contraction comes the ST
segment. The ST segment is fairly quiet electrically as it is the time where the
ventricals waiting to be “re-polarized”. Finally the T wave becomes present to
actively “re-ploarize”, or relax the ventricles. This relaxation phase resets
the ventricles to be filled again by the atriums.
Heartbeat with corresponding ECG Credit Wikipedia.org