Assessment findings like blood pressure readings, heart sounds, and observable signs and symptoms associated with cardiovascular malfunction are an importiant part of a full cardiovascular assessment. But once you suspect a heart ailment, you need to use a diagnositc tool called an ElectroKardioGram (or EKG). This machine is like a camera, except for instead of measuring wavelengths of light, it measures electrical activity in various locations of the heart. This is very importiant because in many cases the electrical activity of the heart is altered even before other signs and symptoms of an illness or malfunction manifest themselves. This allows a cardiac problem to be treated earlier, and decreases the chance of death (mortality).
An EKG machine has 12 'leads' created by 'electrode' sensors that are basically adhesive stickers that attach to specific locations on the patients chest or body. These electrode sensors create the 'leads' that act as a camera for electrical activity.
Positive electrode sensors detect when a wave of positively charged ions are moving (depolarization) towards them and record the impulse as an upward deflection on the squiggly line (very scientific term, I know) along a strip of graphing paper or recording device called an EKG strip.
The horazontal plane on an EKG strip represents time elapsed, the vertical plane on an EKG strip represents electrical voltage being generated.
These electrodes can also sense when a wave of positively charged ions (depolarization) is moving away from them. This is recorded as a downward deflection on the squiggly line.
Leads
Three of the leads are 'Bipolar limb leads'. This means that a pair of electrodes (one functioning as a positive sensor and another functioning as a negative sensor) work together to form an EKG reading from one of three angles. These leads are numberd: I, II, III.
Another three 'limb leads' are called 'Augmented limb leads' formed from one positive electrode senser and two negative electrode sensors. These leads are numbered: AVR, AVL, and AVF. Each of these reveal the electrical activity of the heart at a different angle.
Additionally, there are also six 'chest' leads'-created by positive electrode sensors arranged on the chest horazontally (no negative electrode sensors). They are numbered V1, V2, V3, V4, V5, V6 and they reveal the electrical activity along the front of the heart from various angles.
Each of these leads form a page of squggly lines called a full EKG.
(Each of the lines look a bit different from each other, and are still confusiong to me. But never fear! I will investigate further and include my findings in a future post!)
Wave Amplitude:
An upward deflection on the squggly line means that a positive wave of depolarized cells is moving towards the positive electrode sensor.
In a healthy individual, the quiggly line often forms a pattern of waves chararacteristic of a healthy cardiac cycle.
These waves are named for letters in the alphabet (But not ABCDE, because that would sound weird)
They are called PQRST
Factors such as the shape and the length of each wave, the length of the intervals between each wave, the length of overall complexes and the frequency of complexes or sets of waves are really importiant to assess when interpreting an EKG reading.
Lets go over the waves one at a time:
P-
This wave is usually a small upward deflection on the squiggly line, rounded at the top. It indicates depolarization/contraction in the atria.
In between the P wave and the next wave in the PQRST complex is a brief 'pause' that appears as a flat 'baseline' called the PQ segment or PQ Interval. This 'delay' is caused by the impulse being conducted through the AV Node, Bundle of His, Left and Right Bundle Branches, and Perjinki fibers. It allows time for blood to move from the atria to the ventricles.
QRS-
Even though these are actually three 'waves' they all indicate ventricular depolarization and the beginning of ventricular contraction/systole so they are often treated as one wave. The initial wave is a small downward deflection called the Q wave (not always visable). The second wave is tall, slender and has a peaked top; it is called the R wave. The third is usually medium-sized downward deflection called the S wave.
After this QRS complex, the squiggly line becomes horazontal again in a segment called the ST interval. This area represents the plateu or 'slow' phase of ventricular repolarization. (The heart is still physically contracting or 'pumping' at this time, but electrically it begins to revert to it's polarized state.) The ST Interval is an importiant area to assess, because if this segamented is elevated or depressed it can indicate a myocardial infarct.
T-
This wave occurs at the end of the of the PQRS complex and represents the end/'rapid' phase of ventricular repolarization. It appears as a wide, round upward deflection on the squggly line.
The whole process starts over after an isoelectric pause...Allowing the ventricles relax and the atria fills up with more blood.
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