I just thought I'd brag about how smart I am ...
Hello Dear Readers,
Since I started my first blog by writing about the world most famous cardiologist, the Late Michael Dabaghy (by sheer coincidence I might add) I thought it would be appropriate if I were to continue my second blog by writing about the heart and attempt to explain the tracing of ECG (ElectroCardioGram) which is heavily relied upon by General Practitioners and cardiologists to diagnose arrythmia (abnormal rhythm), flutter (fast heart rate), fibrilation (beats from abnormal sources than SA Node), infarcts (heart muscle cells that had been damaged or died) both past and present.
The main leads of the ECG machine are placed on the body in the form of a triangle in which the heart is in the middle. The other leads that labelled V1 to V6 ar placed in different positions on the spaced of the ribs. The ideas being to observe the hear from different angles. Lead V4 provided important information useful to tell whether there had been damage to the muscle of the ventricles from previous infarcts (heart attacks). Some of the tracing from the V leads are inverted images of the main leads in which the heart is in the middle of the triangle.
In brief the heart is a pump that is split into two halfs. Each half has upped chamber and lower chamber. The upper is known as the auricle and the lower is known as the ventricle. The opening between the auricle and ventricle is controlled by one way valve. On the right hand side the valve is known as the mitral valve (from the Bishop collar) and on the left is the pulmonary valve which allow the passage of blood to the lungs. On the question of valves it is interesting to note that the mitral valve is damaged in childhood diseases such as rheumatic fever. Australia's former Prime Minister, Kevin Rudd, who suffered rheumatic fever as a child had last week undergone surgery to replace the mitral valve and is now recovering in Queensland hospital. The right side of the heart receive cifrculating blood that had shed its oxygen content (not the full content). This blood is pumped to be oxygenated by the air we breath and is then pumped by the left side of the heart to nourish the body and return back after releasing its oxygen for bodily metabolism. The pumping by the left ventricle requres much greater energy than the pumping of the right ventricle. As a result the mucscle mass of the left ventricle is significantly greater than that of the right ventricle. Depending on their severity heart attacks (myocardial infarcts) normally leave damaged areas in the left venticle. This often show on lead V4 and the 'T' wave of the tracing in which the heart is at the centre of the triangle.
The above diagram shows normal ECG tracing taken from the three leads in which the heart is at the centre of the triangle. The letters are P, QRS, and T. Every cell of the heart could potentially fire a signal which could be picked up by ECG. However, in a normal heart the firing begins with the Sino Atrial Node (SA Node) located in the right atrium. This is a collections of cell with a firing threshold lower than the rest of the myocardial cells. When the SA node fires it gives the 'P" wave of the ECG. As this wave travels in the atrium it triggers the firing of cells that allows the left ventricle to fire giving the QRS wave of the ECG. As the heart comes back to rest the 'T' wave records the resting electrical activities of the myocardial cells. The 'T" wave is important in picking upand diagnosing prior heart attacks. Elevated blood potassioum level could also give you abnormal 'T' wave.
I realised that I may have written too much for a blog I will attempt to briefly summarise the essentials of what i have written:
If you listen to the heart you will hear the sound "Lubb" "Dubb", "Lubb" "Dubb" etc... The "Lubb" is the sound of the right side of the heart filling with blood coming from the body. The "Dubb" is the sound of the firing of the left ventricle pushing the oxygenated blood to the body. The 'P' wave is the firing of the SA Node. The distance between the 'P' wave and rthe 'QRS' wave is measured in milliseconds. If there is anorther wave that means some cell is firing on the pathway of the wave. A road block or a pump on the road. It could suggest damage or ectopic beat (arrythmia). The width and the height of the 'QRS' wave is important reflection of the state of the muscle cells of the left ventricle. The height of the 'T' wave is an indicator of prior damage to the heart muscle. The reading is normally confirmed by the V leads to which I referred earlier.
So dear Readers if you find what I have written about is interesting and you wish me to continue writing about the drugs that is norally prescribed to treat heart ailments you may care telling me. I will be happy to write about drugs that doctors normally prescribe to treat either chronotropic conditions (rates and rythems) and ionotropic conditions (weakened heart muscles).
If you are mad I wasted your time with this information, please feel free to kick me in the nuts...
Cheers for now
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