Electrocardiography (ECG)

During lecture, we learned about electrocardiograms.  My first job in the medical field was an EKG technician.  I was only 19 and worked in the EKG department at Hudson Valley Medical Center in NY.  

 I enjoyed reviewing what EKG's can measure and what the waves represent.  It is always good to refresh your memory so when patients ask you why you are performing the test and what problems can be be assessed from the test, we will have good and clear informative explanations. 

An electrocardiogram is simply a recording of the electrical activity of your heart.  By interpreting an ECG tracing, your doctor can diagnose several abnormal conditions that can affect your heart.  Some of these conditions include: rhythm disturbances, a heart attack, or other abnormalities of the heart's structure.  Two rhythm abnormalities include: tachycardia, which is an elevated resting heart rate and bradycardia, which is a resting heart rate under 50 beats a minute.  Adult heart rates are normally about 75 beats per minute.  

Transmission of action potentials through the conduction system generates electric currents that can be detected by electrodes placed on the body's surface.  The ECG is a composite of all the action potentials, graphed as a series of up and down waves, produced by cardiac muscle fibers during each heartbeat.  The electrocardiograph amplifies the heart's electrical signals and produces 12 different tracings from different combinations of limb and chest leads.

It has been about 9 years since I got certified as an EKG technician.  I am now a Medical Assistant and I perform EKG's everyday at work. I realized in class that I had forgotten what parts of the wave represents.  I learned that the P wave, is a small upward deflection on the ECG. It represents atrial depolarization.  A fraction of a second after the P wave begins, the atria contract.  The second wave, called the QRS complex, begins as a downward deflection.  The QRS complex represents the onset of ventricular depolarization as the cardiac action potential spreads through ventricular contractile fibers.  Shortly after the QRS complex begins, the ventricles start to contract.  The third wave is a dome shaped upward deflection called the T wave.  It indicates ventricular repolarization and occurs just before the ventricles start to relax.  Repolarization (relaxation) of the atria is not usually evident in an ECG because it is masked by the larger QRS complex.

The simplest piece of information the ECG can provide is the rate of your heartbeat at the time you had this test.  If 10 QRS complexes are recorded on the ECG paper or monitor in 10 seconds, then your heart rate is 60 beats per minute.  The ECG can distinguish normal sinus rhythm from all types of tachycardia and bradycardia rhythms. 

The ECG can also tell a physician if a heart attack has happened in the past.  An elevated portion between the QRS complex and the T wave will show a strong indication that heart muscle injury, such as a heart attack, is occurring.  If there is a deep early portion of the QRS complex, this may be evidence that a heart attack may have happened in the past.

Even if your not a doctor, I feel it is important to know how to look for this if you are the person performing the EKG.  When I was only 19 and doing one of the morning rounds of EKG's for patients staying in the hospital, I noticed that there was a large rounded portion after the QRS wave. The patient was an elderly man and was sleeping.  Instead of bringing the EKG down to my department to be viewed later by the cardiologist that comes in the afternoon, I brought it to one of the physicians on the floors.  Indeed the patient was having a heart attack.  I was thankful that I trusted my gut, to show it to someone and was thankful that I had learned what to look for in an EKG.

Arterial thrombosis and embolism

Just as in the coronary arteries, blood clots can develop at other atherosclerotic sites.  They can rapidly block a vessel (thrombosis) or break into fragments and block branches of vessels farther downstream ( embolism).  This results in a sudden cessation of blood flow to the areas supplied by the artery and branches.  With a sudden blockage, there is no time for collateral arteries to develop.  The body can't compensate for this blood flow reduction.

After learning this, I wanted to know what can cause clotting in an unbroken blood vessel.  I learned that the endothelial surfaces of a blood vessel may be roughened as a result of atherosclerosis. Atherosclerosis is the accumulation of fatty substances on arterial walls.  This condition can induce the adhesion of platelets.  Clots may also form in blood vessels when blood flows too slowly, allowing clotting factors to accumulate in high enough concentrations to initiate a clot.

Clotting in an unbroken blood vessel is called thrombosis.  The clot itself is called a thrombus.  If it remains intact, the thrombus may become dislodged and be swept away in the blood.  This can lead to an embolism.  An embolus is a blood clot, bubble of air, fat from a broken bone, or even a piece of debris transported in the bloodstream.  An embolus that breaks away from an arterial wall may lodge in a smaller diameter artery downstream. If it blocks blood flow to the brain, kidney, or heart, the embolism can cause a stroke, kidney failure or even a heart attack.

I work as a Medical Assistant for family medicine.  Just recently, I had to set up a patient for a CT scan to rule out whether or not the patient had a pulmonary embolism.  His symptoms were shortness of breath and coughing that did not go away after various treatments. He also had an elevated D-Dimer level.  Luckily, the test was negative.  After taking care of this patient, and learning about clots and embolisms in class, I wanted to learn more about medications and treatments that can be used in case I know someone who does have one.

Through research, I learned that thrombolytic medication that dissolves the clot may be given through a catheter directly to the affected area.  If you've had arterial thrombosis or embolism or are at risk of their development, you'll receive blood thinners (anticoagulants) to reduce the likelihood of blood clotting and future problems.  I also learned that there are surgical treatments available.  A surgeon can remove a clot in an artery by making a small opening upstream from the blockage and passing a balloon-tipped catheter past the blood clot.  Once the balloon is downstream from the blood clot, the doctor inflates it and pulls the catheter back to the opening in the artery.  The balloon pulls the blood clot upstream where it can be removed.  Occasionally, it's necessary to replace or bypass the blocked vessel.

I found this very interesting.  I have many patients at my office who are on coumadin which is a type of anticoagulant.  It is nice to know that there are also some surgical options to help remove a clot once it has been formed and then to have medications to take afterwards to help prevent this from happening again.