# Electrocardiogram --- An **electrocardiogram**, often abbreviated as **ECG** or **EKG** (which is from the German spelling) is a diagnostic tool to measure the [[action potential|electrical]] activity of the [[heart]]. Since the electrical activity of the heart controls the [[cardiac cycle]], this is a good way to understand how well the heart is functioning. It is useful for monitoring [[arrhythmia|arrhythmias]] or determining the severity of an [[myocardial infarction|MI]]. **5-lead** ECGs are used for continuous monitoring. **12-leads** are a big more bulky, but give you a more accurate picture of what is going on. If you suspect your patient is having an MI, this happens as soon as possible. ![[ECG paper.png]] ## The Waveform The ECG **waveform** represents the amount of electrical activity that is happening over. For some reason, the features of the waveform are labeled P, Q, R, S and T. The amplitude of the line just has to do with the size of the muscle that is being polarized. ![[ECG waveform.png]] We know that each particular segment represents a specific segment of the [[cardiac cycle]]. The P wave represents the start of the cardiac cycle with the depolarization of the SA node/ventricles. The big QRS complex (with the big R spike in the middle) represents the depolarization of the ventricles. The ventricles are massive, which is why the R is so high up. (The atria also repolarize at this time, which would show up on the ECG, but it's compleatly overshadowed by the depolarization of the ventricles.) The T wave represents the repolarization of the ventricles. ![[ECG waveform segments.png]] ## Normal Sinus Rhythm A **normal sinus rhythm** is a standard regular healthy heartbeat. It has all the shapes and parts of the waveform that we expect. ![[normal sinus.png]] Just because a rhythm is sinus doesn't necessarily mean that it's healthy. [[arrhythmia|Sinus bradycardia]] and [[arrhythmia|sinus tachycardia]] are both examples of arrhythmias that could be a problem. ## Interpreting ECGs 1 rhythm look at r-r peaks 2 rate count the peaks in 6 seconds and times by 10 3 P waves is there one p wave for every qrs complex? 4 p-r intervals count the boxes, normal is 0.12-0.20 5 qrs width count the boxes, normal is less than 0.12 ## ST Elevation This is the sign that indicates a [[myocardial infarction|STEMI]]. ## Meds that Increase the QT Interval This is a relatively common kind of reaction to some meds, notably Zofran and Haloperidol. ___