Electrocardiogram (ECG)

What is an ECG? ECG: a graphical representation of the electrical activity of the heart. Each movement of electricity through the heart creates a wave on the ECG.

Each movement of electricity through the heart creates a wave on the ECG.

Depolarization Depolarization: the sudden change in electrical potential of a cardiac muscle cell, from negative to slightly positive. Results in the contraction of the muscle. Cardiac muscle stimulation and contraction is the result of a very complex sequence of events – it relies on cells quickly pumping electrolytes across the cell membranes. These electrolytes include Calcium (Ca), Sodium (Na), and Potassium (K).

12 - Leads A full ECG is done using twelve leads. 10 electrodes are placed on a patient’s chest, and each one collects electrical data from a different area of the heart. Leads are: I II III aVL aVR aVF V1 V2 V3 V4 V5 V6

Deflections on the ECG When electric current moves towards an ECG lead, there is an upward deflection. When it moves away, there is a downward deflection.

Each lead tells us information about a different area of the heart.

Rates and Rhythms ECG’s are recorded on special graph paper, where each box along the horizontal (x) axis is worth 0.2 seconds, and each box vertically measures amplitude (usually in mm)

Rates and Rhythms The grid to the left helps to give a general idea of the speed of the heart rate. You can mark a QRS complex, and then see how far away the next one is.

Rate and Rhythm What is the Rate? ABOUT 150 BPM

Rate and Rhythm What is the rate? ABOUT 37 BPM

Rate and Rhythm What is the rate? ABOUT 75 BPM

Got Rhythm? There are many, many cardiac rhythms and rhythm disturbances. Some cause very few problems while others are deadly. In this course we’re going to break it down into small, general groups.

Rhythm Normal Sinus Rhythm This is considered “normal” rhythm for 90% of us. Rate between 60 and 100 BPM Regular (rhythmic) beats Normal P, QRS, and T waves on every beat.

Rhythm Bradycardia: TOO SLOW! Technically any rate less than 60 BPM. Slow heart rates generally drop blood pressure. Rates less than 30 usually cause people to lose consciousness, and are not able to sustain adequate perfusion (SHOCK!)

Rhythm Tachycardia: TOO FAST! Technically any rate above 100. Fast heart rates decrease ventricular filling time, so less blood is pumped to the body. Can result in a drop in blood pressure. Rates above 180-190 often cause dizziness and can result in lose of consciousness. Extremely fast rates can result in loss of pulses altogether (cardiac arrest).

Rhythm Ventricular Tachycardia – Very Bad. Ventricular Tachycardia (V-Tach) may or may not produce pulses, but has a bad habit of devolving into ventricular fibriallation. This is a SHOCKABLE RHYTHM!

Rhythm Ventricular Fibrillation – Very, Very Bad. “Quivering” heart. Chaotic electrical activity means that the chambers do not pump at all… Cardiac Arrest. Can begin instantly (Sudden Cardiac Arrest) This is also a SHOCKABLE RHYTHM!

Rhythm Asystole – “dead heart” – Very Bad as well. Very bad sign. People rarely come back from asystole. There is no electrical activity in the heart, no pacemaker, no contractions. Nothing.

Ectopy Often called “Skipped beats” or “Extra Beats”. Caused by over-excitation of individual heart cells. They are very common, and most are harmless unless there is heart damage or heart attack. Can be caused by several factorsincluding: Anxiety Caffeine or other drugs Heart attack or heart damage http://www.skillstat.com/ecg_sim_demo.html

Ectopy Premature Atrial contractions (PAC’s) Early excitation of the atrial myocardium. Common and almost always harmless. Premature Ventricular contractions (PVC’s) Early excitation of the ventricular myocardium. Somewhat common and almost always harmless. As long as there are no structural heart problems.