Electrocardiogram (ECG) Basics PDF

STRIPS -​ STRIP 13 -​ PREMATURE ATRIAL CONTRACTION -​ Sinus arrhythmia not on exam Objectives Draw and explain the P wave, QRS complex, T wave, and U wave. Explain where the PR and ST segments are. Define the absolute and relative refractory periods and the implications of each. Be able t...

STRIPS -​ STRIP 13 -​ PREMATURE ATRIAL CONTRACTION -​ Sinus arrhythmia not on exam Objectives Draw and explain the P wave, QRS complex, T wave, and U wave. Explain where the PR and ST segments are. Define the absolute and relative refractory periods and the implications of each. Be able to label, on a rhythm strip, all the waves and complexes. P wave Atrial depolarization PR Interval Conduction of impulse from SA → AV node → ventricles QRS Complex Ventricular depolarization Atrial repolarization (hidden)  Q wave Negative deflection Can only be one, sometimes not present R wave One or more positive deflection More than one is labeled R and R’ (R prime) S wave Negative deflection If no R wave, it is labeled “QS” QT interval Ventricular depolarization and repolarization S-T Segment Completion of ventricular depolarization, beginning of ventricular repolarization T wave Ventricular repolarization “Resting phase” U wave After T wave Not always observed due to small size Maybe purkinje repo Refractoriness Period of recovery that cells need after being discharged before they are able to respond to a stimulus Refractory period is longer than the contraction itself Absolute Refractory AKA Effective refractory period Period Cell cannot respond to further stimulation, so ​ Myocardial mechanical cells cannot contract ​ Electrical conduction system cannot conduct an electrical impulse ○​ Tetanic (sustained) contractions cannot be provoked in cardiac muscle Phases 0-3 of Cardiac Action Potential Onset of QRS complex to the peak of the T wave Relative Refractory AKA vulnerable period Period Some cardiac cells have repolarized to their threshold potential an can be stimulated to respond (depo) to a stronger then normal stimulus Downslope of the T wave Supernormal period After the relative refractory period Weaker than normal stimulus can cause cardiac cells to depolarize, and dysrhythmias can develop  End of the T wave Define "pacemaker of the heart". List the different pacemakers of the heart and their inherent rates. Track the cardiac impulse from the sinus node through the conduction system. Memorize picture SA node Right atrial wall, just inferior to Primary pacemaker 60-100 bpm superior vena cava opening Impulse → atria AV Floor of right atrium Impulse from SA node, delays 40-60 bpm junction immediately behind tricuspid relay to BoH so atria contract valve and near opening of before ventricles coronary sinus Bundle of Superior portion of Receive impulse from AV, relays His interventricular septum to R and L BB Bundle Interventricular septum Receives impulse from BB, Branches relays to Purkinje Purkinje Ventricular myocardium Receives from BB, relays to 20-40 bpm fibers ventricular myocardium Define arrhythmia. Explain what happens when an inherent pacemaker fails to fire. Dysrhythmias Usually due to 3 basic mechanisms 1.​ Enhanced automaticity 2.​ Triggered activity 3.​ Reentry Enhanced Abnormal condition in which Automaticity 1.​ Cardiac cells that are not normally associated with a pacemaker function begin to depolarize spontaneously 2.​ A pacemaker site other than the SA node increases its firing rate beyond that which is considered normal Possible causes of enhanced automaticity ​ Catecholamines (epinephrine) ​ Administration of atropine sulfate ​ Digitalis toxicity ​ Acidosis ​ Alkalosis ​ Hypoxia ​ Myocardial ischemia or infarction ​ Electrolyte disturbances ○​ Hypokalemia, hyperkalemia, hypocalcemia Triggered activity If area of delayed impulse is relatively refractory, the impulse can cause + reentry depolarization, leading to ​ Single premature beat ​ Repetitive electrical impulses ○​ Leads to short periods of abnormally fast HR Common causes ​ Hyperkalemia ​ Myocardial ischemia ​ Some antiarrhythmics Escape When the SA node slows down or fails to initiate depo, and a lower site spontaneously produces impulses (assumes responsibility for pacing the heart) Escape beats or Protective mechanisms to maintain cardiac output rhythms Originate in AV junction or ventricles  Ex. ​ Junctional escape beats ​ Junctional rhythm ​ Idioventricular rhythm (AKA ventricular escape rhythm) ​ Ventricular escape beats Conduction May occur because disturbances ​ Trauma ​ Drug toxicity ​ Electrolyte disturbances ​ Myocardial ischemia ​ Infarction Conduction may be too rapid or slow Ex. AV blocks In ECG QRS Absent/abnormally shaped complex/interval Abnormally prolonged P wave Absent, multiple in number. Or abnormally shaped PR intervals Abnormally shortened or prolonged HR Abnormally fast/slow Irregular rhythm/interrupted rhythm Count HR on 6 second strip x 10 = HR Count number of little blocks between QRS complexes and divide by 1500 Define electrode. Electrodes Small adhesive patches with conducting gel placed on the skin that pick up electrical impulses and sends them through attached lead wired to a cable on the ECG/cardiac monitor Paper, plastic, or metal device containing conductive media and is applied to the skin. Applied at specific locations 3 types Metal disk Metal suction cup Disposable disk Adhesive ring w/ conductive substance in the center  ​ Remove oil + dead cells first ○​ Alcohol swabs dry out skin, not recommended ○​ Brisk dry rub of skin used instead (gauze sponge) Explain the delineations of EKG paper: How many seconds in a small block and big block? How many small blocks in one minute? How many big blocks in a minute? Small block 0.04 sec per box 1500 small box per min Big block 5 small boxes 0.20 sec per box 300 big box per min On a rhythm strip, determine if the PR, QRS, and QT intervals are normal or abnormal. PR interval 0.16 (normal is 0.12-0.20 sec or 3-5 small blocks) QRS complex 0.08 (normal is