SA node depolarizes at a rate of 80-100 times per minute and sets the resting heartrate of about 75 bpm. Not every depolarization of the SA leads to a heart beat. Components of the intrinsic conduction systemSA node(sinoatrial) - a.k.a. the pacemakerAV node (atrioventricular)AV bundle (bundle of HIS) - splits left and right bundle branchesPurkinje fibersIntrinsic Conduction SystemMake sure you can label the important parts of the conduction system on this diagram.The actual cells of the conduction system are imbedded in the walls of the heart musle and not visible to the naked eye.4
Nur 0003B. Electrocardiography: the ECGImportant ConceptECG - only tests to see if the electrical conduction system is working properly, you still need to ausculate to determine if valves and pumps are working correctly.Waves and intervals of the ECGP wave - indicates depolarization of atria immediately before atrial contraction.QRS complex- precedes ventricular contraction, signals ventricular depolarization.T wave - signifies the repolarization of the ventriclesPR interval (.12-.20sec) - represents the time between atrial depolarization and ventricular depolarization.Too long - may represent AV node damage.Total heart block - atria and ventricles beat independently of one another.QT interval(~.28-.40sec) - represents the period between the beginning of ventricular depolarization through RepolarizationIf HR increases - QT becomes shorterIf HR decreases - QT becomes longerRR interval (~.8 sec)- the time it takes for one complete cycle.PQ segment– When the atria are contracting, should be isoelectric.ST segment– When the ventricles are contracting, should be isoelectric.Tachycardia - HR over 100 bpm. Can lead to fibrillation if sustained over long periods.Bradycardia- HR under 60 bpm. Good in conditioned athletes, otherwise it can lead to O2deprivation of the brain.5
Nur 0003C.Normal ECG1.Label the following: Waveforms: P wave, QRS complex P waveIntervals: RR interval, PR interval, QT intervalSegments: PQ, QT2.Determine the followingEach small box = .04secRR interval = PR interval = QT interval = 3.Heart RateDetermine RR intervalHR = (60sec/min) / RR interval
Nur 0003D.Other ECG examples1stDegree Block1.Calculate the PR interval _____2.Calculate the RR interval and heart rate _____1stDegree Block VideoAtrial Tachycardia1.Where are the p waves?