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Transcript
Cardiovascular Physiology Today Anatomy Requirements of an effective heart ECG’ ECG’s Arrhythmias in the normal heart Abnormal arrhythmias 1 The Heart Aorta Pulmonary artery Superior vena cava Pulmonary veins Pulmonary veins Left atrium Right atrium Right ventricle Left ventricle Interventricular septum Inferior vena cava Sherwood Fig. 9-4a, p. 303 The Heart Wall Endocardium (inner) Myocardium (middle) Cardiac muscle Epicardium (outer) Layer of endothelial cells External membrane Pericardium 2 Cardiac Muscle (myocardium) 99% contractile cells 1% autorhythmicity cells Aerobic muscle Self-excitate Properties of skeletal and smooth muscle Intercalated discs Gap junctions Desmosomes Electrical activity of the heart Autorhythmicity the ability to generate own rhythm Pacemaker/autorhythmic cells Conductive system (fibers) spreads excitation throughout heart 3 Anatomy of conduction system Interatrial pathway Atrioventricular (AV) node Sinoatrial (SA) node Right atrium Left atrium Internodal pathway Left branch of bundle of His Right branch of bundle of His Left ventricle Right ventricle Purkinje fibers Sherwood Fig. 9-8, p. 306 Delay between Atrial and Ventricular contractions Impulse does not travel from to ventricles before atria contract Atria must empty contents into ventricles before ventricular contraction AV valves If both contracted together – not efficient AV nodal delay (at least .1s) 4 Electrical Activity in Pacemaker Cell (SA nodal fibre) Sherwood Fig. 9-15, p. 313 Pacemaker cells SA node = pacemaker of the heart If SA node is damaged, other cardiac cells can take over Latent pacemakers- AV node and purkinje fibers Action potentials can be changed 5 Electrical Activity in Contractile Cells Sherwood Fig 9.15, p.279 Comparison of nodal fibre and cardiac muscle fibre Guyton & Hall Fig. 10-2, pg.122 6 Coordination and pressure generation for left and right outputs Both members of a pair contact simultaneously Each atria and ventricle contract as a syncytium Pressure generation determined by force of contraction Guaranteed time for filling Refractory period Tetanus cannot occur Ventricle .25.30sec Atria .15sec Sherwood Fig. 9-17, p. 281 7 Electrocardiogram Non-invasive Body fluids are conductors Comparison of voltages detected by electrodes at two points SUM of activity in ALL cardiac muscle Exact pattern of activity depends on orientation of electrodes ECG diagram R T P Q PR P S ST TP interval Sherwood Fig. 9-15, p. 313 8 Normal ECG Heart beat reciprocal of time interval between two successive beats ??? Shape/ organization of heart http://library.med.utah.edu/kw/ecg/image_index/index.html Athletes ECG’s 1 horizontal box= .2s (small box 0.04s), 5 boxes = 1sec 10 small division upward or downward= 1millivolt Respiratory Sinus Arrhythmia Normal phenomom HR ↑ with inspiration HR ↓ with expiration Expressed more in young and fit Marquette Electronics Copyright 1996 http://library.med.utah.edu/kw/ecg/image_index/index.html 9 Bradycardia & Tachycardia Bradycardia ≤60bts/min Tachycardia ≥ 100 bts/min Timing of P-QRS-T same but more/less frequent Guyton & Hall fig. 13-1 & 13-2, pg. 150 Abnormal Arrhythmias Abnormal rhythmicity of pacemaker Shift of pacemaker from SA node Blocks during transmission of impulse Abnormal transmission pathways Spontaneous generation of abnormal impulses 10 Breakdown of SA node Pacemaker Authority 152 Guyton & Hall fig. 13-4 pg.152 Impulse from SA node is blocked before it enters atria Latent pacemakers pick up authority No/small p-waves clue: Atrial fibrillation Breakdown of AV coupling Causes: ischaemia, compression, inflammation, extreme stimulation 1st degree: delay in conduction, prolonged P-R interval 0.2s, QRS same 2nd degree: incomplete heart block, P-R interval between .25-.45sec, atria beating faster than ventriclesdropped beats Compete AV block: P-wave regular frequency completely unrelated to ventricular firing, Ventricular QRS followed by T wave normal. 11 Breakdown of ventricular coupling and refractory period Breakdown of left/right ventricular coupling Same mechanisms that cause AV block QRS may be considerable abnormal Breakdown of refractory safety period Hypertrophy can cause different refractory periods in epicardium & endocardium Left Ventricular Hypertrophy In exerciseadaptation to increased preload/afterload Enhances pumping capacity http://library.med.utah.edu/kw/ecg/image_index/index.html Increased QRS amplitude 12 Exercise Hyperkalaemia Elevated potassiumspeeds recovery of action potentials Tall peaked T-wave with narrow base http://library.med.utah.edu/kw/ecg/image_index/index.html Widened QRS complex Review: Cardiac Pumping Efficient cardiac pumping requires: Atrial excitation and contraction to be complete before onset of ventricular contraction Each heart chamber to contract as a unit Both atria to contract simultaneously and both ventricles to contract simultaneously 13