05. PHYSIOLOGICAL BASIS OF ARRHYTHMIAS.ppt.pdf

ECG Interpretation and Arrhythmias Dr K. Thaxter Nesbeth Physiology Section Department of Basic Medical Sciences Anatomy of a 12-Lead ECG normal simes rythegm  Anatomy of a 12-Lead ECG aye Lead I Lead II Lead III Cal...

ECG Interpretation and Arrhythmias Dr K. Thaxter Nesbeth Physiology Section Department of Basic Medical Sciences Anatomy of a 12-Lead ECG normal simes rythegm  Anatomy of a 12-Lead ECG aye Lead I Lead II Lead III Calibration tracing Anatomy of a 12-Lead ECG inverted ground Anatomy of a 12-Lead ECG  Anatomy of a 12-Lead ECG (cont.) At the bottom of this 12-lead is a rhythm strip Any of the 12-leads can be shown as rhythm strips – you configure the device. Lead II is most often chosen as rhythm strip  Analyzing the ECG Using the 12-lead tracing – Look at each lead (from left to right), starting at the top and moving to the bottom in the first column – Then in the second column, next in the third column, and then lastly, in the fourth column 7  Interpreting ECGs: Nine-Step Process A systematic process Ensures important aspects become the focus for planning patient care  thesame PwaveandOrscomplexhas P wave DURATION 021s P Wave Amp Duration s 0.2s mV 006 0.10 seconds Amplitude 0.05-0.25mV Duration 0.06-0.10 seconds Waveform is upright and slightly asymmetrical 9  PR Interval Duration 0.12-0.20 seconds PR interval 0.12 0.20 Seondse 0.20 0.12 20 0.12 0 0.12 020  QRS Complex Amplitude 0.5-3.0mV Duration 0.06-0.10 seconds 0.5 3 mV 5 30 mm A  ST Segment and T Wave ST segment is isoelectric line that follows QRS complex T wave is larger, slightly asymmetrical waveform that follows ST segment J point is start of ST segment  QT Interval Distance from onset of QRS complex until end of T wave – Measures time of ventricular depolarization and repolarization Has normal duration of 0.36 to 0.44 seconds Normal deportatiation and repolarization of ventrilels has a duration of 0.36 0.44 seconds  Small upright seen U Wave following the T wave, but before the next P wave Repolarisation of papillary muscles / Purkinje fibers Voltage low U wave often goes unnoticed  Heart Rate The average heart rate in the adult is 60 to 100 beats per minute A heart rate that is slower or faster is considered abnormal Calculate as 300/ # large boxes in R-R interval  Characteristics of Normal Sinus Rhythm Waveforms and intervals at a rate of 60 to 100 impulses /min (adult) Upright and slightly asymmetrical P waves, each followed by a QRS complex of normal upright contour, duration, and configuration  Characteristics of Normal Sinus Rhythm A PR interval (PRI) of normal duration that precedes each QRS complex A flat ST segment followed by an upright and slightly asymmetrical T wave A normal QT interval Sometimes the presence of a U wave  Step 1: Calculate Rate Number of big Rate boxes 1 300 2 150 3 100 R wave 4 75 5 60 6 50 Rule of 300- Divide 300 by the number of large boxes between each QRS = rate  Short cut: Calculate Rate 3 1 1 0 5 0 7 6 5 0 0 0 5 0 0 Option 2 (cont) – Memorize the sequence: 300 - 150 - 100 - 75 - 60 - 50 Approx. 1 box less than Interpretation? 100 = 95 bpm What is the heart rate? www.uptodate.com (300 / 6) = 50 bpm  Step 2: Determine regularity R R Mark one R-R interval on a paper. Move the paper so the markings sit over two successive R-R intervals Do the marks match up? = Regular rhythm  Checking Regularity R-R intervals equidistant apart = Regular rhythm R-R intervals at different distances apart = Irregular rhythm  Step 3: Assess the P waves Are there P waves? Do the P waves all look alike? Do the P waves occur at a regular rate? Is there one P wave before each QRS? Interpretation? Normal P waves with 1 P wave for every QRS  Step 4: Determine PR interval Start of P wave to start of QRS complex Normal: 0.12 - 0.20 seconds. (3 - 5 boxes) Interpretation? 0.12 seconds  Step 5: QRS duration Start of Q wave to end of S wave Normal: 0.04 - 0.12 seconds. (1 - 3 small boxes) Interpretation? 0.08 seconds  Rhythm Summary Rate 90-95 bpm Regularity regular P waves normal PR interval 0.12 s QRS duration 0.08 s Interpretation? Normal Sinus Rhythm  Arrhythmias 8 Abnormal formation of action potentials Anatomical problems Drugs Electrolyte imbalances Degenerative changes  Sinus Arrhythmias Heart rate 100/min is tachycardia Bpm appor 130180  of High rate Atrial Flutter depolarization of Atria Contraction rates can be 250-350/min Abnormal recurrent Contraction rate of atria is so high that not all P depolarizations waves are followed by a QRS complex arising from abnormal forces in the Atria Only some impulses transmitted by AV node (Variable block) Atrial Arythmic ps  Atrial fibrillation Not via SA node Depolarisation currents arise from many sites within the atria Uncoordinated, low voltage, high frequency depolarisations (fireworks display) No discernable P waves Ventricular rate irregular and rapid Ventricular rate >200 leads to a fall in Cardiac output as ventricles do not have enough time to fill  Ventricular fibrillation NO discernable waves requires defibrilation No ventricular filling No cardiac output  AV Nodal Blocks 1st Degree AV Block PR interval 0.2 long 2nd Degree AV Block, Mobitz Type I Pr interval is gradually lengthened Wenkebac 2nd Degree AV Block, Mobitz Type II PR interval is fixed but PR drops randomly 3rd Degree AV Block PR and QRS are discounted San_ Au Bundle of His Purkinje Gore  AV nodal Blocks AV blocks Abnormal or depressed impulse conduction Atrial rate is normal – First degree block PR interval fixed and > 0.2 sec – Second degree block, Mobitz type 1 (Wenkebach PR gradually lengthened, then drop QRS – Second degree block, Mobitz type 2 PR fixed, but drop QRS randomly – Type 3 block PR and QRS dissociated  Rhythm test Rate? 60 bpm Regularity? regular P waves? normal PR interval? 0.36 s prolonged PRinterval QRS duration? 0.08 s Interpretation? 1st Degree AV Block  sick is Av node of the bundle 1st Degree AV Block or not is his Consistent 1:1 relationship between P and QRS Etiology: Prolonged conduction delay in the AV node or Bundle of His. Deviation from NSR – PR Interval > 0.20 s  Rhythm test Rate? 50 bpm Regularity? regularly irregular P waves? nl, but 4th no QRS Ecm PR interval? lengthens QRS duration? 0.08 s Interpretation? 2nd Degree AV Block, Type I Wentrebuch  2nd Degree AV Block, Type I (Wenkebach block) Normal atrial impulse Longer and longer delay in the AV node One impulse (usually the 3rd or 4th) fails to make it through the AV node. Deviation from NSR – PR interval progressively lengthens, then the impulse is completely blocked (P wave not followed by QRS).  Rhythm test Rate? 40 bpm Regularity? regular P waves? nl, 2 of 3 no QRS PR interval? 0.14 s QRS duration? 0.08 s Interpretation? 2nd Degree AV Block, Type II  2nd Degree AV Block, Type II: (Mobitz II) Consistently prolonged PR interval Beats are ‘dropped’ intermittently Deviation from NSR – Occasional P waves are completely blocked (P wave not followed by QRS).  Rhythm test Rate? 40 bpm Purkinje fibres Regularity? regular P waves? no relation to QRS PR interval? none QRS duration? wide (> 0.12 s) Interpretation? 3rd Degree AV Block miscommunication  messages from the sinoatrialnodeis no reaching the AV node 3rd Degree AV Block Complete block of conduction in the AV junction Atria and ventricles form impulses independently of each other. Without impulses from the atria, the ventricles own intrinsic pacemaker kicks in at around 30 - 45 beats/minute.  Summary The key to making sense of what is seen on any ECG tracing is to approach it in a logical and systematic manner The Nine-Step Process assesses the main elements of the ECG tracing  Summary The average heart rate in the adult is 60 to 100 beats per minute. – A heart rate that is slower or faster is considered abnormal The heart beats in a regular, rhythmic, cyclical fashion, producing specific waveforms and intervals with each heartbeat. – An irregular rhythm is abnormal  Summary Throughout the ECG tracing, there should be one normal upright P wave preceding each narrow upright QRS complex The PR interval that precedes each QRS complex should be of the same duration and within 0.12 and 0.20 seconds  Summary After each QRS complex of the ECG tracing, there should be a flat ST segment, followed by an upright and slightly asymmetrical T wave The QT intervals should be between 0.30 and 0.44 seconds in duration U waves may or may not be present