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EKG lab

EKG readings. There must be a full 12 leads recorded and labelled plus a rhythm strip, usually from lead II. The baseline must be stable and not wandering. Leads must be well attached, even if it means shaving a hairy chest. There should be little interference from skeletal muscle. The patient mu

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EKG lab

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    1. EKG lab

    2. EKG readings There must be a full 12 leads recorded and labelled plus a rhythm strip, usually from lead II. The baseline must be stable and not wandering. Leads must be well attached, even if it means shaving a hairy chest. There should be little interference from skeletal muscle. The patient must be relaxed and comfortable. There should be a square wave calibration to show that 1mV is equivalent to 1cm in height. Speed should be 25mm/sec. Hence 1 large square is 200msec and 1 small square is 40msec. Rhythm and Rate Are there P waves? Are they regular? Does every one precede a QRS? Is the PR interval constant? What is the PR interval? The PR interval should be between 120 and 240 msec (3 to 6 small squares)

    3. Normal EKG A positive wave form (QRS mainly above the baseline) results from the wave of depolarization moving towards the positive end of the lead. A negative waveform (QRS mainly below the baseline) is when a wave of depolarization is moving away from the positive electrode (towards the negative end of the lead). ECG paper has 1 millimeter small squares - so height and depth of wave is measured in millimeters. 10 mm = 1.0 mVolt Horizontal axis is time. .04 seconds for 1 mm (1 small box). 0.2 seconds for 1 large box = 5 small boxes = 5 x .04 seconds.

    4. ECG interpretation: look at five areas, in order, on each ECG. Rate Rhythm (Intervals) Axis Hypertrophy Infarct

    6. Mathematical method: Use this method if there is a regular bradycardia, i.e. - rate < 50. If the distance between the two R waves is too long to use the common method, use the approach: 300/[# large boxes between two R waves].                                                       Figure 5: Count number of large boxes between first and second R waves=7.5. 300/7.5 large boxes = rate 40. Six-second method: Count off 30 large boxes = 6 seconds (remember 1 large box = 0.2 seconds, so 30 large boxes = 6 seconds). Then, count the number of R-R intervals in six seconds and multiply by 10. This is the number of beats per minute. This is most useful if you have an irregular rhythm (like atrial fibrillation) when you want to know an average rate.                                                      Figure 6: Count 30 large boxes, starting from the first R wave. There are 8 R-R intervals within 30 boxes. Multiply 8 x 10 = Rate 80.

    7. Estimating rate - quiz

    10. Rhythm A reasonable way to group arrhythmias is in four general groups. 1. Irregular rhythms 2. Escape & premature beats 3. Ectopic beats 4. AV blocks

    11. Group 1: Irregular rhythms A) Sinus arrhythmia. P waves and P-R intervals are all identical because they originate from the sinus node. Sinus rate may vary normally a bit (increase with inspiration, decrease with expiration) but if the rate varies a lot, this term is used. Figure 7: Sinus arrhythmia: P waves are identical.

    12. B) Wandering atrial pacemaker. Pacemaker discharges from different atrial locations - the clue here is the P waves are of varying shape and differing PR intervals. PR interval is measured from the beginning of the the P wave to the beginning of the QRS - if the atrial pacemaker location varies it will take different lengths of time to get to the ventricle - resulting in different PR intervals. If the rate of the wandering atrial pacemaker is >100 it is descriptively called multifocal atrial tachycardia.

    13. C) Atrial fibrillation. You will frequently see this arrhythmia. there are no P waves, only irregular or wavy baseline. the QRSs are irregularly spaced, therefore it is included under irregular rhythms.

    14. Group 2: Escape & Premature beats escape beat is late premature beat is early Atrial escape Different appearing and late P wave. Ventricular escape No P, wide, bizarre QRS. An ectopic pacemaker fires early before the next scheduled beat.

    15. Premature atrial contraction "PAC", early and differently shaped P wave, narrow QRS. Premature ventricular contraction No P, wide bizarre QRS. PVCs that occur three (3) or more in a row (ventricular tachycardia) multifocal PVCs (different shapes), PVCs that land on a previous T wave (R on T phenomenon) can be dangerous in a patient with underlying heart disease.

    16. Group 3: Ectopic Beats [150-250] Paroxysmal tachycardia [250-350] Flutter [350+] Fibrillation

    17. Paroxysmal supraventricular tachycardia: note accelerated rate and narrow QRS complexes.

    18. Ventricular tachycardia: note fast rate and wide bizarre QRS.

    19. Ventricular fibrillation: erratic and wavy baseline.

    20. Group 4: AV blocks

    21. 2nd degree block - type 1 Also called "Wenkebach". PR interval gets progressively longer each beat until finally a QRS is "dropped" (missing).                                                                    Figure 20: Note the increasing PR interval before the QRS is dropped, then the cycle is repeated. 2nd degree block - type 2 Also called "Mobitz II". Look out! A more serious conduction problem than Type 1. PR intervals are constant and a QRS is "dropped" intermittently. Figure 21: Note the dropped QRS after the second and sixth P wave in lead II (the rhythm strip).

    22. 3rd degree block The atrial rate is independent of the ventricular rate (P wave and QRS march out separately. The clue here is no relationship at all of the P-R intervals). The P-R interval is constantly changing, the QRS is usually wide and bizarre because it is ventricular origin.                                                                          Figure 22: Note the P waves and QRS waves are independent of each other.

    23. Intervals An interval is a portion of the baseline and at least one wave. We measure an interval on the horizontal axis in seconds. The PR, QRS, and QT are the intervals which should be routinely scanned on each ECG. For measuring intervals, look at the widest form in any lead. Figure 23: Intervals. PR interval (beginning of P wave to the beginning of the next QRS). Normally, < .2 seconds or one large box. If it is > .2 seconds, it is a first degree block. (Note: this concept was introduced under blocks). Figure 24: Note the prolonged PR interval (.28 seconds), especially at the second beat.

    25. Atrial Flutter P waves are well demonstrated in II, III and aVF but are best examined in V1. Atrial flutter shows clear P waves like the teeth of a saw. There is usually a rapid ventricular rate and a 2:1 A-V block. The atrial rate is usually around 300 a minute with a ventricular rate around 150. Atrial fibrillation In atrial fibrillation the pattern is far less obvious. There may be rapid, small undulations, no apparent pattern or a pattern like a worn out saw, compared to the new saw pattern of flutter. Abnormal PR Interval. The PR interval is short in Wolff-Parkinson-White syndrome. In 1st degree heart block there is a prolonged but constant PR interval. It is over 200 msec and all P waves are followed by a QRS. 2nd degree heart block is called Mobitz I or Mobitz II, the latter also known as Wenckebach phenomenon. In Mobitz I the PR interval is prolonged but at regular intervals, like 1 beat in 3 or 1 in 4, a P wave is not followed by a QRS. In Mobitz II or Wenckebach the PR interval becomes longer after each beat until a QRS is dropped and the pattern starts again. 3rd degree heart block is complete A-V dissociation and there is no relationship between the P waves and the QRS complexes. They are fired from different pacemakers. Bradycardia is usual. Myocardial Infarction The picture with myocardial infarction will vary according to the site of the infarction and whether it is partial or full thickness. Leads I and aVR are anterior leads. II, III, and aVF are inferior leads. The V leads will show if it is anterior-septal with early V leads affected or anterior-lateral with late V leads involved. In the acute phase (within minutes) there is ST elevation over the affected area. With a full thickness infarct there may be ST depression over the reciprocal leads (inferior leads in an anterior infarct and vice versa in an inferior infarct) T waves are higher and wider. This is called hyperacute T wave changes. Pathological Q waves are defined as duration beyond 40 msec or >Ľ of R-wave amplitude Over the next few hours the ST segments return to normal and shortly after, the T waves become inverted but Q waves remain. Common abnormalities

    26. Common abnormalities Bundle Branch Block Right bundle branch block occurs as a congenital anomaly or is associated with volume overload in the right ventricle. Left bundle branch block is almost always pathological, reflecting disease of the left ventricle. Right bundle branch block produces a prolonged QRS, usually about 160 msecs or 4 small squares Left bundle branch block produces a longer QRS, usually around 200 msec with a more square pattern than RBBB. The changes are best seen in the lateral V leads. Causes of Left Axis Deviation left anterior hemiblock inferior myocardial infarction pacemaker emphysema hyperkalaemia Wolff-Parkinson-White syndrome ostium primum ASD some authorities say that left ventricular hypertrophy causes LAD whilst others are adamant that it does not. Causes of Right Axis Deviation normal finding in children and tall thin adults right ventricular hypertrophy chronic lung disease even without pulmonary hypertension anterolateral myocardial infarction left posterior hemiblock pulmonary embolus Wolff-Parkinson-White syndrome Ostium secundum ASD ventricular septal defect

    27. Causes of Extreme Axis Deviation emphysema hyperkalaemia. pacemaker ventricular tachycardia Causes of ST Segment Changes Digoxin produces a down sloping ST depression. Pericarditis causes ST elevation that tends to be generalised and not located to the area supplied by one coronary artery. Ventricular aneurism causes ST elevation. This usually follows a large anterior infarct and if the ST segment fails to return to the baseline an echocardiogram is required to exclude aneurism. ST depression suggests ischaemia and/or unstable angina. Extensive ST depressions with a clinical picture of MI can indicate subendocardial damage. Right ventricular hypertrophy The R wave is bigger than the S in V1. T waves Inverted T waves in a predominantly positive lead suggest ischaemia or old MI. T waves should be upright in V3 to V6. Tall T waves occur in the acute phase of MI and in hyperkalaemia.

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