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Electrocardiogram Concepts

Lead I (-) on right arm, (+) on left arm; vector dipole points in +0 degrees from horizontal (to the right)
Lead II (-) on right arm, (+) on left leg; + dipole points +60 degrees below x-axis (Southeast)
Lead III (-) left arm, (+) left leg; + dipole points +120 degrees below x-axis (Southwest)
V1 4th ICS right of sternum
V2 4th ICS left of sternum
V4 5th ICS at the mid-axillary line
V5 horizontal with V4 at the anterior axillary line
V6 mix-axillary line horizontal with V4 and V5
V3 Between V2 and V4
Precordial labeled V1-V6, unipolar leads that reflect the vector axis in the "horizontal plane"
Bipolar limb leads Leads I, II, and III; Make one lead positive and the other negative
Augmented limb leads Leads aVR, aVL, and aVF; represent vector angles in between the angles of the bipolar limb leads
aVR (+) is right arm, other limbs connected as one; vector points to the upper left (NW), or -150 from right x-axis
aVL (+) is left arm, other limbs connected as one; vector points to the upper right (NE), or -30 degrees from x-axis
aVF (+) is left leg, other limbs connected as one; venctor points directly south (+90 from x-axis)
What event does the P denote? Atrial contraction (systole); the signal travels down from the atrial tissue and propagates downward and inferiorly-->hence, upward deflection of P wave
What is the PR interval? What are normal value for it? It's the time required for signal to pass from sinus to atria to the AV node to the ventricle; Time between onset of P wave and the beginning of the QRS complex; 120-200 ms
What waves denote ventricular depolarization? What's normal for a this? QRS complex; Q is first wave down, R is spike up, S is any subsequent downward wave; up to 100 ms
What event occurs during the T wave? Repolarization of ventricle
What is the ST segment? Time period between end of QRS and the beginning of T wave
What is the QT interval? What's normal? The interval between the onset of the QRS wave and the end of the T wave; normal ~ 440-450 ms; Correct QT = QT / (RR interval)^1/2; QT = QT,c when HR = 60 bpm
What's the order you should look at ECGs? Calibrations and connections; measurable values (rate, axis, intervals); rhythm (sinus, other atrial, junctional, ventricular); conduction; hypetrophy; ischemia, injury, and infarction; other ST and T abnormalities
What are the normal calibration values for an EKG? paper speed of 25 mm/sec, gain setting of 10 mm/mV (or 1 mm = 40 msec, 5 mm = 200 msec)
How can you check that calibrations are correct? Lead I + Lead III = Lead II; Lead I and Lead V6 shold be similar in appearance; R wave should increase in amplitude as you progress from Lead V1 to Lead V6
What are normal heart rates? 60 - 100 bpm
How do you determine the axis? Orthogonal: draw vectors of leads aVF and lead I and plot them on frontal axis plane, then add them using vector addition. Isoelectric: find limb lead with total vector ~0 (equal - and +)--limb lead that is orthogonal is the frontal plane axis
What's normal for frontal plane axis? -30-110 degrees.
What frontal plane axis will you get in Left arm deviation? -30 to -90
What frontal plane axis will you get in right axis deviation? -110 to -180 degrees
What frontal plane axis will you get in extreme left/right axis deviation? What is this often called? -90 to 180; indeterminate axis or (superior / northwest axis)
What would a short PR interval indicate? Indicates accelerated AV conduction (Wolf-Parkinson-White syndrome)
What would a prolonged PR interval indicate? first degree AV block
What should you suspect if QRS is prolonged? Some type of bundle branch block
What is the most common type of rhythm? Sinus rhythm; characterized by p-wave being upright in Lead II
How do you distinguish sinus rhythm? Upright p-waves in lead II
What is rhythm? Relationship between atrial and ventricular activity; can begin in atrium, atrioventricular junction, or ventricle
What is the most common abnormal rhythm? Atrial fibrillation
How do you distinguish atrial fibrillation? irregularly irregular grouping of QRS complexes and absence of clear p-waves
Describe ventricular rhythms as seen on an ECG QRS complex is wider than normal; different axis or morphology than normal; can be slow (<100 bpm; accelerated idioventricular rhythm) or fast (ventricular tachycardia)
What is conduction? Assessment of how cardiac signal passes from atrium to ventricular tissues
Where can conduction block occur? Atrioventricular node or distal connection tissues (proximal conduction block, distal conduction block)
1st degree AV block All signals travel through, but take longer than normal (PR interval > 200 ms); anatomically @ AV node
2nd degree AV block Most signals successfully travel
2nd degree AV block, Mobitz type 1 (Wenkebach block) progressive prolongation of consecutively conducted p waves before non-conducted or "dropped" beat; anatomically @ AV node
2nd degree AV block, Mobitz type II absence of PR interval prolongation before dropped beat; anatomically below bundle of His
3rd degree AV block many signals fail to arrive @ ventricle; complete heart block is when none of the signals reach the ventricle; anatomically below bundle of his
Right bundle branch block QRS>.120 sec; rsR' or rSR QRS pattern in right precordial leads V1 and V2; wide S wave in left lateral leads (I, V5, V6)
Left bundle branch block QRS duration > .120 sec; broad R wave in left lateral leads (I, V5, V6); R wave may be notched; absence of Q waves in left lateral leads (I, V5, V6)
Left anterior fascicular block (hemiblock) Left axis deviation; qR (or just R) in leads I and aVL (lateral location leads) with rS complex in inferior leads (II, III, aVF)
Left posterior fascicular block (hemiblock) Right axis deviation (RAD) from 90 to 180 degrees; rS complex in Leads I and aVL and a qR complex in inferior leads (II, III, and aVF)
Right atrial abnormality (hypertrophy) increased amplitude of p-wave; in inferior leads (Lead II), p-wave > 2.5 mm in height, while in V1 or V2, p-wave (+) deflection >1.5 mm
Left atrial abnormality (hypertrophy) increased duration of the p-wave; lead II, notched p-wave with duration >0.120 seconds; Lead V1, terminal p-wave forces negative and greater than one small box wide (0.04 sec) and one mm deep
* * Right ventricular hypertrophy Not easily determined, but generally expect large R wave (greater than S) in leads V1 or V2; when QRS width normal (<120 msec) and amplitude of R-wave in lead V1 greater than amplitude of S-wave in Lead V1
* * Left ventricular hypertrophy Estes criteria (>=5 points: definite LVH; 4 points: likely LVH; <= 3 points: LVH unlikely); in general, large R wave in Lead I (R>20 mm) or precordial leads V5 or V6 (R>30 mm)-->consider LVH
What might you expect to see associated with long standing systemic hypertension or significant aortic valve stenosis? left ventricular hypertrophy
Ischemia T-wave inversion
Injury ST segment elevation
Infarction Q waves ~0.04 seconds in duration and at least 25% of the following QRS height to be considered significant markers of infarction
Septal location leads V1, V2
Lateral location leads leads 1 and aVL
inferior location leads II, III, aVF
anterior location leads V2-V4
What should you suspect if you see ST elevation in Leads V1-V5 (i.e. tombstone sign?) anterior injury: acute anterior myocardial infarction
What should you suspect if ST elevation in leads II, III, and aVF? Inferior injury; acute inferior infarction
How would digoxin therapy alter ECG results? ST segment depression (sagging) with an inverted (scooped out) T-wave; frequently biphasic T-wave
What would you expect to see with diffuse ST segment elevation and diffuse PR segment depression? acute pericarditis
What would you expect to see in patients with early depolarization? Diffuse ST segment elevation often seen in young individuals associated with tall T-wves in same leads that show ST change
What would you expect to see in someone with hyperkalemia? tall, narrow, and peaked T-waves followed by interventricular conduction defects and ST segment elevation
What would you expect to see in patients with hypokalemia? ST segment depression, decreased T-wave amplitude, and development of U waves
What would you expect to see in someone with hypercalcemia? Decrease in QTc interval (slower depolarization)
hypocalcemia increase in QTc inteval
What does brugada syndrome look like? downward slope on R, depressed baseline during ST; associated with death in young people
Created by: karkis77



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