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ECG
Electrocardiogram Concepts
| Question | Answer |
|---|---|
| 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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