Transcript less than half of a large box

EKG for ACLS
AMANDA HOOPER
2008-2009
Let’s start with some basics…
 V1: right 4th intercostal space
 V2: left 4th intercostal space
 V3: halfway between V2 and V4
 V4: left 5th intercostal space,
mid-clavicular line
 V5: horizontal to V4, anterior
axillary line
 V6: horizontal to V5, midaxillar line
Conduction System of the Heart
 Sinus node is the pacemaker of the
heart, the dominant center of
automaticity.
 Generates continuous regular
depolarization stimuli at a rate of
60-100 bpm
 There are other potential
pacemakers that can take over if
SA node fails, and they have
different intrinsic rates. These are
in the atria, AV junction, and the
ventricles.
EKG Paper
 EKG machine moves at
25 mm/sec, each small
box is 1 mm
 Small boxes represent
0.04 sec
 Large boxes represent
0.2 sec
 Five large boxes equal
one second
EKG Waves and Intervals
 P wave: the sequential activation (depolarization) of the right and left atria
 QRS complex: right and left ventricular depolarization (normally the ventricles




are activated simultaneously)
ST-T wave: ventricular repolarization
PR interval: time interval from onset of atrial depolarization (P wave) to onset
of ventricular depolarization (QRS complex)
QRS duration: duration of ventricular muscle depolarization
QT interval: duration of ventricular depolarization and repolarization
Systematic Approach to ECG Interpretation
 Rate
 Rhythm
 Axis
 Intervals
 Hypertrophy
 Infarct (QRST Changes)
Determining Rate
 R-R interval is ventricular rate
 p-p interval is atrial rate. Usually the same but not always
 Several ways to do this…
 1) Count down the number of large boxes: 300, 150, 100, 75, 60, 50, ....
 Ex: this one is between 150 and 100, closer to 150 so we might say ~130-140 bpm
 2) Count the number of large boxes and divide by 300
 Ex: 300/2 = 150 but it is a little slower than that so we might say ~130-140 bpm
 3) Count the number of small boxes between beats and divide into 1500
 Ex: 1500/11 = 136 bpm
Analyzing A Rhythm Strip
 Is the rhythm regular?
 What is the rate?
 Is the QRS complex
narrow or wide?
 Are P waves present?
 Are P waves related to
the QRS complexes?
 What is the PR
interval ?
Intervals
 PR interval


From the onset of atrial depolarization
to the onset of ventricular
depolarization
Normal between 0.12 and 0.20 sec—so
should be less than a large box
 QRS interval:


Time it takes for ventricular
depolarization to occur
Normal is 0.10 sec or less—so should be
less than half of a large box
 QT interval


From the beginning of ventricular
depolarization to the end of ventricular
repolarization
Normal is les than half of a R-R interval
(can’t always rely on this if rate is very
tachycardic)
Atrial Flutter with 2:1 AV Block
Aflutter With Carotid Massage
Supraventricular Tachycardia (SVT)
 Supraventricular rhythms start by definition at or
above the AV node. If the QRS is narrow in all leads,
you can almost be guaranteed the rhythm is
supraventricular.
 Sinus rhythm, atrial fibrillation, atrial flutter,
junctional/nodal rhythms, and PSVT
 PSVT is a reentry rhythm
SVT
Myocardial Infarction
 Look for QRST changes in each lead
 Note each lead where Q waves are found
 Look for R wave progression—transition normally
occurs between V2 and V4
 Look at ST segments and note depression or
elevation
 Look for T wave inversion
 Q waves or T wave inversion may be a normal
finding in leads III, aVF, aVL, aVR, and V1
Basic Lead Groupings
 Inferior leads: II, III, aVF
 Lateral (left-sided) leads: V4 to V6 and I, aVL
 Septal leads: V1, V2
 Anterior leads: V2 to V4
 Right coronary artery:
 SA node, IV septum, inferior heart, +/- posterior heart
 Left coronary artery:
 LAD- anterior heart
 Left circumflex- lateral heart
12 EKG with Acute MI
Anteroseptal MI
Inferior MI with RV Infarction
From: Heart Disease 6th Edition. Braunwald E, Zipes D, and Libby P. 2001