|In patients without known heart disease, the ECG is used as a screening test for coronary artery disease, cardiomyopathies, or left ventricular hypertrophy and is then used as a baseline for future reference and comparison.|
|Preoperatively, it is used to rule out silent coronary artery disease. This is very important as the presence of disease can cause complications with arrythmias during surgery and after, as well as anesthesia problems. It will not, definately rule out the surgery, if disease is present, but will help staff to be better prepared for what may happen. If it is bad enough, however, it can be a deciding factor.|
|The ECG may also provide information in the presence of metabolic alterations, such as hypercalcemia and hypocalcemia and hyperkalemia and hypokalemia.|
|In patients with known heart disease, the ECG serves as a baseline for the severity and progression of the disease process. The ECG is invaluable in the evaluation of patients with chest pain and in the management of patients with suspected or known to have acute myocardial infarction or coronary insufficiency. Most patients with myocardial, valvular, and congenital heart disease will eventually demonstrate ECG abnormalities.|
|Rhythm disorders can effectively be evaluated through an ECG rhythm strip. This can be done with bedside EKG monitoring or "telemetry", but is much better seen and diagnosed with a 12 lead EKG, as many views of the heat can be viewed all at once.|
|First wave of complex||
1.Is negative/below isoelectric line
2.Must be first wave of complex and must be negative and small
3.Amplitude (normal q wave) is less than one fourth height of its R-wave
1.Is always positive (above isoelectric line)
2.No such thing as a "negative R-wave"
|S wave||1. Is a negative deflection following the R wave.|
1. Represents ventricular repolarization
2. Normal T waves are in the same direction as their complex 3. Normal T wave is asymmetrical and it peaks toward the end, instead of the middle.
4. Normal T: in frontal plan <= 5mm, in precordial plane <= 10mm tall.
1. Is measured from the end of complex to the beginning of T wave
2. ST is the beginning of ventricular repolarization
3. Normal ST is on the isoelectric line or no more than 1mm above or below isoelectric line
4. Elevated ST is more than 1mm above isoelectric line
5. Depressed ST is more than 1 mm below isoelectric line
|PRI (normal PRI 0.12 - .20 seconds)||
1. Normal PRI is measured from beginning of the P to the beginning of
2. This measurement represents the time it takes for a wave of depolarization to spread through the atria, AV node, and AV junction
1.RCA supplies the inferior wall of the ventricle
2.MI's involving inferior surface of the heart will be seen in leads II, III, and aVF
1.Leads I, aVL, V5, V6.
2.Lateral infarctions are usually associated with obstruction of the left circumflex artery.
|Septum and Anterior Leads||
1.Intraventricular septum - leads V1 and V2.
2.Anterior Wall - V2, V3, V4.
3.Anterior infarctions are usually associated with occlusion of the left anterior descending branch of the left coronary artery.
|Elevated ST segments (myocardial injury)||
1.Normal ST segments are in the isoelectric line or no more than 1mm
above or below it.
2.An abnormal electrical charge is produced on membrane of myocardial cell resulting in abnormal current flow causing an elevation of ST segment.
3.Myocardial injury causes elevation of ST segments over affected area of the ventricle. ST segments changes are the earliest indication on EKG.
4.ST segment changes occur within a few hours or a few days and should return to the isoelectric line within 2 weeks.
|Inverted T waves (myocardial ischemia)||
1.Myocardial ischemia causes symmetrical inversion of the T wave. T wave abnormalities
reflect a change in ventricular repolarization.
2.As the ST segment begins to return to the isoelectric line, the symmetrical inversion of the T wave appears.
3.The T wave will become progressively deeper as the ST segment returns to the isoelectric line.
|Pathological Q waves (myocardial infarction)||
1.Normal Q waves are small, less than 1 mm deep or wide and one fourth the height of
their R wave.
2.Pathological Q waves usually develop when ST segments are elevated and appear several hours or days after the clinical manifestations of the MI.
3.Abnormal Q must be one small square (0.04 sec) wide and greater than one-third of QRS height in Lead III.
4.Myocardial infarction causes pathological Q waves over the affected area of the ventricle. The age of the infarction can be determined.
a.Q waves only - old infarction
b.Q waves with elevated ST segments (with or without T wave inversion) - acute infarction
c.Q waves with inverted T waves - age undetermined.
|hyperacute phase||ST elevation and upright T waves. Occurs in first few hours and lasts 1-6 weeks. ST elevation beyond 6 weeks - suspect ventricular aneurysm.|
|fully evolved phase||after hours or days. Deep T waves and appearance of diagnostic q waves.|
|resolution phase||T waves return to normal within weeks to months.|
|stabilized chronic phase||q waves remain permanent|
|P Wave Morphology||
The P wave in general should not be more than 1 box wide or 1 box tall.
If it exceeds these, it
generally means that either or both atria is enlarged (hypertrophied).
The best lead to look at the P wave is V1. In lead V1, the following
1.Positive deflection greater than 1 box wide or 1 box in height --> right atrial hypertrophy
2.Total P wave duration greater than 0.12 sec and negative deflection of P wave greater than 1 box wide or 1 box in depth --> left atrial hypertophy
The PR interval indicates AV conduction time which is normally between
0.12 - 0.20 msec (3 - 5
boxes wide). If the PR interval is greater than 0.2 sec, then an AV block
is present. There are
several types of AV blocks:
1st degree AV Block: PR>0.20 sec.
2nd degree AV Block: 2 types:
a.Type I (Mobitz I or Wenckeback): increasing PR interval until a QRS complex is dropped. It is usually benign.
b.Type 2 (Mobitz II): QRS dropped without any progressive increase in PR interval (i.e., PR interval is constant but still >0.20 sec).
3rd degree AV Block: atria and ventricles are electrically dissociated. Therefore, P waves and QRS complexes will occur independent of each other. As always, use the QRS complexes to determine heart rate.
***A PR interval that is <0.12 sec (when associated with a prolonged QRS) should prompt evaluation for Wolff-Parkinson-White Syndrome (WPW).***
The QRS complex can be quite difficult to interpret. However, stepwise
evaluation will make it
easier. The things to consider are the following:
Duration: should be 0.08 - 0.10 sec (2 - 2.5 boxes). If duration is prolonged, then the presence of bundle branch blocks and WPW (if PR interval is also abnormally shortened in duration).
Presence of Q waves: can indicate presence of infarct if present in V1, V2, and V3. A Q wave in III and aVR is normal. A Q wave is significant if it is greater than 1 box wide or greater than 1/3 the amplitude of the QRS complex.
|ST Segment Morphology||
The ST segment is important because it can show whether ischemia or
infarct is present. In general,
an ST segment depression indicates ischemia while elevation generally
indicates infarction. When
examining the ST segment, evaluate elevations or depressions 0.06 seconds
after the J point (since
the ST segment can at times be sloping). The location of the ST elevations
on the ECG can help to
identify a location of the infarct:
Anterior Wall Infarct (corresponding to Left Anterior Descending Artery): V1, V2
Lateral Wall Infarct (Circumflex Artery): V3, V4
Inferior Wall Infarct (can be combination of Circumflex or Right Coronary Artery): V5, V6, I, aVL
ST depression in V1 and V2 associated with large R waves may indicate Posterior Wall infarction (corresponding with Right Coronary Artery).
|T Wave Morphology||
In general, T waves are in the same direction as the largest deflection
of the QRS (normally the R
wave). The following pathology can be associated with T wave changes:
Ischemia: when T waves are in an opposite direction (inverted), it
may indicate that ischemia
is present, especially when it occurs in a pattern as previously
described for ST segment
Hyperkalemia: associated with tall peaked T waves, flat P waves, and wide QRS complexes
Hypokalemia:associated with flat T waves, U waves, U waves taller than T waves
|U Wave Morphology||The presence of U waves may indicate hypokalemia.|
May be lengthened in the following:
May be shortened in hypocalcemia.