Electrocardiography Hilal Al Saffar College of Medicine,Baghdad University
Which of the following is True 1. PR interval, represent the time taken for the impulse to travel from SA node to AV nose. 2. QT interval represent Atrial depolarization and depolarization. 3. Q waves are almost always pathological 4. ORS complex duration should be less than 0.1 sec 5. The next lecture will be on Heart failure
Heart rate
CALCULATING RATE As a general interpretation, look at lead II at the bottom part of the ECG strip. This lead is the rhythm strip which shows the rhythm for the whole time the ECG is recorded. Look at the number of square between one R-R interval. To calculate rate, use any of the following formulas: Rate = 300 the number of BIG SQUARE between R-R interval OR Rate = 1500 the number of SMALL SQUARE between R-R interval
CALCULATING RATE For example: Rate = 300 3 or Rate = 1500 15 Rate = 100 beats per minute
CALCULATING RATE If you think that the rhythm is not regular, count the number of electrical beats in a 6-second strip and multiply that number by 10.(Note that some ECG strips have 3 seconds and 6 seconds marks) Example below: 1 2 3 4 5 6 7 8 There are 8 waves in this 6-seconds strip. Rate = (Number of waves in 6-second strips) x 10 = 8 x 10 = 80 bpm
RHYTHM
Cardiac Rhythm Is the rhythm regular or not? The intervals between various points are equal. R R R P P P
RHYTHM Look at p waves and their relationship to QRS complexes. Lead II is commonly used Regular or irregular? If in doubt, use a paper strip to map out consecutive beats and see whether the rate is the same further along the ECG. Measure ventricular rhythm by measuring the R-R interval and atrial rhythm by measuring P-P interval.
CARDIAC AXIS
Cardiac Axis (QRS Axis) It is the average direction of spread of ventricular depolarization. We have to chose 2 leads perpendicular on each other : Lead I X avf Lead II X avl Lead III X avr
avr = 210-90 -VE -VE avl -30 + 180 Lead I +ve Zero Lead III + 120 Lead avf + 90 Lead II +60
-VE 90 -VE Lead I +ve Zero avf + 90
Lead I = +ve 9 mm, -ve 3 mm =+ve 6 mm put in on the +ve side of it Lead avf = +ve 9mm put it on the +ve side of it and get the Axis I +ve * * * * * * * * * * * * avf + 90 + 70
The normal Axis ( - 30 +110) - 30 + 110
RT Axis Deviation > + 120 avl -30 Lead III
LT Axis Deviation > - 30 avl - 30
ECG changes in ischemic heart Spectrum of IHD : ( IHD) Stable Angina Unstable angina Myocardial infarction Acute coronary syndrome
Coronary artery atherosclerosis
Sable Angina pectoris ECG -- could be normal even during the attack. May show ST segment depression in various leads. May need exercise test (TMT ) to provoke the changes
Normal ECG
ST segment depression
Treadmill test
Myocardial Infarction Indicate Myocardial necrosis and death Mainly of two types : 1.ST Elevation MI STEMI, full thickness MI, transmural MI, Q MI 2.Non ST Elevation MI, NSTEMI, Sub Endocrinal MI, Non Q MI
ST Elevation MI STEMI
One way to diagnose an acute MI is to look for elevation of the ST segment. ST Elevation
Myocardial infarction
Beginning of ST Elev. Pecked T wave
ST ELEV
Anterior infarction I II III avr avl avf V1 V2 V3 V4 V5 V6 Left anterior descending artery (LAD)
Inferior infarction I II III avr avl avf V1 V2 V3 V4 V5 V6 Right coronary Artery( RCA) OR Circumflex (LCX)
Lateral infarction I II III avr avl avf V1 V2 V3 V4 V5 V6 Left circumflex coronary Artery OR DAIAGONAL branch of LAD
Age of Myocardial Infarction Acute : peaked T wave,st segment elevation. Recent : ST segment Elevation, T wave inversion beginning of Q wave. Old : If only Q wave.
STEMI : stages Stage 1 : peaked T wave + ST segment Elevation, sub endocrinal injury, no cell death( 1 st few hours) Clinical implications : Time limit for reperfusion therapy, 6 hours after the onset of symptoms to preserve myocardial mass (salvage)
Stage 2 : Loss of amplitude of R wave, still ST elevation, 1 st day, injury extend to epicardium Stage 3 : T inversion,beginning of Q wave, decrease of ST elevation, 2-3 day Stage 4 : Deep T wave inversion, Marked Q wave, ST my back to base line, > 3 day. Stage 5 :after several weeks : ST back normal wave, T inversion less, Q wave
ST Elevation (cont) Elevation of the ST segment (greater than 1 small box) in 2 leads is consistent with a myocardial infarction.
What are the abnormalities
The 12-Lead ECG The 12-Lead ECG sees the heart from 12 different views. Therefore, the 12-Lead ECG helps you see what is happening in different portions of the heart. The rhythm strip is only 1 of these 12 views.
Views of the Heart Some leads get a good view of the: Lateral portion of the heart Anterior portion of the heart Inferior portion of the heart
Localization of the Myocardial infarction Lateral surface avl Anterior V1,V2,V3,V4 I V5 V6 III avf II Inferior surface
Localization of MI Anterior V1V2V3V4 Septal V3,V4 Inferior II III avf Lateral avl I V5, V6
NSTEMI No ST segment elevation ST segment depression, T wave inversion. Clinical implication Since the pathophysiology differ from that of STEMI, thrombolytic therapy is not indicated
NSTEMI
A 55 year old male patient presents to the ER with central chest pian radiate to the jaw of 3 hours duration associated with SOB, sever exhaustion and sweating.he was heavy smoker, hypertensive on Atenolole 100mg. If you are on call in the ER, your immediate step will be : 1.Do an ECG and if the result is normal, reassure the patient,send him back home and ask to seek medical advice if symptoms worsen. 2.Do an ECG and if the result is normal, do cardiac enzymes (troponin,cpk) and if it was normal, reassure the patient and send him home. 3.Do and ECG and cardiac enzymes and admit the patient to the hospital for observation even if both are normal.
The cardiac enzymes were elevated and ECG after 3 hours is shown below ; Your next step will be : 1.Thrombolytic therapy 2.Aspirin 3.Anticoaglent 4.CEI 5.Beta Blocker