anaesthesia.com: MANAGING MYOCARDIAL INFARCTION-The role of ECG

P - atrial electrical activation
PR-Interval bet. atrial and ventricular activation
QRS - ventricular electrical activation
ST-interval bet.end of ventricular activation and ventricular recovery
T- ventricular recovery
U - ? Purkinje fibers recovery
QT- total duration of ventricular activation & recovery

P : upright in I,II, V2-V6 , ht <>

Q : Ht <>

QRS : <>

ST segment : isoelectric or <>

T: upright I,II, V3*, V4-V6

QTc =QT / ÖRR ( €<0.39s>

ST deviation : measure 0.08s ( 2 small boxes ) from J point

ECG IN ST ELEVATION MI

COMMON MISTAKES

- Poor interpretation of ECG changes in STEMI
- Failure to identify concomitant ECG changes / complications
e.g. – arrhythmias, conduction disturbances,RV and posterior MI changes
- Failure to do right sided ECG in inferior MI
- Failure to repeat / monitor ECG when earlier ECGs were normal

- Delay in performing / review ECGs
- Failure to compare earlier/old ECGs if available
- Failure to write name, date and time of ECG performed
- Never assess objectively ST segment elevation pre and post reperfusion therapy

ROLES OF 12 LEAD ECG IN STEMI

- Diagnosis of MI
- Correlate ECG changes and candidate for reperfusion therapy
- Identify location , extent of MI including RV and posterior MI .
- Identify conduction and rhythm disturbances
- Assess the success of reperfusion therapy

Diagnosis

The diagnosis of MI is based on the presence of at least two of the following three criteria:
(1) a clinical history of ischemic-type chest discomfort
(2) changes on serially obtained electrocardiographic tracings
(3) a rise and fall in serum cardiac markers

ECG DIAGNOSIS

A. ST elevation in 2 or more contiguous leads of standard 12 lead ECG
- ≥ 1mm limb leads ( II , III , AVF, AVL , I )
- ≥ 2mm precordial leads ( V1 – V6 )
- WITH OR WITHOUT Q WAVE
B. New onset of LBBB
C. ECG changes of RV INFARCTION – IN RIGHT SIDED
ECG OF V4 /V5
D. ECG changes of POSTERIOR INFARCTION – V1 AND V2

ECG : Evolutionary changes

Hyperacute T waves

•Present for only five to thirty minutes after onset of MI
•T waves more prominent, symmetrical and pointed.

ST segment changes

–Within hours of symptoms
–ST segment straighten, with loss of ST-T wave angle. Then T wave becomes broad and ST segment elevates, losing its normal concavity. As further elevation occurs, the ST segment tends to become convex upward.

Pathological Q waves- Evidence of myocardial necrosis

•Usually develop after 9 hours, occasionally after 24 hours.
-Loss of R wave after 12 hours

Ischemia