Coronary Artery Disease is the most common acquired disease of modern era.
Depending on the severity of ischaemia, it can present as-
- Chronic Stable Angina
- Chronic Unstable Angina
- Vasospastic Angina
- Myocardial Infarction
ECG is an important, easily available and reliable tool for diagnosing and planning treatment of a patient with CAD. However, clinical judgement other investigations are often required to confirm the diagnosis because ECG may not reflect the actual severity of ischaemia and underlying damage.
ECG can be normal in 1-6% of patients with Acute Coronary Syndrome, so, it becomes important to repeat the ECG at regular intervals in such cases. Repeating the ECG may reveal the diagnostic changes.
Angina pectoris is a clinical syndrome which is caused due to myocardial ischaemia which is manifested by retrosternal chest pain. Depending on the severity of occlusion Angina can be classified into three types :-
1. Chronic stable angina
2. Chronic unstable angina
3. Prinzmetal angina
ECG manifestations of Chronic stable angina :-
- 50% have normal ECG
- STD and T wave inversion may be present at rest
- STD >1mm especially in leads V5 and V6 forms the basis of reporting a positive stress test
- T wave inversion may also be found during stress test
ST segment depression and T wave inversion
ECG manifestations of Chronic unstable angina :-
- 50% will have abnormal ECG
- T wave inversion with or without STD
- Pseudonormalisation of resting STD can also be seen
ECG manifestations of Prinzmetal angina:-
- ST segment elevation
- Tall, upright, widened and pointed T wave
- R wave amplitude inceases
- S wave amplitude decreases
- Transient conduction abnormalities like transient Left Axis Deviation, transient left or right bundle branch blocks
- Arrhythmias like ventricular ectopics , non sustained VT and transient heart blocks can also occur.
Myocardial Infarction (MI)
ECG, being simple, reliable and easily available is universally accepted tool for diagnosing and risk stratifying the Myocardial Infarction.
In patients with ischaemic symptoms, one of the following abnormalities must be present for diagnosis of MI:-
- Development of New Pathological Q- Waves.
- Presence of ST segment elevation or Depression.
- New onset Left Bundle Branch Block.
The changes in ECG should be present in two contiguous leads.
Depending upon the abnormalities in ECG, MI is divided into two main types:-
- STEMI (ST segment elevation MI)
- NSTEMI(Non ST segment elevation MI)
ECG changes in STEMI
ST segment elevation indicates subepicardial ischaemia.
STEMI has three phases of evolution-
1. Hyper-acute phase :- It is recognised by following ECG changes-
- Tall, Symmetrical, Peaked and Widened T-waves
- Slope elevation of ST segment
- Increased amplitude of the R wave
- Increased ventricular activation time
Hyperacute T waves of acute anterior MI – Tall, Symmetrical, Widened and Elevated T waves in V1 V2 and V3 .
2. Evolved phase :- It is recognised by following ECG changes-
- Appearance of new q waves
- Decreased R wave amplitude
- ST segment and J point elevation
- T wave inversion
- QRS broadening due to increased ventricular activation time
- QT prolongation due to increased depolarisation and repolarisation time.
Q waves, ST elevation and T wave inversion in evolved phase of STEMI
3. Chronic stabilised phase :-
- Q wave evolves maximally
- Elevated ST segment and J point returns to baseline
- T wave gradually regains positivity
- QT interval normalises
Localisation of the MI and culprit artery
1. Left Ventricular Myocardial Infarction
Left ventricle has three walls :-
Anterior wall is further divided into different areas like Antero-septal, Antero-apical, Antero-lateral etc.
The below table tells us the site of MI, coronaries affected and lead showing ST elevation.
Remember that there is reciprocal ST depression also which is not described in this table.
Anterior Wall MI
STE in lead V1, V2 and V3
Posterior Wall MI
Reciprocal STE in lead III and aVF
Inferior Wall MI
STE in lead II , III and aVF
2. Right Ventricular Myocardial Infarction (RVMI)
Not very common but present in 30% cases of Inferior wall MI.
RVMI is more often related to arrhythmias than to pump failure.
ECG manifestations are as follows-
- STE in lead V1 or extra right precordial leads(V4r-V6R) of >/= 1mm.
- V4R being the most sensitive lead.
- Failure of reciprocal STD unlike AWMI so, this point is used to differentiate acute AWMI from RVMI.
3. Infarction of the Atria
Isolated infarction of atria is rarely recognised or reported because it is inconpicuous, small and difficult to evaluate and there is no distinctive clinical presentation.
ECG findings in atrial infarction
There is minimal elevation of PTa segment, in same direction as that of P wave
Sometimes there may be horizontal depression of PTa segment
P wave may become widened, slurred and notched
Atrial arrhythmias like Atrial Tachycardia, Atrial extrasystoles, Atrial fluter and Atrial fibrillation may be seen.
ECG changes in NSTEMI
When ischaemia of sub-endocardial region occurs, there is STD instead of STE and the resultant entity is named as NSTEMI. NSTEMI may evolve into STEMI , so it is treated aggressively like that of STEMI.
ECG diagnosis of NSTEMI :-
- ST segment depression in precordial leads and lead I and II
- T wave inversion in precordial leads and lead I and II
STD in leads II, III and precordial leads V3 V4 V5
Arrhythmias in MI
1. Sinus Tachycardia
2. Ventricular Arrhythmias
Ventricular arrhythmias are most common cause of sudden cardiac death in a patient with MI.
- Ventricular ectopics
- Idioventricular rhythm
- Polymorphic VT
- Ventricular fibrillation
3. Atrial Arrhythmias
- Atrial ectopics
- Atrial tachycardia
- Atrial fibrillation
4. Sinus Bradycardia
5. Conduction blocks and heart block
- New onset LBBB (a criterion for diagnosis of acute MI)
- Complete AV block in IWMI
- Second degree Mobitz II heart block occurs in AWMI due to IVS infarction
Diagnosing MI with LBBB
Diagnosing acute MI with previous LBBB
New onset LBBB is common in acute MI but diagnosing old LBBB in acute AWMI is a challenge because Old LBBB will mask the manifestations of acute AWMI.
This problem was solved by Sgarbossa et al by giving us criteria for diagnosing acute AWMI with old LBBB and is as follows :-
- Concordant STE of >1mm in atleast one lead (5 points)
- Concordant STD of >1mm in leads V1 – V3 (3 points)
- Discordant STE of >5mm in atleast one lead (2 points)
A total of 3 or more points is suggestive of acute MI in presence of previous LBBB without the need of further investigations.
Diagnosing Old AWMI with LBBB
- Cabrera’s sign – Notching in ascending Limb of S wave in leads V3 – V5
- Chapman’s sign – Notching in the upstroke of R wave in leads I, aVL or V6
- Presence of q waves in leads V5, V6, I, aVL is suggestive of old MI