ECG interpretation

1. ECG interpretation,
Echocardiography and
Cardiac catheterization
BY OLADAPO OLUWATIMILEHIN (213375)

2. Electrocardiogram interpretation
 An electrocardiogram (ECG), also known as EKG, is a non-invasive test that records
the electrical activity of the heart.
 It’s a vital tool in cardiology, offering a glimpse into the heart’s rhythm and
potential underlying issues. It provides information about chamber size.
 It is the main test used to assess for myocardial ischaemia and infarction. How is
an ECG generated?
 The basis of an ECG recording is that the electrical depolarisation of myocardial
tissue produces a small dipole current which can be detected by electrode pairs
on the body surface.
 These signals are amplified and either printed or displayed on a monitor.

3. ECG INTERPRETATION
 P Wave:
During sinus rhythm, the SA node triggers atrial depolarisation, producing a P wave.
Abnormal P wave morphology can indicate atrial enlargement, hypertrophy, or
conduction abnormalities.

4. ECG INTERPRETATION
 Depolarisation proceeds slowly through the AV node, which is too small to
produce a depolarisation wave detectable from the body surface.
QRS complex:
- The bundle of His, bundle branches and Purkinje system are then activated,
initiating ventricular myocardial depolarisation, which produces the QRS complex. It
lasts for about 0.10 seconds.
- The muscle mass of the ventricles is much larger than that of the atria, so the QRS
complex is larger than the P wave.

5. ECG INTERPRETATION
 The duration and morphology are crucial. A wide QRS complex (>120 ms)
suggests potential ventricular conduction delay or abnormal activation sequence.
Injury to the left or right bundle branch delays ventricular depolarisation,
widening the QRS complex.
 PR interval:
The interval between the onset of the P wave and the onset of the QRS complex is
termed the ‘PR interval’ and largely reflects the duration of AV nodal conduction. It
reflects conduction time from the atria to the ventricles. A prolonged PR segment can
suggest AV block.

6. ECG INTERPRETATION

7.  T wave:
Atrial repolarisation does not cause a detectable signal but ventricular repolarisation
produces the T wave.
Normally upright in most leads, T wave inversion can suggest ischemia, electrolyte
imbalances, or cardiomyopathy.
QT interval:
- The QT interval represents the total duration Of ventricular depolarisation and
repolarisation.
- Prolonged QT interval (QTc > 450 ms) increases the risk of arrhythmias.

8. ECG INTERPRETATION
ST Segment:
Represents the period between ventricular depolarization and repolarization. ST
segment elevation can indicate acute ischemia, while depression might suggest
ischemia or other etiologies.

9. ECG INTERPRETATION
The standard 12–lead ECG
The 12-lead ECG is generated from ten physical electrodes that are attached to the
skin. One electrode is attached to each limb and six electrodes are attached to the
chest.
In addition, the left arm, right arm and left leg electrodes are attached to a central
terminal acting as an additional virtual electrode in the centre of the
chest (the right leg electrode acts as an earthing electrode). The twelve ‘leads’ of the
ECG refer to recordings made from pairs or sets of these electrodes.
They comprise three groups: three dipole limb leads, three augmented voltage
limb leads and six unipole chest leads (V1-V6)

10. ECG INTERPRETATION
Dipole Limb Leads
- Leads I, II and III are the dipole limb leads and refer to recordings obtained from
pairs of limb electrodes.
- Lead I records the electric potential difference between the right (negative)
and left (positive) arms.
- Lead II: EPD between the right arm (negative) and left leg (positive).
- Lead III: EPD between the left arm (negative) and left leg (positive).
- These three leads thus record electrical activity along three different axes in the
frontal plane.

11. ECG INTERPRETATION
These three bipolar leads
roughly form an equilateral
triangle (with the heart at the
center) that is called
Einthoven’s triangle in honor
of Willem Einthoven, who
developed the
electrocardiogram in the
early 1900s.

12. ECG INTERPRETATION
Augmented voltage limb leads
Leads aVR, aVL and aVF are the augmented
voltage limb leads. These record electrical activity between a limb electrode and a
modified central terminal.

13. ECG INTERPRETATION

14. ECG INTERPRETATION
 For example, lead aVL records the signal between the left arm (positive) and a
central (negative) terminal, formed by connecting the right arm and left leg
electrodes. Similarly augmented signals are obtained from the right arm (aVR) and
left leg (aVF).
 These leads also record electrical activity in the frontal plane, with each lead 120°
apart. Lead aVF thus examines activity along the axis +90°, and lead aVL
along the axis −30°, and so on.
 The three augmented unipolar leads, coupled with the three standard bipolar limb
leads, comprise the six limb leads of the ECG. The 6 chest leads (V1-V6) make it 12
in total.

15. ECG INTERPRETATION

16. ECG INTERPRETATION
Note:
When depolarisation moves towards a positive electrode, it produces a positive
deflection in the ECG.
Depolarisation in the opposite direction produces a negative deflection. When the
vector is at right angles to a lead, the depolarisation in
that lead is equally negative and positive (isoelectric).

17. ECG INTERPRETATION
- In this figure, the QRS
complex is isoelectric in
aVL, negative in aVR and
most strongly positive in
lead II; the main vector
or axis of depolarisation
is therefore 60°. The
normal cardiac axis lies
between −30° and +90°.

18. ECG Correlates of Common Cardiac
Conditions:
1.Acute Coronary Syndrome (ACS):
ST segment elevation in specific leads
suggests ongoing ischemia. Conversely,
ST segment depression can indicate
ongoing ischemia or other aetiologies.
Could be ST elevation Myocardial
infarction (STEMI) or Non-ST elevation
Myocardial infarction (NSTEMI).

19. ECG Correlates of Common Cardiac
Conditions:
2. Arrhythmias:
ECG findings vary depending on the
specific arrhythmia. Atrial fibrillation
shows irregular R-R intervals and
absent P waves.

20. ECG Correlates of Common Cardiac
Conditions:
3. Premature ventricular contractions (PVCs):
There will be abnormal QRS morphology
originating from the ventricles.

21. ECG Correlates of Common Cardiac
Conditions:
4. Electrolyte Imbalances: Hyperkalemia can cause
peaked T waves, while hypokalemia can lead to flat
T waves and U waves.

22. Echocardiography
Echocardiography, or cardiac ultrasound, is obtained by placing an ultrasound
transducer on the chest wall to image the heart structures as a real-time,
two.dimensional ‘slice’. This permits the rapid assessment of cardiac structure and
function. Left ventricular wall thickness and ejection fraction can be estimated.

23. Echocardiography
 Doppler echocardiography:
This is an ultrasound technique that uses the Doppler effect to assess blood flow
within the heart.
It works by bouncing sound waves off blood cells and analyzing the shift in frequency
to determine how fast and in what direction the blood is moving.
This helps doctors evaluate heart valve function, detect abnormal blood flow patterns,
and calculate how well the heart is pumping blood.

24. Echocardiography

25. Echocardiography
2. Transoesophageal echocardiography (TEE):
Transthoracic echocardiography sometimes produces
poor images, especially if the patient is overweight or has obstructive airways disease.
Some structures are difficult to visualise in transthoracic views, such as the left atrial
appendage, pulmonary veins, thoracic aorta and interatrial septum.
TEE is a special type of echocardiogram where a thin ultrasound probe is inserted
through the esophagus to get a closer look at the heart.
It is done under light sedation and positioned at the back of the left atrium.

26. Echocardiography
 This can provide clearer images of certain heart structures, especially those at the
back of the heart, compared to a regular echocardiogram done on the chest.
 This technique produces high-resolution images, which makes the technique
particularly valuable for investigating patients with prosthetic (especially mitral)
valve dysfunction, congenital abnormalities (e.g. Atrial septal defect), aortic
dissection, infective endocarditis (vegetations that are too small to be detected by
transthoracic echocardiography) and systemic embolism (intracardiac thrombus or
masses).

27. Echocardiography
3. Stress echocardiography:
- This combines a regular echocardiogram with a stress test, such as exercise or
medication administration, to see how the heart functions under stress.
- It is usually used to investigate patients with suspected coronary artery disease who
are unsuitable for exercise stress testing, such as those with mobility problems or pre-
existing bundle branch block.
- A two-dimensional echo is performed before and after infusion of a moderate to
high dose of an inotrope, such as dobutamine.

28. Echocardiography
 Myocardial segments with poor perfusion become ischaemic and contract poorly
under stress, showing as a wall motion abnormality on the scan.
 This helps diagnose coronary artery disease, a condition where plaque buildup
narrows the arteries supplying blood to the heart muscle.

29. Cardiac catheterisation
 This involves passage of a preshaped catheter via a vein or artery into the heart under
X-ray guidance, which allows the measurement of pressure and oxygen saturation in
the cardiac chambers and great vessels; it also involves the the performance of
angiograms by injecting contrast media into a chamber or blood vessel.
Left heart catheterization
- Left heart catheterisation involves accessing the arterial circulation, usually via the radial
artery, to allow catheterisation of the aorta, LV and coronary arteries.
- Coronary angiography is the most widely performed procedure, in which the left and
right coronary arteries are selectively cannulated and imaged, providing information about
the extent and severity of coronary stenoses, thrombus and calcification.

31. Cardiac catheterisation
This permits planning of percutaneous coronary intervention and
coronary artery bypass graft surgery.
- Left ventriculography can be performed during the procedure to determine the
size and function of the LV and to demonstrate mitral regurgitation.
- Aortography defines the size of the aortic root and thoracic aorta, and can help
quantify aortic regurgitation.
- Left heart catheterisation is a daycase procedure and is relatively safe, with serious
complications occurring in fewer than 1 in 1000 cases.

32. Cardiac catheterisation
Right heart catheterization
Right heart catheterisation is used to assess right heart and pulmonary artery
pressures, and to detect intracardiac shunts by measuring oxygen saturations in
different chambers.
For example, a step up in oxygen saturation from 65% in the right atrium to
80% in the pulmonary artery is indicative of a large left-to-right shunt that
might be due to a ventricular septal defect.

33. Thank you.