Pressure over load Volume over load
Like in hypertension, ischemic heart disease (IHD)
LV strain pattern—ST depression with T inversion in V5, V6, L1,
and aVL leads
Like in mitral or aortic regurgitation
Shows prominent Q waves, positive T waves in V5, V6,
L1, and aVL
Step 7: Look for Evidence of Infarction/St Segment Abnormalities
ST Segment
ST segment is isoelectric and at the same level as subsequent PR-interval
The length between the end of the S wave (end of ventricular depolarization) and the beginning of
repolarization
From J point on the end of QRS complex, to inclination of T wave.
Causes of ST segment elevation
Ischemia
Early repolarization
Acute pericarditis: ST elevation in all leads except aVR
Pulmonary embolism
Hypothermia
Hypertrophic cardiomyopathy
High potassium
Cerebrovascular accident
Acute sympathetic stress
Brugada syndrome
Cardiac aneurysm
Left ventricular hypertrophy
Idioventricular rhythm including paced rhythm.
Causes of ST segment depression
Myocardial ischemia/non-ST-elevation myocardial infarction (NSTEMI)
Reciprocal change in STEMI
Posterior MI
Digoxin effect (reverse tick mark/“sagging” morphology, resembling Salvador Dali’s moustache)
Hypokalemia
Bundle branch block
Ventricular hypertrophy
Ventricular pacing.
ECG CHANGES IN MYOCARDIAL INFARCTION (MI)
There are two types of MI. ST segment elevation myocardial infarction (STEMI) and non-STEMI
(NSTEMI). ST elevation myocardial infarction criteria:
ST elevation in >2 chest leads >2 mm elevation
ST elevation in >2 limb leads >1 mm elevation
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Q wave >0.04 s (1 small square).
Location of MI Lead with ST changes Affected coronary artery
Anterior V1, V2, V3, V4 Left anterior descending (LAD) artery
Septum V1, V2 LAD
Left Lateral I, aVL, V5, V6 Left circumflex
Inferior II, III, aVF Right coronary artery (RCA)
Right atrium aVR, V1 RCA
Posterior Posterior chest leads RCA
Right ventricle Right sided leads RCA
Ischemia Injury Infarct
T-wave inversion (flipped T)
ST segment depression
T wave flattening
Biphasic T waves
ST segment elevation of greater than 1 mm in at
least 2 contiguous leads
Heightened or peaked T waves
Directly related to portions of myocardium
rendered electrically inactive
Significant Q wave where none
previously existed
Why?
Impulse traveling away from the
positive lead
Necrotic tissue is electrically dead
Sequential ECG changes in STEMI
0 hour Pronounced/hyperacute Tall T wave initially ST elevation (convex type)
1–24
hours
Depressed R wave, and pronounced T wave. Pathological Q waves may appear within hours or may take greater than 24 hours indicating full-thickness MI. Q wave is pathological if it is wider
than 40 ms or deeper than a third of the height of the entire QRS complex
Days Exaggeration of T wave continues for 24 hours
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1–2
Days
later
T wave inverts as the ST elevation begins to resolve. Persistent ST elevation is rare except in the
presence of a ventricular aneurysm
Weeks
later
ECG returns to normal T wave, but retains pronounced Q wave
Non-ST-Elevation MI
Non-ST-elevation MI is also known as subendocardial or non-Q-wave MI.
In a PT with acute coronary syndrome (ACS) in which the ECG does not show ST elevation,
NSTEMI (subendocardial MI) is suspected if
ST depression (A)
T wave inversion with or without ST depression (B)
Q wave and ST elevation will never happen
A ST depression is more suggestive of myocardial ischemia than infarction.
ELECTROLYTES AND ECG
Hypocalcemia: Prolonged ST segment and QT intervals.
Hypercalcemia
Shortened ST segment
Widened T wave and short QT
Hypokalemia
ST depression
Shallow, flat, and inverted T wave
Prominent U wave and P waves.
Hyperkalemia
Tall, peaked T waves
Flat P waves
Widened QRS complex
Prolonged PR interval
Sine wave.
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Fig. 11.8: ECG changes in seen with potassium.
Hypomagnesemia
Tall T waves
Depressed ST segment.
Hypermagnesemia
Prolonged PR interval
Widened QRS complexes.
EXAMPLES
Example 1
12-lead ECG showing
Rate 110 bpm
Rhythm Sinus rhythm
Axis Normal
P wave Duration 0.08 sec and normal morphology
PR interval/segment 0.12 sec
PR segment elevation in aVR
QRS 0.08 sec
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ST segment Elevation in V2-V6, I, aVL
Depression in aVR
T wave Normal
QT interval 0.32 sec
Final diagnosis Acute pericarditis
Example 2
12-lead ECG showing
Rate 85 bpm
Rhythm Sinus
Axis Normal
P wave Duration 0.12 sec and normal morphology
PR interval/segment 0.16 sec
QRS 0.08 sec
ST segment Elevation in II, III, aVF (elevation in Lead III > II)
Depression in V1-V6, I, aVL
T wave Corresponds to ST–T changes.
QT interval 0.36 sec
Final diagnosis Inferior wall MI with signs of RV infarction
Example 3
12-lead ECG showing
Rate 200 bpm
Rhythm Regular
Axis Normal
P wave Retrograde
PR interval/segment
QRS 0.08 sec (narrow complex)
ST segment Normal
T wave Normal
QT interval 0.28 sec
Final diagnosis Supraventricular tachycardia-atrioventricular nodal reentry tachycardia (SVT-AVNRT)
Example 4
12-lead ECG showing
Rate 75 bpm
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Rhythm Junctional
Axis Normal
P wave Absent
PR interval/segment –
QRS 0.14 sec notching at J point (V2)
ST segment Minimal elevation in V3-V5
No reciprocal changes
T wave Tall T steeple waves in precordial leads, concordant with QRS
QT interval 0.36 sec
Final diagnosis Hyperkalemia
Example 5
12-lead ECG showing
Rate Atrial—80 bpm; Ventricular—50 bpm
Rhythm Junctional escape
Axis Normal
P wave Present
PR interval/segment –
QRS 0.08 sec independent of P waves
ST segment Normal
T wave Normal
QT interval 0.36 sec
Final diagnosis Complete heart block
Example 6
12-lead ECG showing
Rate 70 bpm (6 sec rule)
Rhythm Irregular
Axis Normal
P wave Absent, presence of fibrillary waves
PR interval/segment –
QRS 0.08 sec varying RR interval
ST segment Normal
T wave Normal
QT interval 0.32 sec
Final diagnosis Atrial fibrillation
Example 7
12-lead ECG showing
Rate 250 bpm
Rhythm Regular
Axis Left-northwest
P wave AV dissociation
PR interval/segment –
QRS 0.28 sec (Broad complex)
Positive concordance
ST segment –
T wave -
QT interval -
Final diagnosis Monomorphic ventricular tachycardia (VT)
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A Systematic Approach to Chest X-rays
C H A P T E R
12
RADIOLOGY
We shall discuss practical aspects of radiology under following sections:
Approach to chest X-rays
Approach to CT scans
Approach to MRI scans
Contrast agents
APPROACH TO CHEST X-RAYS
Reading into the Chest Radiograph
The 10 Step Program
What type of view
Exposure/penetration
Inspiratory versus expiratory film
Rotation
Angulation
Soft tissues and bony structures
Trachea
Hilum/mediastinum
Diaphragm
Lung fields
Cardia
Type of View
Chest X-ray
PA view
AP view
Lateral view
PA view (posteroanterior view) (Fig. 12.1)
The ray of beam is from posteroanteriorly with the film in front of the patient.
AP view (anteroposterior view) (Fig. 12.2)
The ray of beam is from anteroposteriorly with the film behind the patient.
3.
Fig. 12.1: Posteroanterior view.
Fig. 12.2: Anteroposterior view.
Lateral view (Fig. 12.3)
The ray of beam is from one side with the film placed on the opposite side of the patient.
Fig. 12.3: Lateral view.
Differences between PA view and AP view of chest X-ray
PA view (Fig. 12.4) AP view (Fig. 12.5)
Fundic gas shadow Usually present Absent
Clavicles Seen over the lung fields and more
horizontal
Seen above the apex of lung field and more oblique
Scapula Inner borders are away form the lung
fields
Inner borders are seen over the lung
fields
Ribs Posterior ribs are better seen and more oblique
Anterior ribs are better seen
Apparent cardiomegaly Not seen Seen
Spine Better seen Not seen
The distance between the projector and
the patient
6 feet 40 inches
Fig. 12.4: PA view. Fig. 12.5: AP view.
Exposure/Penetration
Penetration is the degree to which X-ray passes through the body. Figure 12.6 depicts the grading of
shadow in X-ray film.
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