8
Now Test Yourself
You should now be able to recognize the common ECG patterns, and this final chapter contains ten 12-lead records for you to interpret. But do not forget two important things: first, an ECG comes from an individual patient and must be interpreted with the patient in mind, and second, there is little point in recording and interpreting an ECG unless you are prepared to take some action based on your findings. This is a theme developed in the companion to this book, 150 ECG Problems.
When reporting an ECG, remember:
2. A report has two parts – a description and an interpretation.
3. Look at all the leads, and describe the ECG in the same order every time: rate and rhythm
4. The range of normality, and especially which leads can show an inverted T wave in a normal ECG.
REMINDERS
WHAT TO LOOK FOR
• right axis deviation – QRS complex predominantly downward in lead I
• left axis deviation – QRS complex predominantly downward in leads II and III.
− R and S waves are equal in the chest leads over the interventricular septum (normally lead V3 or V4)
− clockwise rotation (persistent S wave in lead V6) indicates chronic lung disease.
REMINDERS
CONDUCTION PROBLEMS
First degree block
Second degree block
• Wenckebach (Mobitz type 1): progressive PR lengthening then a nonconducted P wave, and then repetition of the cycle.
• Mobitz type 2: occasional nonconducted beats.
• 2:1 (or 3:1) block: two (or three) P waves per QRS complex, with a normal P wave rate.
Third degree (complete) block
• No relationship between P waves and QRS complexes.
• Usually, wide QRS complexes.
• Usual QRS complex rate less than 50/min.
Right bundle branch block
• QRS complex duration greater than 120 ms.
• Usually, dominant R1 wave in lead V1.
• Inverted T waves in lead V1, and sometimes in leads V2-V3.
Left anterior hemiblock
• Marked left axis deviation – deep S waves in leads II and III, usually with a slightly wide QRS complex.
Left bundle branch block
• QRS complex duration greater than 120 ms.
• ‘M’ pattern in lead V6, and sometimes in leads V4-V5.
• Inverted T waves in leads I, VL, V5-V6 and, sometimes, V4.
Bifascicular block
REMINDERS
CAUSES OF AXIS DEVIATION
Right axis deviation
• Normal variant – tall thin people.
• Right ventricular hypertrophy.
• Lateral myocardial infarction (peri-infarction block).
• Dextrocardia or right/left arm lead switch.
• The Wolff-Parkinson-White (WPW) syndrome.
Left axis deviation
REMINDERS
POSSIBLE IMPLICATIONS OF ECG PATTERNS
P:QRS apparently not 1:1
If you cannot see one P wave per QRS complex, consider the following:
• If the P wave is actually present but not easily visible, look particularly at leads II and Vv
• If the QRS complexes are irregular, the rhythm is probably atrial fibrillation, and what seem to be P waves actually are not.
• If the QRS complex rate is rapid and there are no P waves, a wide QRS complex indicates ventricular tachycardia, and a narrow QRS complex indicates atrioventricular nodal (junctional or AV nodal) re-entry tachycardia.
• If the QRS complex rate is low, it is probably an escape rhythm.
P:QRS more than 1:1
If you can see more P waves than QRS complexes, consider the following:
• If the P wave rate is 300/min, the rhythm is atrial flutter.
• If the P wave rate is 150-200/min and there are two P waves per QRS complex, the rhythm is atrial tachycardia with block.
• If the P wave rate is normal (i.e. 60-100/min) and there is 2:1 conduction, the rhythm is sinus with second degree block.
• If the PR interval appears to be different with each beat, complete (third degree) heart block is probably present.
Wide QRS complexes (greater than 120 ms)
Wide QRS complexes are characteristic of:
Q waves
• Small (septal) Q waves are normal in leads I, VL and V6.
• A Q wave in lead III but not in VF is a normal variant.
• Q waves probably indicate infarction if present in more than one lead, are longer than 40 ms in duration and are deeper than 2 mm.
• Q waves in lead III but not in VF, plus right axis deviation, may indicate pulmonary embolism.
• The leads showing Q waves indicate the site of an infarction.
ST segment depression
T wave inversion
• Normal in leads III, VR and V-,; and in V2-V3 in black people.
• Right or left ventricular hypertrophy.
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