ECG and Arrhythmia (Ref. Hari. 18 ed., pg -1831)

1. Rate: To calculate the rate, divide 1500 bythe number of small squares per R-R interval.

2. Rhythm

Af has no discernible P waves and the QRScomplexes are irregularly irregular.

3. P wave:

a. Absent P wave: Af

b. P mitrale: wide P wave (>2.5mm),indicates left atrial enlargement

(AIIMS May 2014)

c. P pulmonale: peaked P wave (> 2.5mm), indicates right atrialenlargement .

4. P-R interval:

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Atrial flutter has a 'sawtooth' baseline ofatrial depolarization and regular QRScomplexes.

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Important point.

1. P wave is due to: Atrial depolarization

2. QRS complex indicates:Ventriculardepolarization

a. Normal range: 0.12 - 0.20 Sec.

b. A prolonged P-R interval (> 0.20 Sec) =1st degree heart block .

c. A short P-R interval (< 0.12 Sec) =WPW syndrome.

5. Ventricular hypertrophy:

a. LVH sum of S wave in V1 and R wave inV6 is >35mm (SV1 + RV6 > 35) .

b. Pathological Q waves : acute MI: LVaneurysm

6. QT Interval

a. Normal QT': 0.36-0.44s.

b. QT interval: It varies with rate. Calculatecorrected QT interval (QTc) (By usingBAZZETTS Formula )

c. Prolonged QT interval : Congenital,Electrolyte imbalance (Hypokalemia,Hypocalcemia , Hypomagnesemia ),Class 1A anti arrhythmic drugs (quinidine

), bradycardia, head injury, hypothermia,sotalol , antihistamines, macrolides (egerythromycin), amiodarone ,Phenothiazine , Tricyclic , Torse DePointes cerebrovascular accident.

d. Short QT interval: Hypercalcemia,Hypermagnesemia, Class 1 B antiarrhythmic drugs, Digoxin, Acute MI.

Extra Edge:

Congenital prolong QT is associated with neonatalbradycardia.

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Extra Edge:

In case of Sub arachnoid hemorrhage increase QTinterval with wide T wave inversion occurs This isknown as CVA T wave pattern

7. ST segment:

a. ST elevation: Acute MI, Prinzmetal'sangina, acute pericarditis (saddle-shaped), left ventricular aneurysm.

b. ST depression: digoxin, angina, acuteposterior MI.

8. T wave:

a. Peaked in hyperkalemia and Hyperacutephase of acute MI.

b. Flattened in hypokalemia .

9. Hyperkalemia:

a. Tall, tented T wave ,

b. Prolong PR

c. P-Wave disappear (atrial arrest)

d. Wide RS ('sine wave' appearance).

e. The terminal event is either ventricularfibrillation or Asystole.

10. Hypokalemia: T waves become smaller and thendisappear, prominent U waves , prolong PR, STsegment sagging.

11. Hypercalcemia: Short QT interval

12. Hypocalcaemia: Long QT interval .

13. Digoxin effect: ST depression in V5-6 (Hockey

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stick sign) .

14. In digoxin toxicity, any arrhythmia or block mayoccur (ventricular ectopics and nodal bradycardiaare common) bigeminy is also common. Non-paroxysmal atrial tachycardia with variable blockis characteristic.

Extra Edge:

In digoxin toxicity all types of arrhythmias and blockscan happened but atrial flutter, type II B block do notoccur .

15. Bundle branch block Delayed conduction isevidenced by prolongation of QRS >0.11s (LQ2012).

a. In RBBB, the following pattern is seen:QRS >0.11s, 'RSR' pattern in V1 dominantR in V1, inverted T waves in V1-V4, deepwide S wave in V6.

Causes: normal variant (isolated RBBB),pulmonary embolism, cor pulmonale, MI,ASD, Ashman syndrome (AIIMS May2013)

b. In LBBB, the following pattern is seen:QRS >0.11s, W pattern in V1, 'M' patternin V5 V6, no septal Q waves, inverted Twaves in I, aVL, V5-V6.

Causes: IHD, hypertension,cardiomyopathy, idiopathic fibrosis.

16. Bifascicular block is the combination of RBBBand left bundle hemiblock Either left anteriorfascicular blockor left posterior fascicular block

17. Trifascicular block include:

a. Prolongation of the PR interval (first

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degree AV block)

b. Right Bundle Branch Block

c. Either left anterior fascicular block or leftposterior fascicular block

Important Points:

Trifascicular block also is said to occur in cases ofalternating RBBB with LBBB (Ref. Hari. 18 ed., pg-1835)

18. Pulmonary embolism: Sinus tachycardia isthe commonest. There may be RAD, RBBB,

Characteristic feature: the S Q T patternoccurs : i.e deep S waves in I, pathological Qwaves in III, inverted T waves in III.

19. Axis: The mean frontal axis is the sum of allthe ventricular forces during ventriculardepolarization. The axis lies at 90 to theisoelectric complex (ie the one in whichpositive and negative deflections are equal).

Normal axis is between -30 and +100 (LQ2012) (Ref. Hari. 18 ed., pg -1832).As asimple rule of thumb, if the complexes in leadsI and II are both 'positive', the axis is normal.

a. Left axis deviation (LAD) is -30' to -90.

Causes:

i. left anterior hemiblock ,

ii. Inferior MI.

iii. Right pneumothorax

iv. LVH

v. ASD (septum primum)(LQ2012)

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b. Right axis deviation (RAD) is +100 to +180.

Causes :

i. RVH,

ii. PE,

iii. Anterolateral MI,

iv. Left posterior hemiblock,

v. Left pneumothorax.

vi. ASD (Septum secundum)

20. Causes of low voltage QRS complex : (QRS

24. MI:

a. Within minutes, the T wave maybecome peaked (Earliest features)

.

b. With in 2-3 hrs, ST segments maybegin to rise (Pardees sign)

c. Within 8-12 hrs, the T wave inverts

d. Within 24 48 hrs, pathological waves begin to form. wavesusually persist in old MI .

Extra Edge:

Tall T is the earliest manifestation of acute MI. (FAQ)

Extra Edge:

Causes of ST elevation in ECG (LQ 2012)

1. Acute MI

2. Prinzmetal angina

3. LV aneurysm

4. Acute pericarditis

Site of MI

1. The leads affected reflect the site of the infarct:

a. Inferior (II, III, aVF) ,

b. Anteroseptal (V1-V3) ,

c. Anterolateral (V4- V6, I, aVL) ,

d. Posterior (tall R and ST depression in V V ).

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Comment

2. 'Non-Q wave infarcts' (formerly calledsubendocardial infarcts) have changes without Qwaves.

There is symmetrical T wave inversion.

Exercise ECG testing

The patient undergoes a graduated, treadmill exercisetest, with continuous 12-lead ECG and blood pressuremonitoring. There are numerous treadmill protocols' the'Bruce protocol' is the most widely used.'

Stress echocardiography is used to evaluate ventricularfunction, ejection fraction, myocardial thickening, andregional wall motion pre- and post-exercise

Extra Edge:

Dobutamine or dipyridamole may be used if thepatient cannot exercise:

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