ECG

·         Many types of ECG

o    Holter monitor

§  The patient wears it for a long time - when patient experience discomfort, they may press a button to record it.

o    Ambulatory ECG

o    12-lead ECG

·         When you see an ECG…

o    Look at the rhythm

§  Usually, there is a R-R variation - sinus arrhythmia.

§  If not - may be diabetic neuropathy (no SA node reaction to vagal stimulation)

o    Look at the rate

§  Fast method - divide 300 by the number of big boxes.

§  Accurate method - divide 1500 by number of small boxes

o    P wave

§  Shows SA node activity

§  Inversion of P-wave (junctional rhythm)

·         Sometimes P wave inside QRS

·         Inversion of P wave plus slow conduction is usually indicative of junctional rhythm

·         In a junctional rhythm, the conduction does NOT start from atrium. From AV node instead

§  Sometimes P wave is absent - junctional bradycardia

·         In junctional bradycardia, usually rate = 40 to 60

§  If P wave is present but sometimes missing / irregular / dysmorphic, the beat may originate from the atrium BUT not from SA node.

·         It may be a wondering pacemaker if the P wave is “misbehaving”

§  Saw-tooth appearance

·         Several P waves per QRS - atrium firing impulse rapidly, but each beat not getting permitted to enter the ventricles.

o    Atrial flutter.

o    In atrial flutter, you would like to count the PP- rate and RR rate ratio. - see if the heart block is varying  / uniform.

o    In atrial flutter - the saw-tooth pattern is nice and regular - NEW saw - as compared to atrial fibrillation - where you would have an OLD saw.

·         Sometimes P wave occurs alone - without a QRS - if this happens uniformly, i.e. every 2 beats, or 3 beats, it is a heart block.

o    QRS complex

§  When QRS narrow (less than 3.5 small boxes), the impulse is proper in the ventricles - the arrhythmia is supraventricular

§  When QRS broad, the arrhythmia is ventricular arrhythmia (broad QRS complex tachycardia)

o    Tiny, vertical pulse just before a broad QRS complex - it may be a pacemaker artifact. (ventricular pacemaker artifact)

o    avR

§  is always negative in normal ECG - a positive AVR may suggest dextrocardia

o    ST segment

§  REGIONAL changes in ST segment suggests MI - if it is systemic, e.g. drugs, neurogenic, electrolyte etc the whole ECG changes.

§  Differential diagnosis of ST elevation

·         Intrinsic myocardial disease (e.g., myocarditis, ischemia, infarction, infiltrative or myopathic processes)

o    Contiguous leads elevations diagnostic

·          Drugs (e.g., digoxin, quinidine, tricyclics, and many others)

·          Electrolyte abnormalities of potassium, magnesium, calcium

·          Neurogenic factors (e.g., stroke, hemorrhage, trauma, tumor, etc.)

·          Metabolic factors (e.g., hypoglycemia, hyperventilation)

·          Atrial repolarization (e.g., at fast heart rates the atrial T wave may pull down the beginning of the ST segment)

·          Ventricular conduction abnormalities and rhythms originating in the ventricles

o    T wave

§  In the normal ECG (see below) the T wave is always upright in leads I, II, V3-6, and always inverted in lead aVR

§  The normal T wave is usually in the same direction as the QRS except in the right precordial leads e.g. V2

§  Also, the normal T wave is asymmetric with the first half moving more slowly than the second half.

§  Electrolyte changes

May be seen in the T-wave (tall, tenting T-wave in hyperkalemia etc )