ECG traceDraw me the tracing of lead II ECG.

What is the y axis? Potential difference between two electrodes placed on the surface of the body (mV)

What happens in P, QRS and T? P = atrial depolarisation, normally <0.3mV and <0.12 seconds QRS = ventricular depolarisation (atrial repolarisation is obscured) T = ventricular repolarisation

What about the intervals? PR = atrial depolarisation and conduction through AV node, normally 0.12-0.2 seconds QT = ventricular depolarisation and repolarisation, normally 0.3-0.4 seconds but varies

inversely with HR

What will increase PR? First degree heart block = PR interval >0.2 s; all impulses pass through the AV node Second degree heart block = some impulses pass through the AV node

o Mobitz type I = Wenckebach block = progressive lengthening of the PR interval until an impulse is not conducted and the beat is dropped

o Mobitz type II block = dropped beats without any progressive lengthening of the PR interval; may progress to complete heart block

Third degree heart block = no impulses pass through the AV node

Is there any factor that affects the value? Physiological

o Neural SNS: left sided fibres → ↓ PR interval PNS: left vagus → ↑ PR interval

o Chemical Hypokalaemia → ↑ PR interval

o Metabolic Hypothermia → ↑ PR interval

Pathological

o Inferior MIo Wolff-Parkinson-White syndrome

Pharmacologicalo Adenosine o β blockers o Calcium channel blockerso Digoxin

Do you know another other waves in ECG? U wave = repolarisation of the papillary muscles

What changes will you see in sequence if we infuse K to a renal failure patient? T wave height is normally <5 mm ~5 mmol/L: normal ~7 mmol/L: peaked T waves ~9 mmol/L: no p waves, wide QRS Higher: VT, sine wave VF