Introduction to EKG

And then a little more

• To get an accurate EKG, leads must be properly applied:

I: RA(-) to LA(+)II RA(-) to LL(+)III:LA(-) to LL(+)

aVR: RA(-) to [LA & LL(+)] aVL: LA(+) to [RA & LL(+)]aVF: LL(+) to [RA & LA(-)]

Precordial lead is +

• Normal activation

• Interpretation:– Rhythm: look for P waves, regularity, reproducible intervals, PR

interval, shape– Rate– Axis– Intervals: PR, QRS, QTc– Conduction – R wave progression– ST segments and T waves– Ectopic beats– Q waves: where they should and should not be– Other stuff

• Some general guidelines:– P waves

• Best seen in lead II• Upright or biphasic (neg component smaller) in V1-V2, upright in V4-V6

– QRS complex• V1 shows rS, V6 shows qR• Size of r wave progressively increases, transition V3-V4• QRS duration < .120 sec• One R wave in precordial leads should be > 8mm• No R wave in precordial leads > 27mm• Sum of tallest R in left leads and S in right leads should be < 35-40mm• Precordial q waves should not exceed .04 sec nor have a depth greater than ¼

the height of the R wave following• R wave in aVL <12-13mm

– ST segment• Should not be more than 1mm above or below baseline. Normal minor

elevation in leads with large S waves ( V1-V3) and normal configuration is concave up.

• T waves– Often inverted in V1. May be inverted in V2 if already inverted in V1.– Always upright in leads I, II, V3-V6– Always inverted aVL

• U waves– Amplitude usually < 1/3 T wave height in same lead– Direction is same as T wave in that lead

• Axis– Frontal plane lead with the sum of r wave and s wave most

closely approximates 0.– Look at QRS in the lead perpendicular to original lead– If QRS id positive, axis along that direction. If negative, axis

in opposite direction.

• Axis- contNormal axis

Left axis

Right axis

• Heart block– Normal PR interval < .2 sec– 1st degree AV block- prolonged PR

• Heart Block– 2nd degree AV block- Wenchebach- Mobitz 1• Prolonged PR until dropped QRS• 1st PR interval always the shortest• 1 dropped QRS only• RR intervals shorten

• 2nd Degree- 2 to 1 block

• 2nd degree type 2- mobitz 2

• Complete heart block

• Bundle branch block– QRS > .120 sec– RBBB- R-R’ in V1-V2, s wave in lead 1 & V6

• LBBB– QRS >.120 sec– Neg QRS in V1– Lack of small q in lead 1, V5-V6