EKG basics

Life in the Fast Lane - EKG basics

BRRAICE

Basics

  • Right patient/time; symptoms; prior EKG
  • Normal standard (25 mm/s)
    •   Time Voltage
      Small box 40 ms 0.1 mV
      Big box (5 small boxes)

      200 ms

      5 big boxes = 1 s

      0.5 mV

      2 big boxes = 1.0 mV

Rate

  • # of big boxes between complexes = 300, 150, 100, 75, 60, 50
  • # of QRS complexes in 10s (1 page) and multiply by 6

Rhythm

  • Regular/irregular?
  • P waves present? 1:1 with QRS?
  • Constant PR intervals? Buried P waves?
  • Different complex morphologies?
Sinus rhythm P wave upright in II, biphasic in V1 (RA anterior, LA posterior)
Afib P waves not reliably identified; irregular rhythm

Axis

  • Normal: -30 to +90
  • If net of I + II is positive, axis is normal
  • LAD: LVH, L anterior fascicular block (LAFB), inferior MI
  • RAD: normal in children/young adults; RVH; chronic lung disease; pulmonary HTN; pulmonary embolism; L posterior fascicular block (LPFB)
QRS deflection Axis
I II  
↑ ↑ Normal
↑ ↓ LAD (< -30)
↓ ↑ RAD (> +90)
↓ ↓ Extreme LAD/RAD

Intervals

PR 120-200 ms (3-5 small boxes)

↓ = Pre-excitation, junctional escape rhythm (sometimes)

↑ = 1st degree AV block
QRS 80-100 ms (2-2.5 small boxes)

Inefficient ventricular activation, not through intact His-Purkinje system

  • Supraventricular + aberrant conduction (IRBBB, LAFB/LPFB, RBBB, LBBB)
    • IRBBB = 100-120 ms; LBBB/RBBB = > 120 ms
  • Supraventricular + accessory pathway (WPW)
  • Ventricular (PVC, idioventricular rhythm, VT, ventricular pacing)
QT

450 ms (men)
470 ms (women)

QT should be < 1/2 RR

QTc (corrected) = QT/(sqrt(R-R)

Medications, ↓K, ↓Mg,  genetic channelopathies, SAH, stress cardiomyopathy

ECG leads

Conformations

P  LAE V1: total negative area > 1x1 box; II: > 120 ms (looks like 'm')
RAE II: > 2.5 boxes tall
PR Pericarditis Diffuse depression, except elevation in aVR
QRS       LVH R in aVL > 11; S in V1 + R in V5/V6 ≥ 35 (Sokolov-Lyon)
RVH RAD + R>S in V1
RBBB Delayed activation of R side: V1: rSR'; I/V6: deep terminal S
IRBBB Incomplete RBBB; QRS 100-120 ms
LBBB Delayed activation of L side: V1: rS or QS; I/V6: monophasic R
LAFB/LPFB LAFB a/w LAD; LPFB a/w RAD
Infarct Pathologic Q wave = > 1 mm wide, at least 25% of total QRS magnitude/height, present in 2 contiguous leads
R wave progression Should be R > S by V3 or V4
Poor progression = possible prior anterior MI, rotation of heart, or poor lead positioning
ST Elevation

≥ 0.1 mV in all leads except V2-V3 (require 0.2 mV)
- anatomic pattern = STEMI
- Diffuse ST elevation + PR depression = pericarditis
- 100% CFX occlusion can be silent on EKG in some cases 
J point

= transition point between QRS and ST segment; can be elevated without ischemia
Vertical notching at J point suggests no STEMI
Depression

Ischemia; LVH "strain pattern"; digoxin
T Inversion ischemia, LVH, RBBB, LBB
Deep T wave inversion can be a/w meds, intracerebral process, Takotsubo/stress cardiomyopathy
↑K Tall, peaked
↓K Flattened
MI Hyperacute T waves
U   Normal vs. hypokalemia
TP   Isoelectric baseline

 

Bundle branch mnemonic: WilliaM MarroW

  V1   V6
LBBB Wi LL iaM
RBBB Ma RR oW

 

EKG - anatomic sites of infarct

I aVR V1 V4
II aVL V2 V5
III aVF V3 V6
  • Inferior (RCA; posterior descending) OR CFX
    •  III > II (points to right) = RCA
    • II > III (points to left) = CFX
  • Anterolateral (LCX)
  • Anteroseptal (LAD)
  • Anteroapical (LAD)
author: admin | last edited: March 9, 2018, 9:57 a.m. | pk: 95