Quick Notes‎ > ‎

### cardiology

For my 1-2 page summary sheets on cardiology topics, based on the text by Myung Park, please see the File Cabinet
For other Cardiology notes & references, see Cardiology.

Harriet Lane Cardiology Chapter:

V. ELECTROCARDIOGRAPHY A. BASIC ELECTROCARDIOGRAPHY PRINCIPLES

1.
Lead placement ( Fig. 7-8 ).

2.
ECG complexes (see Fig. 7-1 ).
 a. P wave: Represents atrial depolarization. b. QRS complex: Represents ventricular depolarization. c. T wave: Represents ventricular repolarization. d. U wave: May follow T wave, representing late phases of ventricular repolarization.

3.
Systematic approach for evaluating ECGs ( Table 7-4 shows normal ECG parameters): [3] [5]

a.
Rate.
 (1) Standardization: Paper speed is 25 mm/sec. One small square = 1 mm = 0.04 sec. One large square = 5 mm = 0.2 sec. Amplitude standard: 10 mm = 1 mV. (2) Calculation: Heart rate (beats per minute) = 60 divided by the average R-R interval in seconds, or 1500 divided by the R-R interval in millimeters.

b.
Rhythm.
 (1) Sinus rhythm: Every QRS complex is preceded by a P wave, normal PR interval (the PR interval may be prolonged, as in first-degree atrioventricular [AV] block), and normal P-wave axis (upright P in lead I and aVF). (2) There is normal respiratory variation of the R-R interval without morphologic changes of the P wave or QRS complex.

c.
Axis: Determine quadrant and compare with age-matched normal values ( Fig. 7-9 ; see Table 7-4 ).

d.
Intervals (PR, QRS, QTc): See Table 7-4 for normal PR and QRS intervals. The QTc is calculated as

QTc = QT (sec) √R-R (average 3 measurements taken from same lead)

The R-R interval should extend from the R wave in the QRS complex in which you are measuring QT to the preceding R wave. Normal values for QTc are as follows:
 (1) 0.44 sec is 97th percentile for infants 3 to 4 days old.[6] (2) ≤0.45 sec in infants <6 months old. (3) ≤0.45 sec in males >1 week old and prepubescent females. (4) ≤0.46 sec for postpubescent females.

e.
P-wave size and shape: Normal P wave should be <0.10 sec in children, <0.08 sec in infants, with amplitude < 0.3 mV (3 mm in height, with normal standardization).

f.
R-wave progression: There is generally a normal increase in R-wave size and decrease in S-wave size from leads V1 to V6 (with dominant S waves in right precordial leads and dominant R waves in left precordial leads), representing dominance of left ventricular forces. However, newborns and infants have a normal dominance of the right ventricle.

g.
Q waves: Normal Q waves are usually <0.04 sec in duration and <25% of the total QRS amplitude. Q waves are <5 mm deep in left precordial leads and aVF and ≤8 mm deep in lead III for children <3 years of age.

h.
ST-segment and T-wave evaluation: ST-segment elevation or depression >1 mm in limb leads and >2 mm in precordial leads is consistent with myocardial ischemia or injury. Tall, peaked T waves may be seen in hyperkalemia. Flat or low T waves may be seen in hypokalemia, hypothyroidism, normal newborn, and myocardial and pericardial ischemia and inflammation ( Table 7-5 and Fig. 7-10 ).

i.
Hypertrophy.
 (1) Atrial ( Fig. 7-11 ). (2) Ventricular: Diagnosed by QRS axis, voltage, and R/S ratio ( Box 7-3 ; see also Table 7-4 ).

 FIG. 7-8  A, Hexaxial reference system. B, Horizontal reference system.  (Modified from Park MK, Guntheroth WG: How to Read Pediatric ECGs, 4th ed. Philadelphia, Mosby, 2006, p 3.)

TABLE 7-4   -- NORMAL PEDIATRIC ECG PARAMETERS

Age
Heart Rate (bpm)
QRS Axis[*]
PR Interval (sec)[*]
QRS Duration (sec)
R Wave Amplitude (mm)[]
S Wave Amplitude (mm)[]
R/S Ratio
R Wave Amplitude (mm)[]
S Wave Amplitude (mm)
R/S Ratio
0–7 days
95–160 (125)
+30 to 180 (110)
0.08–0.12 (0.10)
0.05 (0.07)
13.3 (25.5)
7.7 (18.8)
2.5
4.8 (11.8)
3.2 (9.6)
2.2
1–3 wk
105–180 (145)
+30 to 180 (110)
0.08–0.12 (0.10)
0.05 (0.07)
10.6 (20.8)
4.2 (10.8)
2.9
7.6 (16.4)
3.4 (9.8)
3.3
1–6 mo
110–180 (145)
+10 to +125 (+70)
0.08–0.13 (0.11)
0.05 (0.07)
9.7 (19)
5.4 (15)
2.3
12.4 (22)
2.8 (8.3)
5.6
6–12 mo
110–170 (135)
+10 to +125 (+60)
0.10–0.14 (0.12)
0.05 (0.07)
9.4 (20.3)
6.4 (18.1)
1.6
12.6 (22.7)
2.1 (7.2)
7.6
1–3 yr
90–150 (120)
+10 to +125 (+60)
0.10–0.14 (0.12)
0.06 (0.07)
8.5 (18)
9 (21)
1.2
14 (23.3)
1.7 (6)
10
4–5 yr
65–135 (110)
0 to +110 (+60)
0.11–0.15 (0.13)
0.07 (0.08)
7.6 (16)
11 (22.5)
0.8
15.6 (25)
1.4 (4.7)
11.2
6–8 yr
60–130 (100)
- 15 to +110 (+60)
0.12–0.16 (0.14)
0.07 (0.08)
6 (13)
12 (24.5)
0.6
16.3 (26)
1.1 (3.9)
13
9–11 yr
60–110 (85)
- 15 to +110 (+60)
0.12–0.17 (0.14)
0.07 (0.09)
5.4 (12.1)
11.9 (25.4)
0.5
16.3 (25.4)
1.0 (3.9)
14.3
12–16 yr
60–110 (85)
- 15 to +110 (+60)
0.12–0.17 (0.15)
0.07 (0.10)
4.1 (9.9)
10.8 (21.2)
0.5
14.3 (23)
0.8 (3.7)
14.7
>16 yr
60–100 (80)
- 15 to +110 (+60)
0.12–0.20 (0.15)
0.08 (0.10)
3 (9)
10 (20)
0.3
10 (20)
0.8 (3.7)
12
 New data compiled from Park MK: Pediatric Cardiology for Practitioners, 4th ed. St Louis, Mosby, 2002, and Davignon A et al: Normal ECG standards for infants and children. Pediatr Cardiol 1979; 1:123–131.

 * Normal range and (mean). † Mean and (98th percentile).

 FIG. 7-9  Locating quadrants of mean QRS axis from leads I and aVF.  (From Park MK, Guntheroth WG: How to Read Pediatric ECGs, 4th ed. Philadelphia, Mosby, 2006, p 17.)

TABLE 7-5   -- NORMAL T-WAVE AXIS
Age
V1, V2
AVF
I, V5, V6
Birth–1 day
±
+
±
1–4 days
±
+
+
-
+
+
+
+
+
 +, T wave positive; -, T wave negative; ±, T wave normally either positive or negative.

 FIG. 7-10  Nonpathologic (nonischemic) and pathologic (ischemic) ST and T changes. A, Characteristic nonischemic ST-segment alteration called J depression; note that the ST slope is upward. B and C, Ischemic or pathologic ST-segment alterations. B, Downward slope of the ST segment. C, Horizontal segment is sustained.  (From Park MK, Guntheroth WG: How to Read Pediatric ECGs, 4th ed. Philadelphia, Mosby; 2006, p 107.)

 FIG. 7-11  Criteria for atrial enlargement. CAE, combined atrial enlargement; LAE, left atrial enlargement; RAE, right atrial enlargement.  (From Park MK: Pediatric Cardiology for Practitioners, 4th ed. St. Louis, Mosby, 2002, p 44.)

BOX 7-3
VENTRICULAR HYPERTROPHY CRITERIA
Right Ventricular Hypertrophy (RVH) Criteria

Must Have at Least One of the Following:

Increased right and anterior QRS voltage (with normal QRS duration):
 R in lead V1, >98th percentile for age S in lead V6, >98th percentile for age Upright T wave in lead V1 after 3 days of age to adolescence

Supplemental Criteria
 Right ventricle strain (associated with inverted T wave in V1 with tall R wave) Presence of Q wave in V1 (QR or QRS pattern) Right axis deviation (RAD) for patient's age
Left Ventricular Hypertrophy (LVH) Criteria

Increased QRS voltage in left leads (with normal QRS duration):
 R in lead V6 (and I, aVL, V5), >98th percentile for age S in lead V1, >98th percentile for age Left ventricle strain (associated with inverted T wave in leads V6, I, and/or aVF)

Supplemental Criteria
 Left axis deviation (LAD) for patient's age Volume overload (associated with Q wave >5 mm and tall T waves in V5 or V6)

B. ECG ABNORMALITIES

 1 Nonventricular arrhythmias ( Table 7-6 ).[7] 2 Ventricular arrhythmias ( Table 7-7 ; Figs. 7-12, 7-13, and 7-14 [12] [13] [14]). 3 Nonventricular conduction disturbances ( Fig. 7-15 and Table 7-8 ).[8] 4 Ventricular conduction disturbance ( Table 7-9 ).