Electrocardiography (EKG) and Cardiovascular Examination: Study Notes

Electrocardiography (EKG)

EKG Waves and Intervals

The electrocardiogram (EKG or ECG) is a graphical representation of the heart's electrical activity, recorded via electrodes placed on the skin. It is essential for diagnosing cardiac rhythm, conduction abnormalities, and myocardial injury.

• P wave: Represents atrial depolarization (contraction of the atria).

• QRS complex: Represents ventricular depolarization (contraction of the ventricles).

• T wave: Represents ventricular repolarization (recovery phase of the ventricles).

• P-R interval: Time from the onset of the P wave to the start of the QRS complex; reflects the duration between the beginning of atrial and ventricular contraction.

• Q-T interval: Time required for a single cycle of ventricular depolarization and repolarization.

• U wave: Represents late ventricular repolarization; significance is not fully understood but a prominent U wave may indicate hypokalemia.

Normal durations and amplitudes:

• P wave: 0.04 – 0.12 s, amplitude ≤ 25 mm

• QRS complex: 0.04 – 0.12 s

• T wave: 0.08 – 0.12 s

• P-R interval: 0.12 – 0.20 s

• Q-T interval: ~0.36 s

Normal heart rate: 60–100 beats per minute (bpm)

• >100 bpm: Tachycardia

• <60 bpm: Bradycardia

EKG Paper and Measurement

EKG tracings are recorded on standardized grid paper, which allows for accurate measurement of time and voltage.

• Each small box: 1 mm2

• Paper speed: 25 mm/sec; each small box horizontally = 0.04 s

• 5 mm horizontally = 0.2 s (5 × 0.04 s)

• Vertically: 1 mm = 0.1 mV; 10 mm = 1.0 mV

• Wave deflection: Upward = positive, downward = negative

• Isoelectric line: No deflection from baseline

• Biphasic wave: Both positive and negative deflection

Calculating Heart Rate from EKG

• Count the number of large boxes between two successive QRS complexes and divide 300 by this number:

• $\text{Heart Rate} = \frac{300}{\text{Number of large boxes between R waves}}$

• If rhythm is irregular, count the number of QRS complexes in 6 seconds and multiply by 10.

Cardiac Conduction System

The heart's electrical impulses originate in the SA node, travel through the atria, then to the AV node, down the Bundle of His, and through the right and left bundle branches and Purkinje fibers to the ventricular myocardium.

• EKG records the sum of all cardiac action potentials.

• Electrodes are placed on the left arm (LA), right arm (RA), and left leg (LL); right leg (RL) is ground.

EKG Leads

Limb Leads

• Lead I: LA (+) vs. RA

• Lead II: LL (+) vs. RA

• Lead III: LL (+) vs. LA

Unipolar Leads

• Three augmented limb leads: aVL (left arm), aVR (right arm), aVF (left leg)

• Six precordial (chest) leads: V1–V6

• V1–V2: Right ventricle

• V4–V6: Lateral wall of left ventricle

• R and S wave progression across precordial leads:

  • V1: Small R, large S

  • V2–V4: R ≈ S

  • V5–V6: Large R, small S

Mean QRS Axis

• Normal: –30° to +110°

• Left-axis deviation: < –30°

• Right-axis deviation: > +110°

• Extreme axis deviation: –90° to +180°

EKG Interpretation: 14-Point Approach

Systematic interpretation ensures accurate diagnosis. The following steps are recommended:

1. Standardization: Confirm machine calibration.

2. Heart rate: Calculate as above; normal 60–100 bpm.

3. Rhythm: Check for uniformity between QRS complexes.

4. PR interval: Normal 0.12–0.20 s; prolonged interval suggests first-degree AV block.

5. P wave size: Should not exceed 25 mm; tall P wave = right atrial enlargement, wide P wave = left atrial abnormality.

6. QRS width: Normal ≤ 0.1 s.

7. QT interval: Normal ~0.36 s; prolonged QT may indicate electrolyte imbalance, drug effect, or ischemia; shortened QT in hypercalcemia or digitalis use.

8. QRS voltage: High voltage may indicate ventricular hypertrophy; low voltage may be due to obesity, emphysema, pericardial effusion, hypothyroidism, or myocardial injury.

9. Mean QRS axis: Normal –30° to +110°.

10. R wave progression: Inspect V1–V6 for increasing R wave; poor progression may indicate MI, LVH, COPD, or LBBB.

11. Abnormal Q wave: In II, III, aVF = inferior MI; in I, aVL, V1–V6 = anterior MI.

12. ST-segment: Elevation or depression may indicate MI (early or late).

13. T wave: Normally positive in leads with positive QRS; negative in aVR.

14. U wave: Prominent U wave may indicate hypokalemia or drug toxicity (e.g., quinidine).

Cardiovascular Examination

Inspection

• Jugular venous pulsation (JVP): Best assessed with patient at 30°; normal < 8 cm; increased JVP suggests right-sided heart pressure increase.

• Jugular contour: Inspect for 'a' (synchronous with S1) and 'v' (synchronous with S2) waves.

• Point of maximal impulse (PMI): Visible or palpable apex beat of the heart.

Palpation

• Palpate major arteries: carotid, brachial, radial, femoral, popliteal, dorsalis pedis, posterior tibial.

• Listen for bruits (turbulent flow).

• Palpate for PMI and any thrills (vibrations).

Percussion

• Used to estimate the lateral border of the heart; less commonly performed due to low sensitivity and availability of chest X-ray.

• Less reliable in women with large breasts, patients with barrel chest, or obesity.

Auscultation

• Performed with patient supine or sitting.

• Listen for murmurs, rubs, snaps, bruits, or extra heart sounds.

• Four major auscultation zones:

  • Aortic: right 2nd intercostal space

  • Pulmonic: left 2nd intercostal space

  • Tricuspid: left 4th intercostal space

  • Mitral: left 5th or 6th intercostal space, midclavicular line

• S1: Closure of AV valves (mitral, tricuspid)

• S2: Closure of semilunar valves (aortic, pulmonary)

• S3: Early diastole; may be normal in children, athletes, pregnancy, or indicate ventricular dysfunction

• S4: Late diastole; may indicate pathology ("S4 gallop")

Heart Murmurs

Heart murmurs are prolonged vibrations due to turbulent blood flow, often from structural heart defects.

• Systolic murmurs: Occur during ventricular contraction; can be ejection (crescendo-decrescendo, e.g., aortic stenosis) or holosystolic (uniform, e.g., mitral regurgitation).

• Diastolic murmurs: Occur during ventricular relaxation; can be early (decrescendo, e.g., aortic regurgitation), mid-diastolic (rumble, e.g., mitral stenosis), or continuous (e.g., patent ductus arteriosus).

• Clinical note: Systolic murmurs are more common and may be benign; diastolic murmurs are usually pathological and require further evaluation.

Summary Table: EKG Waves and Intervals

Wave/Interval	Represents	Normal Duration	Clinical Significance
P wave	Atrial depolarization	0.04–0.12 s	Right/left atrial enlargement if abnormal
QRS complex	Ventricular depolarization	0.04–0.12 s	Bundle branch block, ventricular hypertrophy if wide
T wave	Ventricular repolarization	0.08–0.12 s	Ischemia, electrolyte imbalance if abnormal
P-R interval	Atrial to ventricular conduction	0.12–0.20 s	First-degree AV block if prolonged
Q-T interval	Ventricular depolarization & repolarization	~0.36 s	Electrolyte/drug effects if abnormal
U wave	Late ventricular repolarization	Variable	Hypokalemia if prominent

Example: Calculating Heart Rate from EKG

• If there are 4 large boxes between two R waves, heart rate is:

$\text{Heart Rate} = \frac{300}{4} = 75$ bpm

Additional info: The above notes expand on the clinical significance of EKG findings and heart sounds, and provide context for the systematic approach to cardiovascular examination.