EKG Quiz 5

I. EKG Axis Interpretation

• Definition: The cardiac axis refers to the overall direction of the heart’s electrical depolarization during ventricular contraction, as viewed in the frontal plane (using limb leads). It primarily reflects the direction of the QRS complex.

• Normal Axis: The normal axis should point down and to the left.

  • Common ranges: Approximately -30 to +120 degrees or 0 to +90 degrees.

• Quadrant Method:

  • Lead I: Positive electrode on the left arm (0 degrees).

  • Lead aVF: Positive electrode on the left foot (+90 degrees).

  • Normal Axis: 0 to +90 degrees (QRS positive in Lead I and Lead aVF).

  • Left Axis Deviation (LAD): 0 to -90 degrees.

  • Right Axis Deviation (RAD): +90 to +180 degrees.

  • Extreme Right Axis Deviation (ERAD): -180 to -90 degrees.

  • To determine: Evaluate the QRS in Lead I and then in aVF (positive, negative, or equiphasic).

• Axis Shift Causes:

  • Hypertrophy: The axis shifts towards the hypertrophied area.

  • Myocardial Infarction (MI): The axis shifts away from the infarcted (electrically dead) area.

  • Ventricular Ectopy/Pacing: Can cause significant axis deviations.

II. Hypertrophy

• Definition: Abnormal enlargement of the myocardium due to increased pressure, volume overload, or genetic abnormalities. It involves myocyte remodeling, fibrosis, and stiffness, potentially leading to decreased ventricular function and arrhythmias.

• EKG Limitations: EKG can provide clues (increased voltage, prolonged depolarization) but is not a definitive diagnosis.

• Best Test: Echocardiogram is the best test to detect hypertrophy and provides comprehensive information about atrial and ventricular structure.

• Atrial Enlargement (P Wave):

  • P wave represents atrial depolarization.

  • Normal P wave duration: < 0.12 seconds.

  • Normal P wave height: < 2.5 mm.

  • V1 is key: Biphasic wave, first half right atrium, second half left atrium.

• Right Atrial Abnormality (RAA) / P Pulmonale:

  • Caused by delayed or prolonged depolarization of the right atria.

  • Usually results from pulmonary disease (e.g., COPD) or congenital heart disease.

  • EKG finding: Abnormally tall P wave (> 2.5 mm), often peaked (P pulmonale).

• Left Atrial Abnormality (LAA) / P Mitrale:

  • Prolonged or notched P wave duration (> 0.12 seconds).

  • Often associated with mitral valve disease or left ventricular dysfunction.

• Left Ventricular Hypertrophy (LVH):

  • Enlargement of the left ventricle due to systemic hypertension, aortic stenosis/regurgitation.

  • EKG Findings:

    • Increased R-wave amplitude in left-sided/lateral leads (V4–V6, I, aVL).

    • Deeper S waves in right-sided leads.

    • Left-axis deviation.

    • ST/T wave discordance.

  • Most Specific Finding for LVH: R wave in aVL > 11 mm.

  • Voltage Criteria Limitations: Sensitive but can cause false positives (e.g., young healthy men, thin patients, mastectomy, African Americans, or false negatives with obesity, large breasts, low hematocrit).

III. Electrolytes and Disease on the EKG

• Potassium (K+):

  • Hyperkalemia (> 5.5 mEq/L): Renal failure, Addison’s disease, ACE inhibitors.

    • Characteristics:

      • Tall peaked T waves (earliest sign).

      • Wide, bizarre QRS complexes.

      • Decreased P-wave amplitude, eventually disappearing.

      • Progresses to high-grade AV blocks, ventricular standstill, asystole, PEA.

  • Hypokalemia (< 3.5 mEq/L): Decreased intake, increased GI excretion.

    • Characteristics:

      • Flattened T waves and ST depression.

      • Increased amplitude of U waves (prominent after T wave).

      • Prolonged QTc interval.

• Calcium (Ca2+):

  • Hypercalcemia:

    • Short ST segment and short QTc interval.

  • Hypocalcemia:

    • Prolonged ST segment and prolonged QTc interval.

• Pericardial Effusion:

  • Abnormally large fluid in the pericardial sac (can lead to cardiac tamponade).

  • Specific Triad:

    • Low QRS voltage (fluid insulates the heart).

    • Electrical alternans (heart swinging in fluid).

    • Tachycardia (compensation).

• Hypothermia:

  • Osborn wave (J point deflection): A slow, upright deflection between the end of the QRS and the ST segment.

  • Other findings: Prolonged PR, QRS, and QTc intervals; bradycardia; atrial/ventricular arrhythmias.

• Elevated Intracranial Pressure (ICP):

  • Widespread giant T-wave inversions (cerebral T waves).

  • Prolonged QT interval.

  • Bradycardia.

• Digitalis Toxicity:

  • Therapeutic levels: "Scooped" ST segments (hockey-stick appearance).

  • Toxicity: PVCs, junctional rhythms, classic atrial tachycardia with AV block.

• Brugada Syndrome:

  • Genetic sodium channelopathy.

  • EKG: Coved ST elevation in V1–V3, followed by inverted T waves. Risk of sudden cardiac death.