EKG Refresher Practice Flashcards

EKG Refresher Instructional Objectives and Logistics

Session Details: Part of Advanced Clinical Medicine-I, presented by L. Richardson, MD on June 8, 2026.
Instructional Objectives:
- Review a basic approach to EKG interpretation as introduced in Clin Med-II.
- Review common EKG diagnostic criteria.
- Apply these criteria to interpret tracings.
- Prepare for small-group practice sessions scheduled for Wednesday of the current week.
EKG Exam Information:
- Date: Monday, June 15th.
- Time: $7:30 - 8:30\,\text{AM}$ .
- Location: Testing Center.
- Format: 25-question objective, computer-based test.
- Content: $12$ -lead EKG tracings, rhythm strips, and stand-alone multiple-choice questions (MCQs).
- Passing Score: > 70\%.
EKG Re-take Information:
- Date: Wednesday, June 17th.
- Time: $8:00 - 9:00\,\text{AM}$ .
- Location: AH-341.
- Format: Covers the same material as the first exam but includes no MCQs. It features short-answer questions and the full interpretation of $2$ EKG tracings.
- Passing Score: $\ge 70\%$ (partial credit is possible).

Electrical Activity on EKG Paper

Standard Calibration and Grid Measurements:
- Standard Paper Speed: $25\,\text{mm/sec}$ .
- Voltage Calibration: $10\,\text{mm/mv}$ ( $1\,\text{mm} = 0.1\,\text{mV}$ ; $5\,\text{mm} = 0.5\,\text{mV}$ ).
- Time (Horizontal Axis):
  - $1$ small box ( $1\,\text{mm}$ ) = $0.04\,\text{sec}$ .
  - $5$ small boxes ( $1$ large box) = $0.2\,\text{sec}$ .
Waveforms and Intervals:
- P-wave: Represents atrial depolarization.
- P-R interval: Measured from the beginning of the P-wave to the beginning of the QRS complex.
- P-R segment: The flat line between the end of the P-wave and the start of the QRS.
- QRS complex: Represents ventricular depolarization (includes Q, R, and S waves).
- S-T segment: The flat line between the end of the QRS and the start of the T-wave.
- S-T interval: Measured from the J-point to the end of the T-wave.
- T-wave: Represents ventricular repolarization.
- Q-T interval: Represents total time in systole.
- U-wave: A small wave sometimes following the T-wave.

Leads and Anatomical Correlations of the Heart Walls

Simplified Lead-Wall Mapping (Note: These apply best to ST-elevation; correlation is less reliable for ST-depression):
- Inferior Wall: Leads II, III, and aVF.
- Lateral Wall: Leads I, aVL, V5, and V6.
  - High Lateral Wall: I and aVL (some sources specify only aVL).
  - Low Lateral Wall: V5 and V6.
- Septal Wall: V1 and V2.
- Anterior Wall: V3 and V4.
- Anteroseptal Wall: V1, V2, V3, and V4.
- True Posterior Wall (MI Indicators): Tall R-waves (R > S) and ST depression in V1 and V2.
- Apical Wall: Leads II, III, aVL, and any leads from V1 through V4.
Supplemental Lead Placement:
- Right Ventricular (RV) MI Concerns: Use Leads V1R through V6R.
- Posterior Wall Concerns: Use Leads V7, V8, and V9 (placed on the back near the left scapula).

Evaluation of Lead aVR

Reason for Frequent Exclusion: Lead aVR views the heart from the right superior aspect, opposite of most other leads. Consequently, electrical depolarizations move away from it, causing normally inverted P-waves, net negative QRS complexes, and inverted T-waves.
Advanced Diagnostic Utility:
- Proximal LAD Obstruction: Suggested by ST elevation in aVR and V1 in the presence of anterior ST elevation (specifically when ST elevation in V1 is greater than in aVR).
- Left Main Coronary Artery Disease: Suggested by ST elevation in aVR in the presence of anterior ST depression (specifically when ST elevation in aVR is greater than in V1).

Basic Interpretation Approach: Rate, Rhythm, and Axis

Heart Rate Estimation: If the R-R interval is regular, use the sequence: $300-150-100-75-60-50$ .
Normal Sinus Rhythm (NSR) Criteria:
- P-waves precede each QRS complex.
- P-waves are upright in Leads I and II.
- RR intervals are constant/evenly spaced.
- Rate is between $60 - 100\,\text{bpm}$ .
- QRS duration is narrow (< 3 small boxes/< 0.12\,\text{sec}).
QRS Axis Determination:
- Normal Quadrant: Net positive polarity in Lead I ( $+$ ) and Lead aVF ( $+$ ).
- Normal Range: Between $0^{\circ}$ and $+90^{\circ}$ (technically $-30^{\circ}$ to $+90^{\circ}$ is considered normal; $-1^{\circ}$ to $-29^{\circ}$ is "leftward" but not significant LAD).
- Left Axis Deviation (LAD): Lead I is ( $+$ ), Lead aVF is ( $-$ ).
  - Associated with: LVH, LBBB, LAFB, inferior wall MI, WPW, pregnancy, obesity, ASD.
- Right Axis Deviation (RAD): Lead I is ( $-$ ), Lead aVF is ( $+$ ).
  - Associated with: RVH, Pulmonary Embolism (PE), lateral wall MI, COPD, WPW, low $K^+$ .
- Extreme RAD: Lead I is ( $-$ ), Lead aVF is ( $-$ ).
  - Associated with: Severe RVH, ventricular rhythms, high $K^+$ .
Calculating Numeric Axis (Biphasic Lead Method):
- Find the limb lead where the QRS is closest to biphasic.
- The axis is perpendicular to that lead.
  - Biphasic in Lead I: Axis is $\pm 90^{\circ}$ (check aVF polarity).
  - Biphasic in Lead aVF: Axis is $0^{\circ}$ or $\pm 180^{\circ}$ (check Lead I polarity).
  - Biphasic in Lead II or III: Axis is $\pm 30^{\circ}$ or $\pm 150^{\circ}$ .
  - Biphasic in Lead aVR or aVL: Axis is $\pm 60^{\circ}$ or $\pm 120^{\circ}$ .
  - If no clear biphasic lead exists, the axis is "indeterminate."

Waveform Detailed Analysis

Atrial Enlargement:
- Right Atrial Enlargement (RAE): Tall, narrow, peaked P-waves in lead II ( $\ge 2.5\,\text{mm}$ ). In V1, the initial deflection of a biphasic P-wave has an amplitude $\ge 2$ small boxes. Shift of P-wave axis to the right.
- Left Atrial Enlargement (LAE): Wide, notched P-wave in lead II (duration > 3 small boxes). In V1, the terminal component of a biphasic P-wave is > 1 \times 1 small box wide/deep. Shift of P-wave axis to the left.
- Biatrial Enlargement: Features of both RAE and LAE. Biphasic P in V1 with terminal component > 1 \times 1 small box; P-wave in lead II with amplitude $\ge 3$ small boxes.
PR Interval:
- Normal: $0.12$ to $0.20\,\text{sec}$ .
- Short PR ( $\le 0.12\,\text{sec}$ ): Consider retrograde junctional P-waves, Lown-Ganong-Levine syndrome, or WPW syndrome.
- Long PR (> 0.20\,\text{sec}): Fixed prolongation indicates 1st-degree AV Block.
Q-Waves:
- Pathologic Criteria: > 1 small box wide ( $0.04\,\text{sec}$ ) AND depth > 1/3 the height of the R-wave. Pathologic Q-waves indicate a completed infarct.
QRS Duration:
- Normal: < 0.10\,\text{sec}.
- Intraventricular Conduction Delay (IVCD): Duration between $0.10 - 0.12\,\text{sec}$ .
- Bundle Branch Blocks (BBB): Duration > 0.12\,\text{sec}.
  - LBBB: "Mu"-shaped (R-R') morphology in I, aVL, V5, V6. QS complex or small "rS" in V1. Tall R-waves in V6.
    - Note: It is difficult to diagnose MI in the presence of LBBB. New LBBB in a symptomatic ACS patient is a STEMI equivalent (seen in $\sim 7\%$ of MI patients).
  - RBBB: R-S-R' (rabbit ears) morphology in V1 and V2.

QT Interval and Repolarization Factors

QT Interval: Represents total time in systole. Varies with heart rate, sex, and age.
Rule of Thumb: Should be less than one-half the preceding R-R interval when HR is $65 - 90\,\text{bpm}$ .
Normal Range: Typically < 0.42\,\text{sec}.
Corrected QT (QTc): Used if HR is outside of normal range; calculated by EKG software.
Prolonged QT Causes: CHF, MI, hypocalcemia, hypokalemia, hypomagnesemia, medications (quinidine, procainamide).
Short QT Causes: Digitalis use, hypercalcemia, hyperkalemia, hypermagnesemia.

ST Segment and T-Wave Pathology

ST Elevation ( $\uparrow$ ): Measured against the preceding PR or TP segment. Suggests acute injury/MI.
- Criteria: Typically > 1\,\text{mm} in limb leads and > 2\,\text{mm} in precordial leads.
- Other Etiologies: Early repolarization, pericarditis, ventricular aneurysm, PE, brain hemorrhage.
ST Depression ( $\downarrow$ ): Suggests ischemia, MI, LVH, angina (transient), IVCD, medications (digitalis), or a positive exercise stress test.
Reciprocal Changes:
- Acute Inferior MI ( $\uparrow$ ST in II, III, aVF): Reciprocal $\downarrow$ ST in I, aVL (high lateral).
- Acute Anteroseptal MI ( $\uparrow$ ST in V1-V4): Reciprocal $\downarrow$ ST in II, III, aVF (inferior) and/or I, aVL, V5, V6 (lateral).
- True Posterior MI: Reciprocal $\downarrow$ ST and tall R-waves in V1, V2.
T-Wave Morphology:
- Symmetric T-Wave Inversion (TWI): Hallmark of acute ischemia.
- Wellens Syndrome: Marked TWI in leads V2 and V3, indicating LAD stenosis.
- Hyperacute T-waves: Broad base with blunted peaks; indicates early acute ischemia.
- Hyperkalemia: Pointy T-waves with narrow base and symmetric, sharp apex.
- Amplitude: Normal is < 6\,\text{mm} in limb leads and < 12\,\text{mm} in precordial leads. Abnormal if > 2/3 the R-wave height.
Typical Sequence of Infarct: Ischemia (TWI, first $1-2$ mins) $\rightarrow$ Hyperacute T-waves (upright/peaked) $\rightarrow$ Acute Injury ( $\uparrow$ ST) $\rightarrow$ Completed Infarct (Pathologic Q-waves).

Specialized Sign: Pulmonary Embolism (PE)

EKG Sign: "S1-Q3-T3" pattern.
- Deep S-wave in lead I.
- Q-wave in lead III.
- Inverted T-wave in lead III.
Note: This finding is highly specific but not sensitive. Other PE signs include TWI in V1-V4 and signs of RV strain (RVH, RBBB).

AV Blocks and Hypertrophy

AV Blocks:
- 1st-degree: Fixed PR interval > 0.20\,\text{sec} (> 5 small boxes).
- 2nd-degree Type I (Wenckebach/Mobitz I): Block in AV node. PR intervals progressively lengthen until a QRS is dropped.
- 2nd-degree Type II (Mobitz II): Block in Purkinje fibers (His/Bundle branches). PR interval is fixed/constant, then a QRS is suddenly dropped.
- 3rd-degree (Complete AVB): Total AV dissociation. P-P and R-R intervals march out independently; rates are different.
Left Ventricular Hypertrophy (LVH):
- Criteria:
  - R-wave in aVL > 11\,\text{mm}.
  - S-wave (V1) + R-wave (V5 or V6) > 35\,\text{mm}.
  - Any R + any S (precordial) > 45\,\text{mm}.
- LVH with Strain: Asymmetric TWI (gradual downslope, rapid return to baseline).
Right Ventricular Hypertrophy (RVH):
- Criteria: R-wave height $\ge$ S-wave depth in V1 ( $R \ge S$ ) usually with RAD. Must rule out RBBB and posterior MI.
Fascicular Blocks:
- LAFB: More common. RAD more negative than $-30^{\circ}$ . S > R in II, III, aVF.
- LPFB: Harder to diagnose. Shift in axis to the right (some require > +120^{\circ}). Normal QRS duration. No RVH.

Arrhythmia Characteristics

Atrial Fibrillation (A-fib): Irregularly irregular rhythm with no discrete P-waves. Atrial rate $350 - 450$ \text{ discharges/min}. Ventricular response can vary (controlled, slow, or rapid).
Atrial Flutter: Sawtooth P-wave pattern. Atrial rate is often $\sim 300\,\text{bpm}$ . Ventricular rate may be regular or irregular based on the AV block ratio (e.g., $4:1$ block results in a ventricular rate of $75\,\text{bpm}$ ).
Junctional Rhythm: Originates near AV node. Normal QRS; rate $40 - 60\,\text{bpm}$ . P-waves may be absent, retrograde, or inverted (preceding or following QRS).
Ventricular Rhythm: Wide QRS complexes; no consistent P-waves. Inherent rate is $20 - 40\,\text{bpm}$ .
WPW Syndrome: Identified by a "Delta wave" (slurred upstroke of QRS). Associated with re-entrant tachycardias (SVT).
Life-Threatening Rhythms: Ventricular Tachycardia (VT) and Ventricular Fibrillation (VF).

Unknown EKG Analysis Examples

Unknown #1 (Answer Key):
- Rate: $\sim 100\,\text{bpm}$ .
- Rhythm: Normal Sinus Rhythm (NSR).
- Axis: Between $+30^{\circ}$ and $+70^{\circ}$ .
- Waveforms: No LAE/RAE; normal PR interval; no QRS prolongation; normal QT interval; no significant ST changes.
- Findings: Q-wave in aVL (non-pathologic) and small R-waves in V1-V3.
- Impression: Normal EKG.
Rate Calculation from Tracing: 8 beats seen on a 5-second tracing $= 8 \times 12 = 96\,\text{bpm}$ .