3.2 12-Lead ECG Interpretation: Ischemia, Transmural Infarction & Conduction

AACVPR CCRP Certified Cardiac Rehab Professional Exam

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1 Chapter 1: Introduction & Cardiac Rehabilitation Foundations

1.1 AACVPR CCRP Credential, Exam Specifications & Core Competencies 1.2 Phases of Cardiac Rehabilitation & Clinical Delivery Models 1.3 Interdisciplinary Team Roles, Clinical Scope of Practice & Safety

2 Chapter 2: Cardiovascular Anatomy, Physiology & Pathology

2.1 Cardiac Anatomy, Coronary Circulation & Hemodynamics 2.2 Atherosclerosis Pathogenesis, Acute Coronary Syndromes (ACS) & Revascularization 2.3 Heart Failure (HFrEF/HFpEF), Cardiomyopathies & Valvular Heart Disease 2.4 Electrical Interventions: Cardioversion, Catheter Ablation & Post-Procedure Rehabilitation

3 Chapter 3: Diagnostic Evaluation, ECG & Clinical Testing

3.1 Baseline Clinical Assessment & AACVPR Risk Stratification 3.2 12-Lead ECG Interpretation: Ischemia, Transmural Infarction & Conduction 3.3 Cardiac Arrhythmias, Conduction Blocks & Device Rhythms (Pacemakers/ICDs) 3.4 Graded Exercise Testing (GXT), Gas Exchange & Termination Criteria

4 Chapter 4: Patient-Centered Assessment: Education, Equity & Social Context

4.1 Learning Readiness: Health Literacy, Learning Styles & Communication Barriers 4.2 Social Determinants of Health, Culture & Spirituality in Cardiac Rehab 4.3 Sex- and Race-Based Differences in Cardiovascular Presentation & Outcomes 4.4 Substance Use Screening: Alcohol, Cannabis, Stimulants & Cardiac Risk

5 Chapter 5: Exercise Prescription & Aerobic Conditioning

5.1 FITT-VP Framework & Aerobic Exercise Intensity Calculation 5.2 Exercise Progression, Environmental Factors & Telemetry Monitoring Guidelines 5.3 High-Intensity Interval Training (HIIT) vs Moderate Continuous Training (MICT) 5.4 Home Exercise Program Design, Prescription & Independent Progression

6 Chapter 6: Exercise Physiology, Monitoring & Session Design

6.1 Health-Related Physical Fitness Components & Functional Capacity Testing 6.2 Acute Cardiovascular Responses to Aerobic Exercise: METs, Rate Pressure Product & VO₂ 6.3 Chronic Training Adaptations in Cardiac Patients 6.4 Structuring the Exercise Session: Warm-Up, Conditioning & Cool-Down 6.5 ECG Telemetry Setup: Skin Preparation, Electrode Placement & Artifact Troubleshooting 6.6 Pulse Oximetry, Exertional Desaturation & Supplemental Oxygen Titration

7 Chapter 7: Resistance, Flexibility & Exercise Safety

7.1 Resistance Training Guidelines, Hemodynamics & Sternal Precautions 7.2 Flexibility, Neuromotor Training & Special CR Populations 7.3 Exercise Contraindications, Adverse Signs/Symptoms & Emergency Protocols

8 Chapter 8: Physical Activity Counseling & Behavior Change

8.1 Physical Activity Guidelines, Sedentary Physiology & NEAT 8.2 Behavioral Change Theories: Transtheoretical Model & Social Cognitive Theory 8.3 Motivational Interviewing Principles & Resolving Ambivalence 8.4 SMART Goal Setting, Activity Tracking & Relapse Prevention

9 Chapter 9: Physical Activity Assessment & Real-World Activity Counseling

9.1 Physical Activity vs Exercise: Assessment Instruments, Logs & Wearables 9.2 Metabolic Requirements of Daily Life: Occupational, Recreational & Sexual Activity 9.3 Environmental & Situational Risk: Heat, Cold, Altitude, Air Quality & High-Risk Activities 9.4 Upper- vs Lower-Body Physiologic Demands & Modality Selection

10 Chapter 10: Hypertension & Blood Pressure Regulation

10.1 2017 ACC/AHA Hypertension Classification & Cardiovascular Risk 10.2 Antihypertensive Pharmacology & Exercise Hemodynamics 10.3 Exertional Blood Pressure Dynamics, Exertional Hypotension & Crisis 10.4 Home Blood Pressure Monitoring, Sodium Restriction & Lifestyle Interventions 10.5 Blood Pressure Measurement Technique, Device Validation & Renal Protection

11 Chapter 11: Diabetes Mellitus & Metabolic Regulation

11.1 Diabetes Pathophysiology, Diagnostic Criteria & Glycemic Targets 11.2 Antidiabetic Pharmacotherapy (Insulin, Sulfonylureas, SGLT2i, GLP-1 RA) 11.3 Exercise-Induced Hypoglycemia Management (Rule of 15) & Hyperglycemia 11.4 Diabetic Complications & Exercise Adaptations (Autonomic & Peripheral Neuropathy) 11.5 Blood Glucose Self-Monitoring, CGM Interpretation & Peri-Exercise Testing 11.6 Diabetic Foot Care, Skin Integrity & Footwear Assessment

12 Chapter 12: Blood Lipid Management & Atherosclerosis Prevention

12.1 Lipid Metabolism, Atherogenic Lipoproteins & Advanced Lipid Testing 12.2 Statin Therapy, Dosing Intensity & Secondary Prevention Targets 12.3 Non-Statin Pharmacotherapies & Statin-Associated Muscle Symptoms (SAMS)

13 Chapter 13: Medical Nutrition Therapy & Dietary Patterns

13.1 Nutritional Assessment & Macronutrient Guidelines in Cardiovascular Disease 13.2 Cardioprotective Dietary Patterns: Mediterranean, DASH & Plant-Based 13.3 Dietary Lipids, Sodium, Soluble Fiber & Plant Stanols/Sterols 13.4 Clinical Scope: CR Professional Counseling Boundaries vs RD/RDN Referral

14 Chapter 14: Body Composition & Weight Management

14.1 Anthropometric Assessment: BMI, Waist Circumference & Obesity Paradox 14.2 Behavioral Weight Management, Energy Balance & Caloric Deficits 14.3 Anti-Obesity Pharmacotherapy (GLP-1/GIP) & Bariatric Surgery Considerations

15 Chapter 15: Tobacco Cessation Interventions

15.1 Cardiovascular Pathophysiology of Tobacco, Nicotine & Secondhand Smoke 15.2 Clinical Cessation Frameworks: The 5 A's & 5 R's Models 15.3 Pharmacotherapy for Nicotine Dependence: NRT, Varenicline & Bupropion 15.4 Behavioral Counseling, Coping Strategies & Relapse Prevention

16 Chapter 16: Psychosocial Health, Screening & Behavioral Support

16.1 Psychosocial Risk Factors & Prognostic Impact in Heart Disease 16.2 Validated Screening Instruments: PHQ-9, GAD-7 & Administration 16.3 Evidence-Based Interventions: Stress Management, CBT Principles & Social Support 16.4 Crisis Protocols, Suicidal Ideation & Mental Health Referral Pathways 16.5 Psychotropic Pharmacology & Cardiac Safety 16.6 Sleep Disturbance, Chronic Pain & Somatic Comorbidity in Psychosocial Management

17 Chapter 17: Regulatory Compliance, Documentation & Program Outcomes

17.1 CMS Coverage Guidelines, Qualifying Diagnoses & Practitioner Supervision 17.2 Individualized Treatment Plan (ITP) Components, 30-Day Updates & Goals 17.3 AACVPR Outcome Domains & Program Certification Performance Measures 17.4 Program Certification, Quality Improvement & Medical Emergency Preparedness

3.2 12-Lead ECG Interpretation: Ischemia, Transmural Infarction & Conduction

Key Takeaways Explain This Topic AI

Significant myocardial ischemia is identified on a 12-lead ECG or exercise stress ECG by horizontal or downsloping ST-segment depression >= 1.0 mm (0.10 mV) measured 80 ms past the J-point.

Acute transmural myocardial injury (STEMI) requires J-point ST elevation >= 1.0 mm in at least two contiguous limb leads, or >= 1.5 to 2.5 mm in precordial leads V2–V3, accompanied by reciprocal ST depression in opposing leads.

Pathologic Q waves indicate irreversible myocardial necrosis and are defined as a duration >= 0.04 seconds (40 ms) or a depth exceeding 25% of the corresponding R-wave amplitude in contiguous leads.

Coronary artery occlusion localization correlates directly with lead groupings: Inferior (II, III, aVF) reflects the Right Coronary Artery (RCA); Anterior/Septal (V1–V4) reflects the Left Anterior Descending (LAD); Lateral (I, aVL, V5, V6) reflects the Left Circumflex (LCx).

The ECG electrical axis is rapidly determined using leads I and aVF: positive QRS in both indicates a normal axis (0° to +90°); positive in Lead I and negative in aVF indicates left axis deviation (-30° to -90° when Lead II is negative).

Last updated: September 2026

3.2 12-Lead ECG Interpretation: Ischemia, Transmural Infarction & Conduction

In cardiac rehabilitation, the 12-lead electrocardiogram (ECG) is the primary non-invasive diagnostic tool used to monitor myocardial perfusion, detect subclinical ischemia, confirm anatomical infarction patterns, and evaluate intraventricular conduction delays. Clinicians must master lead orientation, axis determination, ischemic repolarization markers, and coronary artery localization.

12-Lead Electrode Placement & Anatomical Orientation

The 12-lead ECG evaluates cardiac electrical forces in two perpendicular planes:

Frontal Plane (Limb Leads)

Comprises three bipolar limb leads ( I, II, III ) and three augmented unipolar leads ( aVR, aVL, aVF ). In cardiac rehabilitation telemetry, Mason-Likar torso electrode placement replaces wrist/ankle electrodes with infraclavicular and anterior iliac crest locations to eliminate skeletal muscle motion artifact during treadmill walking and cycle ergometry.

Horizontal Plane (Precordial Leads)

Six unipolar chest leads ( V1 through V6 ) view transverse electrical vectors:

V 1 V_1 V 1 ​ : 4th intercostal space (ICS) at the right sternal border (septal view).

V 2 V_2 V 2 ​ : 4th ICS at the left sternal border (septal view).

V 3 V_3 V 3 ​ : Midway between V 2 V_2 V 2 ​ and V 4 V_4 V 4 ​ diagonally (anterior view).

V 4 V_4 V 4 ​ : 5th ICS in the left midclavicular line (apical/anterior view).

V 5 V_5 V 5 ​ : 5th ICS in the left anterior axillary line, horizontal to V 4 V_4 V 4 ​ (lateral view).

V 6 V_6 V 6 ​ : 5th ICS in the left midaxillary line, horizontal to V 4 V_4 V 4 ​ (low lateral view).

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Mean Electrical Axis Determination

The mean QRS electrical axis represents the net frontal plane vector of ventricular depolarization. It is evaluated rapidly using the Quadrant Method with Lead I ( 0 ∘ 0^\circ 0 ∘ ) and Lead aVF ( + 90 ∘ +90^\circ + 9 0 ∘ ):

Lead I Net QRS Lead aVF Net QRS Lead II Net QRS Electrical Axis Quadrant Common Clinical Causes

Positive Positive Positive Normal Axis ( 0 ∘ to + 90 ∘ 0^\circ \text{ to } +90^\circ 0 ∘ to + 9 0 ∘ ) Normal cardiac orientation

Positive Negative Positive Physiologic Axis ( 0 ∘ to − 30 ∘ 0^\circ \text{ to } -30^\circ 0 ∘ to − 3 0 ∘ ) Horizontal heart, pregnancy, obesity

Positive Negative Negative Pathologic Left Axis Deviation (LAD) ( − 30 ∘ to − 90 ∘ -30^\circ \text{ to } -90^\circ − 3 0 ∘ to − 9 0 ∘ ) Left anterior fascicular block (LAFB), inferior MI, LVH

Negative Positive Positive Right Axis Deviation (RAD) ( + 90 ∘ to + 180 ∘ +90^\circ \text{ to } +180^\circ + 9 0 ∘ to + 18 0 ∘ ) RVH, pulmonary embolism, COPD, lateral MI, LPFB

Negative Negative Negative Extreme / Northwest Axis ( − 90 ∘ to 180 ∘ -90^\circ \text{ to } 180^\circ − 9 0 ∘ to 18 0 ∘ ) Ventricular tachycardia, hyperkalemia, severe RV strain

Electrocardiographic Evolution: Ischemia, Injury & Infarction

Acute coronary artery disease produces a sequential triad of repolarization and depolarization abnormalities:

1. Myocardial Ischemia (Subendocardial)

Subendocardial ischemia delays repolarization without causing immediate necrosis:

ST-Segment Depression : Measured at the ST 80 point (80 ms past the J-point) or at 60 ms when H R > 130 bpm HR > 130\text{ bpm} H R > 130 bpm :

Horizontal ST Depression : ≥ 1.0 mm \ge 1.0\text{ mm} ≥ 1.0 mm ( 0.10 mV 0.10\text{ mV} 0.10 mV ) flat depression; highly predictive of CAD.

Downsloping ST Depression : ≥ 1.0 mm \ge 1.0\text{ mm} ≥ 1.0 mm downward-sloping depression; highest specificity for multivessel/left main CAD.

Upsloping ST Depression : Rapidly ascending depression; requires ≥ 1.5 mm \ge 1.5\text{ mm} ≥ 1.5 mm measured 80 ms past J-point to be considered abnormal.

T-Wave Inversion : Symmetrical, narrow, deeply inverted T waves ( ≥ 1.0 mm \ge 1.0\text{ mm} ≥ 1.0 mm ) in contiguous leads.

2. Myocardial Injury (Acute Transmural STEMI)

Transmural epicardial injury generates a systolic injury current manifesting as ST-Segment Elevation at the J-point in ≥ 2 \ge 2 ≥ 2 contiguous leads:

Limb Leads (I, II, III, aVL, aVF) and V 4 – V 6 V_4\text{--}V_6 V 4 ​ – V 6 ​ : J-point elevation ≥ 1.0 mm \ge 1.0\text{ mm} ≥ 1.0 mm ( 0.10 mV 0.10\text{ mV} 0.10 mV ).

Leads V 2 V_2 V 2 ​ and V 3 V_3 V 3 ​ : Men ≥ 40 \ge 40 ≥ 40 years: ≥ 2.0 mm \ge 2.0\text{ mm} ≥ 2.0 mm ; Men < 40 < 40 < 40 years: ≥ 2.5 mm \ge 2.5\text{ mm} ≥ 2.5 mm ; Women: ≥ 1.5 mm \ge 1.5\text{ mm} ≥ 1.5 mm .

Reciprocal Depression : Coexisting ST depression in electrically opposing leads (e.g., inferior elevation with high lateral depression in I and aVL) differentiates acute STEMI from pericarditis.

3. Myocardial Infarction (Necrosis & Scar)

Necrotic myocardium creates an electrical void:

Pathologic Q Waves : Duration ≥ 0.04 seconds \ge 0.04\text{ seconds} ≥ 0.04 seconds (40 ms) or depth > 25 % > 25\% > 25% of ensuing R-wave amplitude in contiguous leads.

Poor R-Wave Progression : Failure of the R wave to grow progressively across precordial leads ( R < 3 mm R < 3\text{ mm} R < 3 mm in V 3 V_3 V 3 ​ ) indicates anterior or septal scar.

Coronary Artery Localization Matrix

Lead Group Anatomical Wall Culprit Coronary Artery Associated Complications

II, III, aVF Inferior Right Coronary Artery (RCA) ( 85 % 85\% 85% ) or LCx ( 15 % 15\% 15% ) Bradycardia, 1st degree AV block, Wenckebach, complete AV block; check right-sided leads ( V 3 R , V 4 R V_3R, V_4R V 3 ​ R , V 4 ​ R ) for RV infarction

V 1 , V 2 V_1, V_2 V 1 ​ , V 2 ​ Septal Proximal LAD / Septal branches Bundle branch blocks, infranodal Mobitz II block, severe LV dysfunction

V 3 , V 4 V_3, V_4 V 3 ​ , V 4 ​ Anterior Left Anterior Descending (LAD) / Diagonals Cardiogenic shock, congestive heart failure, ventricular aneurysms

I, aVL High Lateral Left Circumflex (LCx) or Diagonal LAD Reciprocal ST depression in inferior leads (II, III, aVF)

V 5 , V 6 V_5, V_6 V 5 ​ , V 6 ​ Low Lateral Distal LCx or Diagonal LAD Apical hypokinesis; often coexists with anterior infarction

V 7 , V 8 , V 9 V_7, V_8, V_9 V 7 ​ , V 8 ​ , V 9 ​ True Posterior PDA / LCx or Distal RCA Standard 12-lead shows mirror image in V 1 – V 2 V_1\text{--}V_2 V 1 ​ – V 2 ​ : tall R waves ( R / S > 1.0 R/S > 1.0 R / S > 1.0 ), ST depression, upright T waves

Intraventricular Conduction Abnormalities: Bundle Branch Blocks

A widened QRS complex ( ≥ 0.12 seconds \ge 0.12\text{ seconds} ≥ 0.12 seconds / 120 ms 120\text{ ms} 120 ms ) indicates intraventricular conduction delay:

Right Bundle Branch Block (RBBB)

Criteria : Q R S ≥ 0.12 s QRS \ge 0.12\text{ s} QRS ≥ 0.12 s ; broad, notched R R R wave ( r s R ′ rsR' rs R ′ , "bunny ears") in anterior leads V 1 V_1 V 1 ​ and V 2 V_2 V 2 ​ ; wide, slurred S S S wave in lateral leads I, aVL, V 5 , V 6 V_5, V_6 V 5 ​ , V 6 ​ .

Exercise Testing : RBBB causes secondary ST-T changes in V 1 – V 3 V_1\text{--}V_3 V 1 ​ – V 3 ​ , but does not invalidate ST interpretation in lateral leads ( V 5 , V 6 V_5, V_6 V 5 ​ , V 6 ​ , I, aVL) . Lateral ST depression remains diagnostic for exercise-induced ischemia.

Left Bundle Branch Block (LBBB)

Criteria : Q R S ≥ 0.12 s QRS \ge 0.12\text{ s} QRS ≥ 0.12 s ; broad, monophasic, notched R R R waves in lateral leads I, aVL, V 5 , V 6 V_5, V_6 V 5 ​ , V 6 ​ with absent septal Q waves; deep, wide Q S QS QS complexes in leads V 1 V_1 V 1 ​ and V 2 V_2 V 2 ​ .

Exercise Testing : LBBB profoundly distorts repolarization across all 12 leads. Standard ST-segment depression or elevation cannot be used to diagnose myocardial ischemia. Graded exercise tests without imaging are non-diagnostic; patients require pharmacological or imaging stress modalities (stress echo or nuclear SPECT).