What are the best practices for obtaining optimal ECag (Electrocorticography) readings?

ECG Reading Tips: Best Practices for Optimal Recordings

Critical Technical Standards for Acquisition

To obtain optimal ECG readings, ensure proper electrode placement, use appropriate bandwidth settings (minimum 150 Hz for adults, 250 Hz for children), and verify signal quality before interpretation. 1, 2

Electrode Placement and Lead Configuration

• Position precordial leads accurately as misplacement is one of the most common errors that significantly alters ECG interpretation and leads to false diagnoses 2, 3
• Use standard 12-lead configuration with additional leads (V3R, V4R, V7) when evaluating congenital heart lesions or specific coronary territories 1
• Ensure limb electrodes are placed on the extremities rather than the torso to avoid signal distortion 3
• Verify electrode contact quality to minimize baseline wander and electrical interference 1, 3

Bandwidth and Filtering Requirements

• Set high-frequency response to minimum 150 Hz for adults and adolescents, and 250 Hz for children to maintain diagnostic precision 1, 2
• Inadequate high-frequency response causes systematic underestimation of signal amplitude by up to 46% and smooths critical features like Q waves and notched QRS components 2
• Apply appropriate low-frequency filters to reduce baseline drift while preserving ST-segment morphology 1
• Avoid over-filtering which can distort waveforms and affect measurements 2

Signal Quality Assessment

• Evaluate recording quality before interpretation by checking for artifacts, electrical interference (60 Hz noise from monitors/warmers), and baseline stability 1, 2
• Distinguish true cardiac signals from artifacts by verifying that any signal within 80 ms of a QRS complex could not occur from an electrophysiologic standpoint 1
• Recognize common neonatal artifacts including respiratory variation (30-60 breaths/min causing cyclic baseline wander), muscle tremors, and movement artifacts 1
• Digital electrocardiographs improve measurement reproducibility by creating representative templates from accurately aligned complexes 2

Systematic Interpretation Approach

Rate and Rhythm Analysis

• Calculate heart rate using the 300-divided-by-large-boxes method (300 ÷ number of large boxes between R waves) or count QRS complexes in 6 seconds and multiply by 10 2, 4
• Normal sinus rhythm: 60-100 bpm in adults with P wave before each QRS and consistent PR interval 2
• Assess R-R interval regularity to identify arrhythmias—completely irregular patterns suggest atrial fibrillation 2, 4

Interval Measurements

• Measure PR interval (normal 120-200 ms or 3-5 small squares) to assess AV conduction; prolongation indicates first-degree AV block 2, 4
• Evaluate QRS duration (normal <120 ms or <3 small squares) to identify bundle branch blocks or ventricular conduction delays 2, 4
• Calculate corrected QT interval (QTc) using Bazett's formula; normal <450 ms for men, <460 ms for women 2, 4
• Measure QRS duration in a lead with an initial Q wave for accuracy 1

Axis Determination

• Examine leads I and aVF simultaneously to determine axis quadrant: normal axis (+90° to -30°) shows positive deflections in both leads 2, 4
• Left axis deviation (-30° to -90°): positive in lead I, negative in aVF 2, 4
• Right axis deviation (+90° to +180°): negative in lead I, positive in aVF 2, 4
• In neonates, normal axis ranges 55-200° at birth, decreasing to ≤160° by 1 month 1

Waveform Morphology Analysis

• Identify pathological Q waves (>40 ms duration or >25% of R wave amplitude) suggesting prior myocardial infarction 2, 4
• Assess ST-segment deviations: elevation >1 mm in limb leads or >1.5-2 mm in precordial leads indicates acute injury 2, 4
• Evaluate T-wave abnormalities (inversion, hyperacute, flattening) for ischemia 2
• Note location of abnormalities to determine affected coronary territory 2

Hypertrophy Assessment

• Apply Sokolow-Lyon criteria for left ventricular hypertrophy: S in V1 + R in V5 or V6 >3.5 mV (35 mm) 2
• Recognize that QRS voltage criteria decline with age and vary by population 2
• Cornell voltage criteria (S in V3 + R in aVL) provides alternative assessment 2

Critical Pitfalls to Avoid

Computer Interpretation Limitations

• Never accept computer interpretation without physician verification—automated systems still produce frequent errors 1, 2, 4
• Computer-generated ECGs are not recognized as properly interpreted without qualified physician review 1, 5
• Sensitivity and specificity of automated diagnostic statements continue to improve but remain imperfect 1

Technical Errors

• Verify electrode placement before recording—precordial lead misplacement is the most common technical error 2, 3
• Check for limb lead reversal which produces characteristic abnormal patterns 3
• Ensure adequate filtering settings to avoid signal distortion while removing noise 2
• Use sampling rate of at least 500 Hz (preferably 1200 Hz) for digital systems to capture high-frequency components accurately 1

Clinical Context Integration

• Always interpret ECG findings in conjunction with clinical presentation—the same ECG pattern may have different implications depending on symptoms 1, 2, 5
• Compare with previous ECGs when available to identify new changes 2
• Consider patient age, gender, medications, and comorbidities that affect normal parameters 4
• Recognize that ECG diagnoses of structural changes (infarction, hypertrophy) are made by inference and subject to error 1, 2

Special Population Considerations

• In neonates, expect higher heart rates (93-182 bpm), right axis deviation, and prominent R waves in V1 as normal variants 1
• In athletes, sinus bradycardia ≥30 bpm is a normal variant 2
• In children >1 month, T wave inversion in V1-V3 is normal 2
• Women typically have longer QT intervals than men 4

Maintaining Competency

• Engage in continuing medical education through seminars or self-assessment programs, especially if reading ECGs infrequently 2, 5
• Recognize that interpretation varies significantly even among expert electrocardiographers, emphasizing need for ongoing skill maintenance 2, 5
• Practice systematic interpretation approach consistently to avoid missing subtle findings 4