Stemi and mimics

STEMI and Its Mimics

Overview

  • Bundle Branch Blocks

    • Right Bundle Branch Block (RBBB)

    • Left Bundle Branch Block (LBBB)

  • Left Ventricular Hypertrophy

  • Pericarditis

  • Benign Early Repolarization (BER)

  • Other Conditions:

    • Left Main Coronary Artery (LMCA) disease

    • Triple vessel disease

    • Pulmonary Embolism

    • Brugada syndrome

    • Hypertrophic Obstructive Cardiomyopathy (HOCM)

    • Wellen's sign

    • De Winter's sign

Normal Impulse Conduction

  • The normal pathway of cardiac impulse conduction is:

    • SA Node → AV Node → Bundle of His → Bundle Branches → Purkinje Fibers

Bundle Branch Blocks (BBB)

  • ECG Changes for Bundle Branch Blocks:

    • QRS Complex:

    • Duration: > 0.12 seconds

    • Morphology changes depending on type (Right or Left)

Right Bundle Branch Block (RBBB)

  • Identifiable morphology includes 'M' shaped pattern in lead V1 and 'W' in V6.

Left Bundle Branch Block (LBBB)

  • Requires specific diagnostic criteria:

    1. QRS Duration:

    • ≥ 120 ms

    1. Dominant S wave in lead V1

    2. Broad monophasic R wave in lateral leads (I, aVL, V5-6)

    3. Absence of Q waves in lateral leads

    4. Prolonged R wave peak time:

    • > 60 ms in leads V5-6

Causes of Left Bundle Branch Block

  • Etiologies include:

    • Aortic stenosis

    • Ischemic heart disease

    • Hypertension

    • Dilated cardiomyopathy

    • Anterior Myocardial Infarction (MI)

    • Lenègre-Lev disease (degenerative disease of the conducting system)

    • Hyperkalemia

    • Digoxin toxicity

Summary of Bundle Branch Blocks

  • Syncytium: Necessary for efficient contractions and maintaining good cardiac output.

  • Wide QRS (>170ms): Indicates reduced ejection fraction (<50%).

  • In presence of AMI: A BBB increases mortality rate by four times.

Left Ventricular Hypertrophy (LVH)

  • Voltage Criteria:

    • S wave in V1 or V2 + R wave in V5 or V6 > 35 mm

Pericarditis

  • ECG Markers:

    • Widespread concave ST elevation and PR depression across most limb leads (I, II, III, aVL, aVF) and precordial leads (V2-6).

    • Reciprocal ST depression and PR elevation in lead aVR (± V1).

    • Sinus tachycardia common due to pain or pericardial effusion.

Diagnostic Criteria for Pericarditis

  1. Global ST changes across leads

  2. ST Morphology analysis necessary

  3. Lead II > Lead III: Indicative changes

  4. No reciprocal ST depressions (except in aVR and V1)

ST Segment and T Wave in Pericarditis

  • ST Segment / T Wave Ratio:

    • Measured from the end of the PR segment to the J point in V6.

    • A ratio > 0.25 indicates pericarditis, whereas < 0.25 indicates BER.

Distinguishing Between Pericarditis and STEMI

  • Common Features:

    • Both conditions exhibit concave ST segment elevation.

  • Distinguishing Features:

    • STEMI causes convex or horizontal ST elevation only.

    • ST elevation greater in III than II is a strong indicator of STEMI.

    • PR segment depression is typically seen in viral pericarditis.

  • Caution: History alone cannot distinguish, as STEMI can also present with similar symptoms.

Benign Early Repolarization (BER)

  • Morphological Characteristics:

    • Elevation of the J point

    • T wave: peaked and asymmetrical

    • ST segment and ascending T wave limb create an upward concavity

    • Descending limb of T wave is straighter than the ascending limb

ST Segment / T Wave Ratio in BER

  • Example measurements:

    • ST segment height = 1 mm

    • T wave height = 6 mm

    • ST / T wave ratio = 0.16 (consistent with BER since < 0.25)

Fish Hook Pattern in BER

  • Notched or irregular J point forming a 'fish hook' pattern is often noted in lead V4.

Terminal QRS Distortion

  • Defined as the absence of both an S wave and J wave in V2 or V3.

    • S wave: any deflection at the end of the R wave dipping below the PQ junction.

    • J wave: any positive deflection observed above the ST segment at the J point.

ECG Indicators of Hyperkalemia

  • Extreme caution required as peaked T waves can occur.

    • Other Features:

    • Widening of QRS complexes

    • Prolonged PR intervals

    • Flattening and eventual loss of P waves

    • Can lead to tachycardias, bradyarrhythmias, AV blocks, and sinus pauses

    • Possible outcomes include: - Pseudo-ACS with new BBBs and ST changes.

Conclusion

  • Successful assessment of cardiac conditions requires an understanding of ECG features, the relationship between different pathologies, and careful analysis of waveform changes.

  • Early recognition can potentially guide therapeutic interventions effectively.