Conduction Disturbances

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    Sino-Atrial Exit Block

    • In a normal sinus beat, the SA node depolarizes first, but is too small to generate a tracing on a surface ECG.  This impulse is then propagated to the rest of the atrium, which generates a P-wave. 
    • In sino-atrial exit blocks, the SA node fires, but is blocked, and the impulse is not able to exit the SA node to depolarize the atrium.  Hence the P-wave is not seen. 
    • The next time the SA node fires, you see a conducted P-wave that comes on schedule. 

     

    SinoAtrialBlock.png

       

    Types

    • The example above demonstrates a 2nd degree "Mobitz II" (Type II) Sinoatrial Exit Block. 
    • Types:
      • 2nd degree Type I ("Wenckebach")
        • SA Blocks resulting from progressive lengthening of the SA-to-Atrial conduction, leading to progressively shorter P-P intervals until one P-wave is blocked. Gouped P-waves are observed. 
      • 2nd Degree Type II ("Mobitz II")
        • SA is blocked without progressive lengthening of P-P intervals.
      • NOTE: 1st Degree SA Block is not detectable on surface ECG because depolarization of the SA node is not visible.

     

    Brugada Pattern

    • Brugada syndrome (BrS) is a genetically inherited channelopathy that increases an individual’s susceptibility to develop polymorphic ventricular tachycardia (VT) and sudden cardiac death (SCD).
    • It is transmitted via an autosomal dominant trait.
    • ECG is the best test for initial diagnosis.

     

    • Characteristic Pattern:
    • Brugada Type 1.pngBrugada Type 2.png

       

    • If Brugada Pattern is not obvious, base of the triangle is a well-validated method of examining the ECG for Brugada Pattern.
      • A line is drawn from the top of R', along the downslope for 5mm vertical distance.  At that point a horizontal is extended until reaches the upslope of S-wave.  Distance of the horizontal is measured (if ≥4mm = high risk of Brugada Pattern)
    • Base of the Triangle Method for

      determining the presence of Brugada Pattern

    • Brugada Example.png            Brugada Base of Triangle.png
    • Management
      • Both symptomatic and asymptomatic individuals should be assessed by an electrophysiologist. 
      • ICD
        • Recommended for survivors of cardiac arrest or if polymorphic VT is seen on ECG.
      • Avoid drugs (mainly sodium channel blockers) that may induce/aggravate ST-segment elevation in the right precordial leads (see www.brugadadrugs.org);
      • Lifestyle Interventions
        • Avoid excessive alcohol consumption
        • Reducing fever with antipyretic medications
    • Reference:
      • Charles Nadeau-Routhier & Adrian Baranchuk. “Electrocardiography In Practice: What To Do?.” Charles Nadeau-Routhier, 2016. iBooks. https://itun.es/ca/QR6Wcb.n

     

    Interatrial Block

    • A P-wave abnormality associated with a risk of supraventricular arrhythmias
    • There are two types:
    • IAB2.jpg

         
      Partial Interatrial Block P-wave duration ≥ 120ms
      Complete Interatrial Block

      P-wave duration ≥ 120ms

      AND

      Biphasic P-wave

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