Cardio 3

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  • Created by: Mohsin
  • Created on: 09-04-18 13:09
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  • Cardio Therapeutics 3
    • ECG leads
      • recorded using 3 limb electrodes
        • one on each arm and one on the left leg
          • each limb acts as an electrical conductor
          • Form a triangle = Einthoven's triangles
      • 6 skin electrodes used in clinical practice
      • angle of the largest dipole =  electrical axis of the heart
    • ECG
      • T wave is upright - repolarisationoccurs in reverse sequence to de-polarisation
        • due to short action potentials of epicardial and basal myocytes
    • Cardiac excitation- contraction coupling
      • Electrical excitation of the myocyte
        • mishandling of Ca2+
          • causes contractile dysfunction and arrhythmias
        • myofilament Ca2+ sensitivity
          • reduced by acidosis, elevated Mg2+ and P levels
          • occurs during ischaemia
    • Effects of electrolytes on the myocardium
      • Causes of voltage across a semi-permeable membrane
        • Na
          • 135 - 146 mmol/L
        • K
          • arrhythmia is associated with potassium disorders
          • 3.5 - 5.0 mmol/L
          • Potassium
            • High intracellular conc.
            • maintains the excitability of nerve and muscle cells
            • regulated by: aldosterone, pH, catecholamines, insulin and levels of bicarbonate
            • hyper/ hypo kalaemia can cause abnormalitiescardiac conduction
              • HYPER- kalaemia
                • suppressed conduction
                • Peaked T wave or prolonged PR interval and widened QRS interval
                • Cardiac arrest when serum conc. is greater than 0.8mmol/L
                • repolarisationabnormalities
              • HYPO- kalaemia
                • affects conduction of action potential
                • flattened T waves
                  • prolonged PR interval
                    • ST depression
                      • Predominent U waves
                • can be caused by insulin, dopamine and B2 antagonists
        • Mg
          • 0.7 - 1.1 mmol/L
        • Ca
          • 2.20 - 2.67 mmol/L
          • spontaneous release of Ca2+ can lead to tachycardia
            • happens after a period of sympathetic nerve stimulation or adrenaline influx
        • Generates action potential
          • Muscle contraction
      • Renal excretion = maintain electrolyte balance
        • changes to renal function can affect electrolyte concentration
          • Impaired balance of electrolytes caused by...
            • Kidney disease
            • Hypoaldesteronism
            • adrenal insufficiency
    • Classification of SUPER ventricular dysrhythmias
      • Atrial flutter
        • caused by re-entry circuit within the RIGHT atrium
      • Atria ventricular nodal reentry tachycardia (AVNRT)
        • above bundle of His
        • common cause palpitations in patients with no structural heart abnormalities
      • Atrial fibrillation
        • irregularly irregular rhythm
        • No P waves
        • absence of isoelectric baseline
      • Atrial ectopic beat
        • irregular P wave
        • arise from ectopic pacemaking tissue within the atria
    • Classification - Ventricular Dysrhythmias
      • Ventricular Tachycardia
        • Rapid heart beat which starts in the ventricles
          • pulse rate over 100bpm
            • 3 irregular heartbeats in a row
      • Ventricular fibrillation
        • irregular electrical currents
          • heart contracts in disorganised way
            • lots of energy used but no function
              • can cause sudden death
      • Ventricular flutter
        • loss of organised electrical activity
          • extreme form of VT
            • non identifiable P, QRS or T waves
              • rate more than 200bpm
      • Torsade de Pointes
        • Form of VT associated with long QT syndrome
          • lots of drugs can cause this
          • Long QT syndrome
            • prolonged ventricular repolarisation
              • caused by: TCA's, fluconazole, erythromycin, methadone, SSRI's, haloperidol
      • Accelerated idio-ventricular rhythm
        • ectopic ventricular pacemaker exceeds that of the sinus node
          • ventricular rhythm between 40-120bpm
            • benign rhythm usually self limiting
  • Heart block (Atrio-ventricular)
    • block in the electrical conduction system in the heart
      • heart beats more slowly
    • defined by PR interval
      • 1st degree: benign. lengthening of the PR interval
      • 2nd degree: Atrial flutter (2 P waves to every QRS)
      • 3rd degree: drug induced (verapamil and b-blockers)
        • 3 P waves to every QRS
          • potentially fatal

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