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• Adenosine


  Drugs to treat abnormal fast heart rhythms – tachycardia
• Adenosine


  Treatment for AV node re-entry supraventricular tachycardia e.g. Wolff-Parkinson-White syndrome
• Adenosine

  Hyperpolarisation of SA and AV node
• Drug treatment of cardiac arrest

  1. Asystole - Adrenaline/epinephrine

  2. Ventricular fibrillation - Amiodarone

  3. Lignocaine
• Atropine

  • Naturally occurring antimuscarinic alkaloid
  • Blocks vagal inhibition of Sinus and AV node
  • Intravenous bolus administration
  • Predominantly hepatic metabolism
  • Short half life (~3 h)
  • Anticholinergic adverse effects - dry mouth, mydriasis, postural hypotension
• Belladonna


  Deadly Nightshade
• Class 1 Drugs


  • Subdivided into 3 groups according to effect on action potential duration
  • Class Ia - Lengthen action potential duration and refractory period
  • Class Ib - Shorten action potential duration and refractory period
  • Class Ic - No effect on action potential duration and refractory period
  • Delay conduction velocity in Purkinje fibres
• Class Ib Drugs - Lidocaine


  • Blocks fast sodium channels and slows Phase 0 depolarisation
  • Shortens action potential duration
  • Specific effect on rapidly depolarising tissue (use-dependent effect)
• Class Ib Drugs - Lidocaine


  • Indications - Ventricular arrhythmias
  • Pharmacology - Short half life - must be given as bolus plus IV infusion, Not absorbed via oral route (hepatic first pass metabolism), Hepatic clearance decreased in elderly, heart failure, liver disease
  • Adverse effects - Hypotension, heart block, Neurotoxicity, fits
• If a nerves fires more often

  The action of lidocaine increases
• Class II Drugs - BETA-BLOCKERS


  • Non-Cardioselective - Also block β2 receptors
  • Cardioselective - Less potent blockers of β2 receptors
  • Others - Bretyllium
• Class II Drugs - BETA-BLOCKERS


  • May be β1 selective (atenolol, metoprolol) or β1, β2 non-selective (propranolol)
  • Oral and i.v. (metoprolol, propranolol) use
  • First pass hepatic metabolism e.g. propranolol
  • Renal excretion e.g. atenolol
  • Actions - Beta adrenoceptor antagonist, Reduce intrinsic rate in sinus and AV nodes, Reduces heart rate, blood pressure and cardiac work, Reduces renin secretion
• What type of fast rhythms are beta blockers useful in treating?

  Supraventricular tachycardias and atrial fibrillation
• Beta blockers - adverse effects

  • β1 effects - Bradycardias, Heart failure
  • β2 effects - Exacerbation of asthma, Cool peripheries, Muscular aches, Worsening intermittent claudication
  • Other - Fatigue, Nightmares, sleep disturbances, Withdrawal effects (angina, MI), Unawareness of hypoglycaemia
• Class III Drugs - Amiodarone

  • Actions - Prolongs action potential duration and refractory period, Lengthened QT interval on ECG
  • Indications - Effective for ventricular and supraventricular tachycardia, First line for treatment of ventricular fibrillation, Improves survival in patients with recurrent ventricular tachycardia
  • Pharmacology - Long half life, Hepatic metabolism
  • Adverse effects - Serious adverse effects limit use to high risk patients
• Class III Drugs - Amiodarone

  Serious adverse effects - Thyroid disturbances, Pulmonary fibrosis, Pro-arrhythmia and torsade de pointes, Peripheral neuropathy, Hepatitis, Blue-grey skin discolouration
• Calcium channel blockers


  • 3 classes - Dihydropyridines (nifedipine, amlodipine - predominantly vascular effects), Benzothiazepines (diltiazem - mixed vascular and cardiac effects), Phenylalkylamine (verapamil - predominantly cardiac effects)
• Class IV Drugs - Verapamil

  • Actions - Calcium channel blocker, Slows phase 1 / 2 slow calcium entry, Reduces rate and conduction velocity in sinus and AV nodes
  • Indications - Supraventricular arrhythmias
  • Pharmacology - Actions on heart >> actions on blood vessels (c.f. nifedipine), Oral and i.v. use, First pass hepatic metabolism
  • Adverse effects - Heart failure, hypotension, Constipation, Vasodilatation, oedema, flushing
• How could verapamil cause heart failure?

  Stroke volume reduced and heart rate reduced = cardiac output reduced