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Tachyarrhythmias

Sinus tachycardia

Sinus tachycardia is characterized by narrow fast QRS complexes that are preceded by normal P waves. The heart rate depends on patient age and may reach 240 beat/min in neonates. Sinus tachycardia may be a physiologic response to exercise, anxiety, fever, hypovolemia, hypoxemia or hyperthyroidism.

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Premature atrial complexes (PACs)

PACs represent origination of atrial electrical activity outside the SA node. On the EKG, PACs may appear in one of three forms:

  • premature P wave followed by a narrow QRS complex,
  • non-conducted premature P wave not followed by QRS complex, and
  • premature P wave followed by wide QRS complex due to aberrant conduction (bundle branch block).

PACs are commonly seen in infants and disappear with increasing age. This arrhythmia is usually benign and needs no treatment

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Atrial Flutter and Atrial Fibrillation

Atrial flutter is characterized by rapid atrial activity at a rate 200- 350 beat/min. The P waves have saw-tooth appearance. Some of the atrial impulses are not conducted through the AV node, so the ventricular rate is slower than the atrial rate and is usually regular. Atrial flutter is caused by a re-entry circuit in the atrium and is usually seen in a diseased heart. The symptoms depend on the ventricular rate. Cardioversion is indicated in symptomatic patients.

Atrial fibrillation is a chaotic atrial rhythm (300-600 impulses per minute) with no well defined P waves. The ventricular rate is irregularly irregular. Atrial fibrillation usually requires treatment with anti-arrhythmic medications such as B-blockers or Ca++ channel antagonists. Systemic anticoagulation is also usually undertaken to reduce the risk of thrombus formation in the fibrillating atrium with downstream embolization.

More info: Borczuk, P. Atrial Flutter. eMedicine

More info: Atrial flutter from Healthsquare.com

More info: Atrial Fibrillation, from National Heart , Lung and Blood Institute

Supraventricular Tachycardia (SVT)

SVT is characterized by a narrow QRS complex tachycardia with a heart rate 250-350 beat/min that shows no variation with respiration. It is commonly seen in normal children but may associated with CHD as in Ebstein anomaly. SVT is usually caused by an accessory pathway between the atria and the ventricles, or by a reentry circuit within the AV node.

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In infants, SVT presents with poor feeding, irritability, sweating and respiratory distress. If not treated, CHF and death may occur.

Compensated SVT should be treated promptly with vagal maneuvers such as application of ice to the face. If this is unsuccessful, then adenosine should be administered intravenously. Children with uncompensated SVT should be treated with cardioversion.

WPW syndrome is an example of pre-excitation due to an accessory pathway between the atria and ventricles. It is characterized by a short PR intervals, delta waves, and wide QRS complexes.

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Ventricular arrhythmias
Ventricular arrhythmias are characterized by a wide QRS complexes and abnormal T waves. The symptoms depend on the heart rate and are usually due to poor ventricular filling.

Premature ventricular contractions (PVC's)

PVCs are premature, wide QRS complexes that are not preceded by P waves. Isolated unifocal PVCs originate from the same spot in the ventricles, have uniform morphology, usually benign in nature and disappear with exercise. Multifocal PVCs usually occur in diseased myocardium and often increase with exercise.

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Ventricular tachycardia (VT)

VT is a rapid, wide QRS-complex tachycardia with a heart rate 150-250 beat/min. It is a serious condition that may result from drug toxicity (digoxin), myocarditis or severe metabolic derangement. It should be treated promptly with cardioversion if the patient is hemodynamically unstable. Stable VT may be treated with IV lidocaine infusion.

Ventricular Fibrillation (VF)

VF is a terminal cardiac rhythm characterized by irregular wide bizarre shaped QRS complexes. It needs to be treated immediately with unsynchronized DC cardioversion.