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Tachycardia

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22 Aug, 2018

Tachycardia is defined as atrial and/or ventricular rate of greater than 100 beats per minute. This high rate can result due to an underlying disease condition or other causes:

  • Hyperthyroidism
  • Heart valve disorder
  • Congenital heart defect
  • Anemia
  • Heart failure
  • Strenuous exercise
  • Stress
  • Anxiety
  • Excessive alcohol consumption

 

If left untreated tachycardia can cause:

  • Myocardial ischemia
  • Hypotension
  • Low cardiac output
  • Cardiomyopathy
  • Cardiac arrest  and death

 

Electrical conduction in the human heart

The cardiac impulse originates from the sinoatrial(SA) node/pacemaker. From the SA node, the impulse travels to the atrioventricular(AV) node and spreads throughout the atria causing them to contract, then to the Bundle of His and finally to the Purkinje fibers which are in the ventricular walls. This causes the ventricles to contract.

 

Tachycardia is classified as

  • Sinus tachycardia(appropriate physiologically and inappropriate)
  • Postural orthostatic tachycardia syndrome(POTS): Number of beats >30 from the baseline or a heart rate >120 bpm and no drastic changes in the blood pressure of the patient.
  • Supraventricular tachycardia: It originates at or above the atrioventricular node and has a narrow QRS complex <120 milliseconds.
  • Atrial flutter with a rapid ventricular response: Fast but regular heart rate and resultant weak atrial contractions
  • Atrial fibrillation with rapid ventricular response: Fast but irregular heart rate again leading to weak atrial contractions
  • Ventricular tachycardia(VT):
    • Sustained VT lasts longer than 30 seconds and needs medical intervention to terminate it else it is non-sustained VT.
    • Monomorphic VT is characterized by continuous similar QRS complexes. When subsequent QRS complexes vary in appearance, it is said to polymorphic VT.

 

Symptoms

  • Chest pain
  • Shortness of breath
  • Dizziness

 

Diagnosis

  • ECG(Electrocardiogram)—To check for any abnormalities in the electrical activity of the heart
  • Echocardiogram/Ultrasound—To look for structural abnormalities in the heart
  • Exercise Stress Test
  • Blood tests—To check for hyperthyroidism
  • Tilt table test—To measure the change in heart rate and blood pressure in a patient moved from a lying to sitting position

 

Prevention

  • Radiofrequency catheter ablation—Used to destroy the heart tissue which is conducting faulty electrical signals and causing abnormal heart rhythm
  • Medication—Long-acting calcium channel blockers, beta blockers
  • Implantable cardioverter defibrillator(ICD) —This device is surgically implanted into the chest and constantly monitors the heart rate. Minor electric shocks are given when the heart rate fluctuates to set the rhythm right again.
  • Warfarin—It helps to slow the formation of blood clots and is administered to people who are at high risk of stroke

 

Treatment

  • Cardioversion—applying an electric shock to the heart to set the rhythm of the heart back to normal.
  • Vagal maneuvers—Valsalva maneuver and carotid sinus massage
  • Valsalva maneuver causes an increase in intrathoracic pressure and stimulates aortic and carotid baroreceptors. This leads to increased vagal input into the atrioventricular node.
  • Beta-Blockers and angiotensin-converting enzyme inhibitors for VT.