Tachyarrhythmias

Supraventricular Tachycardia (SVT)

SVT is a broad term for a number of tachyarrhythmias that originate above the ventricular electrical conduction system (purkinje fibers). Classic Paroxysmal SVT has a narrow QRS complex & has a very regular rhythm. Inverted P waves are sometimes seen after the QRS complex. These are called retrograde p waves.
Supraventricular Tachycardia EKG Rhythm Strip
Supraventricular Tachycardia EKG Rhythm Strip

The heart fills during diastole, and diastole is normally 2/3 the cardiac cycle. A rapid heart rate will significantly reduce the time which the ventricles have to fill. The reduced filling time results in a smaller amount of blood ejected from the heart during systole. The end result is a drop in cardiac output & hypotension. With the drop in cardiac output, a patient may experience the following symptoms. These symptoms occur more frequently with a heart rate >150 beats per minute:
  • Shortness of air (S)
  • Palpitation feeling in chest (S)
  • Ongoing chest pain (U)
  • Dizziness (S)
  • Rapid breathing (S)
  • Loss of consciousness (U)
  • Numbness of body parts (S)

The pathway of choice for SVT in the tachycardia algorithm is based on whether the patient is stable or unstable. The symptoms listed above that would indicate the patient is unstable are noted with the letter (U). Stable but serious symptoms are indicated with the letter (S). Unstable patients with SVT and a pulse are always treated with cardioversion. The appropriate voltage for cardioverting SVT is 50-100 J. This is what AHA recommends and also SVT converts quite readily with 50-100 J.

Atrial Flutter

This abnormal heart rhythm technically falls under the category of supra-ventricular tachycardias. Atrial flutter is typically not a stable rhythm and will frequently degenerate into atrial fibrillation.
atrial-flutter-1
atrial-flutter-1

Atrial Flutter will usually present with atrial rates between 240-350 beats per minute. These rapid atrial rates are caused by electrical activity that moves in a self-perpetuating loop within the atria. The impact and symptoms of atrial flutter depend upon the ventricular rate of the patient (i.e. cardiac output). Usually, with atrial flutter, not all of the atrial impulses will be conducted to the ventricles, and the more atrial impulses that are conducted, the greater the negative effect.

Symptoms

Symptoms of atrial flutter are similar to those of atrial fibrillation and may include the following:
  • palpitations, chest pain or discomfort
  • shortness of air
  • lightheadedness or dizziness
  • nausea
  • nervousness and feelings of impending doom
  • symptoms of heart failure such as activity intolerance and swelling of the legs occur with prolonged fast flutter)

Complications

As with its symptoms, atrial flutter shares the same complications as atrial fibrillation. These complications are usually due to ineffective atrial contractions and rapid ventricular rates. Ineffective atrial contractions can lead to thrombus formation in the atria and rapid ventricular rates can cause decompensation and heart failure. Prevent complications from atrial flutter with early cardioversion.

Treatment

Atrial flutter is treated the same as atrial fibrillation. When atrial flutter produces hemodynamic instability and serious signs and symptoms, it is treated using ACLS protocol. For the patient with unstable tachycardia due to this tachyarrhythmia (atrial flutter), immediate cardioversion is recommended. Drugs are not used to manage unstable tachycardia.

Cardioversion

Atrial flutter is considerably more sensitive to electrical direct-current cardioversion than atrial fibrillation, and usually requires a lower energy shock. 20-50J is commonly enough to revert to sinus rhythm. AHA recommends an initial shock dose of 50-100 J for cardioverting unstable atrial flutter.

Atrial Fibrillation

The most common cardiac arrhythmia, atrial fibrillation, occurs when the normal electrical impulses that are generated by the SA node are overwhelmed by disorganized electrical impulses in the atria.
Atrial Fibrillation EKG Tracing
Atrial Fibrillation EKG Tracing

These disorganized impulses cause the muscles of the upper chambers of the heart to quiver (fibrillate) and this leads to the conduction of irregular impulses to the ventricles. Atrial fibrillation becomes a problem when the fibrillation produces a rapid heart rate which reduces cardiac output and causes symptoms or an unstable condition. When atrial fibrillation occurs with a (RVR) rapid ventricular rate (rate > 100 beats/min), this is called a tachyarrhythmia. This tachyarrhythmia may or may not produce symptoms. Significant symptoms that occur are due to a reduction in cardiac output. The following is a list of the most common symptoms.
  • palpitations or chest discomfort
  • shortness of air and possibly respiratory distress
  • hypotension, light-headedness and possibly loss of consciousness
  • peripheral edema, jugular vein distention, and possibly pulmonary edema
It is important to be able to recognize atrial fibrillation when the patient is symptomatic. On an ECG monitor, there are two major characteristics that will help you identify atrial fibrillation.
  1. No p-waves before the QRS on the ECG. This is because there are no coordinated atrial contractions.
  2. The heart rate will be irregular. Irregular impulses that the ventricles are receiving cause the irregular heart rate.

When the heart rate is extremely rapid, it may be difficult to determine if the rate is irregular, and the absence of p-waves will be the best indicator of atrial fibrillation.

Atrial fibrillation is treated when the arrhythmia/tachyarrhythmia produces hemodynamic instability and serious signs and symptoms. For the patient with unstable tachycardia due to a tachyarrhythmia, immediate cardioversion is recommended. Drugs are not used to manage unstable tachycardia. The appropriate voltage for cardioverting unstable atrial fibrillation is 120-200 J. Cardioversion of stable atrial fibrillation should be performed with caution if the arrhythmia is more than 48 hours old and no anticoagulant therapy has been initiated due to the risk of emboli that can cause MI and stroke.


Other Tachycardia Rhythms

There are several other tachycardia rhythms that can be seen with both stable and unstable tachycardia. These rhythms include monomorphic ventricular tachycardia and polymorphic ventricular tachycardia both of which are wide-complex tachycardias.

Wide complex tachycardias are defined as a QRS of ≥ 0.12 second. Expert consultation should be considered with these rhythms. These wide-complex tachycardias are the most common forms of tachycardia that will deteriorate to ventricular fibrillation.

Monomorphic Ventricular Tachycardia

Monomorphic Tachycardia
Monomorphic Tachycardia


With monomorphic VT all of the QRS waves will be symmetrical. Each ventricular impulse is being generated from the same place in the ventricles thus all of the QRS waves look the same. Treatment of monomorphic VT is dependent upon whether the patient is stable or unstable. Expert consultation is always advised, and if unstable, the ACLS tachycardia algorithm should be followed.

Polymorphic Ventricular Tachycardia

Polymorphic Ventricular Tachycardia
Polymorphic Ventricular Tachycardia


With polymorphic ventricular tachycardia, the QRS waves will not be symmetrical. This is because each ventricular impulse can be generated from a different location. On the rhythm strip, the QRS might be somewhat taller or wider. One commonly seen type of polymorphic ventricular tachycardia is torsades de pointes. Torsades and other polymorphic VT are advanced rhythms which require additional expertise and expert consultation is advised. If polymorphic VT is stable the ACLS tachycardia algorithm should be used to treat the patient. Unstable polymorphic ventricular tachycardia is treated with unsynchronized shocks (defibrillation). Defibrillation is used because synchronization is not possible. These wide complex tachycardias tend to originate in the ventricles rather than like a normal rhythm which originates in the atria.