Matters Of The Heart-Normal and Abnormal Heart Rhythms (Part 2)

Atrial Rhythms Continued-

Bradycardia-
This rhythm is defined as abnormally slow heart action. Although heart rates will vary from individual to individual, a heart rate of less then 50 bpm is usually considered bradycardic. If a slow heartbeat is accompanied by any signs and symptoms of poor cardiac output (such as dyspnea, fatigue, dizzyness (esspecially with movement) and cyanosis), this rhythm will need to recieve medical attention.

Although I placed this in the catergory of atrial rhythms, this rhythm can actually originate from anywhere in the heart:
SA node- With simulation of the parasympathetic nervous system.
Atria Foci-which has an inherent range of 80- 60 bpm, but can become depressed to run at even lower rates.
Junctional foci-Which have an inherent rate of 60-40bpm.
And Ventricular Foci-Which have an inherent rate of 40-20 bpm.

Tachycardia-

This rhythim occurs when the heart rate is greater than or equal to 100 beats per minute. (In this instance, the SA node acts as the pacer). In many cases, this rhythm is a response to sympathetic stimulation from stressors such as exercise, dehydration, or pain. When this is the case, the rhythm is not inherently harmful and the rate will decrease when the stressors are relieved.

Atrial Flutter-
This rhythm is similar to Atrial Fibrillation; in both, irritable automaticity foci in the atria stimulate depolarization. However, in a fib, several pacers emit an impulse simultaneously, in Atrial Flutter one pacer emits an impulse at a rate of 250-350 beats per minute. Not all of these 'pacer' impulses are conducted to the ventricles. This contributes to the 'sawtooth' appearance of multiple small ampletude 'P' waves (meaning they indicate atrial depolarization) precieding a QRS complex.

Depending on the ratio that the atrial pacer is able to simulate the ventricles to contract, this rhythm can be hard to identify (Sometimes the ratio can be 2 'P' waves to one QRS, which looks similar to a PQRST complex in tachicardia) Sometimes healthcare professionals suggest the patient perform a vagal manuver (such as carotid massage, testing the gag reflex or bearing down with breath held) this stimulates the parasympathetic nervious system to lower the heart rate...If atrial flutter is the rhythm, the 'sawtooth' pattern will become more visable.

There is another rhythm in which it is helpful to use the vagal manuver to lower the heart rate, it is called Supraventricular tachycardia

Atrial/Junctional Rhythms-

Supraventricular Tachycardia-
The location of the 'pacer' for this rhythm can be in the atria (this is sometimes called Atrial Tachycardia), it may also be found in or near the AV Node or Bundle of His. (this is sometimes called Junctional Tachycardia)

However, in many cases, it is impossible to distinquish the location of the pacer because it is firing so fast (150-250 bpm) and every supraventricular impulse is conducted to the ventricles. (Fortunately, both types of supraventricular tachycardia are treated in pretty much the same way)
If the onset of these types of tachycardia is sudden, it is called 'Paroxymal' Paroxysmal Supraventricular Tachycardia (PST).

One treatment for this rhythm is to (as I mentioned above) perform a vagal manuver. There is also a drug called adenosine that interupts the electrical conduction of the heart, allowing normal pacing to resume.

Ventricular Rhythms-

Ventricular Tachycardia-

This rhythm has one irritated foci acting as pacers for ventricular depolarization. This rhythm is rapid (150-250 bpm), and because the route of electrical depolarization is reversed (usually it ends, not starts in the ventricles) the ventricular contractions appear dissimilar to the normal QRS complexes and are wide and tall.

This rhythm indicates the heart is in severe stress and (if persistant) is not able to provide an adequate cardiac output to maintain consiousness. If the rhythm persists, it will progress to ventricular fibrillation. 

Torsades de Pointes-

This rhythm is a subtype of ventricular tachycardia. The name is french for 'Twisting of Points' which is pretty much how this rhythm looks on an EKG strip: Multiple ventricular depolarization complexes that gradually grow, and then deminish, in ampletude. (Rate 250-350 bpm). This rhythm is thought to be caused by two ventricular pacing sites (foci) competing to be the dominant pacer. It is most often associated with severe magnesium deficiency. (Magnesium is primarily intracellular an has a role in maintaining muscle tone).

Ventricular Flutter-

This rhythm originates from a single irritable foci in the ventricles, which paces at a rate of 250-350 bpm. It is similar in appearance to the wide ventricular complexes of Torsades de Pointes, however the waves are smooth (because there is still only one irritable foci acting as pacer). This is a sign of degeneration of the rhythm from V-Tach to V-Fib.

Ventricular Fibrillation-
Multiple uncoordinated and irritated foci attempt to pace the ventricles. This rhythm appears as a series of wide, rapid (350-450bpm) waves of low ampletude. In ventricular fibrillation, depolarization is not able to produce contraction. This rhythm requires immediate ACLS intervention.