Ventricular ArrhythmiasPremature Ventricular Contractions (PVC’s)
PVC’s are extra beats which occur from an ectopic focus on the ventricle wall. This focus is usually below the bifurcation of the bundle of HIS. In the normal person these may be caused by smoking, alcohol, or coffee ingestion. They usually are rare & inconsequential in normal persons. PVC’s may also, and more frequently, occur as the result of an mày or due lớn arteriosclerotic heart disease. This irritable spot on the myocardium sends out a powerful electrical impulse which spreads across the ventricles, causing them to lớn contract out of proper sequence. In other words, the ventricles contract before they have had a chance lớn completely fill with blood from the contraction of the atria.
PVC’s may be unifocal (from one spot on the ventricle wall) or they may be multifocal (from two or more different spots
PVC’s may be single và isolated (rare), which are usually normal. They may also be more frequent, occurring at regular intervals.
When they occur at regular intervals, they are called:
Bigeminy – every other beat. Trigeminy – every third beat. Quadrageminy – every fourth beat
If the beats occur less frequently than every fourth beat there is usually no regular pattern. They will tend khổng lồ be irregular in the pattern. However, it can be noted that PVC’s might occur regularly, every fifth beat, sixth beat, etc.
If they occur more frequently than every 4th beat the condition can be serious & possibly require treatment. Multifocal PVC’s are also more dangerous then unifocal. If they appear in groups of two or more together (coupled), the situation could also be dangerous. In addition, the most dangerous situation is called the R-on-T Phenomenon. When the PVC falls on a T wave from the previous contraction, ventricular fibrillation and death can occur. During the T wave (repolarization), heart muscle is very sensitive to outside stimulus thus a strong PVC can send the myocardium into fibrillation. Treatment of PVC’s is complex. In the “normal” situation, Lidocaine is administered to lớn decrease the irritability of the myocardium. An initially high intravenous dose (bolus) is given and then the patient is monitored on a lower maintenance dose (intravenous drip). If the PVC’s continue after the Lidocaine is terminated, the patient is maintained on an oral dose of some similar type drug.
A case where Lidocaine may not be used would be in Bradycardia. If the SA node rate falls below 60 per minute, the heart may try to compensate by the use of PVC’s. Another case is after carefully studying the ECG tracing and determining that the underlying arrhythmia is Sinus Bradycardia, Lidocaine may not be used. The MD will usually give Atropine lớn increase the SA node firing. This increase in the pulse rate will then give rise to lớn the termination of the inefficient PVC’s needed to lớn maintain circulation.
Ventricular Tachycardia (V-Tach)
This is a very serious arrhythmia. Whenever three or more consecutive PVS’s are seen, at a rate of 100 bpm or more, the term used is Ventricular Tachycardia (V. Tach). In the strictest definition, V. Tach is the same as PVC’s, except that there are many of them in a row. The onset and termination of V. Tach may be may be abrupt or not. V. Tach may occur in paroxysms of three or more PVC’s separated by the underlying rhythm (non-sustained V Tach or Paroxysmal Ventricular Tachycardia), or persist for a long period of time (sustained ventricular tachycardia). The rhythm is usually regular, but it may be slightly irregular.
When V. Tach occurs, the ventricles vì chưng not have sufficient time to lớn fill and thus, cardiac output is greatly reduced. This arrhythmia may also lead khổng lồ ventricular fibrillation và death. The pacemaker site for V. Tach is an ectopic pacemaker in the bundle branches, Purkinje network, or in the ventricular myocardium itself.
The rate of V. Tach is from about 100-250 bpm. P. Waves may be present or absent. Phường Waves are usually not seen if the rate is increased. If present, the p Waves have no relation to lớn the QRS complexes of the V. Tach. P. Waves, if present, may be positive or negative in Lead II. If p Waves are present and occur independently of the QRS complexes, the P-R intervals will vary widely.
QRS complexes are described as “wild-looking” & with great swings và exceed 0.12 second. They are followed by large T Waves that are opposite in direction of the major deflection of the QRS complexes. The QRS complexes may look alike in shape and form or they may be multiform (markedly different from beat lớn beat).
The treatment of V. Tach is essentially the same as for severe cases of PVC’s. Lidocaine is given intravenously in a large bolus, 75mg to 100mg over two minutes IV push. Meanwhile, a Liodocaine drip is started & another bolus is given if the V. Tach does not stop. Two new drugs, Verapamil và Bretylium may also be used for this và other similar arrhythmias. If the drug therapy fails, or if drug therapy is contraindicated, cardio version may be used. Quick treatment is necessary, as death can result quickly.
Ventricular Fibrillation (V. Fib) means sudden death. The blood pressure drops immediately to zero và so does the cardiac output. The heart is merely quivering due lớn the rapid multiple electrical discharges in the myocardium. V. Fib is one of the most common causes of cardiac arrest. It usually occurs in the presence of significant cardiac disease. It occurs most commonly in coronary artery disease, myocardial ischemia, acute myocardial infarction, and third degree AV Block with a slow ventricular response. V. Fib may also occur in cardiomyopathy, mitral valve prolapsed, cardiac trauma (blunt trauma), and in digitalis toxicity. V. Fib may also occur during anesthesia, cardiac and noncardiac surgery, cardiac catheterization, during cardiac pacing, following cardio version, accidental, or non-accidental electrocution.
A PVC may also initiate V. Fib when the PVC occurs during the vulnerable period of ventricular repolarization, coincident with the peak of the T. Wave (i.e. R on T phenomenon), particularly when electoral instability of the heart has been altered by ischemia và acute MI. Sustained V. Tack và Ventricular flutter may precipitate V. Fib.
The impulses are discharging from many random foci và the heard cannot respond with an organized contraction. There is no specific pattern khổng lồ the discharge. No QRS complexes can be seen, no p waves are present, no P-R intervals, & no R-R intervals can be seen. The ECG shows different types of wavering baseline patterns in the presence of V. Fib. Shown in the below figure are several examples of fibrillation, course fibrillation, fine fibrillation, & more. Course fibrillation is more likely lớn be reversed because it indicates a recent onset of fibrillation. Fine fibrillation indicates a more advanced fibrillation và is less likely khổng lồ be reversed with treatment.
The treatment for this condition is defibrillation by DC shock. CPR will be started until the defibrillation can be performed. The large electrical shock to lớn the myocardium stops the fibrillation và allows the heart to return khổng lồ its normal rhythm.
Ventricular Escape Rhythm (Idoventricular Rhythm)
This rhythm is characterized by a heart rate usually between 30 to lớn 40 bpm. But may be lower than 30. An escape rhythm refers to the “automatic” or “escape” pacemaker of the heart located in the bundle branches, Perkinje network, or ventricular myocardium. When the “normal” pacemaker (usually the SA node) is blocked, the escape mechanism takes over. This can be caused by sinus arrest, third degree heart block, and other heart problems that block the normal pacemaker.
Ventricular escape rhythm is a “protective” mechanism of the heart. It allows the heart lớn keep beating (even though is it at a very slow rate) when there is a major blockage of the impulses that make the ventricles beat. Another protective mechanism of the body toàn thân is lớn “faint” when this happens. More blood goes khổng lồ the brain when you faint và lay flat on the floor and the ventricles continue to lớn beat at the idoventricular rate.
The ventricular escape rhythm is usually regular but it may be irregular. P Waves may be present or absent. If present, they do not have a mix relation to the QRS complexes. If present, the phường Waves may be positive (upright) or negative (inverted). If present, p. Waves may precede, be buried in, or follow the QRS complexes haphazardly. When the atria and ventricles beat independently, atriventricular (AV) dissociation is present. P-R intervals are absent. R-R intervals may be equal or may vary. QRS complexes exceed 0.12 second và are bizarre. Sometimes the shape of the QRS complexes may even vary in each different lead.
Ventricular escape rhythm is usually very symptomatic. The patients will usually develop hypotension with marked decrease in cardiac output and decreased perfusion of the brain & other vital organs. This results in syncope, shock, and congestive heart failure. Ventricular escape rhythm must be treated promptly in order khổng lồ reverse the consequences of the reduced Cardiac output.