Diseases

Mobitz II (Heart Rhythm Disorders) Information

Atrial fibrillation (A-fib)

Atrial fibrillation occurs when the atrium has lost the ability to beat in a coordinated fashion. Instead of the SA node generating a single electrical signal, numerous areas of the atrium become irritated and produce electrical impulses. This causes the atrium to jiggle, or fibrillate, instead of beating. The AV node sees all the electrical signals, but because there are so many, and because they are so erratic, only some of the hundreds of signals per minute are passed through to the ventricle. The ventricles then fire irregularly and often very quickly.As in PSVT, the symptoms may include palpitations, lightheadedness, and shortness of breath. The cause of atrial fibrillation, however, may be more significant, since it may be due to aging of the conducting system of the heart and there may be associated atherosclerotic heart disease. Therefore, atrial fibrillation with rapid ventricular response associated with chest pain or shortness of breath may need emergent cardioversion (a procedure that uses electricity to shock the heart back into a normal rhythm) or intravenous medications to control the heart rate.One significant complication of atrial fibrillation is the formation of blood clots along the inside of the heart wall. These clots may break off and travel to different organs in the body (embolize), blocking blood vessels and causing the affected organs to malfunction because of the loss of blood supply. A common complication is a clot traveling to the brain, resulting in a stroke.The treatment of atrial fibrillation depends upon many factors including how long it has been present, what symptoms it causes, and the underlying health of the individual. The patient and his or her doctor will decide whether or not to restore a normal sinus rhythm or to simply keep the heart rate under control.Atrial fibrillation can be a safe rhythm and not life threatening when the rate is controlled. Medications are used to slow the electrical impulses through the AV node, so that the ventricles do not try to capture each signal being produced. The reason to return people to a regular rhythm has to do with cardiac output. In atrial fibrillation, the atria do not beat and pump blood to the ventricles. Instead, blood flows into the ventricles by gravity alone. This lack of atrial kick can decrease the heart's efficiency and cardiac output by 10% to 15%.Blood thinning, or anticoagulation, may be recommended for those patients with atrial fibrillation and elevated risk for stroke. Oral drugs that anticoagulate are warfarin (Coumadin), dabigatran (Pradaxa), rivaroxaban (Xarelto), and apixaban (Eliquis). There are other injectable drugs that are used in a hospital setting. If the patient is at low risk, the doctor may recommend aspirin alone for stroke prevention. If atrial fibrillation is poorly tolerated due to symptomatic palpitations or symptoms of reduced cardiac output, or if there are concerns with lifelong anticoagulation therapy, more definitive therapy may include specific medications, electrical cardioversion, or catheter based ablation (sometimes with a pacemaker inserted). Atrial fibrillation is a common condition, with many implications, and the best plan for each patient should be discussed at length with one's physician.

Atrial flutter

Atrial flutter is similar to atrial fibrillation except that instead of having chaotic electrical firing from all points in the atrium, one point has become irritated and can fire 300 times per minute or more. Many issues that exist for atrial fibrillation apply to atrial flutter. Atrial flutter may degenerate into atrial fibrillation, and the two can often coexist.

Bradycardia

Aside from medications that are meant to slow the heart for treatment of a variety of medical problems, bradycardia (brady = low + cardia = heart) is usually due to heart block and the aging of the electrical wiring of the heart. This is no different than the aging of your home's electrical system; but instead of being able to rewire the heart, these conditions may need to be treated with an implantable pacemaker.

Heart blocks

Heart blocks involving the ventricle may be asymptomatic and of little consequence except to point to underlying heart or lung disease. They are diagnosed by EKG.Heart blocks involving the atrium can be classified as first-, second-, and third-degree.

• First-degree heart block is common and usually of little significance. There is a slight delay in getting the electrical signal from the SA node to the AV node, but the heart functions normally.
• There are two types of second-degree heart block (Mobitz I and Mobitz II, with Type II being more serious than Type I.
• Third-degree heart block describes the complete loss of connection between the electrical activity of the atria and the ventricles. Second- and third-degree heart blocks are diagnosed by analyzing heart rhythm strips and EKGs.

Paroxysmal supraventricular tachycardia (PSVT)

Paroxysmal supraventricular tachycardia (PSVT) occurs when the pathways in the AV node or atrium allow an altered conduction of electricity, and the atrium begins firing in a fast but regular rate, sometimes more than 150 to 200 times per minute. The ventricles, sensing the electrical activity coming through the AV node, try to beat along with each electrical impulse and PSVT occurs.This is rarely a life-threatening event, but people may feel uncomfortable when PSVT occurs. They may become lightheaded, weak, have shortness of breath, and describe a feeling of fullness in the throat. PSVT may also be tolerated and may stop on its own. If this is a first time event, activating EMS (emergency medical services) and calling 9-1-1 is important, since other tachycardias can be life threatening.The treatment for PSVT includes attempts to stimulate the vagus nerve to slow the heart (see vasovagal syncope above) by holding one's breath and bearing down as if to have a bowel movement. Intravenous medications are often used to interrupt the episode. Many patients have PSVT due to congenital abnormalities in the electrical conduction system of the heart. External causes can include hyperthyroidism, electrolyte imbalances, and the use of caffeine, alcohol, over-the-counter cold medications containing stimulants, or illegal drugs like cocaine and methamphetamine.

Premature atrial contractions (PACs) and premature ventricular contractions (PVCs)

Every person experiences the occasional palpitation in which the atrium or the ventricle beats early. These premature atrial contractions (PACs) or premature ventricular contractions (PVCs) are normal variants and most people are unaware of their occurrence. However, some patients report a palpitation in the chest and neck, often described as a "thump" or "thud." PACs and PVCs in otherwise healthy individuals do not pose any health risks.

Sinus bradycardia

The heart, its cells, and its electricity may come under the many outside influences causing it to beat more slowly. Sinus bradycardia (brady = slow + cardia = heart) by definition, is a heartbeat generated by the SA node at a rate slower than 60 beats per minute. This may be normal in people who are active and athletic or in patients taking medications designed to slow the heart such as beta blockers and some calcium channel blockers.Vasovagal syncope is an episode of profound sinus bradycardia associated with a noxious stimulus that causes the vagal system of the body to kick in and slow the heart rate. While the sympathetic system of the body is mediated by adrenaline, the parasympathetic system is mediated by the vagus nerve and the chemical acetylcholine, which promotes the exact opposite body reaction than adrenaline. In some people, exposure to pain or a difficult emotional situation can stimulate the vagus nerve, slow the heart, and dilate blood vessels (veins), causing cardiac output to decrease and making a person feel lightheaded or faint. The vagus nerve also can be stimulated to slow the heart when one bears down to urinate (micturition syncope) or have a bowel movement.

Sinus tachycardia

The heart, its cells, and its electricity may come under many outside influences that may cause it to beat more quickly. Sinus tachycardia (sinus = from the SA node + tachy = rapid + cardia = heart), or a rapid regular heartbeat, is a common rhythm issue. It occurs when the body signals the heart to pump more blood, or when the electrical system is stimulated by chemicals.The body needs increased cardiac output in times of physiologic stress. Cardiac output is the amount of blood the heart pumps in the course of 1 minute. It can be calculated by the amount of blood that the heart pumps with each beat (stroke volume) multiplied by the heart rate.Cardiac output = (stroke volume) x (heart rate)The stroke volume tends to be relatively constant. When the body requires extra oxygen delivery, the heart rate needs to increase to meet that demand. Examples include:

• exercise, in which the muscles have greater oxygen requirements and the heart rate speeds up to pump more blood to meet that need;
• dehydration, in which there is less fluid in the body and the heart rate has to speed up to compensate; or
• in cases of acute bleeding that may occur after trauma.

Tachycardia

Rapid heart rates can originate from either the atrium or the ventricle, but rhythms from the ventricle are more often life threatening. The initial approach to rapid heart rates is to quickly identify the rhythm, and if blood pressure is maintained and there is no evidence of a failing heart, then treatment is directed to rate control with the eventual return of the heart back to normal sinus rhythm. If, however, there is evidence that the heart is failing because of the rapid rate, then emergency measures, including using electricity to shock the heart back into a regular rhythm, may be necessary.

Ventricular fibrillation (V-fib)

Ventricular fibrillation is technically not a rapid heart rhythm because the heart ceases to beat. In ventricular fibrillation, the ventricles do not have a coordinated electrical pattern and the ventricles, instead of beating, just jiggle, or fibrillate. Since the heart doesn't beat, blood is not circulated to the body or brain and all bodily functions stop. Without a coordinated impulse to signal the ventricle to beat, sudden cardiac death occurs.The treatment for V-fib is defibrillation with an electrical shock. Automated external defibrillators (AEDs) in public places have helped decrease the mortality from sudden cardiac death, but prevention remains the mainstay to survive this event. Some people, such as those with a very weak heart muscle or who have a prior history of ventricular fibrillation will require an implantable defibrillator to prevent future episodes of sudden death and treat this rhythm.This rhythm is often associated with a heart attack in which the heart muscle doesn't get enough blood supply (myocardial ischemia), becomes irritated, and causes secondary irritation of the electrical system. Aside from myocardial ischemia, other causes of ventricular fibrillation may include severe weakness of the heart muscle (cardiomyopathy), electrolyte disturbances, drug overdose, and poisoning.

Ventricular tachycardia (V-tach)

Ventricular tachycardia is another rapid heart rate that originates in the ventricle. The causes are the same as those for ventricular fibrillation, but because of the electrical conduction pattern in the heart pathways, an organized signal is provided to the ventricles, potentially allowing them to beat. This remains an emergency, since V-tach may degenerate into ventricular fibrillation.

When to seek medical care

Unexplained palpitations are not normal, especially when associated with shortness of breath, sweating, feelings of chest pressure, or passing out. The person should be made comfortable and laid flat, and EMS (emergency medical service) should be activated by calling 9-1-1 or the emergency number in your area.If the person is unconscious or unresponsive, Basic life support (American Heart Association) should be initiated. Call 9-1-1, get an AED, and decide whether CPR should be initiated.If the episode is short-lived and resolves spontaneously, the primary care professional should be contacted urgently to seek advice.If the episode is a recurrent problem, the diagnosis is known, and the rhythm disturbance resolves itself, then a less urgent call to the primary care professional is warranted.It is reasonable to seek emergent medical care any time that a heart rhythm disturbance occurs or if there is concern that a heart problem is present.

Wolff-Parkinson-White (WPW) syndrome

Wolff-Parkinson-White syndrome is a specific type of PSVT, in which an inborn error of wiring has occurred near the AV node, and an accessory electrical pathway exists. The diagnosis is made by electrocardiogram (EKG) or electrophysiologic testing, and the treatment may include medication or destruction of the accessory electrical pathway by invasive catheter ablation.