Cardiology Topics

ATRIAL FIBRILLATION

What is atrial fibrillation?
Atrial fibrillation, sometimes called AF, is the most common heart beat disorder affecting approximately 2 million people in the United States. It is a condition whereby the top portion of the heart, the atria, beat uncontrollably in an unorganized quiver. During AF, the pumping chambers of the heart, the ventricles, beat irregularly and fast, typically around 110-130 beats per minute at rest, if untreated. Normally, the ventricles should beat around 60-80 times per minute while the individual is at rest. With activities or exercise, this heart rate will increase.

What are the consequences of atrial fibrillation and what are the therapies available?
The potential consequences of AF are three-fold:

  1. Because there is no organized contraction of the atria, the two upper chambers of the heart, blood flow is sluggish and irregular. This predisposes to formation of clots. Although the clots are typically too small to bother the heart itself, there is some danger the clots will be pumped out of the heart and enter the circulation. If this occurs, the clots will travel to small arteries and plug them up. If in the brain, the most common area to be affected, the patient will have strokes. The risk of this depends on multiple factors, especially age, presence of other forms of heart disease (especially congestive heart failure), hypertension, diabetes and previous strokes. Depending on the patient’s individual risk, the medical caretaker may recommend a blood thinner (anticoagulant) called warfarin (or Coumadin).
  2. Since the pumping chambers in the heartbeat rapidly during AF, this can cause the heart muscle to become weakened and dilated, a condition called cardiomyopathy. For this reason, one of the main strategies in the treatment of AF is to prescribe medications that slow down the rate. These include beta-blockers (such as atenolol, metoprolol, carvedilol and others), rate-limiting calcium-channel-blockers (diltiazem and verapamil) and digoxin.
  3. Owing to the rapid rates and irregular rhythm features of AF, patients may be symptomatic. The symptoms, if present, may be mild to severe in intensity and include palpitations, shortness of breath, fatigue, lack of energy, dizziness, fainting, chest pains and anxiety. The initial strategy of therapy is to slow down the heart rate to alleviate the symptoms, but some patients continue to be symptomatic even with appropriate rates. There are drugs called antiarrhythmics designed to keep the patient in normal rhythm (including amiodarone, dronedarone, sotalol, flecainide and propafenone). Your caregiver may opt to prescribe these or simply use the above stated rate-controlling medications. To establish normal rhythm, you may require a cardioversion or an ablation (see below). You should discuss these with your caregiver, if you are not happy in AF.

Can I have atrial fibrillation and not know it?
The answer is yes. In fact, it has been estimated that up to 90% of episodes of atrial fibrillation are not detected by patients, even in patients who feel AF at times. Occasionally, the patient experiences weakness or decrease in tolerance of physical activities but they attribute it to other causes, such as “getting old” or “the flu” and so on.

What causes atrial fibrillation?
The potential causes of AF are many and include heart disease, over-active thyroid, cardiac stimulants, disordered sleep patterns especially sleep apnea, high blood pressure, lung disease, low potassium and/or magnesium. Aging alone increases the risk of AF probably due to an age-dependent creation of short-circuiting in the heart’s electrical system. Someone once stated that if we live long enough, we’d have developed AF.

What are cardioversions and ablations?
Cardioversions are simple outpatient procedures whereby AF is converted to normal with an electrical shock delivered across the chest. The patient is first sedated heavily to avoid feeling the pain caused by the shock. Cardioversions are highly successful in conversion to normal rhythm but have no lasting effect. If AF recurs, antiarrhythmic agents may be necessary to maintain normal rhythm.

Ablations are procedures designed in simple terms to localize the short circuits that cause AF and either cauterize them or isolate them from spreading to the rest of the heart. These can be done from outside the heart (epicardial) or from inside the heart (endocardial). If AF is persistent and symptomatic despite medications, you should discuss the procedures and their potential risks and benefits of these procedures with your caregiver to see if they are a consideration in your case.


SUDDEN CARDIAC ARREST

What is sudden cardiac arrest?
Sudden cardiac arrest (SCA), sometimes referred to sudden cardiac death (SCD), is a condition whereby the rhythm of the pumping chambers of the heart (ventricles) suddenly changes into a rapid uncontrollable quivering which immediately ceases blood flow. This deadly rhythm is called ventricular fibrillation (VF). Not uncommonly, VF is precipitated by ventricular tachycardia (VT), another potentially deadly heart rhythm. With no effective heart muscle pumping (no pulse), the patient with VF suddenly and unexpectedly collapses, if awake at the onset. Resuscitation, mostly involving an electrical shock across the chest (defibrillation), is necessary to save the life of a SCA victim. Until the shock can be delivered, cardiopulmonary resuscitation (CPR) is necessary to keep some blood flowing into the brain. Devoid of circulation, the brain typically dies within 5-10 minutes.

Approximately one episode of SCA occurs each minute in the United States, making it the number one killer of Americans.

What therapies are available?
The therapy is defibrillation (see above). Unfortunately, once SCA occurs, the chances of survival are very low. Approximately 95% of SCA victim do not survive the event. In places where quick defibrillation is available, either via external defibrillators with someone willing to use it or by activation of 911 (emergency medical services), survival can be as high as 30-45%. External defibrillators are sometimes available in stadiums, airports, airplanes, malls, and so on. For patients known to be at risk for SCA, an implantable defibrillator should be utilized.

What are the risk factors for SCA and how do I find out if I’m at risk?
SCA can rarely occur in patients with normal hearts (typically due to genetic factors). If you have a family history of SCA, you should discuss your particular risk with your medical caregiver. Most patients with SCA have predisposing factors. These include having a weak heart muscle from either a heart attack or a heart muscle disease called cardiomyopathy. Fainting spells, especially in patients known to have heart disease, can be a warning sign of SCA and should be addressed with the medical caregiver.

How do I know if my heart pump is weak?
If you have had a heart attack or if your symptoms suggest a heart pump problem, your caregiver will most likely want to evaluate your heart pump. This is done with measuring your left ventricular ejection fraction (EF), simply, a determination of the percentage of blood volume that the heart pumps with each beat. Normally, this is 50-60%. The lower the EF the more one worries about SCA starting at 40%. If this is detected, there are crucial medications that may improve the situation. If the EF remains low, specifically below 35%, despite medicines, a defibrillator should be implanted.

Tell me more about implantable defibrillators
These devices are referred to as implantable cardioverter-defibrillators or ICDs. They are sometimes also called automatic implantable cardioverter-defibrillators (AICD). There are the size of a small deck of cards and are placed in a pocket that is created over the ribs and under the skin typically below the left collarbone. The ICD is connected to the inside of the heart with electrical connectors termed leads. There are systems that use one, two or three leads. Your physician will determine which type of system is best in your case.

ICDs monitor the heart rhythm for abnormalities. If the heart gets too slow, the ICD is equipped with a pacemaker which comes on to pace the heartbeat to normal range. This is normally not felt by the patient. If the heart goes into ventricular tachycardia (VT – see above), the ICD may try to stop it with the use of the pacemaker. This is typically not felt by the patient, although palpitations or dizziness may be noted, depending on the duration of the event and how fast it gets. If the patient’s rhythm is ventricular fibrillation (VF), the ICD will defibrillate or shock the heart. The shocks are painful but occur quickly (lasting less than one second). These shocks should be reported to the ICD caregiver.


DEVICE THERAPY

What is device therapy?
Different heart conditions have been shown to require implantation of a device for best management. These will be addressed here.

Pacemakers
Pacemakers are devices used to manage patients with slow heartbeats. For patients with heart rates below 40 beats per minute associated with symptoms (such as weakness, fatigue, dizziness, fainting, shortness of breath, chest pains and others) or who are discovered to have pauses in the heartbeat of 3 seconds or more, pacemakers are typically recommended. The devices are the size of a small man’s watch. The device is placed in a pocket that is created under the skin (over the ribs) typically just underneath the left collarbone. The device is hooked up to the heart muscle with electrical wires called leads. These are inserted into a vein (subclavian vein) that runs from the arm, under the collarbone, into the right-sided heart chambers. Pacemakers systems come with one, two or three leads and your caregiver will determine which suits your situation best. Once inserted, the pacemaker monitors the heartbeat continuously. Typically, pacemakers are set to a lower rate of 60 beats per minute. In that case, as long as the patient’s own heartbeat is 60 or higher, the pacemaker is on standby. If the heartbeat goes below 60, the pacemaker comes on pacing at a rate of 60, if the patient is at rest. This rate will increase automatically if the patient is active.

Defibrillators
See the discussion on implantable cardioverter-defibrillators (ICD) under Sudden Cardiac Arrest. These devices are larger than pacemakers, being approximately the size of a small deck of cards. They are implanted in the same way as pacemakers. They too come in one, two and three lead systems. ICDs are used for patients that have had or are at risk of developing life-threatening rapid heartbeats called ventricular tachycardia (VT) and ventricular fibrillation (VF). The latter is the cause of sudden cardiac arrest, whereas VT, in some patients, has the potential to degenerate into VF resulting in sudden cardiac death. ICDs include pacemakers as part of their function. Pacing is used to treat slow heartbeat problems just like pacemakers but also to attempt to stop VT. If pacing techniques cannot stop VT, or if VF develops, a shock (defibrillation) is delivered through the ICD. The shockwave courses through the heart muscle and is very efficient at stopping VF cardiac arrests. These devices save many lives every day.

What do the shocks feel like?
ICD shocks are described as being very painful but short-lived. In fact, they last less than a second. Patients feel most shocks, unless the individual loses consciousness beforehand. The shocks do not harm the patient or anyone that may be touching him/her at the time. Although shocks may be spurious, most shocks are life saving. Find out from your caregiver what you should do if you experience an ICD shock before you leave the hospital post implantation. Find out also if you should drive and what of your usual activities you can and cannot perform. For instance, the ICD wearer should not engage in arc welding and MRIs are typically discouraged.

Tell me more about pacemakers and ICDs
These devices will alert the metal detectors at airports and other places that have anti-theft alerting units such as some libraries, government buildings and so on. The patient will be given a card that identifies the implanted device. The patient should carry this card at all times. The security agents often use a hand-held frisking device in these circumstances.

What is CRT?
Both pacemakers and ICDs can be used with cardiac resynchronization therapy (CRT), although most patients that receive CRT do so in conjunction with an ICD since the criteria to use CRT is nearly identical to those used to prescribe ICDs. CRT utilized three leads, which are used to pace the right atrium, right ventricle and left ventricle. Since both ventricles are paced, CRT is also called bi-ventricular pacing. The standard pacemaker or ICD utilizes only the right-heart leads.

Some patients develop intra- and inter-ventricular dyssynchrony. That is to say, that the right and left ventricles and/or one side of the left ventricle and the other beat uncoordinatedly. This lack on synchrony leads to deterioration of pump performance and causes progression of the heart dysfunction. CRT allows for resynchronization of the ventricular chambers and walls and may lead to significant improvement in quality of life and improved chance of longer term survival. Discuss with your caregiver if CRT is right for you.


CONGESTIVE HEART FAILURE

What is congestive heart failure?
Congestive heart failure (CHF) is a condition characterized by multiple symptoms due to inefficient heart function.

What are the symptoms of CHF?
The typical symptoms associated with CHF are fatigue, shortness of breath, weakness and decreased tolerance to perform physical activities. There may be symptoms associated with lying down flat sometimes associated with frequent awakening during the sleep time due to shortness of breath. Since the main problem is usually retention of water and salt in the central circulation and lungs, patients will often notice lower leg swelling (edema) and increased body weight.

What causes CHF?
CHF is caused by an inefficiency of the heart as a pump. This is often related to having had heart attacks, which weaken the heart muscle due to injury or due to cardiomyopathy, a group of conditions whereby the heart cavities and muscle becomes weak, thick and/or enlarged. Conditions that can aggravate CHF are blocked coronary arteries (those feeding blood to the heart muscle itself), heartbeat disorders (most commonly atrial fibrillation), anemia, kidney dysfunction, thyroid problems and many others. Your caregiver should assess for these conditions that may be aggravating CHF.

How do I know if I have CHF?
If you noticed a significant change in your overall condition with fatigue, weakness, shortness of breath, chest pains, difficulty lying down flat and increasing weight, you should alert your caregiver so that a complete evaluation can be commenced. One of the main assessments that is made early in the assessment of CHF symptoms, is the determination of the heart’s ejection fraction (EF). This is a measurement of how much blood is pumped with each heartbeat, given as a percentage, with normal being 50-60%.

What can I do if I am diagnosed with CHF?
The main thing you can do once you have been diagnosed with CHF is to cut back drastically on sodium (salt) intake. It is imperative to read labels in canned foods, as these tend to be very high in sodium. The same goes for lunchmeats, pretzels, potato chips and popcorn. Going out to eat typically results in patients taking in a lot of sodium and this, too, should be carefully planned. The typical CHF patient is asked to consume less than 2,000 mg of sodium per day. It is important to periodically measure one’s sodium intake to be certain that this is being accomplished. Exercise in crucial for everyone and patients with CHF, too, should strive to remain as physically active as possible. Consult your caregiver for a particular exercise prescription.

What medicines are available to help me?
Your caregiver is your best resource to answer this question since medications need to be individualized to your particular set of circumstances. Diuretics, medications that promote water and sodium excretion via the kidneys, are typically prescribed, especially initially and during exacerbations. More important medication classes include beta-blockers, angiotensin-converting-enzyme (ACE) inhibitors, angiotensin-receptor-blockers (ARBs) and aldosterone antagonists. These are often prescribed along with statins, which is a class of drugs typically used to lower cholesterol but with benefits that go well beyond.


ABLATIONS

What is an ablation?
Rapid heartbeat disorders or arrhythmias are typically caused by reentry, what can be visualized as a short circuit in the heart’s own electrical system. The name given the rapid heartbeat disorder indicates where this short-circuit is located in the heart. An ablation is a procedure where the short-circuit is located precisely then destroyed with either Radiofrequency (cauterized) or cryo. The former destroys the short-circuit with a heat burn whereas the latter provides a freezer burn to accomplish the same. Electrophysiologists are cardiologists who specialize in this procedure. If successful, ablations are curative. The success rates of ablations are typically in the 90 th percentile, except for atrial fibrillation where it is typically in the 60-80 th percentile. The chance of serious complications is very low for most ablation candidates. All these factors should be discussed with your electrophysiologist before consenting to undergo the procedure.

Which rapid heartbeat disorders are amenable to be cured with ablations?
Rapid heartbeat disorders that are commonly managed successfully with an ablation include atrial flutter, atrioventricular nodal reentrant tachycardia (AVNRT), atrioventricular reentrant tachycardia (AVRT), Wolff-Parkinson-White (WPW) syndrome and certain types of atrial and ventricular tachycardias. Atrial fibrillation is also amenable to ablations. Discuss your arrhythmia with your electrophysiologist to see if you are a candidate.

When should I consider an ablation?
Certainly, ablations are important considerations in patients who are symptomatic from their arrhythmia, especially when medications are not effectively preventing the recurrences. The symptoms of arrhythmias include rapid palpitations (awareness of the heartbeat), fainting spells, dizziness, chest pains, anxiety and weakness. Typically, patients are offered a trial of medications first, although many patients prefer to proceed right to an attempt to cure the problem with an ablation. The decision to use medications or ablations to deal with symptomatic arrhythmias is individual. You are encouraged to discuss the pros and cons of the different alternatives before deciding on which course to take.

What can I expect if I undergo an ablation?
Typically your doctor will tell you which, if any, of your medicines to hold before the procedure, usually one week prior. You arrive at the hospital not having eaten for at least 6-8 hours. An intravenous line is hooked up to one of your arm veins to give you hydration and medications. A sedative medication, either by pill or in the IV, will be administered to help relax you. In the laboratory where the procedure is carried out, you are prepped and sedated further. The prep involves scrubbing your right groin, sometimes the left groin and neck area as well. The doctor will insert catheters into the groin(s) and advance them to the heart via a large vein. The catheters are long tubes used to hook up your heart’s own electrical signals to a specialized computer. Your electrophysiologist will attempt to induce your arrhythmia to study it in detail and make a definitive diagnosis. Using the catheters in your heart, your arrhythmia is typically induced and terminated multiple times. Mapping will follow. This is the process of precisely localizing the short-circuit to destroy it with the application of radiofrequency or cryo. Once this is done, the process used to induce your arrhythmia will be repeated to see if it can be re-induced. Some electrophysiologist will discharge their patients the same day; others, will ask the patient to stay in the hospital overnight. Discuss this with your doctor ahead of time. On discharge, you may be asked to take aspirin and other medications. Your electrophysiologist will advise you depending on the situation. You will receive instructions regarding care of the access sites which typically will heal in 3-5 days.