What Is Arrhythmia?
Normal Cardiac Rhythm
The human heart is a double pump: it receives deoxygenated blood from the venous circulation and oxygenates it by propelling it to the lungs, then receives it again so that oxygenated blood can be sent to the rest of the body.
The effectiveness of this double pumping action depends on the slightly skewed contractions of the right and left atria and right and left ventricles, such that a synchrony of directional flow results in an effective cardiac output. This synchrony depends on a normal electrical pathway that originates with a stimulus in the heart’s “pacemaker,” the sinoatrial (SA) node in the right atrium. From there, the conduction wave of impulses travels right-to-left and superior-to-inferior. With the help of the one-way valve mechanisms between atria and ventricles and between ventricles and the extra-cardiac circulation, a vector force outward is affected without any counterproductive reverse or back-flow.
The electrical axis originates in the SA node, then travels to the atrioventricular junctional area where the atrioventricular (AV) node resides. From there, the impulses travel inferior along the Bundle of His fibers, and then spread out along the Purkinje fibers where they terminate deep within the ventricles.
Anywhere along this electrical pathway the signal can be blocked or altered, creating a departure from the normal electrical activities upon which effective cardiac output depends:
- A block at the AV node will result in altered signals–or no signals–being propagated further, leaving the slower pace making automaticity of the ventricles to fire off as an escape rhythm.
- Extra (“ectopic”) pacemakers in the atrium can compete with the SA node’s normal pace making, creating atrial arrhythmias that can impact conduction through to the ventricles or create ineffective atrial contractions.
- Re-entry (“aberrant”) signals can initiate a circular, wasted circuit that augments or defeats the normal electrical activity.
- Damage to the electrical system due to ischemia or cell death (myocardial infarction) can destroy the normal synchrony needed for effective cardiac output.
- Sympathetic and parasympathetic influences can stimulate or inhibit the pace making properties and automaticity of the normal heart.
How Is Arrhythmia Diagnosed?
Cardiac arrhythmias often have symptoms that prompt patients to seek medical attention. Others have silent pathology that is discovered incidentally on a routine physical exam (and the risk-associated extra testing that is assigned as part of routine health management, e.g., blood tests, ECG, etc.).
Symptoms of palpitations and/or syncope (fainting/passing out) and near-syncope (dizziness/light-headedness) prompt diagnostics that can lead to prevention of cardiac events. Alternately, any incidental findings can prompt the same work-up as part of normal health maintenance.
History and Physical Exam
A medical history and family history are the first steps in diagnosing overt and covert warning signals. Diabetes, hypertension, smoking, dyslipidemia (elevated cholesterol/triglycerides), and any previous cardiac history will set a patient apart for extra testing. Chest pain is always significant until proven otherwise.
- A medication history can isolate signs and symptoms of arrhythmias due to side effects of certain drugs used for non-cardiac purposes or even for arrhythmias themselves
- Close relatives with a history of arrhythmia, sudden or unexplained death, or who have required the insertion of pacemakers or defibrillators will also spotlight those at risk
- The physical exam relies on vital signs, examination for arterial pulse rate and (jugular vein) pulsations, blood pressure, as well as the appearance of pallor or diaphoresis that can prompt cardiac diagnostics Auscultation of the heart is an essential component to discern extra heart sounds and murmurs, unusual pauses or separations between heart sounds, or irregularity of contractions (pulse)
Blood tests can identify biomarkers that identify myocardial infarction, but this is has the disadvantage of identification only after-the-fact.
ECG and Other Monitoring Modalities
The 12-lead electrocardiograph is the standard way to identify cardiac disease, ischemia, and arrhythmias. Although it is unsurpassed in getting a true, sweeping picture of the heart’s electrical activity over 360°, it can be limited by its brief 10-second snapshots of cardiac activity. For those with covert, intermittent, or very fleeting cardiac events and arrhythmias, long-term monitoring is accomplished by using a Holter monitor for 24-48 hours, 2-week surveillance using a Zio pad, or even years of monitoring using an implanted loop recorder with wireless technology to stream data on a daily basis to a patient’s doctor.
Problematic arrhythmias that can be diagnosed with the above diagnostics include:
- Atrial premature beats
- Ventricular premature beats
- Bradycardia (sinus bradycardia and “sick sinus” syndrome)
- Ventricular tachycardia
- Supraventricular tachycardia
- Dysrhythmia from atrioventricular block
- Atrial fibrillation
Management of Arrhythmia
Management of cardiac arrhythmias depends on the type of abnormality and its origin. The goals of treatment are:
- Prevent sudden cardiac death
- Eliminate risk of other dangers, such as stroke (e.g., atrial fibrillation or flutter)
- Eliminate discomforting symptoms
- Prevent the compromise that results from the heart being an ineffective pump
Sudden Cardiac Death
Sudden cardiac death is preventable in most cases by the appropriate identification and management (treatment) of risk factors and suspicious symptomatology. Treatment is via proactive anti-arrhythmic drugs and precautionary withdrawal/exchange of pro-arrhythmic drugs. Some arrhythmias from ectopic pacemakers can be treated with catheter-driven radio-frequency ablation of the ectopic sites.
Managing the Risk of Other Dangers
When arrhythmia has been identified, therapeutic management includes the use of anti-arrhythmic drugs and close surveillance with long-term monitoring. Some arrhythmias are fraught with traditional consequences, such as atrial fibrillation and subsequent emboli, and preventing them is prudent to avoid serious untoward events. Prevention may require a cardiac pacemaker.
Elimination of Unpleasant Symptoms
Palpitations are unpleasant perceptions of the heart beating which can be associated with syncope, near syncope, and/or a disturbing psychological premonition of doom. Medical management (beta blockers) is used in certain patients to mitigate their frequency or severity. These drugs may not eliminate the arrhythmia altogether but will lessen the symptoms from it. When valve damage is the cause, valve replacement may be necessary.
Prevention of Dysfunction of Cardiac Output
When the heart is an ineffective pump, all of the end-organs are not perfused optimally, from the internal organs to the heart itself (from its coronary artery supply). Such partial disruptions of flow are prevented or remedied by superseding the electrical conduction abnormalities responsible for arrhythmias via pacing with continuous or on-demand pacemakers.
Anyone with heart disease or cardiac arrhythmia lives under the relentless burden of on-going risk to life. Part of the treatment is to implant devices to intervene automatically upon demand, such as pacemakers and even cardioverters-defibrillators.
How Can I Prevent Arrhythmia?
No initial arrhythmia can be predicted or prevented unless there is congenital heart disease that makes one likely. Such patients undergo cardiac echograms to discern the type and severity of congenital anomalies. The can be monitored using long-term implantable loop recorders to alert their physicians when an arrhythmia might arise de novo.
A major part of diagnostics is the addition of ultrasonographic cardiac imaging (echocardiography) to electrocardiography (ECG). Some arrhythmias can result in heart damage, and some heart damage can cause arrhythmias, so a perspective on anatomy is helpful in preventing complications of either.
For other patients, prevention of arrhythmias can only occur with an established diagnosis of previous or on-going arrhythmia or heart disease. Such patients already will have been treated with medical or electrical cardioversion and prevention of any recurrence relies on scrupulous continued observation using long-term monitoring techniques (implantable loop-recorders).
Medical management can include drugs that inhibit the sympathetic nervous system (e.g., beta blockers). Also, arrhythmias fraught with risk of embolism can prevent embolic ischemia in distal organs by the implementation of anticoagulant therapy.
If a patient’s previous event was significantly life-threatening, prevention of sudden cardiac death may require implantable cardioverters/defibrillators. Regardless of which cardiac event triggered the search for the cause and a definitive diagnosis, prevention of serious consequences relies upon placing such patients in a high-risk pool for continued, close surveillance using electrocardiography, frequent visits to their physicians, and imaging diagnostics.