Published in UAB Insight, Winter 2008
ABSTRACT: By understanding the mechanism of cardiac dysfunction that leads to an arrhythmia, physicians can select the most appropriate treatment for each individual.
CME OBJECTIVE: The reader will understand the indications and options for treatment and referral of people with arrhythmias.
Tom McElderry, MD, no conflicts of interest
More than 14 million Americans have some type of arrhythmia. Many are benign, but some indicate significant cardiac disease and require treatment to reduce risk of complications or sudden cardiac death. Treatment regimens span from lifestyle modification and medical therapy to radiofrequency ablation, pacing, and implantable cardioverter defibrillators (ICD). “Determination of the optimal treatment strategy often involves referral to a cardiologist for a definitive diagnosis and an individually tailored treatment based on the mechanism of the heart’s dysfunction,” says UAB cardiac electrophysiologist Tom McElderry, MD.
Initial evaluation may include noninvasive testing, such as a standard electrocardiogram (ECG) or Holter monitoring, to record heart rates and rhythms during a patient’s daily routine. For more sporadic occurrences, patients can wear event monitors and activate them during episodes. An echocardiogram provides images showing the heart’s size, structure, and motion, and a transesophageal echocardiogram can exclude intracardiac blood clots associated with some arrhythmias.
Stress testing on a treadmill or with drugs can induce arrhythmia triggered by exercise. “For highly symptomatic or frequent arrhythmias, an electrophysiology [EP] study provides targeted testing and precision mapping of the heart’s electrical impulses to pinpoint the location and mechanism of the arrhythmia,” McElderry says. “UAB’s electrophysiology group has extensive experience determining the initiation and maintenance of cardiac arrhythmias and offers diagnostic and therapeutic care for all types of complex arrhythmias.”
Supraventricular Arrhythmias
Atrial arrhythmias are generally not life threatening but can result in syncope or other incapacitating symptoms. Those with infrequent or benign symptoms may only require reassurance or a reminder to limit triggers such as alcohol, caffeine, and certain cough medicines.
The most common supraventricular arrhythmia in patients aged >40 years is atrial fibrillation (AF), which affects more than two million Americans and is increasing in frequency. AF causes hemodynamic compromise, heart failure, a 2 to 7 times increased risk of ischemic stroke, and higher overall mortality.
In AF, electrical signals are conducted abnormally or do not start in the sinoatrial (SA) node, causing the atrial walls to quiver and fail to properly pump blood to the ventricles. Hypertension, hyperthyroidism, coronary artery disease, heart failure, and rheumatic heart disease may cause AF, which increases in frequency as people age.
Atrial flutter is less common than AF but has similar symptoms and stroke risk. “It is important to differentiate this rhythm from AF as atrial flutter can be easily corrected with radiofrequency ablation,” McElderry says. “In patients with symptomatic AF, initiate rhythm control strategy with antiarrhythmics such as flecainide, sotalol, or amiodarone.” Because such drugs have failure rates of 50% at 1 year and 84% at 2 years, radiofrequency ablation is a viable option. “At UAB we perform about 500 catheter ablations for AF a year, with an 80% long-term success rate. About 25% of patients require a repeat procedure,” McElderry says.
Supraventricular Tachycardias
Supraventricular tachycardia (SVT) is a regular but rapid heart rate, often with sudden onset and termination, that does not originate in the SA node. “Differentiation between various types of SVTs can be difficult,” McElderry says. Patients may or may not be symptomatic, depending on their hemodynamic reserve, heart rate, duration of the SVT, and coexisting diseases. The majority of patients with SVT have a reentrant rhythm involving an extra pathway either close to the atrioventricular (AV) node (atrioventricular nodal reentrant tachycardia [AVNRT]) or directly connecting the atria and ventricle (atrioventricular reentrant tachycardia [AVRT]), also known as Wolff-Parkinson-White (WPW) syndrome.
“SVT often occurs in the elderly or in young people during vigorous exercise and is rarely life threatening; however, SVT accompanied by WPW can be dangerous,” McElderry says. Patients with WPW syndrome may be at risk for cardiac arrest if they develop AF or atrial flutter in the presence of a rapidly conducting accessory pathway.
Treatment depends on the type of tachyarrhythmia and frequency and duration of episodes, symptoms, and risks. Patients must be evaluated on an individual basis. In general, if the arrhythmia causes only discomfort, conservative management and lifestyle modification are appropriate. Vagal maneuvers, such as carotid massage, holding the breath and bearing down, or coughing, may correct certain arrhythmias by briefly disrupting conduction through the AV node. “Some patients experience angina, hypotension, anxiety, and generally feel lousy. For these individuals short-term medical management with adenosine or calcium channel blockers is warranted,” McElderry says. Adenosine blocks AV node conduction and terminates tachycardias due to AVNRT or AVRT. Calcium channel blockers may be indicated depending on the arrhythmic mechanism. “Long-term treatment often involves EP study and radiofrequency ablation, which is curative therapy. Our success rates are near 100% for SVT,” he says. Class IA, IC, or III antiarrhythmic drugs are options, but may provide inadequate symptom relief or initiate intolerable side effects. “I do not recommend antiarrhythmic drugs for SVT. They can worsen the arrhythmia or create a new arrhythmia, and with success rates with ablation at a curative level, the drugs’ role is quite limited,” McElderry says.
Ventricular Tachycardia
For patients with an otherwise healthy heart, premature ventricular complexes and ventricular tachycardia (VT) may be a nuisance, but they are not life threatening. These originate from rapidly firing cells in the ventricles. Patients may complain of palpitations or dizziness and, unless highly symptomatic, need only reassurance, or in the case of very bothersome symptoms, a beta-blocker. “Some individuals experience as many at 20,000 extra heartbeats a day but cannot tolerate drug therapy. For those refractory to treatment or with syncope, radiofrequency ablation is an appropriate treatment. Cure rates for these arrhythmias are similar to those for SVTs,” McElderry says.
When associated with coronary heart disease, cardiomyopathy, or congestive heart failure, VT is caused by reentry around areas of scar that significently increases risk of morbidity and mortality. For patients with life-threatening VT or ventricular fibrillation (VF), automatic ICDs are life-saving therapy. A randomized trial of more than 2500 patients with chronic heart failure found that amiodarone was no better than placebo at treating ventricular arrhythmias in structurally abnormal hearts, while ICDs reduced overall mortality by 23% (N Engl J Med. 2005;352:225-237). Patients who should be evaluated for an ICD include those with prior cardiac arrest, VF, sustained VT, and those with ejection fractions of ≤35%. “Even in the absence of a prior documented arrhythmia, patients will derive a survival benefit from ICDs as primary prevention of sudden cardiac death,” McElderry says. ICDs detect ventricular tachyarrhythmias and terminate them with antitachycardia pacing algorithms or, if necessary, defibrillation shocks. “ICDs are implanted transvenously in a low-risk, often outpatient, procedure,” McElderry says. Adjunct antiarrhythmics such as amiodarone or sotalol may prevent recurrent defibrillator shocks. For those who receive ICD shocks despite medication, ablation is an effective palliative treatment.
Research conducted by UAB cardiologist Robert C. Bourge, MD, has shown that implantable hemodynamic monitoring can improve heart failure management. Since the majority of heart failure patients also meet criteria for ICDs, UAB cardiologist Jose A. Tallaj, MD, is currently evaluating the combination of both technologies into a single device. The Chronicle ICD system allows remote monitoring of right ventricular systolic and diastolic pressure as well as estimated pulmonary artery pressure. The device aims to catch heart failure exacerbations early to avoid hospitalizations while also protecting patients against life-threatening arrhythmias.
For more information:
Dr. Tom McElderry
1.800.UAB.MIST
mist@uabmc.edu