Outpatient approach to arrhythmia monitoring
Proper and effective monitoring is required to assess and manage arrhythmias and to document and diagnose the etiology of the problem. Many individuals have symptoms that might appear to be arrhythmic in origin but are not. Many arrhythmias may be of prognostic importance but are not easily diagnosed by symptoms alone. It is not uncommon for individuals to be completely asymptomatic during serious and potentially life-threatening arrhythmias; therefore, proper selection of monitoring techniques is crucial to secure the rhythm diagnosis and develop a management strategy.
There have been important advancements in the technology for monitoring arrhythmias. The 24- to 48-hour Holter monitor provides complete disclosure of rhythm disturbances, but only during a short window of time. These multilead monitors (from which a 12-lead electrocardiogram [ECG] can be constructed to analyze QRS morphology during arrhythmias) can provide information on minimum, maximum, and mean heart rates, all types of arrhythmias, diurnal changes in arrhythmia frequency and duration, heart rate variability, abnormalities in the ST segments and their relationship to rhythm disturbances or heart rate, changes in the QRS and QT intervals, and presence or absence of normal pacing system function. They can also disclose symptoms that occur during recordings, directly by patient triggering or by written diary entries, allowing for rhythm-symptom correlation. They can further determine the “burden” of a specific arrhythmia over time.
If, however, a patient has intermittent symptoms, Holter monitor recordings, performed at a specific point in time, will be of no use. For example, if a patient has syncope and has a Holter recording that does not show any episodes of arrhythmia and the patient does not record an episode of syncope, the monitor is of no use. Furthermore, nonspecific arrhythmias such as atrial and ventricular premature complexes recorded in patients with serious symptoms such as syncope will have little, if any, meaning. For example, recording of a sinus pause in the middle of the night, which is likely vagally mediated, in a patient with syncope has neither specific meaning nor prognostic significance regarding the type of evaluation and management that needs to be performed.
There are other ways to monitor arrhythmias. Event monitors now available are more advanced than in years past. Multilead recordings can be provided with full disclosure over a 24-hour period. Furthermore, the information can be downloaded and sent transtelephonically to a monitoring center; this can be accomplished during symptoms or periodically in patients with previously defined severe arrhythmias. Recordings can be triggered manually or automatically. These monitors can act as real-time or endless loop recorders with memory capability and therefore can provide continuous monitoring and playback should a patient have a symptom that occurred minutes before the device was manually activated and marked. Monitors can be worn for 30 to 60 days. They can also be used intermittently and applied as required in patients with long-standing symptoms. They can provide ample leeway for a patient to apply and then remove the monitor so that the patient does not need to wear the device all the time.
In addition to these noninvasive monitoring techniques, there are now implantable loop recorders (ILRs). These small leadless devices are implanted or injected subcutaneously as a minor operation and provide real-time and endless loop recordings that are stored in the device for a period of up to 3 years. The ILR can transmit information transtelephonically and then send information over the Internet to the physician. Stored data can be interrogated in the same way as pacemakers are interrogated, and the information can be printed. These devices are currently indicated for patients with occasional syncopal spells that are infrequent enough that they cannot be recorded on a Holter monitor or an external loop recorder. The ILR can also be used for diagnosis of the cause of palpitations and other nonspecific but arrhythmia-related symptoms. Ultimately, as this technology advances, these devices may be able to store in memory episodes of asymptomatic atrial fibrillation (AF) and determine its burden.
ILRs are not the only implanted method to record rhythm disturbances. Permanent pacemakers and implantable cardioverter defibrillators (ICDs) can store rhythm disturbances in memory, allowing for diagnosis. Specific criteria for such stored data must be programmed into these devices; otherwise they will not be recognized. Arrhythmia storage capability is not as great as that for the ILR.
Other forms of monitoring are also available, such as treadmill exercise testing. In patients with exercise-induced arrhythmias, a treadmill test may be used to document the rhythm and assess effects of therapy; correlation with myocardial ischemia can also be made, although this is unusual. Development of atrioventricular (AV) block during treadmill testing helps to localize the site of AV block and will aid in the decision to implant a permanent pacemaker. Appropriate shortening of the QT interval with increasing heart rate during exercise can be documented. Ventricular rate in patients with AF can be assessed. Finally, for athletes in whom extreme exertion is the only way to trigger an arrhythmia, monitors can be used during this type of exercise if it is deemed safe enough to measure and diagnose a rhythm disturbance that cannot be found any other way.
Carotid sinus massage
Carotid sinus massage (CSM) is performed to terminate some supraventricular tachycardias (SVTs), such as AV node reentry and AV reentry SVTs. It may also be useful for sinoatrial (SA) reentrant SVT. CSM can be helpful to diagnose the atrial rhythm during a tachycardia by producing AV block. For example, CSM-induced AV block can allow atrial flutter (AFL) waves to be seen. CSM may also be helpful to cause ventriculoatrial conduction block when there is a wide QRS complex tachycardia. CSM may also be useful to determine whether carotid sinus syndrome is present in syncopal patients.
The proper way to perform CSM is to make sure that the carotid pulse is felt directly under the fingertips. Two or three fingertips placed on the carotid artery are important to make sure that a vagal reflex is initiated. It can be performed on the right or the left side, but the left side is more likely to act on the AV node, whereas the right side acts on the sinus node. When performing CSM, it is important to realize that there is a small risk of stroke if there is carotid artery plaque; thus, it is important to check for carotid bruits before performing this procedure. The carotid sinus area should be massaged for about 5 seconds, beginning gently and progressing more rapidly to heavier pressure. Monitoring the patient for signs of cerebral hypoperfusion such as weakness, paresthesias, and numbness are important in avoiding transient ischemic attacks.
The head is turned away from the carotid sinus area to be massaged. For example, if right-sided CSM is to be performed, the head is turned to the left. The patient should be supine or even in a Trendelenburg position to maximize intravascular volume. To terminate tachycardias, it may be useful in some cases to combine CSM with Trendelenburg positioning and with a Valsalva or handgrip maneuver.
Electrophysiology testing is invasive testing in which electrical catheters are placed inside the heart in an attempt to understand the mechanisms responsible for arrhythmias, to help map and localize an arrhythmia for curative procedures, to assess risk of sudden cardiac death and/or arrhythmia recurrence, to determine the need for other therapies such as a pacemaker or defibrillator, to better understand symptoms such as syncope, to determine the effectiveness of a specific drug to treat an arrhythmia, and to determine hemodynamic effects of pacing from various sites. Over the years, the indications and utility of electrophysiology studies have evolved, and many of the hoped-for predictive benefits of electrophysiologic testing have not turned out to be as useful as was initially thought.
An electrophysiology study can be used to assess sinus node dysfunction, AV node and His-Purkinje system conduction disturbances, the possible etiology of syncope, the risk for out-of-hospital cardiac arrest, the presence or absence of accessory pathways, and by induction of SVTs and ventricular tachycardias (VTs), localization and understanding of the mechanisms responsible for specific arrhythmias. Today, electrophysiology studies are mostly used in conjunction with mapping and ablation procedures directed toward potential cure of selected arrhythmias.
Electrophysiology studies can be performed noninvasively, through ICDs or pacemakers, or can be invasive. The invasive studies use 1 to 6 electrical wires with 2 to 20 poles (electrodes) for recording signals inside the heart and for induction of arrhythmias in the atria and ventricles. It can include use of a transseptal catheter for mapping and ablation of AF originating from the left atrium, for localizing left-sided accessory pathways, and for inducing and mapping VTs originating in the left ventricle. There are now new electroanatomical mapping systems that include methodologies to evaluate the cardiac chamber itself, the electrical signals generated in the cardiac chamber, and the activation sequences within different cardiac chambers. For this type of mapping system, there can be noncontact balloon-type mapping systems or contact mapping systems that involve point-by-point or large activation sequences.
The catheters used can have 2, 4, 6, 8, 10, 12, or 20 poles, depending on the purpose of the study. Ablation catheters can have 4-, 6-, 8-, or 10-mm tips.
Attempted induction of arrhythmias can include one or two atrial extrastimuli delivered at one or two fixed cycle lengths using a variety of protocols. Atrial pacing can also be used to determine sinus node function, AV node function, and His refractoriness. In the ventricles, one, two, or three premature ventricular extrastimuli delivered at one to three cycle lengths, and in some cases ventricular burst pacing, can be used to attempt to induce VTs. Often, extrastimulus testing is performed from more than one site.
Occasionally, the infusion of isoproterenol or an antiarrhythmic drug is part of the electrophysiologic test. These tests tend to be performed under some degree of conscious sedation, but it is realized that the conscious sedation itself may affect induction of some tachyarrhythmias, as they may suppress catecholamine effects on various tissues and pathways.
Although electrophysiology testing can be used for the evaluation of sinus node dysfunction, the sensitivity and specificity are relatively modest, if not poor; the same is true for investigation of AV nodal function. On the other hand, the evaluation of presence or absence of His-Purkinje conduction disease is quite accurate. The test is very good for induction of SVTs when they are documented to be present, but it is not good for prediction of who will or will not develop AF. The test is very good for determining the presence or absence and properties of an accessory pathway.
The electrophysiologic test has varying degrees of sensitivity and specificity regarding the induction of VTs, depending on the clinical characteristics of the patients and the arrhythmia. For example, the test has a relatively high sensitivity and specificity for induction of VT when a monomorphic VT is present in a patient with underlying ventricular dysfunction and coronary artery disease (CAD). On the other hand, sensitivity and specificity are not as good for patients with nonischemic dilated cardiomyopathy and are even worse, and therefore not indicated, for patients who have long QT interval syndrome (LQTS), who may be at risk for torsades de pointes (TdP) or sudden death. Occasionally, the test is used to diagnose rhythm disorders that are potential etiologies for syncope; its use in documenting the cause of palpitations is questionable. The electrophysiologic test is not used routinely as a prognostic marker in patients who are at risk for sudden cardiac death and who are already known to have other risk factors that are accepted indications for implantation of an ICD.