A systematic approach to Holter monitor interpretation

Author: Ken Grauer, Brent Leytem
Date: April, 1992

A systematic approach to the interpretation of ambulatory electrocardiographic recordings facilitates analysis and improves accuracy. The method suggested includes a mnemonic and a standardized interpretation form. The mnemonic facilitates recall of key technical and patient-specific parameters involved in the preparation and evaluation of Holter monitor and other ambulatory electrocardiographic recordings. The standardized interpretation form consolidates essential findings from the study into a practical, easy-to-assimilate format.

Ambulatory electrocardiographic (ECG) monitoring has become increasingly popular among family physicians in recent years, and many systems are available. This article suggests a method for analyzing Holter recordings and proposes a format for reporting the interpretation.

The importance of using a systematic approach to improve accuracy in interpreting the 12-lead ECG has been emphasized by several authors.[1-3] We advocate the same principle for facilitating and improving the accuracy of Holter monitor interpretation. The method suggested in this article incorporates the use of a mnemonic and a standardized interpretation form (Table 1). The mnemonic--ESP IDEAS--facilitates recall of key technical and patient-specific parameters involved in the preparation and evaluation of Holter recordings. The standardized form organizes the key components of the interpretation into a practical, user-friendly format (Figure 1). Table 1 Suggested Systematic Approach for Interpreting and Reporting Holter Monitor Results 1. ESP IDEAS: a mnemonic for recalling key technical and patient-specific

parameters involved in the preparation and evaluation of Holter

recordings

Equipment

Settings

Patient specifics

Indications

Diary

Electrocardiogram (ECG)

Analysis

Strips 2. Standardized interpretation form: a method for organizing the key

components of the Holter interpretation

a. Interpretation of the patient's baseline ECG (including assessment of

intervals)

b. Trend analysis (of heart rate and ST-segment deviations)

c. Underlying rhythm

d. Arrhythmias (including ectopic beats, tachyarrhythmias,

bradyarrhythmias and pauses)

e. Diary (including correlation of symptoms with arrhythmias)

f. Summary of findings

ESP IDEAS Mnemonic

EQUIPMENT

Although ambulatory ECG equipment is generally durable, it should be checked routinely for cracked or broken wires, dead batteries and damage to the carrying case. At the time of inspection, the supply of disposable items, such as printer, printer ink and lead attachment kits, can also be checked.

SETTINGS

Most ambulatory ECG systems allow the operator a degree of flexibility in selecting the settings for the abnormalities that will be evaluated. The parameters we favor for routine recordings are shown in Table 2. Table 2 Example of Equipment Settings Automatic high rate: 120 beats per minute Automatic low rate: 40 beats per minute Automatic pause: 2.0 seconds Automatic supraventricular ectopic: 25 percent Automatic ST level: 2 mm Periodic storage: four hours Strips per hour: five Report: full

Automatic limits are the settings beyond which the equipment will automatically record a representative tracing. The method followed to determine which representative tracings are recorded and retained for display on the printout will depend on the particular system used.

Rate. We prefer an upper rate limit of 120 beats per minute. A lower rate limit (100 or 110 beats per minute) is likely to result in the recording of an excessive number of sinus tachycardia strips throughout a typical day. With a higher rate limit (130 beats per minute or greater), potentially significant tachyarrhythmias with a relatively slow rate, such as ventricular tachycardia at 125 beats per minute, may be overlooked. For similar reasons, we favor selection of a lower rate limit of 40 beats per minute, because doing so minimizes the number of episodes of benign sinus bradycardia (45 to 55 beats per minute) that might be recorded.

It is important to realize that deciding on equipment settings represents a clinical compromise. For example, in certain individuals (i.e., symptomatic patients with sick sinus syndrome who are being evaluated for possible pacemaker insertion), it may be more important to document bradycardic episodes that are not excessively slow. Under such circumstances, the lower rate limit may be increased to 50 beats per minute to broaden the information base. On the other hand, in patients with demand pacemakers, a narrower range of high and low rate limits that are closer to the pacemaker firing rate may be selected. This should optimize the chance of demonstrating areas of pacemaker malfunction. Finally, in patients known to have multiple episodes of relatively rapid sinus tachycardia, an upper rate limit of greater than 120 beats per minute may be preferable.

Pauses. Pauses of up to 2.0 seconds are common in the general population and are especially common in the elderly. These pauses are usually benign. The most frequent causes of pauses are blocked (non-conducted) premature atrial contractions (PACs), sinus arrhythmia, temporary pauses in the rate of discharge of the sinoatrial node (i.e., sinus pauses) and medication-induced pauses. Pauses of longer than 2.0 seconds, especially when frequent and accompanied by episodes of significant bradycardia (less than 40 beats per minute), suggest the possibility of sick sinus syndrome.[4] Longer pauses (3.0 seconds or greater) are more likely to be symptomatic and pathologic. Documentation of the number and duration of pauses over 2.0 seconds, along with selective recording of representative strips and appropriate diary notations, helps evaluate the clinical significance of this finding.

Supraventricular Ectopic (SVE) Setting. The automatic SVE setting of 25 percent prompts the Holter monitor to record rhythm strips that demonstrate a greater than 25 percent variation in the R-R interval. This is how SVE activity such as PACs or premature junctional contractions (PJCs) is identified by the machine. With a lower SVE setting, such as 10 percent, additional PACs may be detected, but episodes of sinus arrhythmia would also probably be recorded. With an SVE setting of greater than 25 percent, a substantial number of PACs are likely to be missed. As with the other settings, certain clinical situations may prove to be problematic. Thus, the SVE setting will result in the recording of multiple rhythm strips in a patient with atrial fibrillation.

ST Level. The most controversial parameter is the automatic ST level. Ambulatory ECG monitoring has not been recommended as a tool to screen for silent myocardial ischemia in the general population,[5,6] because the detection of relatively minimal (1-mm) ST-segment depression in unselected individuals is much more likely to reflect a mechanical cause (e.g., lead position change, artifact) or a physiologic event (e.g., tachycardia, hyperventilation, sympathetic nervous system discharge) than silent ischemia.[6-9] As a result, we prefer an automatic ST-level setting of 2 mm, unless the principal reason for monitoring is to look for silent ischemia. The setting can be lowered to 1 mm for patients with a history of coronary artery disease and suspected silent myocardial ischemia. Accuracy and resolution of ST-segment deviations vary greatly with different ambulatory ECG systems. Unfortunately, not all systems are capable of providing dependable ST-segment analysis.

Tracings. Failure to record a representative tracing for the period of time indicated by the periodic storage setting automatically triggers the machine. Thus, selecting four hours for this setting guarantees that the interpreter will have at least six representative tracings to review in a 24-hour recording. If a greater number of tracings are desired, a lower number for the periodic storage (such as two hours) can be selected.

The strips-per-hour setting determines the number of strips per category per hour that are printed in the full-scale report. A setting of five usually provides sufficient tracings for review, while limiting repetitive printouts of a frequent abnormality.

PATIENT SPECIFICS

Knowledge of the patient's cardiac risk factors, medications, activity level and other medical problems permits the monitor reader to interpret ambulatory ECG recordings in light of a particular clinical application.

INDICATIONS

To provide a clinically relevant interpretation, it is essential to know why the recording was obtained. The most commonly cited indications for ambulatory ECG monitoring are listed in Table 3.

TABLE 3

Common Indications for Ambulatory ECG Monitoring Evaluation of patients with symptoms of suspected cardiac origin,

such as palpitations, dizziness and syncope Evaluation of heart disease in which the presence of arrhythmias

[1]Johnson R, Swartz MH. A simplified approach to electrocardiography. Philadelphia: Saunders, 1986:115-6. [2]Dubin D. Rapid interpretation of EKG's: a programmed course. 4th ed. Tampa, Fla.: Cover, 1989:47. [3]Grauer K, Curry RW Jr. Clinical electro-cardiography: a primary care approach. Oradell, N.J.: Medical Economics, 1987:23-7. [4]Mazuz M, Friedman HS. Significance of prolonged electrocardiographic pauses in sinoatrial disease: sick sinus syndrome. Am J Cardiol 1983;52:485-9. [5]Assey ME. Screening for silent myocardial ischemia. Am Fam Physician 1988;38(6):143-6. [6]Fisch C, DeSanctis RW, Dodge HT, Reeves TJ, Weinberg SL. Guidelines for ambulatory electrocardiography. A report of the American College of Cardiology/American Heart Association Task Force on Assessment of Diagnostic and Therapeutic Cardiovascular Procedures. J Am Coll Cardiol 1989;13:249-58. [7]Feldman RL. Ambulatory electrocardiographic monitoring: the test for ischemia in 1988? Ann Intern Med 1988;109:608-10. [8]Grauer K. Silent myocardial ischemia: dilemma or blessing? Am Fam Physician 1990;42 (5 Suppl):13S-6S,21S-8S. [9]Hammill SC, Khandheria BK. Silent myocardial ischemia. Mayo Clin Proc 1990;65:374-83. [10]Pepine CJ. Ambulant myocardial ischemia and its prognostic implications. Circulation 1990;81:1136-8. [11]Epstein SE, Quyyumi AA, Bonow RO. Myocardial ischemia--silent or symptomatic. N Engl J Med 1988;318:1038-43. [12]Gottlieb SO, Weisfeldt ML, Quyang P, Mellits ED, Gerstenblith G. Silent ischemia as a marker for early unfavorable outcomes in patients with unstable angina. N Engl J Med 1986;314:1214-9. [13]Nademanee K, Intarachot V, Josephson MA, Rieders D, Vaghaiwalla Mody F, Singh BN. Prognostic significance of silent myocardial ischemia in patients with unstable angina. J Am Coll Cardiol 1987;10:1-9. KEN GRAUER, M.D. is professor and assistant director of the family practice residency program at the University of Florida College of Medicine, Gainesville. Dr. Grauer received his medical degree from the State University of New York Health Science Center at Syracuse and completed a residency in family practice at St. Margaret Memorial Hospital, Pittsburgh. He is the principal author of four books and several teaching aids on electrocardiography and advanced cardiac life support (ACLS). He has also published numerous articles on cardiography-related topics. Dr. Grauer is a national ACLS affiliate faculty member. BRENT LEYTEM, M.D. is in private practice in Gainesville, Fla. Dr. Leyton received his medical degree from the University of Florida College of Medicine and completed a residency in family practice at the same institution.

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