Clinical Use of Holter ECG Recordings

Luigi De Ambroggi

Dept. of Cardiology,Istituto Policlinico San Donato, University of Milan, Italy

Correspondence: L De Ambroggi, Istituto Policlinico San Donato, 20097 San Donato Milanese, Italy.
E-mail: luigi.deambroggi@unimi.it, phone/fax +39.02.52774520

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1.    Introduction

As early as 1949 Holter demonstrated the ability to transmit the ECG by means of radio frequencies. Further development by Holter and coworkers led to the introduction of the first magnetic tape recording unit. Over the subsequent decades, the usefulness of this technique was demonstrated by a large body of clinical investigations.

Current technologies allow for direct recording of the ECG signals in a digital format using solid-state recording devices. The direct digital recording avoids all of the biases introduced by the mechanical features of tape recording devices and the problems associated with recording data in an analog format, which requires A-D conversion before analysis. ECG signals can be recorded at up to 1000 sample per second, allowing for accurate reproduction of the ECG, necessary to perform sophisticated analysis and signal averaging.

Historically, long-term ECG or Holter-ECG (H-ECG) became initially an important clinical diagnostic test for the recording of cardiac tachyarrhythmias and bradyarrhythmias and later on for evaluation of ST segment changes (myocardial ischemia). More recently H-ECG was used for analysing dynamics of ventricular repolarization and for the autonomic nervous system assessment.

According with the ACC/AHA Guidelines for ambulatory electrocardiography (1999), the major uses of H-ECG are the following.

2.  Assessment of Symptoms of Possible Cardiac Origin

H-ECG is the most widely used method to evaluate symptoms suggestive of cardiac rhythm disturbances (palpitations, dizziness, presyncope). The ECG recording during the precise time that the symptoms are occurring represents crucial information to relate symptoms to arrhythmias. There are different possibilities. Typical symptoms may occur with the simultaneous documentation of cardiac arrhythmias; symptoms may occur even in absence of rhythm disturbances; a patient may remain asymptomatic during cardiac arrhythmias documented on H-ECG (equivocal value); negative test, i.e. no symptoms, no arrhythmias.

H-ECG is also useful in diagnosis of type of arrhythmias and in identification of the likely underlying mechanism (particularly for supraventricular arrhythmias).

As concerns ischemic heart disease, H-ECG is the only available method to assess the presence and severity of myocardial ischemia during daily life. However, ischemic changes in Holter recording are present in only 40-60% of patients with coronary artery disease and positive exercise tests. For this reason and for the high day-to-day variability in ischemic changes, H-ECG cannot be used as screening tool for detecting coronary artery disease or for evaluating severity of ischemia in individual patients. Thus, H-ECG is usually not indicated for evaluation of symptoms suggesting myocardial ischemia, with few exceptions: patients with symptoms suggesting vasospastic, Prinzmetal angina, in whom exercise test is negative; patients with known coronary disease, but atypical chest pains. Moreover, H-ECG has been shown to be a useful and reliable tool to assess the efficacy of various antiischemic drugs.

3.  Prognostic assessment and risk stratification

Ventricular Arrhythmias

Postmyocardial infarction patients have an increase risk of sudden death, and H-ECG is usually performed before hospital discharge. Several studies performed before the advent of thrombolysis have demonstrated that presence of ventricular arrhythmias (frequent PVC and high grade ventricular ectopy, as repetitive, multiform PVC or VT) has been associated with a higher mortality rate among MI survivors (Bigger et al. 1984). Even in thrombolytic era, GISSI II study confirmed that frequent and complex ventricular arrhythmias confer an independent 2 to 3-fold increased risk of all cause mortality and 3 to 4-fold increased risk for sudden death (Maggioni et al.,1993).

H-ECG recording was also used to reveal the occurrence of ventricular arrhythmias for risk evaluation of future cardiac events in patients with various heart diseases, mainly dilated cardiomyopathy, hypertrophic cardiomyopathy, congestive heart failure.

Heart Rate Variability (HRV) Analysis

Time and frequency domain analysis of HRV is today a well recognized technique capable of providing information on autonomic modulation of the sinus node and of stratifying risk, particularly after myocardial infarction (Task Force ESC/NASPE, 1996).

 Many studies showed that patients with decreased HRV have a higher risk of arrhythmic events and all-cause mortality. In the ATRAMI trial HRV was found to be a powerful predictor of prognosis independent of ventricular arrhythmias or LV function (La Rovere et al., 1998).

Heart Rate Turbulence (HRT)

Recently, Schmidt proposed a new method for risk prediction based on the analysis of fluctuations of sinus rhythm cycle length after premature ventricular beats on ECG-Holter recording. Such fluctuations named “heart rate turbulence” were defined by two numerical parameters: turbulence onset (TO) and turbulence slope (TS), which were found to contain independent information on the risk of subsequent mortality. The 2 descriptors were tested, in both univariate and multivariate analysis, in two large independent populations of post-myocardial infarction patients (MPIP and EMIAT trials). TS was the more powerful stratifier of mortality in EMIAT and the second most powerful stratifier in MPIP (Schmidt et al., 1999).

More recently, HRT was calculated on the data-base of ATRAMI and was found to correlate with baroreflex sensitivity and HRV (Ghuran et al., 2002)). The study confirmed the independent value of HRT in predicting fatal and non-fatal cardiac arrest in a low risk post-myocardial infarction population. Moreover the composite autonomic index, including baroreflex sensitivity, HRV, TO, TS, provides a comprehensive assessment of cardiac autonomic reflexes.

Repolarization Dynamics

In normal subjects repolarization duration is dependent on heart rate. In pathological conditions, as long QT syndrome, an altered QT interval heart rate dependency was found (Merri et al., 1992). QT variability has been found to identify patients with sudden cardiac death in a mixed patient population referred for electrophysiologic studies (Atiga et al., 1998).

Recently, Perkiomaki et al. using 12-lead H-ECG recording found that, despite similar HRV, QT variability and variability of T wave complexity (defined by principal component analysis of the 12 leads) are significantly increased in long QT syndrome patients compared with unaffected family members, suggesting that disturbances in temporal dynamics of repolarization and repolarization complexity possibly increase vulnerability to arrhythmias (Perkiomaki et al., 2002).

Viitasalo studied the dynamic variations of T peak-end (TPE) interval, as an index of transmural dispersion of repolarization, in patients with the congenital long QT syndrome. A different behavior of TPE in relation to heart rate was observed in LQT1 and LQT2 patients (Viitasalo et al., 2002).

ST Changes

The possibility of reliably detecting ischemic ST abnormalities on H-ECG led to many clinical studies evaluating the prevalence and prognostic significance of myocardial ischemia (silent and symptomatic) in patients with coronary heart disease. It has been well documented that 60-80% of ischemic episodes detected are asymptomatic (Schang et al., 1997) and identify the high risk patients. Several studies indicated that residual ischemia detected by H-ECG in post-myocardial infarction patients carries a strong predictive value for future events (Gill et al., 1996).

4.  Evaluation of Therapeutic Interventions

Antiarrhythmic Therapy

H-ECG has been widely used to evaluate the effects of antiarrhythmic therapy. However, several limitations affect its usefulness, specifically: day-to-day variability in the frequency and type of arrhythmias in many patients, lack of correlation between arrhythmias suppression after an intervention and subsequent outcome, uncertain guidelines for the degree of suppression required to demonstrate an effect.

H-ECG was compared with serial electrophysiological studies in trials examining patients who survived ventricular tachycardias or VF in respect to the capacity of predicting antiarrhythmic drug efficacy. In the ESVEM study, a large, randomized trial directly comparing electrophysiologic study with Holter monitoring, H-ECG led to predictions of antiarrhythmic drug efficacy more often than did electrophysiologic study (Mason, 1993). However, no significant difference was found between the 2 study groups in the actuarial probability of recurrence of arrhythmias and mortality over a 6-year follow-up period.

H-ECG is useful for documenting an adequate control of the ventricular rate in patients with continuous atrial arrhythmias, as chronic atrial fibrillation, because it provides data on the heart rate during the patient’s typical daily activities.

Assessment of PM and ICD Function

Over the last decade the function and diagnostic capabilities of pacemakers and ICDs have become more and more complex and sophisticated. Thus, the Holter function is performed by the device itself, and usually H-ECG recording is not necessary in the routine follow-up of patients with PM or ICD. However, H-ECG can be a useful adjunct in a more subtle regulation of the device function in particular cases.

5.  Conclusion

In recent years, the great technological advances in Holter recording and analysis have enlarged the field of clinical applications and pathophysiological investigations. Further improvement of diagnostic and prognostic capabilities of the method will result from non-conventional measurements of Holter ECG recording.

References

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