Importance of the standard electrocardiogram in ambulatory (Holter) electrocardiography

Optimum lead positioning for recording bipolar atrial electrocardiograms during sinus rhythm and atrial fibrillation

BACKGROUND

To date, Holter monitoring has been predominantly utilized in the investigation and monitoring of ventricular arrhythmias and myocardial ischemia. Whether currently employed lead configurations are optimal for recording atrial electrocardiograms (ECGs) is unknown.

HYPOTHESIS

This study was undertaken to determine which conventional and novel lead configurations are optimal for recording atrial electrical activity during sinus rhythm and atrial fibrillation.

METHODS

Recordings were performed on eight healthy volunteers in sinus rhythm and four patients in atrial fibrillation. Each subject had 10 ECGs of three bipolar and three augmented unipolar leads recorded during supine rest, while rising to upright, and during standing rest, yielding a total of 60 leads (30 bipolar leads). Each tracing was inspected by two observers, and parameters such as P-wave amplitude and duration, whether the P-wave onset was clearly seen, atrial fibrillatory-wave amplitude, and amplitude of noise during standing were scored.

RESULTS

Leads recording inferiorly and leftward orientated bipoles provided the best registration of sinus P waves. The P-wave amplitude in the standard bipolar C5 lead (0.12 +/- 0.02 mV) was, however, inferior to others such as recordings between C1 and C6 positions (P-wave amplitude 0.16 +/- 0.02 mV) or from below the right clavicle to the left upper quadrant of the abdomen (0.16 +/- 0.01 mV). Optimal recording of fibrillatory waves was from different leads, such as a bipole from below the left clavicle to a low C1 position (fibrillatory wave amplitude 0.27 +/- 0.03 mV).

CONCLUSION

When Holter recordings are performed for the investigation of atrial arrhythmias, nonstandard lead configurations provide superior recording of atrial electrical activity. We advocate the use of electrodes positioned from C1 to C6, from below the left clavicle to a low C1 position, and a vertically orientated lead from the manubium to the twelfth vertebra or the xiphisternum.

Diagnostic and prognostic value of Holter-detected ST-segment deviation in unselected patients with chest pain referred for coronary angiography: a long-term follow-up analysis

OBJECTIVE

To evaluate the diagnostic and prognostic significance of ST-segment deviation detected by ambulatory Holter monitoring in unselected chest pain patients referred for coronary angiography.

METHODS

Two hundred seventy-seven patients (71% were men) who underwent coronary angiography for evaluation of chest pain were studied with 24-h ambulatory Holter monitoring within 72 h of angiography. A lumen diameter reduction of > or = 50% was considered coronary artery disease. The ST-segment deviation was defined as > or = 1-mm deviation from the baseline lasting > or = 1 min separated by a minimum of 1 min. The patients were followed up for 65 +/- 21 months (mean +/- SD) for occurrences of death, myocardial infarction, hospitalization for unstable angina, and need for revascularization.

RESULTS

Of the 277 patients, 223 (80%) had coronary artery disease. The prevalence of coronary artery disease was not significantly different in patients with (43 of 48 patients; 90%) and without (180 of 229 patients; 79%) Holter-detected ST-segment deviation. The diagnostic accuracy of Holter-detected ST-segment deviation in predicting the presence of coronary artery disease was poor (33%), with a sensitivity of 19% and a specificity of 91%. The presence of Holter-detected ST-segment deviation was not predictive of future cardiac events or death.

CONCLUSION

The ST-segment changes detected on ambulatory Holter monitoring are of limited value in identifying coronary artery disease and predicting the future adverse cardiac events or death in unselected patients with chest pain.

Metoprolol CR/XL in patients with heart failure: A pilot study examining the tolerability, safety, and effect on left ventricular ejection fraction

BACKGROUND

This study was designed to investigate the tolerability, safety, and effect on left ventricular function of a new long-acting preparation of metoprolol, metoprolol succinate (CR/XL).

METHODS AND RESULTS

Sixty patients were randomly assigned with a 2:1 ratio, drug versus placebo, administered with a gradually increasing dose of 12.5 to 150 mg of blinded medication during an 8-week period and continued for 6 months. The average peak dose achieved was 99 mg and 132 mg in the metoprolol succinate and placebo groups, respectively. The drug was well tolerated and there was no significant difference in drug withdrawals, New York Heart Association class, or quality of life assessment. The increase in left ventricular ejection fraction measure at baseline and 6 months measured by radioisotopic ventriculography was greater in the metoprolol succinate group (27. 5% to 36.3%) than in the placebo group (26% to 27.9%) (P <.015). Examination of serial Holter electrocardiographic recordings indicate that metoprolol succinate therapy was associated with a significant (P <.05) decrease in total ventricular ectopy at 8 weeks of therapy and a decrease in ventricular couplets and nonsustained ventricular tachycardia at 8 through 26 weeks of therapy. No changes were observed in plasma norepinephrine during therapy except a transitory significant (P <.05) increase in N terminal proatrial natriuretic factor at 8 weeks in the metoprolol succinate group.

CONCLUSIONS

This study indicates that treatment with metoprolol succinate for a 6-month period is safe and well tolerated and is associated with an increase in left ventricular ejection fraction and a decrease in ventricular ectopic beats.

Relative importance of electrode placement over number of channels in transient myocardial ischemia detection by Holter monitoring

To compare the efficacy of 3-channel ambulatory electrocardiographic monitoring (Holter monitoring) with 2-channel Holter monitoring in the detection of transient myocardial ischemia (TMI), channels CM2, CM5, and modified II were studied. Sixty patients with documented coronary artery disease underwent 48-hour Holter monitoring during their normal daily life, followed by exercise stress testing in the laboratory monitored by means of radionuclide ventriculography and standard 12-lead electrocardiography. Analysis revealed that 3-channel Holter monitoring identified 24 patients with a total of 205 TMI episodes and a total ischemic burden of 371.00 mV-min. By itself, CM2 would have detected only 3 patients (13% of the TMI population), 6 TMI episodes (3% of the total TMI episodes), and a 2.4 mV-min ischemic burden (0.7% of the total ischemic burden). Modified II alone would have identified 17 patients (71% of the TMI population), 160 TMI episodes (78% of the total TMI episodes), and 307.24 mV-min of the ischemic burden (82% of the total ischemic burden). The combination of CM5/modified II identified 23 patients (96% of the TMI population), 201 TMI episodes (98% of the total TMI episodes), and 370.44 mV-min of the ischemic burden (98% of the total ischemic burden). These findings suggest that the electrode placement is more important than the absolute number of channels in the detection of TMI by Holter monitoring.

Postoperative myocardial ischemia: etiology of cardiac morbidity or manifestation of underlying disease?

STUDY OBJECTIVE

To determine the relationship between postoperative ST segment changes and clinically apparent cardiac morbidity in noncardiac surgery patients.

DESIGN

Prospective, cohort study.

SETTING

General inpatient and intensive care units at a tertiary care hospital.

PATIENTS

145 high-risk noncardiac surgery patients.

MEASUREMENTS AND MAIN RESULTS

Patients were monitored for ST segment changes using ambulatory electrocardiographic (ECG) recorders from the end of the surgical period for up to the third postoperative day. Patients were evaluated for a clinically apparent cardiac event (cardiac death or myocardial infarction) by daily 12-lead ECGs, and CK-MB isoenzymes, as clinically indicated. Nine patients sustained a clinically apparent cardiac event, 7 of whom had a cardiac event during the period in which they were monitored by ambulatory ECG. All 7 patients who sustained a cardiac event during the monitoring period had at least one episode of myocardial ischemia, which persisted for a minimum of 30 minutes either prior to or at the same time of the event, with no morbidity occurring in the group of patients who had only short durations of myocardial ischemia. Three of the patients with events had continuous ST segment changes, while the other patients had transient ST segment changes.

CONCLUSIONS

These observations suggest that clinically apparent cardiac events are associated with prolonged ST segment changes detected on ambulatory ECG recorders. The cardiac ischemia leading to prolonged postoperative ST segment changes may itself result in cardiac morbidity, or it may be a reflection of underlying pathophysiology.