Current usefulness of the signal-averaged electrocardiogram

Qt Dispersion and Signal-Averaged Electrocardiogram in Hemodialysis and Capd Patients

Objective

The aim of this study was to compare QT dispersion (QTd) and signal-averaged electrocardiogram (SA-ECG) parameters that may predict risk of malignant arrhythmias in patients on hemodialysis (HD), on continuous ambulatory peritoneal dialysis (CAPD), and in controls.

Setting

Controlled cross-sectional study in a tertiary- care setting.

Patients

28 HD (M/F 18/10; mean age 32 ± 9 years), 29 CAPD (M/F 17/12; mean age 34 ± 10 years), and 29 healthy controls (M/F 17/12; mean age 32 ± 8 years) were included.

Interventions

On ECG, minimum (QTmin) and maximum (QTmax) QT duration and their difference (QTd) were measured. In SA-ECG, duration of filtered QRS, HFLA signals less than 40 μV, and RMS voltage (40 ms) were also measured.

Results

Higher serum Ca2+ and lower K+ levels were found in CAPD compared to HD. All QT parameters were increased in HD and CAPD compared to controls. QT dispersion was significantly prolonged in HD compared to CAPD. In HD, QTd was correlated with left ventricular (LV) mass index ( r = 0.53, p = 0.004), but not in CAPD ( r = -0.09, p = 0.63). QT dispersion was significantly prolonged in patients with LV hypertrophy compared to patients without hypertrophy on HD (68 ± 18 ms vs 49 ± 18 ms, p = 0.008). In the analysis of SA-ECG, 3 of the 28 (11%) HD and 2 of the 29 (7%) CAPD patients had abnormal late potentials. Patients on HD and CAPD had significantly higher filtered-QRS duration compared to controls (105 ± 15 ms and 104 ± 12 ms vs 95 ± 5 ms, respectively, p = 0.04). Patients with LV hypertrophy had higher filtered-QRS duration compared to patients without hypertrophy (109 ± 12 ms vs 95 ± 8 ms, p < 0.001).

Conclusion

Dialysis patients had prolonged QTd and increased filtered-QRS duration in SA-ECG compared to controls. Patients on HD had longer QTd than patients on CAPD. QTd has been correlated to LV mass index in HD, but not in CAPD. This difference might be due to the effect of different dialysis modalities on electrolytes, especially the higher serum Ca2+ levels.

Efficacy of signal-averaged electrocardiography in the young orthotopic heart transplant patient to detect allograft rejection

Endomyocardial biopsy is the gold standard survey for cardiac graft rejection. Signal-averaged electrocardiography (SAECG) identifies slowly conducting, diseased myocardium. We sought to determine whether SAECG is a sensitive, noninvasive transplant surveillance method in the young.Ninety-four SAECGs recorded prior to biopsy in 20 young transplant (OHT) patients and those from 15 healthy age-matched controls (CTL) were analyzed. In the OHT group, 56 no-rejection (NOREJ) (ISHLT grades 0 or 1 A) and 37 acute rejection (REJ) (ISHLT grades IB, 2, and 3A) SAECGs were compared, SAECGs were filtered at 40-255 Hz. Total QRS duration (QRSd), duration of terminal low amplitude of QRS under 40 microV (LAS), and root mean square amplitude of terminal 40 msec of QRS (RMS40) were compared.SAECGs were significantly different in CTL vs NOREJ but not in NOREJ vs REJ: QRSd, 81.7 +/- 8, 107.2 +/- 18.4, and 112.3 +/- 21.6 msec, respectively; LAS, (18 +/- 5.8, 23.6 +/- 10.7, and 27 +/- 14.8 msec, respectively; and RMS40, (169.3 +/- 100.4, 68 +/- 48.8, and 57.5 +/- 45.6 microV, respectively. Children following OHT exhibited significant differences in the SAECG compared to controls. Differences between the NOREJ and REJ groups were negligible. Therefore, SAECG may not be effective in detecting OHT rejection in the young.

Late potentials in female triathletes before and after prolonged strenuous exercise

The objectives of this study were to evaluate the prevalence of late potentials (LP) in female triathletes before and after prolonged strenuous exercise (PSE), and to determine whether LP are related to greater left ventricular (LV) dimensions and/or mass. Thirteen female triathletes were examined immediately before (Pre), one hour after (Post), and 24 to 48 hours after PSE (Recovery) using signal-averaged electrocardiography (SAECG). Late potentials were evaluated by two or more standard SAECG anomalies. Left ventricular dimensions and mass were measured Pre using two-dimensional echocardiography. Results revealed that no significant differences existed between Pre, Post, and Recovery in the SAECG parameters. Four athletes displayed LP during Pre. The incidence of LP during did not increase Post. There were no significant relationships between LV dimensions or mass and SAECG parameters. In conclusion, a small portion of female triathletes display LP before and after PSE, which are not worsened by PSE nor related to increased LV dimensions and/or mass.

Effects of half ironman competition on the development of late potentials

OBJECTIVES

The primary purpose was to evaluate the prevalence of late potentials (LPs) in triathletes before and after a half ironman triathlon. The secondary purpose was to examine whether LPs are the electrocardiographic expression of a greater myocardial mass.

METHODS

Nine asymptomatic male triathletes (mean age +/- SD, 32 +/- 5 yr) were examined using signal-averaged ECG (SAECG) 48-72 h before (PRE), immediately after (POST), and 24-48 h after the completion (RECOVERY) of a half ironman triathlon. Late potentials were considered to be present if two of the following SAECG anomalies were observed: 1) a prolonged filtered QRS (/QRS) complex (> or = 114 ms), 2) a lengthened low amplitude signal (LAS) duration (>38 ms), and/or 3) a low root mean square (RMS) voltage of the last 40 ms of the fQRS (<20 microV). Left ventricular dimensions were determined at PRE using M-mode echocardiography.

RESULTS

There were no significant differences between PRE, POST, and RECOVERY in the fQRS duration, the LAS duration, or the RMS voltage. Two athletes displayed a single SAECG abnormality during PRE and two SAECG anomalies (i.e., LPs) during POST. Late potentials remained in one of the two athletes during RECOVERY. A moderate relationship existed between fQRS and left ventricular mass (r = 0.67, P < 0.05).

CONCLUSIONS

Ultra-endurance training and/or events do not lead to LPs in the majority of triathletes who do not possess ventricular arrhythmias. However, a small subset of triathletes do display SAECG anomalies, which are augmented by an ultra-endurance event and may persist even after recovery from the event. Left ventricular mass does not affect overall SAECG parameters.

Risk stratification after acute myocardial infarction in the reperfusion era

Historically, risk stratification for survivors of acute myocardial infarction (AMI) has centered on 3 principles: assessment of left ventricular function, detection of residual myocardial ischemia, and estimation of the risk for sudden cardiac death. Although these factors still have important prognostic implications for these patients, our ability to predict adverse cardiac events has significantly improved over the last several years. Recent studies have identified powerful predictors of adverse cardiac events available from the patient history, physical examination, initial electrocardiogram, and blood testing early in the evaluation of patients with AMI. Numerous studies performed in patients receiving early reperfusion therapy with either thrombolysis or primary angioplasty have emphasized the importance of a patent infarct related artery for long-term survival. The predictive value of a variety of noninvasive and invasive tests to predict myocardial electrical instability have been under active investigation in patients receiving early reperfusion therapy. The current understanding of the clinically important predictors of clinical outcomes in survivors of AMI is reviewed in this article.

Effect of hemodialysis on the signal-averaged electrocardiogram

The presence of late potentials (LPs) on signal-averaged electrocardiography (SAECG) is predictive of ventricular tachycardia. The effect of hemodialysis (HD) on SAECG has not been well studied. SAECG was evaluated in 28 patients with chronic renal failure immediately before and after HD. In each SAECG, QRS duration, low-amplitude signal duration (LASd), and root-mean-square voltage of the terminal 40 milliseconds of the QRS (RMS40) were measured. To evaluate the effect of fluid removal on SAECG, the last 12 patients were studied during two different HD sessions, one with and one without fluid removal. Two-dimensional echocardiography was performed before and after HD on these 12 patients. At baseline, four patients met the criteria for LPs on SAECG. Only one patient met the criteria for LPs on SAECG after HD. After HD, the mean LASd decreased (28.3 +/- 12.9 to 24.9 +/- 10.1 milliseconds; P = 0.041) and RMS40 increased (63.0 +/- 56.9 to 79.0 +/- 59.2 microV; P = 0. 006). Among the 12 patients who underwent HD with and without fluid removal, left ventricular end-diastolic dimension decreased with (5. 4 +/- 0.6 to 5.1 +/- 0.6 cm; P = 0.024) but not without fluid removal (5.2 +/- 0.3 to 5.1 +/- 0.4 cm; P = not significant [NS]). RMS40 improved with (43.8 +/- 23.1 to 53.2 +/- 22.6 microV; P = 0. 03) but not without fluid removal (51.0 +/- 26.5 to 51.5 +/- 24.2 microV; P = NS). A significant negative correlation was found between change in body weight and change in RMS40 parameter (r = 0. 456; P = 0.0381). SAECG parameters are abnormal in a significant proportion of patients with chronic renal failure and improve with HD despite electrolyte and other proarrhythmic changes. Decreased left ventricular dimension because of fluid removal during HD is one possible explanation for this improvement.

An evaluation of serum troponin T and signal-averaged electrocardiography in predicting electrocardiographic abnormalities after blunt chest trauma

OBJECTIVE

Despite multiple inquiries, there are no available tests to definitively detect blunt myocardial injury. The evaluation of patients with chest wall injuries without other indications for intensive care unit (ICU) admission has ranged from a single emergency department electrocardiogram (ECG) to 72 hours of continuous electrocardiographic monitoring. Recently, signal-averaged ECG and serum cardiac troponin T have demonstrated clinical utility in the evaluation of ischemic heart disease. The purpose of this study is to determine the ability of these diagnostic tests to predict the occurrence of significant electrocardiographic rhythm disturbances for patients with chest wall injuries and no other indication for ICU admission.

METHODS

We prospectively evaluated 71 consecutive adult patients admitted to a regional Level I trauma center with chest wall injuries not requiring ICU admission. We obtained admission signal-averaged ECG, serum troponin T level, standard ECG, and creatine phosphokinase (CPK-MB) level. Patients received continuous electrocardiographic monitoring, follow-up 12-lead electrocardiography, and serial monitoring of troponin and CPK-MB. Echocardiography was performed for patients with abnormal CPK-MB levels. Electrocardiographic events were graded as normal, abnormal but clinically insignificant, or clinically significant. Multiple stepwise logistic regression analysis was used to evaluate predictors for the development of clinically significant electrocardiographic events.

RESULTS

On admission, 17 of 71 patients (23.9%) had normal sinus rhythm; 13 (18.3%) had a clinically significant finding. For 50 patients, follow-up ECG was abnormal; for 26, the findings were clinically significant. Of 17 patients with normal initial ECGs, 7 (41%) developed a clinically significant abnormality. Six patients received intervention for ECG findings. Eleven of 71 patients (16%) had positive troponin T; 5 of 71 (7%) had positive CPK-MB; 15 of 71 (21%) had positive signal-averaged ECG; and 4 of 13 had positive echocardiograms. Initial electrocardiographic abnormalities and a troponin T level > 0.20 microg/L were the only variables found to predict clinically significant electrocardiographic events. Sensitivity and specificity of troponin T in predicting clinically significant abnormalities were 27 and 91%, respectively.

CONCLUSIONS

1. The best predictors for the development of significant electrocardiographic changes are an admission ECG abnormality and an elevated serum troponin T level. 2. Both tests have high specificity with low to moderate sensitivity. 3. Patients with normal ECGs may develop clinically significant events. 4. CPK-MB and echocardiograms continue to be poor predictors of significant electrocardiographic events.

Value and limitations of noninvasive assessment of syncope

The noninvasive assessment of patients who present with syncope is based on a thorough, complete history and physical examination. The history requires close attention to precipitating events and the description of the spell. Often, patients are poor historians with regard to symptoms leading up to and following the episode of syncope. Therefore, it is important to interview individuals who observed the spell to improve the accuracy of the history and sort out whether or not the spell was due to cardiogenic syncope, vasodepressor syncope, or a neurologic disorder. Carotid sinus massage is a useful procedure that can be performed during the routine physical examination, identifying patients who are at increased risk for carotid sinus syncope because of hypersensitivity of the carotid sinus. The clinician must be careful to attribute the clinical syncope to carotid sinus hypersensitivity only when the spell induced at the time of carotid massage reproduces the clinical spell. Routine laboratory tests are commonly performed, although the blood tests rarely yield information to confirm the cause of syncope. The routine ECG is often helpful identifying abnormalities of rhythm, conduction, or morphology that give a clue as to the cause for the patient's syncope. The most helpful aspect of ECG recording is to obtain a recording during an episode of syncope when exact correlation can be made between the ECG findings and the patient's symptoms. Recording the ECG during the spell can be achieved using 24-hour ambulatory monitoring, an event recorder, or a memory loop recorder. Twenty-four-hour ambulatory monitoring is useful in patients who have frequent spells that would be expected to be recorded during 1 or 2 days of monitoring. These individuals need to have a non-life-threatening spell and therefore be safe to evaluate as an outpatient. The event recorder and loop memory recorder have proved extremely helpful in evaluating spells that occur too infrequently to be recorded by 24-hour or 48-hour ambulatory monitoring. The nature of these recording devices does require that the patient or a companion be able to activate the monitor at the time of symptoms. If a patient experiences syncope but is unable to activate the device, the important information as to what the rhythm was doing at the time of symptoms is lost. The implantable loop recorder should prove to be uniquely advantageous by allowing extended ECG recording with the device activated by the patient or companion recording 20 minutes before and 4 minutes after device activation. Signal-averaged electrocardiography is most helpful in assessing patients with ischemic heart disease with a substrate capable of supporting a reentrant ventricular arrhythmia. This test should be used in combination with other historical or laboratory predictors of arrhythmic events such as history of myocardial infarction or abnormal ventricular function assessed by echocardiography. In this setting, the signal-averaged ECG helps to identify patients at increased risk for ventricular tachycardia as the cause of syncope who thus may benefit from electrophysiologic testing.

Failure of signal-averaged electrocardiography with use of time-domain variables to predict inducible ventricular tachycardia in patients with conduction defects

OBJECTIVE

To extend the application of signal-averaged electrocardiography (SAECG) to patients with ventricular conduction defects by analysis of electrocardiographic (ECG) time-domain variables.

MATERIAL AND METHODS

In 123 consecutive patients with a QRS duration of 118 ms or more on a resting ECG and without evidence of an accessory pathway, SAECG was done at the time of electrophysiologic (EP) study. For EP testing, up to three stimuli were delivered during two paced drives from two right ventricular sites. A "positive" EP result was defined as monomorphic ventricular tachycardia that lasted for more than 30 seconds or necessitated intervention. Data were obtained for four time-domain variables. All variables were analyzed for differences between patients with EP-positive and those with EP-negative results.

RESULTS

Unfiltered QRS duration was the only time-domain ECG variable that was statistically different (P = 0.02) between patients with EP-positive and those with EP-negative results (141.3 and 147.8 ms, respectively); this difference persisted when patients with right bundle branch block were excluded from analysis. This finding is the opposite of previously reported observations. When only patients with ischemic heart disease were analyzed, no SAECG variables were significantly different between patients with inducible ventricular tachycardia and those without it.

CONCLUSION

High-resolution ECG time-domain variables cannot be used to predict inducibility of ventricular tachycardia during EP testing in patients with conduction defects.