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C J Garratt

Publications and source records attributed to C J Garratt.

At least 37 records · Page 2Linked to original sources
PubMed1997

Reproducibility of the signal averaged P wave: time and frequency domain analysis.

OBJECTIVE: To assess the reproducibility of time and frequency domain variables derived from the signal averaged P wave. DESIGN: Longitudinal within patient study. SETTING: Regional cardiothoracic centre. PATIENTS: 20 patients (10 with documented paroxysmal atrial fibrillation and 10 normal controls) were studied on three occasions to assess the reproducibility of repeated signal averaged P wave recordings. Digital P wave recordings were made on a further 10 patients on a single occasion and the recordings signal averaged twice in order to assess the reproducibility of the averaging system itself in the absence of biological variation. MAIN OUTCOME MEASURES: P wave duration, spatial velocity, and energies contained in frequency bands from 20, 30, and 60-150 Hz of the P wave spectrum were measured after P wave specific signal averaging. Coefficients of reproducibility were calculated for paired signal averaged P waves derived by signal averaging the same digital recordings on two separate occasions, for recordings performed in the same patients immediately after each other ("back to back") and those performed one week apart. RESULTS: System reproducibility when the same digital P wave recordings were signal averaged on two separate occasions was high (< 11% for all variables). For P wave duration the coefficient of reproducibility was 11.4% for back to back recordings and 13.1% for those one week apart. The reproducibility of spatial velocity and P wave energy was low. Variation in P wave morphology was noted when successive P waves from the same subject were examined. If recordings with the same P wave morphology were analysed the reproducibility of spatial velocity and P wave energy improved but remained significantly poorer than that for P wave duration. CONCLUSIONS: P wave duration is reproducible within subjects in the short and medium term. Frequency domain and spatial velocity analysis are poorly reproducible, due more to spontaneous variation in P wave morphology than to instability of the signal averaging process. This may limit the utility of signal averaged P wave variables other than duration for the prediction of atrial arrhythmia.

Adult↗
PubMed1997

Signal averaged P wave compared with standard electrocardiography or echocardiography for prediction of atrial fibrillation after coronary bypass grafting.

OBJECTIVE: To define the clinical value of the signal averaged P wave (SAPW) and to compare it with the standard electrocardiogram (ECG), echocardiogram, and clinical assessment for the prediction of atrial fibrillation after coronary bypass grafting (CABG). DESIGN: Prospective validation cohort study. SETTING: Regional cardiothoracic centre. PATIENTS: 201 unselected patients undergoing first elective CABG were recruited over six months. Patients requiring concomitant valve surgery were excluded. MAIN OUTCOME MEASURES: Age, sex, cardiothoracic ratio, and cardioactive drugs were noted. P wave specific SAPW recordings, ECG, and M mode echocardiograms from which left atrial diameter was measured were performed within 24 hours of surgery. Filtered P wave duration (SAPWD), spatial velocity, and energy were calculated from the SAPW. From the ECG, lead II P wave duration, P terminal force in lead V1, total P wave duration, and isoelectric interval were measured. Patients had Holter monitoring for 48 hours postoperatively and daily ECGs until discharge. RESULTS: Two patients died (1%) and 10 were unsuitable for analysis (5%). Of the remaining 189, 51 (27%) had atrial fibrillation (AF) lasting > 1 hour at a mean of 2 (0.5 to 7) days after CABG. Of the variables examined, only SAPWD (AF group 148 (SD 12), v 142 (14) ms, P = 0.008) and male sex (AF group 96%, v 78%, P < 0.01) were significantly different. A prospectively defined SAPWD of > 141 ms predicted atrial fibrillation with positive and negative predictive accuracies of 34% and 83%. Logistic regression analysis identified both male sex and SAPWD as significant independent predictors of postoperative atrial fibrillation. CONCLUSIONS: Signal averaged P wave duration was a better predictor of atrial fibrillation after coronary bypass grafting than standard electrocardiographic or echocardiographic criteria. The predictive value of this test is such that it is likely to be useful in the design of prospective trials of prophylactic antiarrhythmic treatment but is of limited use using current techniques in the clinical management of individual patients.

Atrial Fibrillation↗
PubMed1996

Dynamics of QT dispersion during myocardial infarction and ischaemia.

We studied the dynamics of QT dispersion over the first few days of myocardial infarction and during coronary angioplasty. Ten patients with anterior myocardial infarction and an equal number with inferior infarction had electrocardiograms (ECGs) recorded on admission to hospital (day 1), on the subsequent 2 days (day 2, 3), and prior to discharge (day 6). Ten patients undergoing therapeutic coronary angioplasty were studied; ECGs were recorded prior to, during, and after balloon inflation. Simultaneous 12-lead ECGs were scanned into a personal computer; specially designed software skeletonised and joined each image. The images were then available for user-interactive measurement of QT dispersion. Mean (S.D.) QTc dispersion on day 1 of acute myocardial infarction was 107 (44.8) ms, rose further over the next 48 h, reaching a maximum on day 3 (QTc dispersion, 162.3 (64.8) ms, P < 0.01), and was falling by hospital discharge (QTc dispersion, 117.4 (67.4) ms). There was no difference in QT dispersion measurement during coronary angioplasty. It is unlikely that acute ischaemia plays an important role in the dynamic changes seen in QT dispersion over the first few days of myocardial infarction. These rapid changes in QT dispersion have important implications in the design of any study of QT dispersion after myocardial infarction, and in comparison of studies.

Angioplasty, Balloon, Coronary↗
PubMed1996

Reproducibility and automatic measurement of QT dispersion.

This study investigated interobserver (two observers) and intrasubject (two measurements) reproducibility of QT dispersion from abnormal electrocardiograms in patients with previous myocardial infarction, and compared a user-interactive with an automatic measurement system. Standard 12-lead electrocardiograms, recorded at 25 mm.s-1, were randomly chosen from 70 patients following myocardial infarction. These were scanned into a personal computer, and specially designed software skeletonized and joined each image. The images were then available for user-interactive (mouse and computer screen), or automatic measurements using a specially designed algorithm. For all methods reproducibility of the RR interval was excellent (mean absolute errors 3-4 ms, relative errors 0.3-0.5%). Reproducibility of the mean QT interval was good; intrasubject error was 6 ms (relative error 1.4%), interobserver error was 7 ms (1.8%), and observers' vs automatic measurement errors were 10 and 11 ms (2.5, 2.8%). However QTc dispersion measurements had large errors for all methods; intrasubject error was 12 ms (17.3%), interobserver error was 15 ms (22.1%), and observers' vs automatic measurement were errors 30 and 28 ms (35.4, 31.9%). QT dispersion measurements rely on the most difficult to measure QT intervals, resulting in a problem of reproducibility. Any automatic system must not only recognize common T wave morphologies, but also these more difficult T waves, if it is to be useful for measuring QT dispersion. The poor reproducibility of QT dispersion limits its role as a useful clinical tool, particularly as a predictor of events.

Diagnosis, Computer-Assisted↗
PubMed1996

Improved recovery of high frequency P wave energy by selective P wave averaging.

Most signal averaging processes used for cardiac signals align successive waveforms using a template matching process. In addition to achieving accurate temporal alignment of the signals, this operation must also ensure that the signal average comprises signals of the same morphology. For P wave signal averaging, systems designed for QRS complex averaging are often used, with the template acquisition window shifted to include the P wave. Theoretically, with this technique, variations in P wave morphology could reduce the high frequency content of the signal. We tested this hypothesis by comparing the performance of a selective P wave averaging system with a conventional system, based on template matching by cross-correlation over a fixed acquisition window, on identical P wave recordings from 15 subjects. The selective system identifies variations in P wave morphology and generates up to five candidate templates for averaging. Subsequently, the most frequently matched template over a 100-beat sample is used for averaging. Only P waves with the same morphology as this template are averaged. Selective averaging mainly increased the measured high frequency P wave energy, without affecting P wave duration after high pass filtering at 40 Hz, (Duration: 157(4)ms selective vs 155(4) nonselective. Energy 80-150 Hz: 1.77(0.28), microV2.s selective vs 1.61(0.3) microV2.s non selective, P < 0.01). These observations confirm that nonselective P wave averaging can reduce apparent P wave energy, especially at high frequency. Before meaningful studies of the value of frequency domain analysis of the P wave can be performed, it is important that signal averaging systems of sufficient fidelity are utilized.

Adult↗
PubMed1996

New training guidelines: what are the implications for cardiological research?

The recognition of the importance of research experience is welcomed; committed research supervisors should be identified for each trainee and research planning should start as early as possible in the traineeship. It would be welcome if employing authorities and postgraduate deans were to provide personal support for up to one year and modest research expenses for trainees undertaking research. In the absence of such support, application would need to be made to grant-giving bodies well in advance. Certain posts may need to be earmarked for the training of future clinical scientists. Academic units should regard themselves as challenged, but not necessarily threatened, by the new proposals. With appropriate consultation and involvement, and a modest allocation of funding, the overall result should enhance the quality of both service and academic communities.

Academic Medical Centers↗
PubMed1996

Effect of sequential radiofrequency ablation lesions at fast and slow atrioventricular nodal pathway positions in patients with paroxysmal atrial fibrillation.

OBJECTIVE: To examine the hypothesis that the anatomic equivalents of the fast and slow pathways identified in patients with atrioventricular (AV) nodal tachycardia may be universal and represent the principal sites of atrial input into the normal compact AV node. METHODS: 15 patients undergoing complete AV junction ablation for paroxysmal atrial fibrillation were studied. Radiofrequency energy was delivered first in the anterior "fast pathway" position so as to prolong the atrium to bundle of His (AH) interval by over 50% of baseline (protocol 1) and then to the "slow pathway" position using the anatomical technique (protocol 2). RESULTS: Ablation protocol 1 resulted in prolongation of AH interval in all patients. Subsequent lesions at the level of the coronary sinus produced complete heart block in four patients, and in five caused a further increase in AH interval above that produced by protocol 1. Four of these latter patients developed complete block after delivery of RF energy slightly anterior to the level of the coronary sinus os, as did three further patients in whom ablation at the level of the coronary sinus had no effect. In four patients complete heart block could not be achieved by protocol 2. CONCLUSIONS: A discrete anterior "fast" pathway and a posterior "slow" pathway or network of posterior pathways form the principal inputs to the compact AV node in most patients with atrial fibrillation. The absence of dual AV nodal physiology in the majority of these patients may be related to the functional properties of the individual components of this posterior network.

Aged↗
PubMed1995

QT dispersion and mortality after myocardial infarction.

QT dispersion may serve as a measure of variability in ventricular recovery time and may be a means of identifying patients at risk of arrhythmias and sudden death after acute myocardial infarction. We investigated this possibility on electrocardiograms (ECGs) recorded 2 or 3 days after infarction (early) and at least 4 weeks later (late). 163 patients who died between 1 day and 5 years after infarct were compared with an equal number of survivors matched for age and sex. 53 of the patients who died and 82 survivors also had late ECGs. There was no difference in early QT dispersion between the patients who died and the survivors (mean QTc dispersion 112.1 [SD 44.4] vs 109.9 [42.7] ms1/2). QTc dispersion fell significantly from early to late ECGs in survivors (110.9 [48.5] to 76.5 [28.8] ms1/2), but not in patients who died during follow-up (108.0 [51.0] to 98.9 [43.1] ms1/2). The difference between the groups in the mean change was significant (34.4 [55.2] vs 9.1 [60.8] ms1/2, p = 0.016). QT dispersion measured on an ECG recorded 2 or 3 days after acute myocardial infarction does not predict mortality during the next 5 years. Increased QT dispersion on ECGs recorded at least 4 weeks after infarct may be associated with subsequent mortality, but this finding must be confirmed in a prospective trial.

Aged↗
PubMed1995

Three-lead measurement of QTc dispersion.

INTRODUCTION: QTc dispersion has traditionally been calculated from all 12 leads of a standard electrocardiogram (ECG). It is possible that alternative, quicker methods using fewer than 12 leads could be used to provide the same information. METHODS AND RESULTS: We have previously shown a difference in QTc dispersion from ECGs recorded at least 1 month after myocardial infarction between patients who subsequently died and long-term survivors. In the current study, we recalculated QTc dispersion in these ECGs using different methods to determine if the observed difference in QTc dispersion measurements between the two groups, as calculated from 12-lead ECGs, persisted when using smaller sets of leads. QTc dispersion was recalculated by four methods: (1) with the two extreme QTc intervals excluded; (2) from the six precordial leads; (3) from the three leads most likely to contribute to QTc dispersion (aVF, V1, V4); and (4) from the three quasi-orthogonal leads (aVF, I, V2). For each of the 270 12-lead ECGs examined, a mean of 9.9 leads (SD 1.5 leads) had a QT interval analyzed; the QT interval could not be accurately measured in the remaining leads. Using the standard 12-lead measurement of QTc dispersion, there was a difference in the fall in QTc dispersion from early to late ECG between the groups: 9.1 (SD 60.8) msec for deaths versus 34.4 (55.2) msec for survivors (P = 0.016). This difference in QTc dispersion between early and late ECGs was maintained using either three-lead method (quasi-orthogonal leads: -2.6 [56.2] msec for deaths vs 26.9 [54.3] msec for survivors [P = 0.003]; "likeliest" leads: 8.6 [64.9] msec vs 29.5 [50.2] msec [P = 0.05]), but not when using the other two methods (precordial leads: 19.1 [55.5] msec vs 22 [50.8] msec [P = 0.76]; extreme leads removed: 9.2 [50.1] msec vs 21.8 [42] msec [P = 0.13]). CONCLUSION: QTc dispersion calculated from three leads may be as useful a measurement as QTc dispersion calculated from all leads of a standard ECG. Its advantages over the standard measurement are its simplicity and the lack of problems with lead adjustment.

Case-Control Studies↗
PubMed1995

Radiofrequency catheter ablation of Mahaim tachycardia by targeting Mahaim potentials at the tricuspid annulus.

BACKGROUND: Reentrant tachycardias associated with Mahaim pathways are rare but potentially troublesome. Various electrophysiological substrates have been postulated and catheter ablation at several sites has been described. OBJECTIVE: To assess the efficacy and feasibility of targeting discrete Mahaim potentials recorded on the tricuspid annulus for the delivery of radiofrequency energy in the treatment of Mahaim tachycardia. PATIENTS: 21 patients out of a consecutive series of 579 patients referred to one of three tertiary centres for catheter ablation of accessory pathways causing tachycardia. All had symptoms and presented with tachycardia of left bundle branch block configuration or had this induced at electrophysiological study. In all cases, the tachycardia was antidromic with anterograde conduction over a Mahaim pathway. RESULTS: 6 patients had additional tachycardia substrates (4 had accessory atrioventricular connections and 2 had dual atrioventricular nodal pathways and atrioventricular nodal reentry). After ablation of the additional pathways, Mahaim potentials were identified in 16 (76%) associated with early activation of the distal right bundle branch and radiofrequency energy at this site on the tricuspid annulus abolished Mahaim conduction in all 16 cases. In 2 patients there was early ventricular activation at the annulus without a Mahaim potential but radiofrequency energy abolished pre-excitation. In the remaining patients no potential could be found (1 patient), no tachycardia could be induced after ablation of an additional pathway (1 patient), or no Mahaim conduction was evident during the study (1 patient). During follow up (1-29 months (median 9 months)) all but 1 patient remained symptom free without medication. CONCLUSIONS: Additional accessory pathways seem to be common in patients with Mahaim tachycardias. The identification of Mahaim potentials at the tricuspid annulus confirms that most of these pathways are in the right free wall and permits their successful ablation and the abolition of associated tachycardia.

Adolescent↗
PubMed1995

Effect of low dose sotalol on the signal averaged P wave in patients with paroxysmal atrial fibrillation.

OBJECTIVE: To investigate the effects of low dose sotalol on the signal averaged surface P wave in patients with paroxysmal atrial fibrillation. DESIGN: A longitudinal within patient crossover study. SETTING: Cardiac departments of a regional cardiothoracic centre and a district general hospital. PATIENTS: Sixteen patients with documented paroxysmal atrial fibrillation. The median (range) age of the patients was 65.5 (36-70) years; 11 were men. MAIN OUTCOME MEASURES: Analysis of the signal averaged P wave recorded from patients not receiving antiarrhythmic medication and after 4-6 weeks' treatment with sotalol. P wave limits were defined automatically by a computer algorithm. Filtered P wave duration and energies contained in frequency bands from 20, 30, 40, 60, and 80 to 150 Hz of the P wave spectrum expressed as absolute values (P20, P30, etc) and as ratios of high to low frequency energy (PR20, PR30, etc) were measured. RESULTS: No difference in P wave duration was observed between the groups studied (mean (SEM) 149 (4) without medication and 152 (3) ms with sotalol). Significant decreases in high frequency P wave energy (for example P60: 4.3 (0.4) v 3.3 (0.3) microV2.s, P = 0.003) and energy ratio (PR60: 5.6 (0.5) v 4.7 (0.6), P = 0.03) were observed during sotalol treatment. These changes were independent of heart rate. CONCLUSIONS: Treatment with low dose sotalol reduces high frequency P wave energy but does not change P wave duration. These results are consistent with the class III effect of the drug and suggest that signal averaging of the surface P wave may be a useful non-invasive measure of drug induced changes in atrial electrophysiology.

Adult↗
PubMed1995

Use of lead adjustment formulas for QT dispersion after myocardial infarction.

OBJECTIVE: To determine whether lead adjustment formulas for correcting QT dispersion measurements are appropriate in patients after myocardial infarction. DESIGN: Retrospective analysis of QTc dispersion measurements in 461 electrocardiograms (ECGs). Data are presented as uncorrected QTc dispersion "adjusted" for a number of measurable leads and coefficient of variation of QTc intervals for ECGs in which between six and 12 leads had a QT interval that could be measured accurately. PATIENTS: Patients were drawn from the placebo arm of the second Leicester Intravenous Magnesium Intervention Trial. Some 163 patients who subsequently died and an equal number of known survivors had ECGs recorded on day 2 or 3 of acute myocardial infarction. ECGs were also available in 135 of these patients from at least 1 month postinfarct. RESULTS: The most common lead in which a QT interval measurement was omitted was aVR (n = 176), the least common lead was V3 (n = 13). The longest QTc interval measured was most usually in lead V4 (n = 72) and the shortest in lead V1 (n = 67). As the number of measurable leads decreased there was a small, nonsignificant increase in QTc dispersion from 12 lead to eight lead ECGs (mean (SD) 100 (35.5) v 109.5 (47.9) ms). Lead adjusted QTc dispersion (QTc dispersion/square root of the number of measurable leads) showed a large, significant increase when the number of measurable leads decreased from 12 to eight (28.9 (10.3) v 38.7 (16.1) ms, P < 0.001). A similar trend was seen for coefficient of variation of QTc intervals (standard deviation of QTc intervals/mean QTc interval 64.3 (2.19) v 8.45 (3.94)%, P < 0.001). CONCLUSIONS: Lead adjustment formulas for QT dispersion are not appropriate in patients with myocardial infarction. Large differences in lead adjusted QTc dispersion are produced, dependent on the number of measurable leads, for very small differences in QTc dispersion. It is recommended that QT dispersion is presented as unadjusted QT and QTc dispersion, stating the mean (SD) of the number of leads in which a QT interval was measured.

Electrocardiography↗
PubMed1995

Management of hypertension in general practice: agreements with and variations from the British Hypertension Society guidelines.

A random sample of 200 East Anglian general practitioners was surveyed to establish current trends in the management of hypertension, including measurement of blood pressure (BP), patient investigation, treatment and follow-up. A total of 125 (62.5%) completed questionnaires was returned. Responses were used to assess the range of self-reported management practice and the extent of conformity with the British Hypertension Society guidelines. Although there was a broad spectrum of reported practice, many respondents adhered closely to the guidelines in relation to BP measurement, use of non-pharmacological treatment, treatment goals, choice of drug and patient investigation. Not surprisingly, the greatest disparity between reported and recommended practice occurred in areas where guidelines have only recently become available: treatment of isolated systolic hypertension and of the elderly hypertensive. Here, the survey provides a useful baseline against which to monitor future changes in management.

Aged↗