Ray J. Wainwright

Detection of pathological tachycardia by analysis of electrogram morphology.

Pacemaker recognition of pathological tachycardia relies on heart rate analysis. This can lead to misdiagnosis when sinus tachycardia exceeds the preset tachycardia response trigger rate. We have explored a method for automatic tachycardia diagnosis by analysis of bipolar endocardial electrogram morphology.

Determining Optimal Atrial Sensitivity Settings for Single Lead VDD Pacing: The Importance of the P Wave Histogram

In order to provide atrioventricular synchrony, VDD pacing systems require reliable atrial sensing. Variations in atrial signals with exercise and daily activities may lead to undersensing, with loss of physiological pacing. The aim of this study was to determine, for a single lead VDD pacing system, the maximal variation in atrial signals in order to facilitate optimal programming of atrial sensitivity. Fifteen patients underwent implantation of a Vitatron Saphir VDD pacemaker with a Vitatron Brilliant electrode. At a mean (± SD) follow‐up of 67.3 ± 38.8 days, resting P wave amplitude was compared with the P wave amplitude histogram obtained from the pacemaker, which recorded atrial signals over the preceding 30 days. Resting P wave amplitude was also compared with P wave amplitudes during variations in posture, respiration, and during exercise. P wave amplitude showed great variation with changes in posture and respiration, but there was no consistent increase or reduction. During exercise, the mean P wave amplitude fell hy 36.6%± 31.3% compared with the resting value (P < 0.05). During daily activities, 22.6% of P wave amplitudes recorded on the P wave histogram were < 0.5 mV. The smallest P wave amplitudes were detected by the P wave histogram in 11 (79%) of 14 patients. These data suggest that atrial sensitivity may need to be programmed higher than that indicated by single readings or exercise. The P wave amplitude histogram is the most reliable indicator of the smallest atrial signal and should be used to opthnize atrial sensitivity settings.

Non-invasive cardiac investigations in patients awaiting renal transplantation.

Patients with chronic renal failure undergoing renal transplantation have a high prevalence of cardiovascular disease. Invasive investigation may identify those at risk of cardiac death during or after renal transplantation, but which patients should undergo cardiac catheterization is currently not clear. In 95 patients awaiting renal transplantation we assessed the ability of echocardiography and exercise electrocardiography to identify patients at risk of cardiac death. Echocardiography identified impaired left ventricular (LV) systolic function in 20%, severe in 8%. Of the patients with severe LV dysfunction, 25% died before transplantation. Of those undergoing exercise electrocardiography, 44% did not achieve 85% of maximum predicted heart rate. No coronary artery disease requiring intervention was identified by exercise testing. These findings indicate that echocardiography, but not exercise electrocardiography, should be part of the assessment for renal transplantation.

Development and validation of a Bayesian index for predicting major adverse cardiac events with percutaneous transluminal coronary angioplasty

OBJECTIVE To create a risk model for predicting major adverse complicating events of percutaneous transluminal coronary angioplasty (PTCA), and to test the accuracy of the model on a prospective cohort of patients SETTING Tertiary cardiac centre METHODS Available software can predict probabilities of events using Bayess theorem. To establish the accuracy of these predictive tools, a Bayes table was created to evaluate major adverse complicating events (MACE)—death, emergency coronary artery bypass grafting (CABG), or Q wave infarct occurring during the in-patient episode—on the first 1500 patients in the department PTCA database (development group); the predictive value of this model was then tested with the subsequent 1000 patients (evaluation group). The following probabilities were assessed to determine their association with MACE: age, sex, left ventricular function, American Heart Association lesion morphology classification, cardiogenic shock, previous CABG, diabetes, hypertension, multivessel PTCA. MAIN OUTCOME MEASURES To establish the discriminatory ability of the predictive index, calibration plots and receiver operating characteristic (ROC) curves were obtained to compare the development and evaluation groups. RESULTS The ROC curve plotted to determine the discriminatory value of the Bayesian table created from the development group (n = 1500) in predicting MACE in the evaluation group (n = 1000) showed a moderately predictive area under the curve of 0.76 (SEM 0.07). This predictive accuracy was confirmed with separately constructed calibration plots. CONCLUSIONS Accurate predictions of MACE can be identified in populations undergoing percutaneous intervention. The database used allows operators to obtain consent from patients appropriately from their own experience rather than from other published data. If a national PTCA database existed along similar lines, individual operators and interventional centres could compare themselves with nationally available data.

Angiographic and clinical restenosis following the use of long coronary Wallstents.

This study assessed clinical and angiographic restenosis following the deployment of the long coronary Wallstent. Between May 1995 and June 1997, 182 Wallstents were deployed in 162 vessels in this unit. Forty‐eight percent had an unstable coronary syndrome and 94% had AHA grade B or C lesions. The mean lesion length was 37 ± 20 mm and the mean stent length was 48 ± 20 mm. The procedural success rate was 99% and the primary success rate was 93%. Six in‐patients suffered subacute stent thrombosis, the majority being in the era of anticoagulation rather than antiplatelet regimes. Seventy‐three percent remained free of major adverse clinical events in the follow‐up period, but 41% had angiographic restenosis. The Wallstent can be deployed in complex lesions with a high primary success rate and an acceptably low restenosis rate. The optimal management of in‐stent restenosis remains to be defined. Cathet. Cardiovasc. Intervent. 48:287–293, 1999.

Safety and Efficacy of Unprotected Left Main Coronary Artery Stenting

To the Editor: We read with interest the report by Tan et al1 of long-term clinical outcomes after unprotected left main coronary artery (LMCA) revascularization in a series of 279 patients from 25 contributing centers in the ULTIMA Registry. Forty-six percent of these patients were deemed high surgical risk. The Veterans Administration Cooperative Study confirmed the benefit of coronary artery bypass graft (CABG) surgery for the treatment of LMCA disease compared with medical therapy.2 Since then, there …