A. Fitzpatrick

The use of the Hilbert transform in ECG signal analysis

This paper presents a new robust algorithm for QRS detection using the first differential of the ECG signal and its Hilbert transformed data to locate the R wave peaks in the ECG waveform. Using this method, the differentiation of R waves from large, peaked T and P waves is achieved with a high degree of accuracy. In addition, problems with baseline drift, motion artifacts and muscular noise are minimised. The performance of the algorithm was tested using standard ECG waveform records from the MIT-BITH Arrhythmia database. An average detection rate of 99.87%, a sensitivity (Se) of 99.94% and a positive prediction (+P) of 99.93% have been achieved against study records from the MIT-BITH Arrhythmia database. A detection error rate of less than 0.8% was achieved in every study case. The reliability of the proposed detector compares very favorably with published results for other QRS detectors.

Vasovagal reactions may occur after orthotopic heart transplantation

OBJECTIVESnThis study evaluated the ability of patients to manifest vasovagal reactions after orthotopic heart transplantation.nnnBACKGROUNDnParadoxic stimulation of left ventricular baroreceptors may be the afferent limb of the vasovagal reflex in humans. Orthotopic heart transplantation causes surgical denervation of these receptors and would therefore be expected to abolish the vasovagal reflex.nnnMETHODSnTo attempt to confirm this hypothesis, 10 patients with orthotopic heart transplantation underwent both head-up tilt testing while resting on a saddle support and testing for parasympathetic innervation of the donor heart before and after atropine infusion. Native and donor heart sinus rates were monitored by using an esophageal pill electrode throughout tilting and during parasympathetic testing.nnnRESULTSnUnexpectedly, seven patients had vasovagal responses at saddle support tilt testing, during which native heart rate decreased by 25 +/- 7 beats/min and mean arterial blood pressure decreased by 55 +/- 9 mm Hg. In three of these patients, there was also a decrease in donor heart rate of 23 +/- 26 beats/min. Parasympathetic testing showed possible evidence of donor heart vagal reinnervation in these patients with donor heart bradycardia during tilt but not in those with vasovagal reactions to tilt without slowing of the donor heart rate.nnnCONCLUSIONSnVagal efferent reinnervation can occur after orthotopic heart transplantation in humans. However, the absence of such reinnervation in some patients with vasovagal responses to tilt calls into question the role of left ventricular receptors in inducing the vasovagal reaction.

Permanent pacing for cardioinhibitory malignant vasovagal syndrome.

OBJECTIVE--To evaluate the effect of permanent pacing in cardioinhibitory malignant vasovagal syndrome. PATIENTS AND METHODS--37 patients with permanent pacemakers for cardioinhibitory malignant vasovagal syndrome. All presented with syncope (median six episodes, median frequency two episodes a year) and after conventional investigation and invasive electrophysiological assessment they remained undiagnosed, and without a generally accepted indication for pacemaker implantation. In all vasovagal syncope with cardioinhibition (heart rate at syncope < 60 beats/min) developed during tilt tests performed according to the Westminster protocol (head up tilt at 60 degrees with a footplate support for 45 minutes or until syncope intervenes). Dual chamber pacemakers were implanted in 35 (95%) and VVI pacemakers in the remaining two (5%). RESULTS--Over a mean (SD) follow up since implantation of 50.2 (23.9) months symptomatic improvement occurred in 89%: 62% remained free of syncope and 27% were completely symptom free. The collective syncopal burden of these 37 patients was reduced from 136 to 11 episodes each year. During follow up three patients died from unrelated causes. Patients who become asystolic during the tilt test (sinus pause of at least four seconds) experienced no greater benefit from pacing than those with less extreme cardioinhibition. Patients who remained free of syncope since implantation were younger than those who continued to experience syncope. Patients who remained completely symptom free after implantation were younger, more likely to be male, and had had fewer syncopal episodes before implantation than those who continued to experience syncope or presyncope. No other demographic, clinical, investigative, or pacing variable suggested a more favourable outcome after implant. CONCLUSIONS--This retrospective and uncontrolled experience suggests a possible role for permanent pacing in selected patients with cardioinhibitory malignant vasovagal syndrome. Improved acquisition of tilt test data may enable better selection of patients who are suitable for permanent pacing. A randomised prospective study to compare permanent pacing with no treatment or with medical treatment in cardioinhibitory malignant vasovagal syndrome is indicated.

Dual Chamber Pacing Aborts Vasovagal Syncope Induced by Head-Up 60° Tilt

To determine if pacing might prevent syncope in cardioinhibitory ‘Malignant Vasovagal Syndrome’ (also known as ‘Neurally‐Mediated Bradycardia/Hypotension’), a study of dual chamber pacing during head‐up 60° tilt was undertaken. Paired invasive tilts were performed in 10 patients who had a history of recurrent syncope, normal routine investigations including electrophysiological study and prior tilt induced vasovagal syncope. Vasovagal reactions of identical severity were produced by prolonged 60° head‐up tilt on consecutive days in seven out of 10 patients. On day 2, without pacing, seven patients had tilt‐induced vasovagal reactions and six became syncopal during the reaction. On day 3, with temporary DVI pacing with rate hysteresis, seven patients had tilt‐induced vasovagal reactions and 1 patient was syncopal. Syncope was aborted in the other five patients. DVI pacing significantly improved cardiac index (CI) (one ± 0.2 to 1.6 ± 0.3 L/min/m2, P < 0.01) and mean arterial blood pressure (MABP) (30 ± 11 to 48 ± 12 mmHg, P < 0.01) during vasovagal reactions on day 3 compared with day 2. The mean period of time that patients could tolerate in the tilted position after the onset of the tilt‐induced vasovagal reaction was significantly prolonged by pacing from 0.9 ± 1.2 to 3.2 ± 1.6 min (P < 0.01). Dual chamber pacing may abort syncope in 85% of patients with cardioinhibitory malignant vasovagal syndrome. Pacing may prolong consciousness sufficiently during a vasovagal reaction to allow injury to be avoided.

A new QRS detection algorithm based on the Hilbert transform

A robust new algorithm for QRS defection using the properties of the Hilbert transform is proposed. The method allows R waves to be differentiated from large, peaked T and P waves with a high degree of accuracy and minimizes the problems associated with baseline drift, motion artifacts and muscular noise. The performance of the algorithm was tested using the records of the MIT-BIH Arrhythmia Database. Beat by beat comparison was performed according to the recommendation of the American National Standard for ambulatory ECG analyzers (ANSI/AAMI EC38-1998). A QRS detection rate of 99.64%, a sensitivity of 99.81% and a positive prediction of 99.83% was achieved against the MIT-BIH Arrhythmia database. The noise tolerance of the new proposed QRS detector was also tested using standard records from the MIT-BIH Noise Stress Test Database. The sensitivity of the detector remains about 94% even for signal-to-noise ratios (SNR) as low as 6 dB.

Clinical evaluation of a policy of early repeated internal cardioversion for recurrence of atrial fibrillation.

Early Repeated Cardioversion for AF Recurrence. Introduction: The clinical value of cardioversion (CV) of persistent atrial fibrillation (AF) is limited by the high rate of early AF recurrence, which may be related to the persistence of atrial electrical remodeling. We examined the hypothesis that the likelihood of maintaining sinus rhythm after CV of persistent AF is significantly enhanced by a policy of early repeated CV.

Safety and acceptability of implantation of internal cardioverter-defibrillators under local anesthetic and conscious sedation.

Background: Implantation and testing of implantable defibrillators (ICDs) using local anesthetic and conscious sedation is widely practiced; however, some centers still use general anesthesia. We assessed safety and patient acceptability for implantation of defibrillators using local anesthetic and conscious sedation.

Prolonged implantable electrocardiographic monitoring indicates a high rate of misdiagnosis of epilepsy—REVISE study

AIMSnSyncope, epilepsy, and psychogenic pseudo-syncope are the most common causes of transient loss of consciousness (T-LOC or blackout). All can present with similar features, including abnormal limb movements. It is reported that somewhere between 13 and 42% of patients with epilepsy may be misdiagnosed. A UK Parliamentary working group found that at least 74 000 English patients are misdiagnosed with epilepsy, and taking antiepileptic drugs. The likely alternative diagnosis is convulsive syncope, mimicking an epileptic seizure. We hypothesized that many patients misdiagnosed with epilepsy have convulsive reflex syncope, and that prolonged electrocardiographic (ECG) monitoring with an implantable ECG recorder (ILR) would show reflex cardioinhibition during T-LOC. This would respond to permanent pacing and allow antiepileptic drugs to be withdrawn. We also aimed to evaluate tilt testing and other tests done in these patients.nnnMETHODS AND RESULTSnWe included patients previously diagnosed with epilepsy, but considered to have a definite or likely misdiagnosis of epilepsy after specialist neurological review. All received an ILR (Reveal Plus(®)/Reveal DX(®), Medtronic Inc.), and tilt-table testing. One hundred and three patients were included, mean age of 46 ± 17 years, with 58 of 103 (56%) female patients. A diagnosis of epilepsy was previously made by a neurologist in 69%, but definite tonic-clonic seizures were only noted in the history in 4%. In 22 patients (21%), the ILR recorded profound bradyarrhythmia or asystole with convulsive features, and they were offered pacemaker implantation. After pacing and withdrawal of antiepileptic drugs, 60% of these patients were asymptomatic. Only 14% of patients had a positive tilt-table test. In these, there was no correlation with the ECG findings of a spontaneous blackout during ILR recording.nnnCONCLUSIONnThis study shows a high incidence of the cardioinhibition of reflex syncope in patients with convulsive T-LOC previously diagnosed as epilepsy and treated with antiepileptic drugs. We believe that reflex syncope with convulsive features mimics generalized epilepsy, leading to a misdiagnosis. This may be a widespread problem accounting for many wrong diagnoses of epilepsy. There was also poor correlation in ECG findings between tilt testing and ILR recording.

Optimisation of cardiac resynchronisation therapy: addressing the problem of “non-responders”

Cardiac resynchronisation therapy has become firmly established as a treatment for patients with symptomatic heart failure. Several randomised controlled trials and numerous observational studies have demonstrated improvements in exercise capacity and quality of life. Despite these advances it is clear that approximately 25% of patients who meet current criteria for implantation of such a device do not show objective evidence of clinical benefit. Implantation of a CRT device is expensive, time consuming and involves some risk so it is important to accurately identify patients who are likely to respond and to optimise pacing lead placement and device programming to maximise the benefit in these selected patients.

Prevalence and Significance of Focal Sources of Atrial Arrhythmia in Patients Undergoing Cardioversion of Persistent Atrial Fibrillation

Atrial Arrhythmias After Cardioversion of AF. Introduction: Recent reports have highlighted the importance of focal atrial arrhythmias as a curable cause fur a group of patients with frequently recurrent paroxysmal atrial fibrillation (AF). The importance of this arrhythmia mechanism in the general population of patients with persistent AF is unknown.