Beat-to-beat wavelet variance of the QRS complex as a marker of arrhythmogenic substrate in ventricular tachycardia patients.

This study proposes a wavelet transform based technique to assess the beat-to-beat variation of the QRS signal in post-myocardial infarction patients with sustained monomorphic ventricular tachycardia. Recent electrophysiological investigations suggested that the diminished synchrony between the normal myocardium and the scarred arrhythmogenic tissue bordering a myocardial infarction area gives rise to beat-variable ECG signal components. Using a mathematical model of small variations in a largely repetitive waveform, we show that the inherent alignment errors (trigger jitter) of the high-resolution ECG (HRECG) can artificially increase the value of the time-domain beat-to-beat variance, making it less valuable as a marker of beat-variable signal components. To overcome this drawback, we propose the wavelet based approach which discriminates between the different factors responsible for the beat variability (the alignment error and the beat-variable signal components). The Morlet wavelet transform is performed on HRECG signals from normal individuals (control group) and postmyocardial infarction patients with documented ventricular tachycardia. Electrical variability is quantitatively assessed via the beat-to-beat wavelet variance measurements. A marker of arrhythmogenic induced variance which achieves a good performance in discrimination of ventricular tachycardia patients from normal subjects was found between 200 Hz and 300 Hz. This finding is in agreement with the proposed mathematical model which states that the useful part of the time-frequency map is shifted upward in a precise mathematical way, as the variance induced by the beat-variable arrhythmogenic signals depend on the frequency characteristics of the first derivative of these signals. We conclude that the dynamics of the arrhythmogenic substrate as revealed by the beat-to-beat wavelet variance can be a new estimator of ventricular tachycardia risk.

Cardiac electrical instability of the arrhythmogenic tissue substrate assessed by means of wavelet transform.

The unstable activation wavefront from the tissue responsible for the production of ventricular tachycardia (VT) gives rise to beat-variable signals components that are eluded during the averaging step of high resolution ECG (HRECG). We used a mathematical model of small variations in a largely repetitive waveform to evaluate the beat-to-beat variance of the HRECG signal. The ability of the Morlet Wavelet Transform to discriminate the different factors responsible for the beat-variability (the alignment error and the beat-variable signal component) has been assessed on simulated signals. The performance evaluation on real ECG signals from normal subjects and patients with a documented history of ventricular tachycardia showed that the dynamics of the arrhythmogenic substrate as revealed by wavelet transform offers a significant improvement in ventricular tachycardia risk assessment.

Current status of radiofrequency ablation in the preexcitation syndromes.

Catheter ablation techniques have become an accepted treatment form for a variety of supraventricular arrhythmias. After the introduction of radiofrequency energy, catheter ablation has become the first line of treatment and has replaced surgery in patients with the preexcitation syndromes. The success rate in large series is very high, while the complication rate in experienced hands is very low. Despite all this progress, the ablation of a small subset of accessory atrioventricular pathways poses some problems. The ideal source of energy is still unknown and improvement in catheter technology are needed. This review will try to focus on some of these issues dealing with a very exciting area of clinical cardiology.

First lessons from radiofrequency catheter ablation in patients with ventricular tachycardia.

UNLABELLED: Fourteen patients (12 men, 2 women; 61 +/- 9 years) with ventricular tachycardia and underlying heart disease underwent an attempt at radiofrequency energy catheter ablation. Twelve patients had coronary disease and two patients had dilated cardiomyopathy. Two patients had two clinical tachycardias, the ejection fraction was 38% +/- 11%. All tachycardias were inducible and hemodynamically well tolerated (cycle length = 357 +/- 56 msec). Ablation was initially successful in nine patients (no tachycardia inducible after ablation and before discharge). Two patients had recurrences (in-hospital and 4 months) and one patient had a tachycardia of a different morphology, which was also successfully ablated. Ablation was overall successful in seven patients and unsuccessful in seven patients (including all patients with cardiomyopathy). Mid-diastolic potentials were observed in all the patients in whom ablation was successful but not observed in four of seven unsuccessful patients. The successful patients remain free of recurrences at 9 +/- 8 months follow-up. CONCLUSIONS: (1) in ventricular tachycardia following an old infarction radiofrequency energy ablation is possible with a high success rate if a critical component of the tachycardia circuit can be localized. Localizing isolated mid-diastolic potentials and ensuring these potentials are part of the reentrant circuit with concealed entrainment can help to enhance the results. (2) A negative predischarge electrophysiological study may be predictive of success.

Clinical experience with the rate responsive pacemaker Sensolog 703.

Pacemaker therapy with rate responsive systems becomes increasingly more important. Numerous clinical and experimental trials have been conducted thus far to investigate different sensors of metabolic demands of the body, functioning independently of an atrial electrogram. To transform mechanical energy into electrical energy, activity-triggered systems utilize a piezo-quartz as their sensor. Thirty five patients suffering from pathological bradyarrhythmias and therefore from an inadequate increase of the heart rate during exercise were supplied with a Sensolog 703. Clinical follow-up was first performed with the help of treadmill ergometry, later on by walking on flat ground and climbing steps. The settings due to the first test caused inadequately high stimulation rates. A 24-h-Holter-ECG was necessary to control the programming and the rate profile in the patient's daily life. Using only the histogram and the rateread function, all rate adaptive parameters of the Sensolog 703 could be set by walking on flat ground and climbing steps. We defined a frequency of 75-85 min-1 to be appropriate during walking, respectively "low work." Individual programming ranged from 2-5/8-15/high-low/very fast-medium/fast-medium (slope, threshold, gain, reaction and recovery time). Reprogramming based on 24-h-Holter ECG was only necessary if the pacemaker was formerly adjusted with the help of treadmill ergometry. Besides, we observed an increase of the stimulation rate due to vibrations not related to exercise, e.g., by driving in a car.

[Successful high-frequency current ablation of three accessory conduction pathways in a single session]. / Erfolgreiche Hochfrequenzstromablation von drei akzessorischen Leitungsbahnen in einer Sitzung.

A case is presented of a 25-year-old symptomatic male with Wolff-Parkinson-White syndrome and three overt accessory atrioventricular connections which were all diagnosed and ablated during the same session. A discordant preexcitation pattern between delta wave and QRS axis was found on the surface electrocardiogram, indicating the presence of two or more accessory pathways. During atrial pacing the appearance of a changing QRS morphology and alternating delta wave suggested the presence of an additional left-sided pathway. After ablation of a right anteroseptal pathway, a second pathway was found located in the left lateral position and was successfully ablated. The final pathway became evident only after the ablation of the first two and was found to be located in a right midseptal position. This pathway was also ablated during this session. There were no complications and the patient remained asymptomatic during an 11-month follow-up.

Electrophysiologic, haemodynamic and antiarrhythmic effects of the new class Ic agent 1-(2'-biphenyloxy)-2-tert.-butylamino-propanol-2-hydrochloride.

The electrophysiological, antiarrhythmic and haemodynamic profile of the new compound GK 23-G (1-(2'-biphenyloxy)-2-tert.-butylamino-propanol-2-hydrochloride, proposed INN: bipranol) was examined using dogs models relevant to conditions in humans. In the first part of the study, dose-related effects of cumulatively increasing doses of GK 23-G (0.2-12.8 mg/kg) on intracardiac conduction, ventricular refractoriness and on haemodynamic parameters of the non-ischemic heart were determined in six anesthetized mongrel dogs. In the second part of the study, antiarrhythmic actions of bipranol on "delayed reperfusion ventricular arrhythmias" following release of coronary artery occlusion after 2 h of obstruction were investigated in another six dogs. The results show: GK 23-G causes a significant prolongation of HV-time, QRS-duration and ventricular refractory period at mid-range and high doses (greater than or equal to 3.2 mg/kg). QT-time does not change. Atrial refractory period is significantly lengthened at the maximum dose of 12.8 mg/kg. There are no significant changes in heart rate, systolic and diastolic aortic pressure and cardiac output. Up to 12.8 mg/kg, GK 23-G does not influence left ventricular contractility (dp/dtmax). In acute myocardial necrosis "delayed reperfusion arrhythmias" are almost completely abolished at a dose of 1.6 mg/kg + 50 micrograms/kg x min. Thus, because of its antiarrhythmic potency, further experimental and clinical testing of the new compound seems promising.

Comparison of signal-averaged electrocardiograms with different levels of noise: time-domain, frequency-domain, and spectrotemporal analysis.

In order to test the effect of noise on the various parameters of the SAECG, 83 patients underwent three consecutive recordings at different noise levels. The high noise (HN) recordings had a noise level of 0.60-0.74 microV, the intermediate noise (IN) had 0.31-0.59 microV, and the low noise (LN) had < or = 0.30 microV. For the calculation of noise we used the standard deviation of the mean noise of the composite lead high pass filtered at 40 Hz. The recordings were compared using time-domain, frequency-domain, and spectrotemporal analysis. The time-domain parameters of the LN recordings, using 25-Hz, 40-Hz, and 60-Hz high pass cutoffs, were significantly different from those of the HN or IN recordings (P < 0.05). In the frequency-domain analysis, significant differences were found in some of the parameters of the LN compared to the HN. The spectrotemporal analysis of the X and Z leads also showed significant differences among the LN and the other recordings. In the time-domain analysis, both at 40 Hz and 25 Hz, there were more abnormal LN compared to the HN recordings (P < 0.05). In the spectrotemporal analysis, there were significantly more abnormal HN and IN recordings compared to the LN (P < 0.001 and P < 0.01, respectively). Therefore, the level of noise, even within the acceptable range, can significantly affect the SAECG. In the time domain at the lower noise levels the parameters become more abnormal, while the opposite seems to occur in the spectral and the spectrotemporal analysis.