Ivan Corazza

Physiologic autonomic arousal heralds motor manifestations of seizures in nocturnal frontal lobe epilepsy: Implications for pathophysiology

OBJECTIVE This study describes changes in heart rate (HR) and HR variability (HRV) related to clinical onset of seizures in nocturnal frontal lobe epilepsy (NFLE) in order to determine whether signs of autonomic activation precede onset of seizure motor manifestations, which was selected as seizure onset (SO). Further, to clarify the nature (epileptic or physiologic) of the changes in autonomic cardiac control presumed to precede SO, time-dependent variations in HR and HRV related to physiological cortical arousals associated with motor activity (phases of transitory activation, PAT) were also investigated. METHODS HR and HRV spectral power, quantified by means of wavelet transform, were analyzed in relation to the onset of motor manifestations in 45 NFLE seizures and 45 PAT derived from whole night video-polysomnographic recordings of ten patients and of ten control subjects, respectively. RESULTS Analysis of HRV showed a shift of sympathetic/parasympathetic cardiac control toward a sympathetic predominance in the 10s immediately preceding SO, while changes in HR were evident only one second before SO. This sympathetic activation was not associated with a sleep-wake transition or changes in respiratory activity, both of which occurred concurrently with SO. Similar changes in HR and HRV were observed in the 10s before the motor and electroencephalographic onset of PAT. CONCLUSIONS Our study demonstrates that a similar autonomic activation precedes the motor manifestations of NFLE seizures and physiological arousal. This autonomic activation could represent part of the arousal response, which could be implicated in the occurrence of both seizure and arousal motor manifestations.

Mechanical simulator of the cardiovascular system

To devise and to build a mechanical simulator of the cardiovascular system of increasing complexity is a fascinating experience for a medical Physicist. We did it, and the effort to match the solutions with the objectives forced us to deepen the knowledge of the physiological aspects, to devise different solutions and to compare their results. This paper describes the final solution and shows the results, discussing the theoretical and practical aspects of the different choices. The ventricle is simulated by a pumping syringe with an external pulsing chamber to accomplish the Frank-Starling mechanism; the coronary circulation by a nonlinear hydraulic resistance device; the aorta by different wall thickness rubber tubes; the arterial vascular resistance by a thin, variable length tube; the venous reservoir by a variable volume chamber connected to a reservoir simulating the atrium. The simulator was mainly devoted to teaching purposes, but the possibility to modify the mechanical characteristics of the single components moved it to be used also for research, with an unexpected satisfaction.

Effect of high-pass filtering on ECG signal on the analysis of patients prone to atrial fibrillation

The aim of this study was to assess the effect of filtering techniques on the time-domain analysis of the ECG. Multi-lead ECG recordings obtained from chronic atrial fibrillation (AF) patients after successful external cardioversion have been acquired. Several high-pass filtering techniques and three cut-off frequency values were used: Bessel and Butterworth four-pole and two-pole bidirectional and unidirectional filters, at 0.01, 0.05 and 0.5 Hz low cut-off frequency. As a reference, a beat-by-beat linear piecewise interpolation was used to remove baseline wander, on each P-wave. Results show that ECG filtering affects the estimation of P-wave duration in a manner that depends upon the type of filter used: particularly, the bidirectional filters caused negligible variation of P-wave duration, while unidirectional ones provoked an increase higher than 8%.

Atrial Signal Analysis and Defibrillation Threshold Assessment in Chronic Persistent and Reinduced Atrial Fibrillation

De. brillation Threshold in Chronic and Reinduced AF. Introduction: Induced versus spontaneous atrial fibrillation (AF) is of interest for assessing atrial defibrillation threshold reproducibility.

On the resolution of ECG acquisition systems for the reliable analysis of the P-wave

The analysis of the P-wave on surface ECG is widely used to assess the risk of atrial arrhythmias. In order to provide reliable results, the automatic analysis of the P-wave must be precise and reliable and must take into account technical aspects, one of those being the resolution of the acquisition system. The aim of this note is to investigate the effects of the amplitude resolution of ECG acquisition systems on the P-wave analysis. Starting from ECG recorded by an acquisition system with a less significant bit (LSB) of 31 nV (24 bit on an input range of 524 mVpp), we reproduced an ECG signal as acquired by systems with lower resolution (16, 15, 14, 13 and 12 bit). We found that, when the LSB is of the order of 128 µV (12 bit), a single P-wave is not recognizable on ECG. However, when averaging is applied, a P-wave template can be extracted, apparently suitable for the P-wave analysis. Results obtained in terms of P-wave duration and morphology revealed that the analysis of ECG at lowest resolutions (from 12 to 14 bit, LSB higher than 30 µV) could lead to misleading results. However, the resolution used nowadays in modern electrocardiographs (15 and 16 bit, LSB <10 µV) is sufficient for the reliable analysis of the P-wave.

Mechanical aspects of CO2 angiography

The aim of this paper is to clarify some physical-mechanical aspects involved in the carbon dioxide angiography procedure (CO₂ angiography), with a particular attention to a possible damage of the vascular wall. CO₂ angiography is widely used on patients with iodine intolerance. The injection of a gaseous element, in most cases manually performed, requires a long training period. Automatic systems allow better control of the injection and the study of the mechanical behaviour of the gas. CO₂ injections have been studied by using manual and automatic systems. Pressures, flows and jet shapes have been monitored by using a cardiovascular mock. Photographic images of liquid and gaseous jet have been recorded in different conditions, and the vascular pressure rises during injection have been monitored. The shape of the liquid jet during the catheter washing phase is straight in the catheter direction and there is no jet during gas injection. Gas bubbles are suddenly formed at the catheters hole and move upwards: buoyancy is the only governing phenomenon and no bubbles fragmentation is detected. The pressure rise in the vessel depends on the injection pressure and volume and in some cases of manual injection it may double the basal vascular pressure values. CO₂ angiography is a powerful and safe procedure which diffusion will certainly increase, although some aspects related to gas injection and chamber filling are not jet well known. The use of an automatic system permits better results, shorter training period and limitation of vascular wall damage risk.

AORTOVENTRICULAR MECHANICAL MATCHING: SIMULATION OF NORMAL AND PATHOLOGICAL CONDITIONS

A mechanical mock of the cardiovascular system was used to simulate different conditions of ventricular-arterial mechanical matching. Four ventricles and four aortas with different elastances were set up, and all possible connection combinations tested by sampling ventricular and aortic pressures and flows. The mechanical energy produced by the simulated ventricles and the amount transferred to the aorta in the different connection conditions were calculated. The results demonstrate a clear dependence between the mechanical work production of the ventricles and the ventricular elastance (slope of the end-systolic pressure–volume relation) (from 20.42 ± 0.02 mJ/beat to 12.10 ± 0.02 mJ/beat), and an efficiency of energy transfer to the aorta strongly dependent on ventricular-aortic mechanical matching (from 56% to 20.7%). These results show that, even in optimal simulated conditions, only 56% of the energy produced is transferred to the load; and highlight the important role of mechanical aspects in conditions of very limited cardiovascular performance (i.e. final stages of heart failure), where energy transfer efficiency may be as low as 20.7%. This evidence emphasizes that the mechanical aspects must also be entertained in the evolution of complex cardiovascular pathologies, evaluating the possibility of combining mechanical and pharmaceutical interventions.

Ventricular dyssynchrony at echo: Detection by two-dimensional tracking and tissue doppler imaging in candidates to biventricular pacing

Left ventricular (LV) dyssynchrony is a predictor of response to biventricular (BIV) pacing in patients with heart failure (HF) and LV dysfunction. In this study we compared a novel two-dimensional speckle tracking technique to standard Tissue Doppler Imaging (TDI) with regard to LV dyssynchrony assessment in 10 HF patients candidated to BiV pacing. Substantial correlation was found between the two techniques in measuring LV dyssynchrony (r=0.69; pLt0,05). Two-dimensional speckle tracking was able to detect variations in LV dyssynchrony induced by simultaneous BiV pacing. This pilot evaluation suggests that two-dimensional speckle tracking may be a valuable alternative to standard TDI to assess LV dyssynchrony before implant and during follow up in candidates to BiV facing.

Changes in exercise capacity induced by heart transplantation: prognostic and therapeutic implications

Survival and exercise performance are key targets of heart transplantation (HT). We designed this study to help in identifying (1) patients with chronic heart failure (CHF) at risk of poor exercise capacity after HT and (2) HT recipients presenting risk factors modifiable with exercise showing a potential impact on outcome. We enrolled 49 HT recipients (age 52 ± 12 years, 84% males) who underwent a cardiopulmonary exercise test before (9 ± 6 months) and after (20 ± 14 months) HT. In the CHF phase, lower peak oxygen consumption (V̇O2) (odds ratio 0.69, P=0.017) independently predicted peak V̇O2 improvement after HT. In the post‐HT phase, body mass index (BMI) [adjusted hazard ratio (HR) 1.16, P=0.034] and V̇E (ventilation)/V̇CO2 (carbon dioxide production) slope (adjusted HR 1.07, P=0.031) independently predicted mortality. In conclusion, CHF patients with only a moderate impairment of peak V̇O2 are at a risk of failing to achieve a significant improvement of exercise performance after HT. In the post‐HT phase, a BMI≥28 and/or a V̇E/V̇CO2 slope ≥47 represent risk factors for death, which are potentially modifiable with exercise. Prospective randomized studies are needed to analyze the effects of training on functional capacity and outcome in the different subsets of HT recipients.

Reproducibility of IVUS measurements in heart transplant recipients: Increased quality of data by using dedicated software for image analysis

Cardiac allograft vasculopathy (CAV) is the major cause limiting long term graft survival after heart transplantation (HT), and is characterized by changes in coronary artery geometry, such as intimal thickening and vessel remodeling. Given the limited strategies available to reduce its impact on outcome, early diagnosis of CAV - for which intravascular ultrasound (IVUS) is the gold standard - is crucial to appropriately modulate therapy and to reduce contributing risk factors. However, a highly reproducible image-analysis method is required to capture the complex mechanisms beyond CAV-related changes in coronary geometry.