Clinical magnetocardiography: the unshielded bet-past, present, and future.

Magnetocardiography (MCG), which is nowadays 60 years old, has not yet been fully accepted as a clinical tool. Nevertheless, a large body of research and several clinical trials have demonstrated its reliability in providing additional diagnostic electrophysiological information if compared with conventional non-invasive electrocardiographic methods. Since the beginning, one major objective difficulty has been the need to clean the weak cardiac magnetic signals from the much higher environmental noise, especially that of urban and hospital environments. The obvious solution to record the magnetocardiogram in highly performant magnetically shielded rooms has provided the ideal setup for decades of research demonstrating the diagnostic potential of this technology. However, only a few clinical institutions have had the resources to install and run routinely such highly expensive and technically demanding systems. Therefore, increasing attempts have been made to develop cheaper alternatives to improve the magnetic signal-to-noise ratio allowing MCG in unshielded hospital environments. In this article, the most relevant milestones in the MCG's journey are reviewed, addressing the possible reasons beyond the currently long-lasting difficulty to reach a clinical breakthrough and leveraging the authors' personal experience since the early 1980s attempting to finally bring MCG to the patient's bedside for many years thus far. Their nearly four decades of foundational experimental and clinical research between shielded and unshielded solutions are summarized and referenced, following the original vision that MCG had to be intended as an unrivaled method for contactless assessment of the cardiac electrophysiology and as an advanced method for non-invasive electroanatomical imaging, through multimodal integration with other non-fluoroscopic imaging techniques. Whereas all the above accounts for the past, with the available innovative sensors and more affordable active shielding technologies, the present demonstrates that several novel systems have been developed and tested in multicenter clinical trials adopting both shielded and unshielded MCG built-in hospital environments. The future of MCG will mostly be dependent on the results from the ongoing progress in novel sensor technology, which is relatively soon foreseen to provide multiple alternatives for the construction of more compact, affordable, portable, and even wearable devices for unshielded MCG inside hospital environments and perhaps also for ambulatory patients.

Enoximone in cardiac arrest caused by propranolol: two case reports.

We report two clinical cases of cardiac arrest, the former due to an adverse effect of intravenous (i.v.) propranolol in a patient with systemic sclerosis, the latter from a propranolol suicidal overdose. In both cases, conventional advanced life support (ALS) was ineffective but both patients eventually responded to the administration of enoximone, a phosphodiesterase III (PDE III) inhibitor. After the arrest, both patients regained consciousness and were discharged home. The chronotropic and inotropic effects of PDE III inhibitors are due to inhibition of intracellular PDEIII and are therefore unaffected by beta-blockers. These cases suggest that PDEIII inhibitors may be useful in restoring spontaneous circulation in cardiac arrest associated with beta-blocker administration when standard ALS is ineffective.

How to use the C-reactive protein in cardiac disease?

Inflammation is an important contributor to atherothrombosis. The C-reactive protein (CRP) is not only an excellent biomarker of inflammation, but it is also a direct participant in atherogenesis. CRP consistently predicts new coronary events, including myocardial infarction and death, in patients with ischemic heart disease. The predictive value of CRP is, in the majority of the studies, independent of and additive to that of the troponins and its levels can be modulated by statins. Prospective observational studies show that moderately elevated levels of CRP are associated with an adverse cardiovascular prognosis among healthy individuals. The availability of high sensibility assays for CRP should provide a valuable tool for identifying patients at risk of cardiovascular events in primary prevention in conjunction with lowering LDL cholesterol and may also have utility in the treatment of acute coronary syndromes with percutaneous coronary intervention (PCI) therapy. High CRP levels, associated with a higher risk, should suggest a more aggressive medical therapy in the long term and also an aggressive and invasive therapy in the short term, including the use of GP IIb/IIIa inhibitors, high doses of statins, and when a PCI is necessary, provisional stenting. Finally, CRP will provide a readily accessible marker for further testing of the inflammatory hypothesis in atherosclerosis.

[Usefulness of magnetic resonance imaging for the diagnosis of acute myocarditis. A case of acute myocarditis as myocardial infarction-like]. / Ruolo della risonanza magnetica nucleare nella diagnosi di miocardite acute. Un caso di miocardite acuta ad esordio simil-infartuale.

According to the Dallas criteria, myocarditis is defined histologically as an inflammatory process involving the myocardium with an inflammatory infiltrate and myocyte necrosis or damage. Clinically, myocarditis is an insidious disease that is usually asymptomatic and commonly underdiagnosed. Infact, the symptoms are often non-specific and the majority of cases recover fully with no sequelae. At present, endomyocardial biopsy remains the gold standard for the diagnosis of myocarditis, despite its limited sensitivity and specificity. However, the lack of an association between biopsy evidence of myocarditis and the presence of autoantibodies in patients with clinical signs of myocarditis, the paucity of the positive biopsy findings in large cohorts of patients with suspected myocarditis, the potential discordance between clinical and histologic features and the inherent limitation of histologic diagnosis, suggest that the diagnosis shouldn't be based on histologic examination alone. The magnetic resonance imaging (MRI) with gadolinium can be useful to visualize the localization, activity and extent of inflammation and may be a powerful noninvasive diagnostic tool in acute myocarditis. Infact, MRI achieves a 100% sensitivity and a 90% specificity. We report the case of a 31-year-old male patient with an acute myocarditis with electrocardiographic manifestations like to acute myocardial infarction, whose diagnosis was based on the clinical signs and on the characteristic pattern of the MRI with paramagnetic contrast. The MRI with gadolinium is suggested as noninvasive study to support the diagnosis of acute myocarditis in the correct clinical setting.

Cardiovascular adaptation during action pistol shooting.

BACKGROUND: Action Pistol Shooting, implies high degree of physical and psychological stress, however cardiovascular adaptation during competition has not been studied so far. METHODS: We studied six healthy males athletes, during the Italian National Dynamic Pistol Shooting Championship. ECG was monitored and blood pressure (BP) manually measured along the match. RESULTS: Mean heart rate (HR) was close to 100 bpm per minute in all but one shooters. Marked tachycardia, above 180 beats per minute was recorded in four shooters, during "field course" stages. In two cases the heart rate under stress reached about 200 bpm, for the occurrence of paroxysmal atrial arrhythmias. BP behavior was different among the six shooters with mean systolic values ranging between 140 and 170 mmHg and maximal systolic values between 160 e 240 mmHg. CONCLUSIONS: Action Pistol Shooting induces acute elevation of HR and BP, which may reach abnormal values and can be associated with impaired performance and score. Further study is warranted in shooters undergoing combat-like tournaments to evaluate unperceived cardiovascular stress and their coping capability.

Bioelectromagnetic localization of a pacing catheter in the heart.

The accuracy of localizing source currents within the human heart by non-invasive magneto- and electrocardiographic methods was investigated in 10 patients. A non-magnetic stimulation catheter inside the heart served as a reference current source. Biplane fluoroscopic imaging with lead ball markers was used to record the catheter position. Simultaneous multichannel magnetocardiographic (MCG) and body surface potential mapping (BSPM) recordings were performed during catheter pacing. Equivalent current dipole localizations were computed from MCG and BSPM data, employing standard and patient-specific boundary element torso models. Using individual models with the lungs included, the average MCG localization error was 7+/-3 mm, whereas the average BSPM localization error was 25+/-4 mm. In the simplified case of a single homogeneous standard torso model, an average error of 9+/-3 mm was obtained from MCG recordings. The MCG localization accuracies obtained in this study imply that the capability of multichannel MCG to locate dipolar sources is sufficient for clinical purposes, even without constructing individual torso models from x-ray or from magnetic resonance images.

Nonfluoroscopic localization of an amagnetic catheter in a realistic torso phantom by magnetocardiographic and body surface potential mapping.

This study was performed to evaluate the accuracy of multichannel magnetocardiographic (MCG) and body surface potential mapping (BSPM) in localizing three-dimensionally the tip of an amagnetic catheter for electrophysiology without fluoroscopy. An amagnetic catheter (AC), specially designed to produce dipolar sources of different geometry without magnetic disturbances, was placed inside a physical thorax phantom at two different depths, 38 mm and 88 mm below the frontal surface of the phantom. Sixty-seven MCG and 123 BSPM signals generated by the 10 mA current stimuli fed into the catheter were then recorded in a magnetically shielded room. Non-invasive localization of the tip of the catheter was computed from measured MCG and BSPM data using an equivalent current dipole source in a phantom-specific boundary element torso model. The mean 3-dimensional error of the MCG localization at the closer level was 2 +/- 1 mm. The corresponding error calculated from the BSPM measurements was 4 +/- 1 mm. At the deeper level, the mean localization errors of MCG and BSPM were 7 +/- 4 mm and 10 +/- 2 mm, respectively. The results showed that MCG and BSPM localization of the tip of the AC is accurate and reproducible provided that the signal-to-noise ratio is sufficiently high. In our study, the MCG method was found to be more accurate than BSPM. This suggests that both methods could be developed towards a useful clinical tool for nonfluoroscopic 3-dimensional electroanatomical imaging during electrophysiological studies, thus minimizing radiation exposure to patients and operators.

Magnetocardiographic pacemapping for nonfluoroscopic localization of intracardiac electrophysiology catheters.

The purpose of the study was to validate, in patients, the accuracy of magnetocardiography (MCG) for three-dimensional localization of an amagnetic catheter (AC) for multiple monophasic action potential (MAP) with a spatial resolution of 4 mm2. The AC was inserted in five patients after routine electrophysiological study. Four MAPs were simultaneously recorded to monitor the stability of endocardial contact of the AC during the MCG localization. MAP signals were band-pass filtered DC-500 Hz and digitized at 2 KHz. The position of the AC was also imaged by biplane fluoroscopy (XR), along with lead markers. MCG studies were performed with a multichannel SQUID system in the Helsinki BioMag shielded room. Current dipoles (5 mm; 10 mA), activated at the tip of the AC, were localized using the equivalent current dipole (ECD) model in patient-specific boundary element torso. The accuracy of the MCG localizations was evaluated by: (1) anatomic location of ECD in the MRI, (2) mismatch with XR. The AC was correctly localized in the right ventricle of all patients using MRI. The mean three-dimensional mismatch between XR and MCG localizations was 6 +/- 2 mm (beat-to-beat analysis). The co efficient of variation of three-dimensional localization of the AC was 1.37% and the coefficient of reproducibility was 2.6 mm. In patients, in the absence of arrhythmias, average local variation coefficients of right ventricular MAP duration at 50% and 90% of repolarization, were 7.4% and 3.1%, respectively. This study demonstrates that with adequate signal-to-noise ratio, MCG three-dimensional localizations are accurate and reproducible enough to provide nonfluoroscopy dependant multimodal imaging for high resolution endocardial mapping of monophasic action potentials.

Reproducibility of transesophageal pacing in patients with Wolff-Parkinson-White syndrome.

The purpose of this study was to assess, in patients with ventricular preexcitation, the time dependent physiological variation of antegrade conduction properties in the AV node and in accessory pathways (Aps) as a function of autonomic tone variation induced by posture and physical effort, using noninvasive transesophageal atrial pacing. In 74 WPW patients (mean age 21.31 +/- 9.46 yrs), AV node and Kent antegrade effective refractory periods (at pacing cycle lengths 600, 400, and 320 ms), Wenckebach point, shortest preexcited RR intervals during sustained atrial fibrillation (AF) or atrial pacing, as well as the inducibility of AV reentry tachycardia (AVRT) and AF/flutter (AFL) were assessed. All measurements were carried out at rest, in supine and upright positions, and during effort. A second study was carried out approximately 3 months after the first study. The coefficient of variation (CVs) and reproducibility (CRs) were calculated. For each parameter, the differences between the mean of the two studies were not statistically significant. The CVs and CRs ranged between 0.4% and 4% and between 2 and 28 ms, respectively. AF was induced in 40 (54%) of 74 patients at the first study and in 30 (40.5%) of 74 patients at the second study. AVRT was induced in 33 (45%) of 74 patients at the first study and in 38 (51.3%) of 74 patients at the second study. The reproducibility was 45% for AF/AFL and 65% for reentry tachycardia. Transesophageal atrial pacing is a reliable method for noninvasive reproducible evaluation of antegrade electrophysiological properties of both the AV node and APs in WPW patients. However, the effect of autonomic balance variation has to be taken into account and precisely defined because it may significantly affect the inducibility of supraventricular arrhythmias and the estimation of the absolute values of the vulnerable parameters.