Unshielded magnetocardiography contributes to non-invasively rule-out ischemic heart disease in patients with chest pain of uncertain origin

Background

Out of millions of patients (pts) screened every year for chest pain in emergency departments (EDs) only 10% to 20% are affected by an acute coronary syndrome (ACS) or angina due to ischemic heart disease (IHD). Unless ECG recording and serum markers are clearly positive, most of them must undergo complete clinical workout to exclude IHD prior to discharge. Moreover, since even effort-ECG and echocardiography don't exhaustively rule-out IHD, second-level exams are frequently needed, enhancing hospitalization time and related costs. Magnetocardiography (MCG) is increasingly reported as a sensitive, non-invasive, radiation-free method with high negative predictive value (PV) to rule out IHD.

Purpose

Retrospective cohort study to evaluate the reliability likelihood of unshielded MCG (uMCG) as a tool for rapid rule-out of IHD.

Method

Rest uMCG data of 263 patients (pts), all chest-pain free at the moment of MCG scan, were retrospectively analyzed. uMCG was recorded with a 36-channel SQUID system (intrinsic sensitivity 30 fT/√Hz, above 1Hz), for 90 seconds. With proprietary software, 13 MCG parameters were automatically calculated from T-wave magnetic field (T-MF): 5 parameters quantifying the dynamics of the MF extrema and eight, obtained from inverse solution with the equivalent magnetic dipole (EMD) model, quantifying the spatial dynamics of the T-wave effective magnetic vector (T-EMV).

Pts were stratified as follows:

– Group A, chest pain pts, with IHD confirmed by subsequent SPECT and coronary angiography (mean age 66±11 years, 36.7% female);

– Group B, chest pain pts, with IHD excluded by subsequent SPECT or coronary angiography (mean age 59±10 years, 28.8% female);

– Group C, healthy control subjects (mean age 25±7 years, 48.6% female).

Only 60 pts in each group were randomly selected for the analysis. Non-parametric Kruskal-Wallis tests were used to compare the 13 MCG predictors among groups. Linear discriminant analysis was employed to assess likelihood ratios (LHR) and PVs, considering a mean IHD prevalence of 13% (range 10–20%) in chest-pain pts.

Results

Positive LHR was 9, while the negative LHR was 0.3, resulting in a helpful reduction of the pre-test probability of IHD. Whereas positive PV ranges from 51 to 70%, hardly confirming IHD diagnosis, negative PV ranges from 92 to 96%, giving confidence for a safe IHD rule-out.

Conclusions

Automatic analysis of T-MF and of T-EMV dynamics from rest MCG provided impressive negative LHR and PV values that, if confirmed in prospective multicenter trials, would rank MCG as a useful tool for quick and early triage of pts with acute chest pain and still non-diagnostic ECG and enzyme patterns, to rule-out those whose symptoms are of non-ischemic origin. Interestingly, a similar high negative PV has been recently reported using MCG QRS predictors. Thus, even better results could be expected by combining algorithms for automatic assessment of both T-wave and QRS predictors.

Funding Acknowledgement

Type of funding sources: None.

P3748Reproducibility of magnetocardiographic imaging of atrial electrophysiology in patients with paroxysmal atrial fibrillation and healthy subjects

Methods

MCG was recorded, in sinus rhythm (SR), with an unshielded 36-channel SQUID-system providing about 30–40 fT/√Hz sensitivity in bandwidth DC-250Hz (sampling frequency 1kHz). MCG data of 40 patients with PAF (PAFp) and 40 age-matched healthy controls (HC), with at least two subsequent recordings to evaluate reproducibility and optimal S/N ratio, were retrospectively analyzed. The dynamics of atrial MFD was studied, at 1 ms time resolution, to identify the onset of atrial repolarization (AR), in respect of the P-wave and PR interval duration. To localize atrial sources, the inverse solution was calculated with the Effective Magnetic Dipole (EMD) model, also after subtraction of the atrial repolarization. MCG parameters of atrial electromagnetic vector (EMV) were also calculated. The reproducibility was evaluated with the intraclass correlation coefficient (ICC).

Results

High resolution analysis of atrial MFD dynamics confirmed that atrial repolarization field overlaps atrial depolarization during the last third of the P-wave in most investigated subjects. Thus, subtraction of average AR MFD is necessary to discover and image the left atrial depolarization pathway. The reproducibility of MCG estimate of atrial MFD and of EMV parameters was good (average ICC >0.7). In PAFp, MCG evidenced abnormality of AR MFD consistent with dispersion of atrial repolarization (Figure 1), as previously reported with simultaneous MCG and MAP recordings (Fenici & Brisinda, 2007); however, such evaluation is reliable only with optimal S/N ratio during the PR interval.

Conclusions

Unshielded MCG in SR is sensitive enough to non-invasively image atrial electrophysiology. Visual analysis of atrial MFD dynamics with high temporal resolution reproductively confirmed that AR MFD initiates early, within the descending limb of the P-wave, masking the deeper magnetic field generated by left atrial depolarization currents. MCG can image abnormality of AR MFD in PAFp, suggestive of dispersion of atrial action potential duration. Quantitative estimate of atrial EMV parameters differentiates PAFp from HC.

P1011Electrophysiological trends in Wolff-Parkinson-White patients: a 33 years follow-up study

Background

The Wolff-Parkinson-White (WPW) syndrome can be associated with sudden cardiac death, therefore risk assessment (RA) with electrophysiological (EP) testing (EPT) is mandatory to identify patients (pts) requiring catheter ablation (CAb). Our retrospective cohort study aimed to evaluate the variability of EP parameters during follow-up of WPW pts and the reliability of trans-esophageal EPT (TEEPT) for RA, evaluation of treatment efficacy, and EP follow-up of untreated athletes/pts.

Method

Data of 335 WPW pts, studied with TEEPT between 1985 and 2018, were retrospectively analyzed. Anterograde effective refractory period (ERP) of accessory pathways (AP) and of the atrioventricular node, Wenckebach point, shortest preexcited RR intervals (SPERRI) during atrial fibrillation (AF) and/or atrial pacing (At-P) and inducibility of supraventricular arrhythmias were assessed, at rest (supine and standing) and during effort. An AP was defined at high arrhythmogenic risk (HAR) if the anterograde AP-ERP and/or SPERRI (in AF or At-P) were ≤240 ms at rest or ≤200 ms during effort test. All patients were followed-up as outpatients or telephonically, as clinically required.

195 pts (17% female) were included, having exhaustive clinical information, two or more TEEPT and exhaustive clinical follow-up until late 2018. Time-evolution of EP parameters was evaluated, using parametric and non-parametric tests, as appropriate.

Results and discussion

Median age at first TEEPT was 20 years (IQR 16–29 years). Median follow- up was 44.3 months (IQR 16.4–122.9 months). Two pts (both identified at HAR and scheduled for surgery when ablation was unavailable) died suddenly, at rest. No other serious arrhythmic complication occurred, during the FU. Out of 19 pts (9.7% - Group A) showing enhanced AP conductivity at follow-up (mean ERP/SPERRI shortening: 30.8 ms, range 10–80 ms), 4 pts were found at HAR and underwent CAb.

176 pts (90.3% – Group B) showed a stable or impaired (25% under pharmacological treatment) AP conductivity during the follow-up. Their mean ERP/SPERRI increase was 39.7 ms (range 0–130 ms). Group A pts were significantly younger (20 vs 28 years old; 88% of Group A pts were <30 years old) and more frequently male (94.1% vs 80.6%). A non-significant trend toward Group A was found for antero-septal APs (35% Group A vs 15.4% Group B).

Conclusions

TEEPT is a safe, non-invasive tool to stratify arrhythmogenic risk of WPW pts. Our data suggest that a watchful waiting is safe for low to moderate risk pts. Younger males with an antero-septal Kent bundle may deserve a more intensive EP follow-up. Aggressive therapy should be considered as mandatory only for symptomatic HAR pts, taking into account complications, risk/benefit ratio and pts' preferences. In other cases, medical therapy and watchful observation could be applied safely under periodical TEEPT, as appropriate.

Compliance in weight control reduces atrial fibrillation worsening: A retrospective cohort study

BACKGROUND AND AIM

Obesity plays a dominant role in the etiology of atrial fibrillation (AF), and the maintenance of a normal body mass index (BMI) seems to prevent and even reduce the incidence of the arrhythmia's recurrence. We selected 270 patients (pts) to assess whether this therapeutic effect was statistically significant even in Mediterranean patients.

METHOD AND RESULTS

In this retrospective cohort study, we analyzed every symptomatic AF relapse during a total follow-up of 657 patient-years. Clinical data, BMI variations, and pts' history were available in our clinical database. We divided the pts in four groups (Gs), according to their BMI variation during the follow-up: G1, normal weight pts, maintaining their weight; G2, overweight pts, losing weight; G3, overweight pts, maintaining their weight; G4, pts gaining weight. Their follow-up (in months) was normalized according to their AF relapses, thus obtaining a mean AF-free period for each patient. Among the overweight groups, G2 showed the best AF-free period (9.7 months). However, G3 and G4 showed a reduced AF-free interval (4.6 and 1.7 months, respectively). G1, predictably, had the longest AF-free period (10 months).

CONCLUSION

The results of the present study confirm that simple non-invasive intervention aimed to normalize BMI and to control risk factors through appropriate lifestyle can be highly effective in reducing the AF burden, by acting on comorbidities and proarrhythmic mechanisms. Therefore, serious attempt should be made to correct risk factors before an ablation therapy is proposed.