The role of beat-by-beat cardiac features in machine learning classification of ischemic heart disease (IHD) in magnetocardiogram (MCG).

Cardiac electrical changes associated with ischemic heart disease (IHD) are subtle and could be detected even in rest condition in magnetocardiography (MCG) which measures weak cardiac magnetic fields. Cardiac features that are derived from MCG recorded from multiple locations on the chest of subjects and some conventional time domain indices are widely used in Machine learning (ML) classifiers to objectively distinguish IHD and control subjects. Most of the earlier studies have employed features that are derived from signal-averaged cardiac beats and have ignored inter-beat information. The present study demonstrates the utility of beat-by-beat features to be useful in classifying IHD subjects (n = 23) and healthy controls (n = 75) in 37-channel MCG data taken under rest condition of subjects. The study reveals the importance of three features (out of eight measured features) namely, the field map angle (FMA) computed from magnetic field map, beat-by-beat variations of alpha angle in the ST-T region and T wave magnitude variations in yielding a better classification accuracy (92.7 %) against that achieved by conventional features (81 %). Further, beat-by-beat features are also found to augment the accuracy in classifying myocardial infarction (MI) Versus control subjects in two public ECG databases (92 % from 88 % and 94 % from 77 %). These demonstrations summarily suggest the importance of beat-by-beat features in clinical diagnosis of ischemia.

An unusual ECG lead reversal.

Lead reversals are a common cause of electrocardiographic abnormality, which can lead to a false diagnosis like chamber enlargement, myocardial ischemia or infarction. Isolated limb lead reversals and chest lead reversals are common in clinical practice. This article reports a rare case where multiple limb and chest leads were reversed due to the reversal of cables leading to a false diagnosis of myocardial ischemia.

A short RP tachycardia in congenitally corrected transposition. What is the mechanism?

A 51-year-old female with congenitally corrected transposition of great arteries (CCTGA), situs solitus, dextrocardia, atrial septal defect and persistent left superior vena cava underwent electrophysiology study for recurrent palpitations with documented narrow complex, short RP tachycardia. With a catheter in the region of the anterior mitral annulus, a His signal was recorded and HV interval was 35 msec. Tachycardia was induced with a ventricular extrastimulus. During the tachycardia there was 1:1 ventriculo-atrial conduction and central atrial activation with a VA interval of 20 msec. The recorded His signal could be seen after the QRS. What is the mechanism of the tachycardia?

Enhancing the efficiency and cost-effectiveness of magnetocardiography by optimal channel selection for cardiac diagnosis.

Background. Magnetocardiography (MCG) is a non-invasive and non-contact technique that measures weak magnetic fields generated by the heart. It is highly effective in the diagnosis of heart abnormalities. Multichannel MCG provides detailed spatio-temporal information of the measured magnetic fields. While multichannel MCG systems are costly, usage of the optimal number of measurement channels to characterize cardiac magnetic fields without any appreciable loss of signal information would be economically beneficial and promote the widespread use of MCG technology.Methods. An optimization method based on the sequential selection approach is used to choose channels containing the maximum signal information while avoiding redundancy. The study comprised 40 healthy individuals, along with two subjects having ischemic heart disease and one subject with premature ventricular contraction. MCG measured using a 37 channel MCG system. After revisiting the existing methods of optimization, the mean error and correlation of the optimal set of measurement channels with those of all 37 channels are evaluated for different sets, and it has been found that 18 channels are adequate.Results. The chosen 18 optimal channels exhibited a strong correlation (0.99 ± 0.006) between the original and reconstructed magnetic field maps for a cardiac cycle in healthy subjects. The root mean square error is 0.295 pT, indicating minimal deviation.Conclusion. This selection method provides an efficient approach for choosing MCG, which could be used for minimizing the number of channels as well as in practical unforeseen measurement conditions where few channels are noisy during the measurement.

Pacing mode survival in patients with single chamber atrial pacemaker for sinus node dysfunction.

BACKGROUND: Single chamber atrial pacemaker should be sufficient for patients with sinus node dysfunction (SND) with normal atrioventricular (AV) conduction. However, most patients undergo dual chamber pacemaker implantation because of concern of new onset AV block. The annual incidence of new AV block has been reported from 0.6 to 4.4 % in various studies. OBJECTIVES: Our aim is to assess mode survival in sinus node dysfunction with normal AV conduction patients implanted with AAIR. METHODS: Patients who underwent single chamber atrial pacemaker implantation for SND with normal AV conduction between January 2014 and December 2021 were followed up for pacemaker device change, new onset AV block, bundle branch block, atrial fibrillation (AF), lead complications, reoperation and mortality rate. RESULTS: A total of 113 patients underwent single chamber atrial pacemaker implantation for SND during the study period. Mean age was 55.6 ± 12.7 years. During a mean follow up of 48.7 ± 24.9 months, none of the patients required pacemaker device change to VVIR/DDDR. Nine patients underwent reoperation, 5 for lead dislodgment, 1 for high threshold, 1 for pocket site erosion and 3 for pulse generator change. None developed AV block or AF with slow ventricular rate. Only 4 patients developed AF (3 paroxysmal,1 permanent). There were 3 deaths during follow up and none were sudden deaths. CONCLUSION: Single chamber atrial pacing is an acceptable mode of pacing in patients with SND in developing countries. Development of AV conduction abnormalities is rare in this relatively younger population.

Para-Hisian pacing: The eyes see what the mind knows.

A young male presented with pre-excited atrial fibrillation. During an electrophysiology study, preexcitation suggestive of a pathway in posteroseptal location was confirmed but no tachycardia was inducible. Para-Hisian pacing was done during sinus rhythm. Is there retrograde conduction through the accessory pathway?

Short term outcomes with dual chamber versus single chamber pacing for atrioventricular block - A crossover trial.

A total of 42 patients were studied for primary outcomes of quality of life and 6MWD between VVIR and DDD modes. At end of 2 months after device implantation, randomization was done and the device was programmed to VVIR or DDD modes. At the end of 2 months in this mode QOL and functional was assessed and the patient was switched to other mode. The same protocol was followed at the end of 2 months. We found no difference in functional capacity and quality of life between the two pacing modes. None of the patients developed pacemaker syndrome and there was no preference for any of the modes.

Coumel's sign reversed: What is the mechanism?

A patient presented with documented narrow QRS tachycardia. During electrophysiological study, he has orthodromic reciprocating tachycardia with atrial activation consistent with left free wall accessory pathway. With induction of tachycardia, beats with LBBB morphology have shorter cycle length than those with narrow QRS. What is the mechanism?

An epoch based methodology to denoise magnetocardiogram (MCG) signals and its application to measurements on subjects with implanted devices.

Magnetocardiograms (MCG) provide clinically useful diagnostic information in a variety of cardiac dysfunctions. Low frequency baseline drifts and high frequency noise are inevitably present in routine MCG even for those measured inside magnetically shielded rooms. These interferences sometimes exceed subtle cardiac features in MCG recorded on subjects with implanted devices like cardiac pacemakers; this makes interpretation of cardiac magnetic fields difficult. The present study proposes a correlation-based beat-by-beat approach and principal component analysis to eliminate drifts and high frequency noise respectively; the approach is suitable for denoising both single and multi-channel MCG data. The methodology is critically evaluated on simulated noisy measurements using a 37 channel MCG system, when objects such as implantable permanent pacemaker and stainless-steel wire are sequentially kept externally on the chests of five healthy subjects. By characterizing the noise introduced by each of these objects, the deterioration in the quality of MCG and its subsequent restoration by using the proposed method is assessed. The performance of the proposed method is also compared with other conventional denoising techniques namely, bandpass filters, wavelets and ensemble empirical mode decomposition. The proposed method not only exhibits least distortion, but also preserves the beat-by-beat dynamics of cardiac time series. The method has also been illustrated on actual MCG measurements on two subjects with implanted pacemaker which highlight the ability of the proposed method for denoising MCG in general and during extremely noisy measurement situations.

Sudden death and its predictors in myocardial infarction survivors in an Indian population.

OBJECTIVE: This study was conducted to assess the incidence of sudden cardiac death (SCD) in post myocardial infarction patients and to determine the predictive value of various risk markers in identifying cardiac mortality and SCD. METHODS: Left ventricular function, arrhythmias on Holter and microvolt T wave alternans (MTWA) were assessed in patients with prior myocardial infarction and ejection fraction ≤ 40%. The primary outcome was a composite of cardiac death and resuscitated cardiac arrest during follow up. Secondary outcomes included total mortality and SCD. RESULTS: Fifty-eight patients were included in the study. Eight patients (15.5%) died during a mean follow-up of 22.3 ± 6.6 months. Seven of them (12.1%) had SCD. Among the various risk markers studied, left ventricular ejection fraction (LVEF) ≤ 30% (Hazard ratio 5.6, 95% CI 1.39 to 23) and non-sustained ventricular tachycardia (NSVT) in holter (5.7, 95% CI 1.14 to 29) were significantly associated with the primary outcome in multivariate analysis. Other measures, including QRS width, heart rate variability, heart rate turbulence and MTWA showed no association. CONCLUSIONS: Among patients with prior myocardial infarction and reduced left ventricular function, the rate of cardiac death was substantial, with most of these being sudden cardiac death. Both LVEF ≤30% and NSVT were associated with cardiac death whereas only LVEF predicted SCD. Other parameters did not appear useful for prediction of events in these patients. These findings have implications for decision making for the use of implantable cardioverter defibrillators for primary prevention in these patients.