Characterization of ventricular depolarization and repolarization changes in a porcine model of myocardial infarction

Quantifying the spatiotemporal influence of acute myocardial ischemia on volumetric conduction velocity

INTRODUCTION

Acute myocardial ischemia occurs when coronary perfusion to the heart is inadequate, which can perturb the highly organized electrical activation of the heart and can result in adverse cardiac events including sudden cardiac death. Ischemia is known to influence the ST and repolarization phases of the ECG, but it also has a marked effect on propagation (QRS); however, studies investigating propagation during ischemia have been limited.

METHODS

We estimated conduction velocity (CV) and ischemic stress prior to and throughout 20 episodes of experimentally induced ischemia in order to quantify the progression and correlation of volumetric conduction changes during ischemia. To estimate volumetric CV, we 1) reconstructed the activation wavefront; 2) calculated the elementwise gradient to approximate propagation direction; and 3) estimated conduction speed (CS) with an inverse-gradient technique.

RESULTS

We found that acute ischemia induces significant conduction slowing, reducing the global median speed by 20 cm/s. We observed a biphasic response in CS (acceleration then deceleration) early in some ischemic episodes. Furthermore, we noted a high temporal correlation between ST-segment changes and CS slowing; however, when comparing these changes over space, we found only moderate correlation (corr. = 0.60).

DISCUSSION

This study is the first to report volumetric CS changes (acceleration and slowing) during episodes of acute ischemia in the whole heart. We showed that while CS changes progress in a similar time course to ischemic stress (measured by ST-segment shifts), the spatial overlap is complex and variable, showing extreme conduction slowing both in and around regions experiencing severe ischemia.

Assessing heart disease using a novel magnetocardiography device

The aim of this paper is to present the use of a portable, unshielded magnetocardiograph (MCG) and identify key characteristics of MCG scans that could be used in future studies to identify parameters that are sensitive to cardiac pathology. We recruited 50 patients with confirmed myocardial infarction (MI) within the past 12 weeks and 46 volunteers with no history of cardiac disease. A set of 38 parameters were extracted from MCG features including both signals from the sensor array and from magnetic images obtained from the device and principal component analysis was used to concentrate the information contained in these parameters into uncorrelated predictors. Linear fits of these parameters were then used to examine the ability of MCG to distinguish between sub-groups of patients. In the fist instance, the primary aim of this study was to ensure that MCG has a basic ability to separate a highly polarised patient group (young controls from post infarction patients) and to identify parameters that could be used in future studies to build a formal diagnostic tool kit. Parameters that parameterised left ventricular ejection fraction (LVEF) were identified and an example is presented to show differential low and high ejection fractions.

A rare transitory change of the De Winter ST/T-wave complex in a patient with cardiac arrest: A case report

RATIONALE

The De Winter ST/T-wave complex is a rare and special electrocardiogram (ECG) manifestation in some patients with a total or subtotal occlusion in the proximal left anterior descending (LAD) coronary artery. It mainly appears as an ST-segment superior oblique depression instead of an ST elevation. However, a transitory change of the De Winter ST/T-wave complex has not been reported previously.

PATIENT CONCERNS

A 40-year-old man developed sudden precordial dull and unrelieved pain. One hour later, he suddenly lost consciousness when he arrived at the emergency department. After successful cardiopulmonary resuscitation (CPR), 2 ECGs were taken at 22-minute interval, which showed completely different manifestations. The first ECG showed acute inferior-wall ST elevation myocardial infarction (STEMI), while the second ECG showed a De Winter ST/T-wave complex, which indicated acute anterior-wall myocardial infarction.

DIAGNOSIS

The patient was diagnosed with acute myocardial infarction.

INTERVENTIONS

The patient responded to urgent treatment by percutaneous coronary intervention (PCI).

OUTCOMES

It was confirmed that the case was consistent with the main characteristics of a De Winter ST/T-wave complex after PCI. The first ECG was a rare transitory change of the De Winter ST/T-wave complex. The patient was well recovered and discharged.

LESSONS

The De Winter ST/T-wave complex is an extremely dangerous and rare ECG manifestation that is not widely recognized at present. Although the mechanism is not very clear, it should be considered as indicating an equivalent risk of STEMI because it may suggest total or subtotal occlusion in the proximal LAD coronary artery. It is believed that in the near future, the mechanism of ECG including its transitory changes, will be fully revealed.