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Published on: July 2, 2018
Quantifying the spatiotemporal influence of acute myocardial ischemia on volumetric conduction velocity
Wilson W Good1, Brian Zenger2, Jake A Bergquist1
1Scientific Computing and Imaging Institute, University of Utah, Salt Lake City, UT, USA; Department of Biomedical Engineering, University of Utah, Salt Lake City, UT, USA; Nora Eccles Cardiovascular Research and Training Institute, University of Utah, Salt Lake City, UT, USA.
Insights
Acute myocardial ischemia significantly slows cardiac electrical conduction, with changes correlating temporally but not spatially with ECG ST-segment shifts. This research quantifies conduction slowing during ischemia.
Area of Science:
- Cardiology
- Electrophysiology
- Medical Imaging
Background:
- Acute myocardial ischemia impairs heart electrical activity, potentially causing sudden cardiac death.
- Ischemia affects ECG ST and repolarization, but its impact on cardiac electrical propagation (QRS) is less understood.
Purpose of the Study:
- To quantify volumetric conduction velocity changes during experimentally induced ischemia.
- To assess the correlation between conduction velocity and ischemic stress.
Main Methods:
- Estimated volumetric conduction velocity (CV) using activation wavefront reconstruction and an inverse-gradient technique.
- Measured ischemic stress via ST-segment changes throughout 20 ischemic episodes.
Main Results:
- Acute ischemia caused significant conduction slowing (median speed reduced by 20 cm/s).
- A biphasic response (acceleration then deceleration) in conduction speed was observed early in some episodes.
- High temporal correlation (but moderate spatial correlation, r=0.60) was found between ST-segment changes and conduction slowing.
Conclusions:
- This study provides the first volumetric assessment of conduction speed changes during acute myocardial ischemia.
- Conduction slowing progresses with ischemic stress, but spatial overlap is complex, with severe slowing in and around ischemic regions.
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.
