Efficacy of cardiac resynchronization in acutely infarcted canine hearts with electromechanical dyssynchrony
Grant V Chow1, Michael G Silverman1, Richard S Tunin1
1Division of Cardiology, Johns Hopkins Medical Institutions, The Johns Hopkins University School of Medicine, Baltimore, Maryland.
Insights
Cardiac resynchronization therapy (CRT) improves heart function in patients experiencing acute myocardial infarction (MI) with left bundle branch block (LBBB). This therapy enhances global systolic function and regional blood flow post-MI.
Area of Science:
- Cardiology
- Biomedical Engineering
- Heart Failure Research
Background:
- Acute myocardial infarction (MI) combined with left bundle branch block (LBBB) and left ventricular (LV) decompensation leads to high early mortality.
- The efficacy of cardiac resynchronization therapy (CRT) in improving hemodynamic status in this critical condition remains largely unknown.
- A canine model was utilized to investigate CRT's effects during and after acute MI with delayed lateral wall activation.
Purpose of the Study:
- To evaluate the acute hemodynamic effects of CRT in a canine model of MI with LBBB.
- To assess how CRT impacts LV function during and immediately following coronary artery occlusion-reperfusion.
Main Methods:
- An open-chest canine model subjected to 2-hour coronary artery occlusion and 1-hour reperfusion.
- Comparison of four pacing modes: right atrial pacing, right ventricular pacing (pseudo-LBBB), LW-CRT, and peri-infarct zone-CRT.
- Continuous monitoring of LV pressure-volume data, regional segment length, and coronary blood flow.
Main Results:
- Both CRT modes and right ventricular pacing reduced anterior wall regional work during occlusion.
- Despite increased dyskinesis with CRT during occlusion, global cardiac output, stroke work, and ejection fraction improved by 11%-23%.
- Post-reperfusion, CRT enhanced infarct zone regional work and blood flow, alongside improved global function compared to pseudo-LBBB.
Conclusions:
- CRT enhances global systolic function in LV with delayed lateral wall activation during and after MI.
- CRT modestly increases infarct zone dyskinesis during occlusion but improves regional function and blood flow post-reperfusion.
- Findings support the use of CRT for early post-MI dyssynchronous heart failure.
Background:
Patients with acute myocardial infarction (MI), left bundle branch block (LBBB), and marked left ventricular (LV) decompensation suffer from nearly 50% early mortality. Whether cardiac resynchronization therapy (CRT) improves hemodynamic status in this condition is unknown. We tested CRT in this setting by using a canine model of delayed lateral wall (LW) activation combined with 2 hours of coronary artery occlusion-reperfusion.
Objective:
This study aimed to evaluate the acute hemodynamic effects of CRT during and immediately after MI.
Methods:
Adult dogs (n = 8) underwent open-chest 2-hour mid-left anterior descending artery occlusion followed by 1-hour reperfusion. Four pacing modes were compared: right atrial pacing, pseudo-left bundle block (right ventricular pacing), and CRT with the LV lead positioned at either the LW (LW-CRT) or the peri-infarct zone (peri-infarct zone-CRT). Continuous LV pressure-volume data, regional segment length, and proximal left anterior descending flow rates were recorded.
Results:
At baseline, both right ventricular pacing and peri-infarct zone CRT reduced anterior wall regional work by ~50% (vs right atrial pacing). During coronary occlusion, this territory became dyskinetic, and dyskinesis rose further with both CRT modes as compared to pseudo-LBBB. Global cardiac output, stroke work, and ejection fraction all still improved by 11%-23%. After reperfusion, both CRT modes elevated infarct zone regional work and blood flow by ~10% as compared to pseudo-LBBB, as well as improved global function.
Conclusion:
CRT improves global chamber systolic function in left ventricles with delayed LW activation during and after sustained coronary occlusion. It does so while modestly augmenting infarct zone dyskinesis during occlusion and improving regional function and blood flow after reperfusion. These findings support CRT in the setting of early post-MI dyssynchronous heart failure.
