Hypothermia Modulates Arrhythmia Substrates During Different Phases of Resuscitation From Ischemic Cardiac Arrest

Figures

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  Figure 1. Experimental design and timeline. A, Multipolar plunge electrode placement near the noninfarct zone (NIZ; solid rectangle), border zone (BZ; dashed rectangle), and infarct zone (IZ; circle). Left anterior descending artery (LAD) occlusion site (asterisk) is placed between the first and second diagonal branch of the LAD. B, Stainless steel transmural needle electrodes with 5 recording sites. C, Experimental timeline. LAD is occluded during the first 60 minutes and reperfused during the final 30 minutes. ACLS indicates advanced cardiac life support; AMI, acute myocardial infarction; CPR, cardiopulmonary resuscitation; CT, control; ENDO endocardium, ; EPI, epinephrine; ROSC, return of spontaneous circulation; TH, therapeutic hypothermia; and VF, ventricular fibrillation.

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  Figure 2. Spontaneous ventricular tachycardia/fibrillation (VT/VF) initiation. A, Electrogram tracings are shown in the noninfarct zone (NIZ), border zone (BZ), and infarct zone (IZ) as well as transmurally (epicardial (EPI) and endocardial (ENDO). ECG tracing is shown. A ventricular ectopic beat (black line) originates in the IZ ENDO, before VT initiation, which quickly degenerates to VF. B, Summary data for the initiation of spontaneous VT/VF during each phase of resuscitation. AMI indicates acute myocardial infarction; LAD, left anterior descending artery; NS, p value not significant; for AMI p=1, for Post ROSC p=1 and ROSC, return of spontaneous circulation.

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  Figure 3. Ventricular ectopy during resuscitation. A, Representative in vivo electrogram tracings from control (CT) and therapeutic hypothermia (TH) at 6 minutes after return of spontaneous circulation (ROSC). In CT, there are frequent ventricular ectopic beats (VEBs; asterisks). B, Summary data for ventricular ectopy. VEBs/min is shown during the phases of resuscitation. VEB/min is significantly increased from baseline during each phase of resuscitation (ANOVA P<0.05). AMI indicates acute myocardial infarction; LAD, left anterior descending artery; NS, not significant, p=.29; and VT, ventricular tachycardia.

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  Figure 4. Cardiac alternans during resuscitation. A, Representative traces of alternans (arrows) and ventricular fibrillation (VF) with therapeutic hypothermia (TH) (bottom panel), and the absence of alternans and VF without TH (top panel) during left anterior descending artery (LAD) reperfusion. B, Summary data of cardiac alternans magnitude from electrogram recordings (as a percentage of full scale) in pigs achieving return of spontaneous circulation (ROSC) during each phase of resuscitation. Alternans is markedly enhanced by TH (blue bars) after LAD reperfusion. AMI indicates acute myocardial infarction; AU arbitrary units, ; CT, control; and NS, not significant: baseline p=.77, AMI p=.66, Post ROSC p=.54.

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  Figure 5. Regional activation recovery interval and global dispersion of repolarization (DOR) during resuscitation. A, Electrogram (EG) recordings at baseline and 24 minutes of left anterior descending artery (LAD) occlusion in the infarct zone (IZ). At baseline, therapeutic hypothermia (TH) lengthens the activation recovery interval (ARI). During ischemia, there is similar shortening of ARIs in both groups, and significant conduction slowing during ischemia (delayed transmural conduction and widened EG) is seen in both groups. B, Global DOR is shown. TH increases DOR during ischemia but returns to baseline during reperfusion. CT indicates control; ENDO endocardium, ; EPI, epicardium; MI, myocardial infarction; NIZ, non‐IZ; and ROSC, return of spontaneous circulation. *P<0.05.