Evaluation of coronary blood flow velocity during cardiac arrest with circulation maintained through mechanical chest compressions in a porcine model

Abstract

Background: Mechanical chest compressions (CCs) have been shown capable of maintaining circulation in humans suffering cardiac arrest for extensive periods of time. Reports have documented a visually normalized coronary blood flow during angiography in such cases (TIMI III flow), but it has never been actually measured. Only indirect measurements of the coronary circulation during cardiac arrest with on-going mechanical CCs have been performed previously through measurement of the coronary perfusion pressure (CPP). In this study our aim was to correlate average peak coronary flow velocity (APV) to CPP during mechanical CCs.

Methods: In a closed chest porcine model, cardiac arrest was established through electrically induced ventricular fibrillation (VF) in eleven pigs. After one minute, mechanical chest compressions were initiated and then maintained for 10 minutes upon which the pigs were defibrillated. Measurements of coronary blood flow in the left anterior descending artery were made at baseline and during VF with a catheter based Doppler flow fire measuring APV. Furthermore measurements of central (thoracic) venous and arterial pressures were also made in order to calculate the theoretical CPP.

Results: Average peak coronary flow velocity was significantly higher compared to baseline during mechanical chests compressions and this was observed during the entire period of mechanical chest compressions (12 - 39% above baseline). The APV slowly declined during the 10 min period of mechanical chest compressions, but was still higher than baseline at the end of mechanical chest compressions. CPP was simultaneously maintained at > 20 mmHg during the 10 minute episode of cardiac arrest.

Conclusion: Our study showed good correlation between CPP and APV which was highly significant, during cardiac arrest with on-going mechanical CCs in a closed chest porcine model. In addition APV was even higher during mechanical CCs compared to baseline. Mechanical CCs can, at minimum, re-establish coronary blood flow in non-diseased coronary arteries during cardiac arrest.

Figure 1

Doppler curves from each of the four different experimental periods. Doppler flow measurement from which the APV is calculated shown for all periods of the experiments and each pig (P n), baseline sinus rhythm (Baseline), untreated VF (VF without CC), VF during chest compressions (VF with CC) and post return of spontaneous circulation (Post ROSC). Note the difference in scale on the y-axis, which is due to automatic adjustments made by the FloMap monitor.

Figure 2

Central Venous Pressure vs. Arterial pressure. The development of minimum, mean and max (Min, Mean and Max) intra-thoracic aortic pressure and right atrial pressure during the total experimental period (28 min). Data are presented as the mean value of the 30 seconds periods of analyzed data, and each individual pigs data are time adjusted to same length for each period of the experiments.

Figure 3

Mean coronary perfusion pressure vs. Average Peak Velocity. The development of the calculated mean coronary perfusion pressure (CPP in mmHg) during the total experimental period (28 min) and the development of coronary flow velocity (cm/s) during the experimental period. Coronary flow is not shown after ROSC due to technical problems after defibrillation. Data are presented as the mean value of the 30 seconds periods of analyzed data, and each individual pigs data are time adjusted to same length for each period of the experiments.

Figure 4

Correlation of Coronary Perfusion Pressure and Average Peak Velocity. Shows the correlation between calculated coronary perfusion pressure (CPP) and average peak velocity (APV) during the 10 min of mechanical chest compressions. To test the null-hypothesis for correlation between APV and CPP, correlation Z-test was used.