Comparative Hemodynamic Effects of Contemporary Percutaneous Mechanical Circulatory Support Devices in a Porcine Model of Acute Myocardial Infarction

Abstract

Objectives: The aim of this study was to directly compare the hemodynamic effects of 2 contemporary percutaneous mechanical circulatory support devices in a porcine model of acute myocardial infarction.

Background: Percutaneous support devices offer the ability to unload the ischemic left ventricle, but the comparative hemodynamic effects of contemporary platforms are unclear.

Methods: Yorkshire swine (mean weight 76 ± 2 kg; n = 7) were instrumented with a left ventricular (LV) pressure-volume (PV) catheter and subjected to a 2-h coronary occlusion. Hemodynamic parameters and PV-derived indexes of LV performance were assessed 30 min after reperfusion and during LV support with Impella CP (ICP) and TandemHeart devices (in randomized order) at comparable flow rates.

Results: Myocardial infarction produced a rightward shift of the PV loop and increased LV end-diastolic pressure (from 9 ± 2 mm Hg to 15 ± 2 mm Hg; p = 0.04). After reperfusion, both devices maintained aortic pressure, shifted the PV loop to the left, and decreased LV end-diastolic pressure (ICP vs. TandemHeart; 11 ± 1 mm Hg vs. 7 ± 4 mm Hg; p = 0.04). However, only TandemHeart elicited significant reductions in native LV stroke volume (from 75 ± 7 ml to 39 ± 7 ml; p < 0.01), dP/dt_max (from 988 ± 77 mm Hg/s to 626 ± 42 mm Hg/s; p < 0.01), stroke work (from 0.70 ± 0.03 J to 0.26 ± 0.05 J; p < 0.01), PV area (from 0.95 ± 0.11 J to 0.47 ± 0.10 J; p < 0.01), and pre-load-recruitable stroke work slope (from 41.7 ± 2.8 J/ml to 30.6 ± 3.9 J/ml; p = 0.05).

Conclusions: At comparable device flow rates, TandemHeart decreased LV pre-load, native LV stroke volume, and myocardial contractility to a greater degree than ICP. Reductions in load-independent indexes of LV performance indicate favorable effects on myocardial oxygen balance and support further study of TandemHeart in clinical scenarios requiring mechanical support in the setting of acute myocardial ischemia.

Keywords: acute myocardial infarction; left ventricular assist device; percutaneous mechanical circulatory support; ventricular unloading.

FIGURE 1. Experimental Protocol

Following baseline data collection, the left circumflex coronary artery was occluded for 2 h. Thirty min after reperfusion, data collection was repeated and animals were randomized to mechanical circulatory support with either Impella CP (ICP) or TandemHeart. After data collection, the first device was removed and data collection was repeated during a second unassisted post–myocardial infarction (MI) time point, followed by insertion of the second circulatory support device. PV = pressure-volume; TTC = triphenyl tetrazolium chloride.

FIGURE 2. Porcine Model of Acute Myocardial Infarction

(A) Example fluoroscopic images illustrating the percutaneous coronary occlusion procedure. (B) Data collected 30 min after reperfusion demonstrated a rightward shift in the pressure-volume (PV) loop, an elevation in left ventricular (LV) end-diastolic pressure, and a reduction in LV ejection fraction. (C) PV loops collected during rapid inferior vena cava occlusion permitted assessment of load-independent parameters of LV performance. Compared with baseline, end-systolic elastance (the slope of the end-systolic PV relationship) was decreased following myocardial infarction (MI). (D) Following excision, the left ventricle was sectioned into 5 short-axis slices for post-mortem assessment of infarct size. LCx = left circumflex coronary artery.

FIGURE 2. Porcine Model of Acute Myocardial Infarction

(A) Example fluoroscopic images illustrating the percutaneous coronary occlusion procedure. (B) Data collected 30 min after reperfusion demonstrated a rightward shift in the pressure-volume (PV) loop, an elevation in left ventricular (LV) end-diastolic pressure, and a reduction in LV ejection fraction. (C) PV loops collected during rapid inferior vena cava occlusion permitted assessment of load-independent parameters of LV performance. Compared with baseline, end-systolic elastance (the slope of the end-systolic PV relationship) was decreased following myocardial infarction (MI). (D) Following excision, the left ventricle was sectioned into 5 short-axis slices for post-mortem assessment of infarct size. LCx = left circumflex coronary artery.

FIGURE 3. Hemodynamic Effects of Impella CP and TandemHeart Following Acute Myocardial Infarction

(A) Example fluoroscopic images demonstrating anatomic placement of each device. (B) Representative pressure-volume (PV) loops illustrate the hemodynamic effects of each device (blue Impella CP and green TandemHeart) compared with the corresponding unassisted post–myocardial infarction (MI) baseline time point (red). Both devices shifted the PV loop to the left and decreased left ventricular (LV) end-diastolic pressure, but only TandemHeart (TH) produced a reduction in native LV stroke volume. (C) The leftward shift of the PV loop with each device is quantitatively illustrated by the reduction in LV end-diastolic volume. However, LV end-systolic volume differed during support with the 2 devices, such that only TH produced a significant reduction in native LV stroke volume. As a result, native LV cardiac output decreased only during TH support despite similar pulmonary blood flow (i.e., total cardiac output) with both devices. (D) TH produced greater reductions in LV dP/dt_max and stroke work compared with Impella CP (ICP), indicative of decreased myocardial contractility and mechanical work during TH unloading. *p < 0.05 versus post-MI; †p < 0.05 versus ICP.

FIGURE 3. Hemodynamic Effects of Impella CP and TandemHeart Following Acute Myocardial Infarction

(A) Example fluoroscopic images demonstrating anatomic placement of each device. (B) Representative pressure-volume (PV) loops illustrate the hemodynamic effects of each device (blue Impella CP and green TandemHeart) compared with the corresponding unassisted post–myocardial infarction (MI) baseline time point (red). Both devices shifted the PV loop to the left and decreased left ventricular (LV) end-diastolic pressure, but only TandemHeart (TH) produced a reduction in native LV stroke volume. (C) The leftward shift of the PV loop with each device is quantitatively illustrated by the reduction in LV end-diastolic volume. However, LV end-systolic volume differed during support with the 2 devices, such that only TH produced a significant reduction in native LV stroke volume. As a result, native LV cardiac output decreased only during TH support despite similar pulmonary blood flow (i.e., total cardiac output) with both devices. (D) TH produced greater reductions in LV dP/dt_max and stroke work compared with Impella CP (ICP), indicative of decreased myocardial contractility and mechanical work during TH unloading. *p < 0.05 versus post-MI; †p < 0.05 versus ICP.

FIGURE 4. Load-Independent Indexes of Left Ventricular Performance During Percutaneous Mechanical Circulatory Support

(A) Representative pressure-volume (PV) loops collected with transient pre-load reduction following reperfused myocardial infarction (MI) (left) with illustration of PV area (PVA) calculation (right). PVA is the product of stroke work (SW) (mechanical energy) and residual (potential) energy and provides an index of myocardial oxygen consumption. (B) Representative PV loops collected with transient pre-load reduction during mechanical circulatory support with Impella CP (ICP) (left) and TandemHeart (TH) (right). (C) Load-independent indexes of myocardial oxygen consumption (PVA) and contractility (pre-load-recruitable SW) were each significantly reduced during TH support. *p < 0.05 versus post-MI; †p < 0.05 versus ICP.

FIGURE 4. Load-Independent Indexes of Left Ventricular Performance During Percutaneous Mechanical Circulatory Support

(A) Representative pressure-volume (PV) loops collected with transient pre-load reduction following reperfused myocardial infarction (MI) (left) with illustration of PV area (PVA) calculation (right). PVA is the product of stroke work (SW) (mechanical energy) and residual (potential) energy and provides an index of myocardial oxygen consumption. (B) Representative PV loops collected with transient pre-load reduction during mechanical circulatory support with Impella CP (ICP) (left) and TandemHeart (TH) (right). (C) Load-independent indexes of myocardial oxygen consumption (PVA) and contractility (pre-load-recruitable SW) were each significantly reduced during TH support. *p < 0.05 versus post-MI; †p < 0.05 versus ICP.