Dag Ole Nordhaug

MD, PhD

E-post
dagn@fagmed.uit.no

Hovedoppgaver
Dag Nordhaug, Truls Myrmel, MD, PhD. et al.

TREATMENT OF ACUTE ISCHEMIC HEART FAILURE

Background:
Despite improved techniques for intraoperative myocardial protection, low cardiac output syndrome (LOS) remains a significant problem after heart surgery (1). The incidence of the syndrome is about 5-10% after coronary artery bypass surgery. LOS is usually treated with contractility augmenting remedies like dopamin, dobutamin or the newer phosphodiesterase inhibitors. In addition, vasodilating agents like nitroprusside can be used. When pharmacological support is inadequate, mechanical support with intraortic balloon pumping (IABP) is instituted (4). Despite an aggressive approach the mortality is 20-50% (2,3). This warrants the need for optimizing the treatment of postoperative acute ischemic heart failure. First step in an improvement process is to characterize existing regimes better, hoping to elucidate weak points amendable for improvement.

Problem:
Even though the mechanisms behind the effect of intra-aortic balloon pumping is partly known, much remains to be characterized (5-6). For instance: How does IABP, alone and combined with different pharmacological agents, influence the contractility and mechanoenergetic properties of the left and right ventricle? How does the combination of IABP and inotropics and/or vasodilating agents affect the periferal circulation?

Methods:
Porcine in vivo open chest model.
Acute ischemic heart failure is induced by coronary injection of polystyrene microspheres, a method previously described in other animal models (7).
Ventricular contractility and work is assessed by the use of conductance catheters, employing the time varying elastance model depicted by Suga and colleagues (8).
Ventricular energetics are evaluated from the integrated use of conductance catheters, coronary flow measurements (ultrasonic flowprobes) and coronary sinus blood gases. This is analyzed in the PVA/MVO2 framework.

Aims:
-Establish a model for stable acute ischemic heart failure.
-Elucidate the effects of IABP on left and right ventricular contractility, mechanoenergetic variables and ventriculoarterial coupling.
-Describe the same varibles when IABP is used in combination with inotropic and/or vasodilating agents.
-Find out how IABP in combination with vasoactive medication affect the perfusion through vital organs like brain, kidneys and liver.

References:
1. Breisblatt, et.al.: Acute myocardial dysfunction and recovery. J Am Coll Cardiol 1990;15 (6): 1261-9.

2. Rao, V et.al.: Predictors of low cardiac output syndrome after coronary artery bypass. J Thorac Cardiovasc Surg 1996;112: 38-51.

3. Kirklin, Barrat-Boyes: Cardiac Surgery, 1993.

4. Harlan, Starr, Harwin: Cardiac Surgery, Springer Verlag, 1996.

5. Kawaguchi et.al.: Ventriculoarterial coupling with intraaortic balloon pumping in acute ischemic heart failure. J Thorac Cardvasc surg 1999; 117:164-171.

6. Gewirtz et.al.: Effect of intraaortic balloon counterpulsation on regional myocardial blood flow and oxygen consumption. Am J Cardiol 1982; 50: 829-837.

7. Smiseth, Mjøs: A reproducible and stable model of acute ischemic heart failure in dogs. Clin phys 1982;2:225-239.
Suga: Ventricular Energetics. Phys rev 1990;70: 247-277.