An Investigation of Cardiac Dynamics and Substrate Metabolism in an Animal Heart Failure Model Anna E. Stanhewicz

Heart Failure Heart disease is the primary cause of death in the US Heart Failure: insufficient blood supply to the body Progressive disease Early Stage Risk Factors Compensated Phase Decompensated End Stage Death Heart Attack, Hypertension May go unnoticed Cardiac output is maintained Patient does not experience symptoms Significant decline in cardiac output Patient experiences symptoms

How the Heart Works Right Atrium Right Ventricle Left Atrium Left Ventricle Systole – contraction Diastole - relaxation

Heart Failure is Characterized by a Combination of Dynamic and Metabolic Changes

Dynamic Changes Decreased Cardiac Output and Ejection Fraction Key element is cardiac hypertrophy Response to increased vascular resistance Changing size and shape Diastolic dysfunction Systolic dysfunction Healthy HeartCompensatedHeart Failure stressor hypertrophy excessive work decompensation

Metabolic Changes Healthy heart: 60-90% fatty acids 10-40% carbohydrate (glucose) In HF we see a change in substrate preference from fatty acids to carbohydrate Expected Metabolic Profile as HF Progresses Time % Substrate Utilization Fatty Acid Carbohydrate

Project Goals: 1.Develop working knowledge of the perfused mouse heart system 2.Use perfused mouse heart to measure cardiac dynamics and substrate metabolism simultaneously

Methods Perfused Working Mouse Heart Allows for measurement of myocardial function and metabolism under defined loading conditions Ex Vivo - Independent of neurohormonal influence Desirable – easy genetic modification, rapid reproductive cycle, similarity to human physiology

Methods Perfused Working Mouse Heart First perfused through the aorta (retrograde) with Krebs- Henseleit solution Then perfused through the left ventricle (anterograde) with physiologic buffers Temperature, filling pressure and resistance to aortic outflow maintained at physiologic levels

Methods Dynamic Measurements 1.4F Millar Mikro-Tip® Ultra-miniature P-V Catheter Inserted through the apex of the heart into the left ventricle Measures changing pressures and volumes Data integrated into PVAN software

Methods Metabolism- Measurement of 3 H 2 O production from radio labeled substrate Glycolysis –5-[ 3 H]glucose → [ 3 H 2 O] Fatty Acid Oxidation –9,10-[ 3 H]palmitate → [ 3 H 2 O] 0.2mL of perfusate taken every 10 min 0.18mL of each sample run through Dowex chromatography column – counted for 3 H 2 O activity

Measures of Dynamic Function HR=300bpm unpaced Time (sec) Left Ventricular Pressure (mmHg) Pressure Waves in Working Mouse Heart

Dynamic Results Obtained from PVAN Software Heart Rate (bpm)340 Stroke Volume (μL)19.79 Ejection fraction (%)11.41 Cardiac output (mL/min)6.68 End-systolic pressure (mmHg) End-systolic volume (μL) End-diastolic pressure (mmHg) End-diastolic volume (μL) Left Ventricular Pressure (mmHg) Left Ventricular Volume (μL) Pressure-Volume Loops in Working Mouse Heart

Metabolism Results Glycolysis Rate = 4.97 μmoles·g -1 dry weight·min -1

Metabolism Results Fatty Acid Oxidation Rate = 0.80 μmoles· g dry weight -1 ·min -1

Discussion With this system dynamic and metabolic measures were obtained simultaneously This holds great potential for drug development studies Lays groundwork for more developed understanding of complexities of heart failure Early detection Intervention

Acknowledgements Thomas Manfredi, Ph.D. Robert Rodgers, Ph.D. Fredrick Vetter, Ph.D. Arthur Cosmos, Ph.D. Michael Dunn, Ph.D. Candidate