Combined Effect of the force–Frequency and Length–Tension Mechanisms on Left Ventricular Function in Patients with Dilated Cardiomyopathy

BACKGROUND: The myocardial length-tension and the force-frequency relations are important mechanisms that regulate the contractile strength of the heart. AIMS: To evaluate in humans the effect on left ventricular function of the interaction between the myocardial length-tension and force-frequency relations. METHODS AND RESULTS: Eight patients with dilated cardiomyopathy (DCM) and 6 control subjects underwent radionuclide monitoring of left ventricular function during atrial pacing, saline loading and atrial pacing at the end of saline loading. In controls, atrial pacing reduced left ventricular end-diastolic (P < 0.001) and end-systolic volumes (P < 0.001) with no change in ejection fraction whereas after volume expansion end-diastolic volume (P < 0.001) and ejection fraction (P < 0.001) increased. Atrial pacing after volume expansion increased ejection fraction (P < 0.05). In patients with DCM, ejection fraction was reduced during atrial pacing (P < 0.001) and volume expansion (P < 0.05) due to an increase in left ventricular end-systolic volume (P < 0.001). Pacing tachycardia after volume expansion further increased end-systolic volume and reduced ejection fraction with a significant 'pacing by load' interaction (P < 0.001). Peak filling rate increased at each step in controls while it remained unchanged in patients with DCM. CONCLUSION: The heart rate increase during left ventricular distension improves ventricular function in normals and has detrimental effects in patients with DCM.