Atrial systole: its role in normal and diseased hearts.

The importance of atrial systole in cardiac physiology was first recognized by William Harvey in 1628: “ ... and if at this time with its auricle alone beating you cut off the apex of the heart with a pair of scissors, you will see the blood flow out of the wound with each beat of the auricle. You will thus realise that the blood gets into the ventricles not through any pull exerted by the distended heart but through the driving force exerted by the beat of the auricles” [ 11. It appears from this quotation, however, that Harvey believed ventricular filling was wholly active and caused by atrial systole. His observations were unsurpassed until the late 19th century when further evidence for the presystolic role of atrial contraction was derived from the intraventricular pressure curve of the horse. Chaveau & Marey in 1863 showed a “small but well defined wave before the sharp systolic rise” [2]. In the early 20th century more exact measurements of cardiac physiology were made and the diastolic filling of the ventricles was studied experimentally. Yandall Henderson [3] in 1906, using an isolated heart preparation and plethysmography to measure volume changes in the ventricle, showed that diastolic ventricular filling was mainly passive and found only a small increase in volume coincident with atrial systole. He concluded that “the contraction of the auricles increases the ventricular volume to the extent of a few drops at most”. Henderson’s results were later criticised by Gesell [2], who felt that the plethysmography equipment used by Henderson was insensitive to rapid changes in volume and that changes in the outer contours of the heart may not represent what was happening inside. This was borne out by the work of Hermann Straub [4], who in 19 10, using isolated mammalian hearts and sensitive plethysmography repeated Henderson’s early experiments. He showed a marked increase in ventricular volume after atrial contraction. Subsequently, Gesell performed a series of experiments [2,5,6] in isolated heart preparations in order to define the role of atrial systole