The Intervention Center, Rikshospitalet, Oslo University Hospital, Oslo, Norway; University of Oslo, Oslo, Norway.
J Am Soc Echocardiogr. 2013 Nov;26(11):1353-63. doi: 10.1016/j.echo.2013.06.021. Epub 2013 Jul 25.
Therapeutic hypothermia is used after cardiac arrest. The aim of this study was to investigate the effects of therapeutic hypothermia on left ventricular (LV) function assessed by ultrasonic imaging.
In 10 pigs, LV volumes, ejection fractions, and longitudinal strain were measured using two-dimensional echocardiography. Midwall fractional shortening and end-systolic wall stress were calculated. Wall thickness was continuously measured using an epicardial ultrasonic transducer placed on the LV anterior wall. Wall thickening velocity (S') and pressure-wall thickness loops were used to assess systolic function. Diastolic function was assessed by echocardiographic transmitral flow and mitral annular velocity (e') measurements, calculation of the LV relaxation constant, and determination of LV stiffness and restoring forces using the end-diastolic pressure-wall thickness relation during volume unloading. Early wall thinning velocity (e'wt) and early diastolic wall thinning were calculated. Measurements were done at 38°C and 33°C, at spontaneous heart rate and at atrial pacing at 100 beats/min.
End-diastolic volume, stroke volume, midwall fractional shortening, and longitudinal strain remained unchanged during hypothermia, but end-systolic wall stress, S', and pressure-wall thickness loop area decreased. A shift from early to late diastolic LV filling occurred during hypothermia, with concurrent decreases in e', e'wt, and early wall thinning fraction. Relaxation was prolonged, LV stiffness was increased, and restoring force was decreased during hypothermia. Hypothermia induced a decrease in relative diastolic duration at spontaneous heart rate, which was further reduced during pacing. During paced heart rate at 33°C, stroke volume, ejection fraction, and strain were reduced.
Hypothermia induced systolic and diastolic dysfunction, with reduced tolerance to increased heart rate. These findings may have implications for patient management during hypothermia.
心脏骤停后会使用治疗性低温。本研究旨在通过超声成像来探究治疗性低温对左心室（LV）功能的影响。
在 10 头猪中，使用二维超声心动图测量 LV 容积、射血分数和纵向应变。计算中层壁缩短率和收缩末期壁应力。通过放置在 LV 前壁的心外膜超声换能器连续测量壁厚度。使用壁增厚速度（S'）和压力-壁厚度环来评估收缩功能。通过测量超声心动图二尖瓣血流和二尖瓣环速度（e'）、计算 LV 松弛常数以及通过在容量卸载期间测量舒张末期压力-壁厚度关系来评估舒张功能，确定 LV 僵硬度和恢复力。计算早期壁变薄速度（e'wt）和早期舒张期壁变薄。在 38°C 和 33°C 下，在自发心率和 100 次/分时的心房起搏下进行测量。
在低温过程中，LV 舒张末期容积、每搏量、中层壁缩短率和纵向应变保持不变，但收缩末期壁应力、S'和压力-壁厚度环面积减小。低温时，LV 从早期向晚期充盈转变，同时 e'、e'wt 和早期壁变薄分数降低。低温时，舒张期延长，LV 僵硬度增加，恢复力降低。低温时，自发性心率下相对舒张期持续时间减少，起搏时进一步减少。在 33°C 时的起搏心率下，每搏量、射血分数和应变降低。
低温引起收缩和舒张功能障碍，对心率增加的耐受性降低。这些发现可能对低温期间患者管理有意义。
