A Pulsatile Assist Device (PAD) for Use During Cardiopulmonary Bypass

A new valveless pulsatile assist device (PAD) has been developed that converts roller pump flow into synchronized pulsatile flow. The PAD can also be used as an arterial counter-pulsator (ACtP) before and after cardiopulmonary bypass (CPB). The PAD was employed in 100 adult patients undergoing open heart surgery for coronary artery and/or valvular heart disease. Seventy-three of these patients were NYHA class III or IV, had ejection fractions of less than 0.3, or an LVEDP greater than or equal to 18 mm Hg. Sixty-one patients underwent coronary artery bypass alone, 17 valve replacement alone, three ventricular aneurysm alone, 12 combined coronaries and valves, and seven combined coronaries and ventricular aneurysms. The device functioned as a hemodynamically effective ACtP before and after CPB. During CPB, pulse pressures of 40-50 mm Hg were readily obtained. Urinary outputs during CPB were increased on the PAD when compared to a control group (9.18 +/- 0.68 cc/min vs 3.90 +/- 0.34 cc/min). In addition, during CPB, coronary graft blood flow (CBF) increased an average of 21.4 +/- 6.1% with the PAD, and after CPB, CBF increased an average of 25.0 +/- 5.9%. Free plasma hemoglobins after CPB were not elevated. Only one patient had a perioperative myocardial infarction, and this patient was successfully treated with intra-aortic balloon pumping. It is suggested from these data that use of the PAD may decrease both the incidence of perioperative myocardial infarction and the need for postoperative intra-aortic balloon pumping.

An improved method of myocardial protection with pulsation during cardiopulmonary bypass.

During the past 9 years, no patient has been denied surgery because of diffuse disease, providing ventricular function was satisfactory (ejection fraction greater than 30%). This means that many secondary coronary branches were used for bypass, and five to seven grafts were commonly inserted. Bypass grafts to smaller arteries have been carefully evaluated. Dilators in 0.5 mm increments are used to measure this size of the distal anastomosis in surgery. Graft patency has been correlated with the largest sized dilator which the coronary would accept. With 1.5 mm lumen, the patency has been 84%, only 3% less than the overall average. With 1 mm lumen, 67% of grafts have remained open. Flows are routinely measured at surgery and no significant change in patency occurs unless the flow is less than 20 cc/min. Even with less than 20 cc/min flow, 68% of grafts were later shown to be open. Long-term studies have shown no accelerated failure in the small vessel group. We have followed a group of patients operated on from 1970 through 1975 with normal ventricular function, but diffuse disease requiring four to eight grafts. Late mortality has been 0.86% per year, which is slightly less than the mortality rate of the general population for a comparable age group. While bypasses to multiple normal secondary branches are routinely performed, endarterectomy of any major artery is done when necessary. The perioperative infarct rate has been carefully monitored in all of our patients using standard EKG and also with pyrophosphate scan. Four percent of the patients developed new Q waves and 8% had positive pyrophosphate scans. In summary, disease so diffuse as to contraindicate surgery is yet to be found in patients with reasonably good ventricular function. Similar results with small arteries have not been achieved by all centers, and it is recommended that all surgery be carefully evaluated and the results of each center should be used as the major criteria in the selection of further patients for surgery. In 1968, when coronary bypass surgery was first introduced to our center, several studies were initiated to evaluate bypass grafts. Operative graft flow measurements were recorded and have been studied ever since that time. Recordings of the lumen size of grafted arteries were made. Postoperative cine studies were performed and preand postoperative bicycle ergometric studies were done. All of this, and more, plus late follow-up data have been continuously recorded in a computer based data registry system. Early angiographic studies of single grafts rarely showed col laterals to other critically ischemic coronaries. Bicycle ergometric studies preoperatively consistently showed marked deterioration in left ventricular function under stress when critical coronary lesions were present. These same stress studies often showed little or no improve-

Coronary Heart Surgery

Introduction: The design of implantable blood pumps is either based on displacement pumps with membranes or rotary pumps. Both pump types have limitations to meet the clinical requirements. Rotary piston blood pumps have the potential to overcome these limitations and to merge the benefits. Compared to membrane pumps, they are smaller and with no need for wear-affected membranes and valves. Compared to rotary pumps, the blood flow is pulsatile instead of a non-physiological continuous flow. Furthermore, the risk of flow-induced blood damage and platelet activation may be reduced due to low shear stress to the blood.Areas covered: The past developments of rotary piston blood pumps are summarized and the main problem for long-term application is identified: insufficient seals. A new approach with seal-less drives is proposed and current research on a simplified rotary piston design is presented.Expert commentary: The development of blood pumps focuses mainly on the improvement of rotary pumps. Howev...

F. Beckett

Papers

Pulsatile flow blood pump based on the principle of the Wankel engine. Preliminary report.