Beijing surgeons achieved total arterial myocardial revascularization in 208 patients through evaluation of the early outcome of off-pump coronary artery bypass grafting (OPCAB) with a bilateral internal mammary artery (BIMA) Y-configuration graft. The patients ranged from 33 to 78 years old. The average age was 56. Of the total, 80.2% had triple-vessel disease; 15.9% cases had left coronary disease, and 3.9% had double-vessel disease.
University of Toronto clinicians studied coronary artery graft patency one year after CABG surgery.
They also investigated any major adverse cardiac events such as death, myocardial infarction or repeat revascularization during that time frame.
A common complication following implantation of a ventricular assist device (VAD) is acute right heart failure. To manage this complication effectively, left ventricular preload and contractility must be estimated reliably.
A 66-year-old female with end-stage heart failure was implanted with a HeartAssist 5 (from Micromed Cardiovascular Inc. of Houston) with a custom Transonic® Flowprobe on the VAD’s outflow graft to continuously measure real-time pump blood flow. On days one and two post-op, mean flow through the graft was 4.8 L/min. On day three post-op, real-time flow began a progressive decline that was accompanied by an increase in central venous pressure and progressive renal failure.
Case No. 1: Y SVG-PLB, PDA Graft with Low Flow in One Branch
A 66-year-old male with multi-vessel coronary artery disease underwent CABG surgery. A saphenous vein Y graft was anastomosed to the Posterior Descending Artery (PDA) and to the Posterior Lateral Branch (PLB). When the PDA branch was occluded and flow was measured in the PLB, mean flow was only 5 mL/min, but the flow exhibited a good systolic/diastolic wave pattern. Negative troughs in the flow profile indicate that the mean flow of that branch of the Y was being compromised by competitive flow from the native coronary. Flow in the PDA branch was 25 mL/min, indicating that most of the flow was going through that branch of the Y graft. A vein graft was subsequently anastomosed to the obtuse marginal coronary (OM) in the patient to improve flow to the distal myocardium.
The following two cases demonstrate how critical flow measurement is in determining the patency of a bypass graft. The bypass grafts in each of the cases first measured 0 ml/min flow. Flow improved appreciably after revision of the grafts.
Analysis of a flow waveform is useful when the mean flow of the bypass graft is questionable, between 5 mL/min and 20 mL/min. But what should one look for? First, the waveform should have a smooth, repeatable flow profile. Secondly, there generally should be clear definition of a biphasic waveform representing systole and diastole as shown in the following example of four patent grafts in an 83-year-old patient.
Intraoperative flow measurements during coronary artery bypass grafting are performed to detect technical problems at the time of surgery when correction is relatively simple. One tool in the surgeon’s arsenal to detect a graft in trouble is Pulsatility Index that combines mean flow and waveform properties into one number. Introduced by D’Ancona and colleagues about 2000, the Pulsatility Index is simply calculated by subtracting the minimum recorded flow from the maximum recorded flow and dividing the difference by the mean flow. D’Ancona and colleagues suggested that a PI between 1 and 5 would indicate a good graft, while a PI greater than 5 would indicate a suspect graft. PI quickly caught on as a reliable indicator of graft patency and was soon added to the display screens and printouts of flowmeters to be used as a major indicator of a good graft. Studies were performed using PI as one endpoint for assessment of grafts and comparison of flowmeters.
Flow-based intraoperative bypass graft patency assessment during CABG confirms a graft’s flow-carrying capacity to prevent early graft failure. But sometimes bypass graft flow does not meet expectations. Where would you look if, after you have constructed a graft and measured flow, the graft flow is less than one would anticipate given the health and size of the conduit and the physiology of the patient?
Mean flow, maximum flow, minimum flow, PI, DF% or D/S Ratio all show up on the flow monitor display. What should the surgeon consider first in assessing the patency of a bypass graft?
Mean flow is the primary indicator of graft patency. It can confirm the patency of a good graft or, conversely, signal an undesirable graft. While flows greater than 20 to 30 mL/min indicate a good graft, flows under 5 mL/min always indicate that there is a problem with the graft. Experience supports a mean flow of 30 mL/min to indicate acceptable patency. For small patients or small target vessels, this number can be reduced to 20 mL/min. European guidelines state: “Flow < 20 mL/min and pulsatility index >5 predict technically inadequate grafts, mandating graft revision before leaving the operating theatre.”1
Flow, the amount of fluid passing a certain point during a defined time frame (mL/min, L/min), is life’s quintessential vital sign. By delivering oxygen and nutrients to cells for metabolism and removing metabolic wastes, blood flow is life-giving. When blood fails to flow, life ends.
Whether a CABG is performed minimally-invasviely, off-pump, on-pump, or robotically-assisted, the end point is the same: to know how much blood flow is going through a newly created anastomosis. A quantitative flow measurement takes only seconds to perform. The flow measurement augments a surgeon’s clinical observations such as the quality of the heart’s contractions, MAP, EKG, CO, and BP. Direct graft flow measurements help a surgeon identify a problem’s source more effectively and efficiently than any other single parameter as illustrated by the following two CABG cases where revisions were triggered by unacceptable flow measurements.