Ronald J. Baird

Permanent Cardiac Pacing After Open-heart Surgery: Acquired Heart Disease

Retrospective review of 5,942 patients who underwent open‐heart surgery for acquired heart disease revealed that 123 patients (2.1%) required permanent cardiac pacing postoperatively; 4.6% of these underwent predominantly valvular surgery and 0.6% had coronary bypass. The most important factors appeared to be: 1) preoperative evidence of a conduction disorder; 2) advanced patient age; 3) dense calcium in the aortic annulus; 4) valvular surgery and, especially, tricuspid valve surgery; and 5) poor myocardial protection. Postoperative permanent pacing had a considerable impact on patient morbidity from maintenance operations; most complications were lead‐related problems.

Improved Myocardial Protection during a Prolonged Cross-Clamp Period

Severe coronary stenoses limit delivery of cardioplegic solution to ischemic regions in patients undergoing bypass operations. A prospective randomized trial was undertaken to determine whether the construction of proximal as well as distal anastomoses during a prolonged cross-clamp period would provide more uniform cardiac cooling and better myocardial protection. Ninety-one consecutive patients undergoing elective coronary bypass operations were randomized into two groups. The long cross-clamp technique was used in 46 patients (Group 1), and a proximal anastomosis was constructed after each distal anastomosis. The short cross-clamp technique was employed in 45 patients (Group 2), and distal anastomoses were constructed during aortic occlusion. Cardiopulmonary bypass time was identical, but the cross-clamp period was longer in Group 1 (59 +/- 15 minutes versus 46 +/- 17 minutes in Group 2; p less than 0.001). The mean temperature in the most ischemic region was colder with the long cross-clamp technique (12.5 +/- 3.1 degrees C in Group 1 versus 14.8 +/- 3.2 degrees C in Group 2; p less than 0.01). The total amount of the myocardial isoenzyme of serum creatine kinase released was greater in Group 2 than in Group 1 (332 +/- 34 IU/L per hour in Group 1 versus 469 +/- 45 IU/L per hour in Group 2). Thirty-six patients had coronary sinus catheters inserted (18 patients in each group). Myocardial lactate extraction returned to normal sooner in the patients who had a long cross-clamp period; time to a normal lactate extraction was 0.8 +/- 0.8 hours in Group 1 versus 2.2 +/- 2.1 hours in Group 2 (p less than 0.001). Volume loading and atrial pacing 2 to 4 hours postoperatively produced a similar hemodynamic response in the two groups, but myocardial lactate extraction increased in Group 1 and decreased in Group 2 (p less than 0.05). The construction of proximal as well as distal anastomoses during a prolonged cross-clamp period produced more uniform cooling and improved myocardial protection.

Cardiac dysfunction during abdominal aortic operation: The limitations of pulmonary wedge pressures

The mortality rate for elective abdominal aortic operations remains between 3% and 8% despite careful hemodynamic monitoring, and half of these deaths are cardiac in origin. An extensive evaluation of ventricular function was performed during abdominal aortic operation to detect subtle abnormalities in systolic or diastolic ventricular function that could precipitate progressive ischemic cardiac injury. Twenty-three patients undergoing elective abdominal aortic operations (14 patients with abdominal aortic aneurysm [AAA] and nine patients with aortoiliac occlusive disease [AIOD] ) had hemodynamic and nuclear ventriculographic measurements performed preoperatively, during aortic clamping, and immediately after aortic declamping. No differences were found in the hemodynamic response to operation between patients with AAA or AIOD. Volume loading was performed at each time period to assess ventricular function. Myocardial performance (the relation between cardiac index and end-diastolic volume index) and systolic function (the relation between systolic blood pressure and end-systolic volume index) were depressed during aortic clamping (p less than 0.05), suggesting decreased contractility, but returned to baseline values after declamping. Diastolic compliance (the relation between pulmonary capillary wedge pressure and end-diastolic volume index) decreased after declamping (p less than 0.05), suggesting early myocardial ischemia. The decrease in diastolic compliance rendered pulmonary capillary wedge pressure a poor index of left ventricular preload after declamping. Higher pressures were required to maintain adequate diastolic volumes. Despite careful hemodynamic monitoring, potentially ischemic ventricular dysfunction was found during abdominal aortic operation.

The Determinants of Mortality and Morbidity after Multiple-Valve Operations

The factors predictive of hospital mortality and morbidity after contemporary multiple-valve surgical procedures were identified to develop strategies to improve the results of such procedures. Preoperative, intraoperative, and postoperative information was collected prospectively on 90 consecutive patients undergoing surgical procedures between 1982 and 1984. The operative mortality was 5.6%, and the incidence of postoperative low-output syndrome was 16.7%. Multivariate logistic regression analysis identified tricuspid regurgitation (p less than .03, improvement-of-fit chi square) and the aortic valve lesion (p less than .03) as the independent predictors of postoperative complications (mortality or low-output syndrome). Patients with tricuspid regurgitation and right ventricular decompensation and those with aortic stenosis and left ventricular hypertrophy had limited ventricular functional reserve and faced an increased risk. Improved methods of myocardial protection may reduce the risk in these patients.

Ascending aorta to bifemoral bypass—a ventral aorta

In the decade since April 1975 we accumulated a series of 18 patients with arterial conduits from the ascending aorta to the femoral arteries, 10 men aged 53 to 75 years (mean, 60 years) and eight women aged 33 to 56 years (mean, 50 years). In the first two patients, the conduit was placed subcutaneously; in the remaining 16 patients, it was placed behind the rectus muscle and in front of the posterior rectus fascia, thus following the ventral anastomotic axis of the internal mammary and inferior epigastric arteries. The conduit is not visible, palpable, or compressible in this position. This approach was usually chosen because of multiple failures of standard intra-abdominal and axillofemoral vascular reconstructions. Five patients had concurrent intramediastinal procedures, mostly coronary bypass or innominate artery repair. The early operations were performed with Dacron grafts with a bifurcation constructed just below the umbilicus. In the last nine patients, we have used an 8 or 10 mm polytetrafluoroethylene (PTFE) prosthesis and connected it to a 6 or 8 mm PTFE crossfemoral bypass. No operative deaths occurred. The 5-year patency rate by life-table analysis is 70%. This operation is an alternative to axillofemoral bypass in patients with an inoperable abdominal aortic aneurysm.

Correlation of the changes in diastolic myocardial tissue pressure and regional coronary blood flow in hemorrhagic and endotoxic shock.

Abstract The changes in systemic hemodynamics, in diastolic myocardial tissue pressure (MTP), and in regional coronary blood flow were observed during two stages of hemorrhagic or endotoxic shock in 17 dogs. Nine dogs were subjected to hemorrhagic shock at a mean arterial pressure of 50 mm Hg for 45 min and at 33 mm Hg for a further 15 min. Eight dogs were subjected to endotoxic shock for 1 hr. Both hemorrhagic and endotoxic shock led to a reduction in the magnitude of the normal diastolic MTP gradient from epicardium to endocardium. They also led to a reduction in the proportion of the left ventricular myocardial flow going to the subendocardial region. These changes occurred at a constant heart rate. It is suggested that the change in regional diastolic MTP is an important contributing factor to the inadequate subendocardial perfusion which can occur in both hemorrhagic and endotoxic shock.

The gradient in regional myocardial tissue pressure in the left ventricle during diastole: Its relationship to regional flow distribution

The myocardial tissue pressure during diastole was measured in the inner and outer halves of the left ventricular wall of eight dogs with open chests and mean left ventricular end-diastolic pressure of 2.3 mm Hg. The myocardial tissue pressures were measured by the flow-cessation technique and modified needle-vein sensors with an accuracy of 0.7 mm Hg (SD 1.0). n nThe lowest tissue pressure in the outer half of the left ventricular wall during diastole was over twice as high, 12.0 mm Hg (SD 2.0), as that in the inner half, 5.6 mm Hg (SD 1.7) (P < 0.001). Within the myocardial wall, the lowest pressure occurs at the end of diastole rather than at the beginning as in the ventricular lumen. n nThus, there is a gradient in myocardial wall tissue pressure in diastole, which is in the reverse direction of that present during systole. The presence of this gradient offers a simple explanation of the preferential flow to the inner layers of the left ventricle during diastole.

A Comparison of Volume Loading and Atrial Pacing Following Aortocoronary Bypass

Although cold potassium cardioplegia provides adequate myocardial protection, transient hemodynamic and metabolic instability occasionally occurs after uncomplicated coronary bypass surgery. Two methods to increase cardiac output were compared 2 to 6 hours postoperatively in 24 patients recovering from elective coronary bypass operation. Volume loading increased cardiac index (CI) from 2.1 +/- 0.5 to 2.7 +/- 0.6 L/min/m2 by increasing left atrial pressure (LAP) from 8.6 +/- 3.6 to 13.0 +/- 4.1 mm Hg. Atrial pacing at a rate of 112 +/- 8 beats per minute increased CI from 2.4 +/- 0.5 to 2.7 +/- 0.8 L/min/m2 without a change in LAP. Ejection fraction by nuclear angiography did not change, but the calculated left ventricular end-diastolic volume index (stroke index/ejection fraction) increased with volume loading and decreased with atrial pacing--a decrease in diastolic compliance. Myocardial oxygen extraction did not change, but myocardial lactate extraction increased with volume loading and decreased with atrial pacing. Coronary sinus blood flow was measured in 5 patients and increased with both methods studied. Volume loading demonstrated that myocardial performance was normal and myocardial metabolism increased commensurate with the increase in work. Atrial pacing increased CI but resulted in anaerobic metabolism and a decrease in diastolic compliance. Volume loading rather than atrial pacing will improve CI without producing ischemia in the early postoperative period.

Improved myocardial protection with blood and crystalloid cardioplegia

Although the results of coronary artery bypass surgery have been excellent, recent studies have demonstrated transient alterations in myocardial function and metabolism in spite of apparently adequate cardioplegic protection. Blood cardioplegia may provide better protection than crystalloid cardioplegia, but clinical studies remain inconclusive. Critical coronary stenoses limit cardioplegic delivery, and myocardial protection would be improved with either blood or crystalloid cardioplegia if the solution could be delivered beyond the coronary stenosis. The construction of proximal as well as distal anastomoses during a prolonged cross-clamp period permits more uniform cardioplegic delivery and immediate reperfusion when the cross clamp is released. This technique was used in a prospective randomized trial comparing blood and crystalloid cardioplegia. The long cross-clamp technique eliminated temperature gradients induced when cardioplegia was delivered into the aortic root. The technique of cardioplegic delivery may be as important as the solution used for cardioplegic protection.

Pressure in a Vascular Implant in the Myocardium During Systole

The systolic pressure in the portion of an internal mammary artery which is within a myocardial tunnel may be much higher than aortic systolic pressure. The high pressure occurs in the distal portion of the tunnel and exists during the isovolumetric and ejection phases of myocardial systole. It occurs consistently in an implant which has passed initially into the inner half of the myocardium and inconsistently in more shallow implants. It is a result of systolic occlusion of the implant as it passes through different myocardial layers. The presence of an implant-to-coronary pressure gradient during systole is probably another factor encouraging the formation of implant-to-coronary anastomoses and the subsequent flow through them.