Regional myocardial strain before and after mitral valve repair for severe mitral regurgitation

Magnetic resonance tagging (MRI) can be used to study intramyocardial trains in human in vivo. We wished to determine whether patients with severe mitral regurgitation demonstrate subtle myocardial contractile dysfunction despite normal left ventricular (LV) ejection fraction (EF) and how, mitral valve repair (MVR) may preserve EF in such patients. MRI was performed on seven patients with severe mitral regurgitation (mean age +/- SD, 65+/-13 years) and normal EF day 1 (range, 0-8 days) before (Pre) and week 8+/-3 after (Post) MVR and on nine normal volunteers (mean age, 32+/-4). LV mass index (LVMI), end-diastolic and end systolic volume, mass/volume ratio, EF, and sphericity index were measured Pre and Post. Two-dimensional strain analysis of MR tagged images was performed and expressed as L1 (greatest systolic lengthening, radial in normal subjects), L2 (greatest systolic shortening, circumferential in normals), and beta (angular deviation of L1 from the radial direction). LVMI fell from 142+/-38 g/m2 Pre to 117+/-44 g/m2 Post (p < or = 0.008) as did LV end-diastolic volume (117+/-26 to 69+/-12 ml, p < or = 0.003), whereas EF remained unchanged (59+/-7% at both time points). LV mass/volume ratio increasedfrom 2.2+/-0.3 g/ml Pre to 3.1+/-0.4 g/ml Post (p < or = 0.02) and sphericity index fell from 0.86+/-0.10 to 0.71+/-0.13 (p = 0.02). In the short axis, L1 was greater in patients with mitral regurgitation than normal subjects (19+/-9% vs 16+/-6%, p < or = 0.003) and tended to increase further after MVR (21+/-8%, p < or = 0.06 vs. Pre). Beta was abnormal in mitral regurgitation (19+/-8 vs. 12+/-8 degrees in control subjects, p < 0.0001) and remained abnormal after MVR (19+/-9 degrees). L2 in the short axis was depressed in mitral regurgitation compared with control subjects (12+/-6% vs. 21+/-6%, p < or = 0.001) and was further depressed after MVR (9+/-7%, p < 0.001 vs. Pre). As detected by MRI, regional myocardial strains are abnormal in severe mitral regurgitation despite normal EF, characterized by increased short-axis systolic lengthening that is abnormally directed and by reduced shortening. After MVR, the further increase in short-axis lengthening may preserve EF despite its abnormal direction and a fall in shortening. The increase in short-axis lengthening may be due in part to the reduction in LV sphericity after MVR.

Clinical results with the AB-180 left ventricular assist device

BACKGROUND

This report reviews the initial clinical experience with the AB-180 ventricular assist device.

METHODS

Between Dec 1997 and July 2000, the AB-180 was implanted in 17 patients at five institutions. The mean age was 52 years (range 21 to 68 years) and 14 of 17 were male. The indications for implantation were postcardiotomy shock (12 of 17, 70%), decompensated cardiomyopathy (2 of 17, 12%), viral myocarditis (2 of 17, 12%), and acute myocardial infarction (1 of 17, 6%).

RESULTS

The mean duration of support was 8.5 days (range 1 to 28 days). In the group of 17 patients, 8 were weaned from the device and 2 underwent transplantation. Four of the weaned patients (4 of 8, 50%) and 1 of the transplant patients (1 of 2, 50%) survived. The overall weaning and survival rates were 58% (10 of 17) and 29% (5 of 17). There were no major device-related complications and no major device malfunctions.

CONCLUSIONS

The AB-180 provides reliable circulatory support for reversible forms of heart failure.

Reduced incidence of atrial fibrillation with minimally invasive direct coronary artery bypass

BACKGROUND

Atrial fibrillation (AF) is a frequent complication after coronary artery bypass graft (CABG) surgery. The purpose of this study was to determine the incidence of postoperative AF after minimally invasive direct coronary artery bypass (MIDCAB) in comparison with CABG.

METHODS

Between November 1995 and May 1997, 96 MIDCAB procedures were performed. During the same period, 42 patients underwent traditional single CABG using the left internal mammary artery graft (S-CABG). The incidence of in-hospital AF, defined as a sustained episode requiring treatment, was compared between the two groups.

RESULTS

There was no difference in age, ejection fraction, or preoperative risk score between the groups. The use of beta-blockers before or after surgery was not different. The incidence of postoperative AF in the first 6 weeks after surgery was 4% (4 of 96) for MIDCAB and 28% (12 of 42) for S-CABG (p = 0.003). Patients with postoperati

Partial versus full sternotomy for aortic valve replacement

BACKGROUND

Recent trends suggest that smaller incisions reduce postoperative morbidity. This study tests the hypothesis that a partial upper sternotomy improves patient outcome for aortic valve replacement.

METHODS

A group of 50 patients who underwent aortic valve surgery through a partial upper sternotomy (group I) were compared to 50 patients who underwent aortic valve replacement through a median sternotomy during the same time period (group II). The mean age (60+/-2 versus 63+/-2 years; mean +/- SEM) and preoperative ejection fractions (53+/-2 versus 54+/-2) were similar. Operations were performed with central cannulation, and antegrade/retrograde blood cardioplegia.

RESULTS

There was one death in each group. No differences were found in aortic occlusion time, mediastinal drainage, transfusion incidence, narcotic requirement, length of stay, or cost. The incidence of pleural and pericardial effusions was increased (18.4% versus 3.9%, p < 0.03), and the need for postoperative inotropic support was higher (38.7% versus 19.6%, p < 0.03) in the partial sternotomy group.

CONCLUSIONS

Aortic valve replacement can be performed through a partial sternotomy with results comparable to full sternotomy. The partial sternotomy offers a cosmetic benefit, but does not significantly reduce postoperative pain, length of stay, or cost.

Aortic valve patch closure: an alternative to replacement with HeartMate LVAS insertion

A PTFE patch sewn to the aortic valve and annulus, to occlude the ventriculoaortic junction is used to successfully correct aortic insufficiency with HeartMate (LVAS) insertion. This represents an inexpensive alternative to aortic valve replacement for aortic insufficiency or the presence of a mechanical aortic valve.

The AB-180 circulatory support system: summary of development and plans for phase I clinical trial

BACKGROUND

The AB-180 circulatory support system is a small, durable, efficient centrifugal pump with low thrombogenic potential. The device was designed to provide a fully implantable, left ventricular assist system for short-term support to address the issues of systemic anticoagulation, thrombus formation, infection, and cost.

METHODS

Extensive bench and animal studies were performed to validate the mechanical integrity of the device and its functionality as an implant.

RESULTS

These studies demonstrated anticoagulation requirements, established operating guidelines, incorporated safety systems, and demonstrated safety and efficacy.

CONCLUSIONS

The AB-180 fulfills the stated goals on initial evaluation. A phase I human trial is underway.

AB-180 circulatory support system: summary of development and phase I clinical trial

The AB-180 Circulatory Support System (AB-180 CSS; Cardiac Assist Technologies, Pittsburgh, PA) is a left ventricular assist system for investigational use in patients with postcardiotomy cardiogenic shock who are refractory to standard treatment with an intra-aortic balloon pump, pharmacologic treatment, or both. The intent of the AB-180 CSS is to provide temporary (up to 14 days) mechanical circulatory support until the heart recovers adequate mechanical function. The system consists of a small implantable centrifugal pump and a controller. A unique infusion system produces a hydrodynamic bearing between rotational and stationary components of the AB-180 CSS pump. This infusion system also provides a source of heparin for localized anticoagulation. Extensive bench and animal work has illustrated anticoagulation requirements, established operating guidelines, and demonstrated safety and efficacy. An investigational device exemption has been granted for a Phase I, five patient feasibility study at Allegheny General Hospital in Pittsburgh, Pennsylvania. To date, the pump has been implanted in one patient. The results from this first case are presented here.

Intermittent hypoxia due to right atrial compression by an ascending aortic aneurysm

Two cases are described wherein right atrial compression from a dilated and elongated ascending aorta caused intermittent positional hypoxia. Extrinsic compression of the right atrium caused shunting though a patent foramen ovale.

Use of sonomicrometry and multidimensional scaling to determine the three-dimensional coordinates of multiple cardiac locations: feasibility and initial implementation

We describe a new method which uses sonomicrometry and the statistical technique of multidimensional scaling (MDS) to measure the three-dimensional (3-D) coordinates of multiple cardiac locations. We refer to this new method as sonomicrometry array localization (SAL). The new method differs from standard sonomicrometry in that each piezoelectric transducer element is used as both transmitter and receiver and the set of intertransducer element distances is measured. MDS calculates the 3-D coordinates of each sonomicrometry transducer element from the set of intertransducer element distances. The feasibility of this new method was tested with mathematical simulations which demonstrated the ability of MDS to compensate for signal error and missing intertransducer element distances. We describe the design elements of a modified digitally controlled sonomicrometer in which a single transducer element can sequentially broadcast to as many as eight receiver elements. That design is used to validate SAL in a water bath and in ex vivo and living hearts. Correlation with caliper measurement in the water bath (y int. = 3.91 +/- 3.36 mm, slope = 1.04 +/- 0.05, r2 = 0.969 +/- 0.027) and with radiography in ex vivo (y int. = -0.87 +/- 0.92 mm, slope = 0.97 +/- 0.02, r2 = 0.960 +/- 0.023) and in vivo hearts (y int. = 2.98 +/- 2.59 mm, slope = 1.01 +/- 0.06, r2 = 0.953 +/- 0.031) was excellent. Sonomicrometry array localization is able to accurately measure the 3-D coordinates of multiple cardiac locations. It can potentially measure myocardial deformation and remodeling after ischemic or valvular injury.

'No touch' dissection, antegrade-retrograde blood cardioplegia, and single aortic cross-clamp significantly reduce operative mortality of reoperative CABG

BACKGROUND

We assessed the improvement in total and cardiac-related operative mortality in 131 consecutive patients after reoperative coronary artery bypass surgery (CABG).

METHODS AND RESULTS

The patients were divided into two consecutive groups, A (1988 to 1989) and B (1990 to 1993), on the basis of the implementation of alternative techniques of myocardial protection. The techniques in group B included the "no touch" technique or minimal dissection before bypass, routine femoral artery and vein exposure, and frequent cannulation for cardiopulmonary bypass and antegrade and retrograde blood cardioplegia, with all vascular anastomoses (proximal and distal) performed with a single aortic cross-clamp and cardioplegic arrest. Cardiac mortality from low cardiac output or myocardial infarction was 15% versus 0%, P = .002. Multivariate analysis of demographics, perioperative risk factors, and myocardial protection techniques revealed that only membership in group A and the requirement for an intra-aortic balloon counterpulsation independently predicted mortality. By univariate analysis, group A had significantly more patients with three-vessel disease and patients who required urgent or emergent procedures, but analysis of patients in these subgroups also demonstrates a significant reduction in mortality in the "no touch" patients (group B). Although no technique was independently responsible for reduced operative mortality, all the myocardial protection techniques implemented in group B combined to reduce the risk of reoperative CABG.

CONCLUSIONS

With appropriate myocardial protection techniques, the risk of reoperative CABG should be similar to that for a primary procedure.

Pituitary apoplexy following cardiopulmonary bypass: considerations for a staged cardiac and neurosurgical procedure

Pituitary apoplexy in a pre-existing pituitary tumor can result in serious and permanent neurologic deficits following cardiac surgical procedures. Several factors related to the altered physiology of cardiopulmonary bypass (CPB) contribute separately or in combination to the development of this syndrome. Over the last year we have encountered two such cases in whom emergency and prompt decompression of the adenoma resulted in an improvement of the initial clinical presentation but nevertheless persistence of residual and devastating ocular manifestations. In the literature six similar cases have been reported following cardiac surgical procedures, with similar outcomes. In this report we describe our experience and management of these two patients, and that published in the literature. We propose a possible role for a staged cardiac and neurosurgical procedure as a prophylactic measure in patients with known pituitary tumor. The role of cerebral monitoring is also discussed.

Myocardial electrical impedance mapping of ischemic sheep hearts and healing aneurysms

BACKGROUND

This study was designed to examine the bulk electrical properties of myocardium and their variation with the evolution of infarction after coronary occlusion. These properties may be useful in distinguishing between normal, ischemic, and infarcted tissue on the basis of electrophysiological parameters.

METHODS AND RESULTS

The electrical impedance of myocardial tissue was studied in a sheep model of infarction. The animal model involved a one-stage ligation of the left anterior descending and second diagonal arteries at a point 40% of the distance from the apex to the base. By use of a four-electrode probe, an epicardial mapping system was developed that allowed for cardiac cycle gated and signal-averaged measurements. Subthreshold current (15 microA) was injected through two of the electrodes at frequencies of 1, 5, and 15 kHz and the induced potential measured with the other two electrodes. Epicardial maps of the left ventricle were obtained during acute infarction and at 1-, 2-, and 6-week intervals after occlusion. Results showed the average specific impedance of the myocardium before infarction to be 158 +/- 26 omega-cm independent of location on the epicardium. By 60 minutes after coronary occlusion, the specific impedance had increased by 199% (p < 0.005, n = 9); it remained elevated for up to 4 hours. One week after infarction, the specific impedance decreased to 59% of the control value (p < 0.025, n = 8). Six weeks after occlusion, the specific impedance remained low at 57% of that of the noninfarcted tissue (p < 0.005, n = 9). The phase angle of the complex impedance was also measured and revealed similar changes. The hydroxyproline content of the tissue was assayed to assess infarct healing.

CONCLUSIONS

In this animal model, impedance is a bulk electrical property of tissue that varies with the evolution of myocardial infarction. Impedance mapping revealed significantly different values for normal, ischemic, and infarcted tissue and may prove useful in better defining the electrophysiological characteristics of such tissue.

The stretched ventricle. Myocardial creep and contractile dysfunction after acute nonischemic ventricular distention

The hypothesis that nonischemic distention of the arrested, flaccid ventricle causes myocardial creep and reduces ventricular contractile force was tested in 16 sheep. Left ventricular volume was calculated from ultrasonic dimension transducers spanning left ventricular major and minor axes and left ventricular wall thickness. Changes in left ventricular volume were plotted against left ventricular pressure, with and without temporary occlusion of both venae cavae before and after nonischemic distention of the continuously perfused, flaccid nonbeating left ventricle arrested with oxygenated, normothermic blood-potassium perfusate. During 12 minutes of cardiac arrest, an apical balloon progressively distended the left ventricle to a peak pressure of 40 mm Hg in 11 sheep using a protocol designed to prevent subendocardial ischemia or mechanical injury. Coronary sinus lactate measurements and myocardial distribution of microspheres confirmed the absence of ischemia in 16 animals. In five control sheep the balloon was inserted but not inflated. Left ventricular volume at zero pressure increased from 5.9 +/- 3.5 to 9.5 +/- 4.4 ml (p < 0.05) after balloon inflation and did not change in the control animals. After maximum distention of the balloon, static left ventricular volumes at identical pressures were significantly greater. After passive distention, the slope of the end-systolic pressure-volume relationship, a measure of contractility, decreased significantly (p < 0.05) from 7.1 +/- 2.8 to 3.5 +/- 1.8 mm Hg/ml and did not change in the control group. Passive distention ("stretching") of the nonischemic flaccid left ventricle thus causes myocardial creep and reduces ventricular contractility.

Repair of left ventricular aneurysm. Changes in ventricular mechanics, hemodynamics, and oxygen consumption

Anteroapical left ventricular aneurysms were produced in 23 sheep by coronary arterial ligation. Plication of the aneurysm does not change stroke volume or cardiac output and does not significantly change left ventricular oxygen consumption from the preoperative value of 5.1 +/- 2.6 ml/100 gm per minute. Plication, however, does increase left ventricular end-systolic elastance from 3.2 +/- 0.9 to 4.4 +/- 1.5 mm Hg/mm (p = 0.005). In nine of these sheep the midsagittal plane of the left ventricle was imaged by means of an array of sonomicrometry crystals before and after plication of the aneurysm. Regional wall stresses at end-systole and end-diastole and changes in diastolic function were calculated for anterior and posterior ventricular walls in the border zone adjacent to the aneurysm and in more basilar myocardium remote from the infarct. Plication significantly reduced end-systolic wall stresses and systolic stress integrals in the posterior border zone and remote myocardium, but it did not significantly change anterior wall systolic stresses or stress integrals. Plication also decreased diastolic stretching of border zone myocardium. Plication of anteroapical left ventricular aneurysm produced a shorter, more spherical ventricle and removed the dyskinetic segments but altered deformation (strain) in both circumferential and longitudinal directions. The changes in ventricular wall geometry and deformation provide an explanation for the increased ventricular end-systolic elastance and unchanged stroke volume observed after aneurysm plication.

Left ventricular assistance without thoracotomy: mediastinal and transseptal approaches to the left heart

Two methods to cannulate the left atrium for initiating mechanical left ventricular circulatory assistance using a centrifugal pump were investigated in 25 sheep. A modified Dennis transatrial septal approach produced flow rates of 88.6 +/- 14 mL.kg-1.min-1 through 21F catheters inserted during fluoroscopy through the jugular vein. In 8 animals the septal perforation was plugged after decannulation with a modified Rashkind umbrella plug. Fibroendothelial tissue covered the plug by 4 week. In 7 other animals, the septal defect was not plugged. The septal defect reached pinpoint size by 2 weeks and was completely closed by 4 weeks. In 10 sheep, the left atrium was cannulated from the neck through the mediastinum. Left ventricular assistance flow averaged 71.6 +/- 14 mL.kg-1.min-1. Mean blood loss during 1 hour of left ventricular assistance was 47 mL. In 8 animals, the atrial perforation was plugged with a mean blood loss of 253 +/- 194 mL. In 2 animals, the perforation was intentionally not plugged; mean blood loss was 700 mL. All animals survived. The modified Dennis transatrial method is recommended as a safe, expeditious, cost-effective method to implement left ventricular assistance without thoracotomy. The mediastinal approach, which is technically possible in humans, is more difficult but feasible. Left ventricular assistance has been proven to be the most effective way to rest the failing, ejecting left ventricle. Implementation without thoracotomy potentially expands applications of left ventricular assistance for temporary support of patients with severe manifestations of ischemic heart disease.

Hydrocortisone rapidly induces aortic rupture in a genetically susceptible mouse

The Blotchy mouse has an X-linked trait that leads to aortic aneurysms and subsequent fatal rupture in nearly all affected male mice. Heterozygous female mice occasionally develop aneurysms, but they rarely rupture. Ten heterozygous female mice received 0.45 mg/mL of hydrocortisone acetate in drinking water. Within 2 weeks, 9 of 10 mice were dead (6 with proved aortic rupture, 3 with presumed rupture). The 10th mouse was documented to have an aortic aneurysm. A dose-response curve was generated. Hydrocortisone's effect was shown to be dose-dependent. In another experiment, normal female mice received 0.10 mg/mL of hydrocortisone acetate for 14 days. Two mice developed aneurysms, and the others developed aortic ectasia. These experiments establish the role of hydrocortisone in the induction of aortic rupture in a mouse with genetic susceptibility and the induction of aneurysms and ectasia in normal mice.

Large animal model of left ventricular aneurysm

In 28 Dorsett sheep, ligation of the distal homonymous (equivalent to human left anterior descending) and second diagonal coronary arteries produced a constant transmural infarct of 22.9% +/- 2.5% (mean +/- standard deviation) of the left ventricular mass. Serial left ventriculograms showed that within four hours the infarct segment expands, wall thickness decreases, and aneurysmal dilatation occurs and progresses over the next 60 days in all sheep. Epicardial ventricular point references indicated that adjacent noninfarcted myocardium participates in the formation of the aneurysm. Anatomy of the coronary vasculature was studied in 22 excised sheep hearts. In sheep, coronary arterial anatomy is remarkably constant. The left coronary artery provides all of the blood supply to the left ventricle and septum and only a small rim of both the anterior and posterior right ventricles. Cardiac veins from the left ventricle drain into the coronary sinus, which also receives the left azygos vein. Right ventricular veins drain separately. The essentially separate coronary circulations to the two ventricles, the paucity of coronary collateral circulation, and the consistent evolution of left ventricular infarcts into aneurysms are important advantages of the ovine model for both metabolic and ventricular mechanical studies of acute myocardial infarction and left ventricular aneurysm.