Gil Bolotin

Relation of Myocardial Mechanics in Severe Aortic Stenosis to Left Ventricular Ejection Fraction and Response to Aortic Valve Replacement

Decreased left ventricular (LV) longitudinal strain and increased circumferential LV strain have been demonstrated in patients with severe aortic stenosis (AS) and normal LV ejection fraction (LVEF). Biplane myocardial mechanics normalize after aortic valve replacement (AVR). This study objective was to examine LV mechanics before and soon after AVR in patients with AS and LV systolic dysfunction. Paired echocardiographic studies before and soon (7 ± 3 days) after AVR were analyzed in 64 patients with severe AS: 32 with normal LVEF (≥ 50%), 16 with mild to moderate LV dysfunction (LVEF <36% to 50%), and 16 with severe LV dysfunction (LVEF ≤ 35%). Longitudinal myocardial function was assessed from 3 apical views (average of 18 segments) and circumferential function was assessed at mid-LV and apical levels (average of 6 segments per view). Strain, strain rate, and mid-LV and apical rotations were measured using 2-dimensional velocity vector imaging. Before AVR (1) longitudinal strain was low in all patients and correlated with LVEF (ρ = 0.74, p <0.001), (2) mid-LV circumferential strain was supranormal in patients with normal LVEF and low in patients with low LVEF (ρ = 0.88, p <0.001), and (3) apical rotation was highest in patients with mild to moderate LV dysfunction. After AVR, LVEF increased in patients with LV dysfunction and myocardial mechanics partly normalized. In conclusion, compensatory mechanisms (high circumferential strain in patients with preserved LVEF and increased apical rotation in patients with mild to moderate LV dysfunction) were observed in patients with severe AS. Compensatory mechanics were lost in patients with severe LV dysfunction. AVR partly reversed these changes in patients with LV dysfunction.

Differential effects of afterload on left ventricular long- and short-axis function: insights from a clinical model of patients with aortic valve stenosis undergoing aortic valve replacement.

BACKGROUND The effects of left ventricular (LV) afterload on longitudinal versus circumferential ventricular mechanics are largely unknown. Our objective was to examine changes in LV deformation before and early after aortic valve replacement (AVR) in patients with severe aortic valve stenosis (AS). METHODS Paired echocardiographic studies before and early (7 +/- 3 days) after AVR were analyzed in 45 patients (age 67 +/- 12 years, 49% men) with severe AS and normal LV ejection fraction without segmental wall motion abnormalities. Longitudinal myocardial function was assessed from 3 apical views (average of 18 segments). Circumferential function was assessed at mid and apical levels (averaging 6 segments per view). Strain, strain rate (SR), and LV twist (relative rotation of the mid and apex) were measured using 2-dimensional strain software. RESULTS Early post-AVR, (1) LV size and LV ejection fraction did not change; (2) longitudinal systolic strain, which was lower than normal before AVR, increased (-12.8 +/- 1.7 to -15.9 +/- 2.2, P < .05), whereas mid-LV circumferential strain, which was higher than normal, decreased (-27.0 +/- 5.1 to -22.3 +/- 4.9, P < .05); (3) longitudinal early diastolic SR increased (0.6 +/- 0.1 to 0.7 +/- 0.2, P < .05), whereas mid-LV circumferential diastolic SR decreased (1.2 +/- 0.5 to 1.0 +/- 0.3, P < .05); and (4) LV twist increased (3.7 degrees +/- 2.1 degrees to 6.1 degrees +/- 2.9 degrees , P < .05). CONCLUSIONS Aortic valve stenosis causes differential changes in longitudinal and circumferential mechanics that partially normalize after AVR. These findings provide new insights into the mechanical adaptation of the LV to chronic afterload elevation and its response to unloading.

Higher Levels of Serum Cytokines and Myocardial Tissue Markers During On-Pump Versus Off-Pump Coronary Artery Bypass Surgery

Abstract  Increased Troponin I levels and pro‐inflammatory cytokines have been reported in most patients undergoing cardiac surgery, ascribed to the type and extent of surgery, reperfusion injury, and the method of myocardial protection. We investigated their levels in patients undergoing on‐pump (CCAB) or off‐pump (OPCAB) coronary artery bypass surgery and whether these correlated with the extent of myocardial injury. One hundred twenty patients were prospectively randomized to undergo OPCAB (n = 60) or CCAB (n = 60). Hemodynamic and respiratory data, as well as serum CK‐MB mass fraction, Troponin I, and interleukin (IL)‐6, IL–8, and IL–10 levels, were collected perioperatively. Demographic, hemodynamic, and respiratory parameters were similar between the two groups. Troponin I was significantly lower in the OPCAB than in the CCAB group, either at the end of ischemia, end of surgery, 6‐hour and 24‐hour postoperatively (4 ± 3, 5 ± 3, 7 ± 5, and 8 ± 3 μg/L, vs. 19 ± 18, 27 ± 19, 28 ± 13.5, and 33 ± 8.5 μg/L, respectively, p < 0.05). Serum cytokine levels in the OPCAB patients were lower compared to the CCAB group at the end of surgery (32 ± 35, 25 ± 30, and 40 ± 30 pg/ml for IL‐6, IL‐8, and IL‐10 vs. 230 ± 30, 140 ± 70, and 125 ± 50 pg/ml, respectively, p < 0.05). Plasma IL‐6 levels correlated with the Troponin I levels at the end of surgery in both groups (r = 0.45, p = 0.01).Thus, OPCAB surgery is associated with reduced levels of Troponin I and activation of cytokines, compared to those in the CCAB group. High levels of these factors could correlate with myocardial damage during coronary artery bypass surgery. This finding warrants further laboratory and clinical confirmation in the future.

Strict Thermoregulation Attenuates Myocardial Injury During Coronary Artery Bypass Graft Surgery as Reflected by Reduced Levels of Cardiac-Specific Troponin I

We assessed the cardioprotective effects of perioperative maintenance of normothermia by determining the perioperative profile of troponin I, a highly cardiac-specific protein important in risk stratification of patients with acute ischemic events. Candidates for their primary coronary artery bypass grafting (CABG) were randomized into a new thermoregulation system group, Allon( thermoregulation (AT; n = 30), and a routine thermal care (RTC; n = 30) group. Anesthetic and operative techniques were similar in both groups. Intraoperative warming was applied before and after cardiopulmonary bypass (CPB) and up to 4 h after surgery. Perioperative temperature and hemodynamic data were recorded. Blood samples for creatine kinase (CK) and its isoform, MB (CK-MB), and for cardiac-specific troponin I (cTnI) were obtained at predetermined intervals throughout the entire operation. Core and skin temperatures were higher in the AT group at all time points. The systemic vascular resistance was lower and the cardiac index higher in the AT group at all intra- and postoperative time points. Increases in CK, CK-MB, and cTnI levels indicated intraoperative ischemic insult in all patients. The respective CK levels for the AT and RTC groups were 53.3 +/- 22.7 IU/L and 47.9 +/- 17.86 IU/L at the time of anesthesia and 64.7 +/- 45.6 IU/L and 47.8 +/- 19.4 IU/L 30 min after the onset of surgery, demonstrating thereafter a steep increase before the discontinuation of CPB. CK-MB mass concentrations in both groups behaved almost identically. Pre-CPB cTnI levels at anesthesia induction were 0.3 +/- 0 ng/mL in both groups, followed by a distinctive profile observed after separation from CPB: 28.1 +/- 11.4 ng/mL, 26.05 +/- 9.20 ng/mL, and 22.3 +/- 8.9 ng/mL at discontinuation from CPB, chest closure, and 2 h after surgery, respectively, in the RTC group, versus 0.6 +/- 4.6 ng/mL, 6.6 +/- 5.5 ng/mL, and 7.9 +/- 4.76 ng/mL at these three time points, respectively, in the AT group (P < 0.01 between groups at the specified time points). Contrary to conventional thinking about the benefits of hypothermia, maintenance of normothermia throughout the non-CPB phases during CABG was demonstrated to be important in attenuating myocardial ischemic injury. Insofar as troponin I was more sensitive than other tested markers, it may provide important data on possible protection from myocardial insult and on other cardioprotective measures.

The efficacy of intraoperative internal intercostal nerve block during video-assisted thoracic surgery on postoperative pain

BACKGROUND Video-assisted thoracic surgery (VATS) is widely used for many thoracic surgical procedures. Post-operative pain is less after VATS than after conventional thoracic surgery, but is still significant. The objective of this study was to assess the efficacy of thoracoscopic, internal intercostal nerve block in alleviating immediate postoperative pain. METHODS Thirty-two patients underwent VATS bilateral sympathectomy for the treatment of hyperhidrosis. The patients were randomly divided into two groups with similar demographic and preoperative physiologic parameters. Group A (n = 16) was submitted to thoracoscopic, internal intercostal nerve blocks performed at T2, T3, and T4 intercostal levels using 3 cc of 0.5% bupivacain in each intercostal space. The injections were performed bilaterally, immediately after the sympathectomy, through the same port. Group B (n = 16) underwent bilateral thoracic sympathectomy without the block. During the immediate postoperative period, heart rate, blood pressure, respiratory rate, pain score, and analgesic requirements were monitored every 30 minutes. RESULTS No morbidity was recorded in association with the thoracoscopic, internal intercostal nerve block. The mean heart rates (77 +/- 6 vs 89 +/- 12 beats per minute, p < 0.001), respiratory rates (15 +/- 2 vs 18 +/- 3 respirations per minute, p < 0.01), pain score (1.9 +/- 0.6 vs 2.7 +/- 0.5, p < 0.01), and postoperative analgesic requirements (20 +/- 18 vs 50 +/- 21 mg pethidine HCL, p < 0.001) were significantly lower in group A. There was no significant difference in blood pressures. CONCLUSIONS Thoracoscopic, internal intercostal nerve block with bupivacain 0.5% during VATS is safe and effectively reduced the immediate postoperative pain and analgesic requirements.

Modeling the dynamic behavior of a shape memory alloy actuated catheter

In this paper we investigate the transient behavior of a simple active catheter: a central tube actuated by a single nitinol tendon enclosed by an outer sleeve. Dynamic models are developed to characterize the transient behavior and optimize the design of an experimental prototype. The bending mechanics are derived using a circular arc model and are experimentally validated. Nitinol actuation is described using the Seelecke–Muller–Achenbach model for single-crystal shape memory alloys using experimentally determined parameters. The dynamic characteristics of this active catheter system are simulated and compared with experimental results. Joule heating is used to generate tip deflections, which are computed in real time using a dual-camera imaging system. The effects of outer sleeve thickness on heat transfer and transient response characteristics are studied.

A Dynamic Heart System to Facilitate the Development of Mitral Valve Repair Techniques

Objective: The development of a novel surgical tool or technique for mitral valve repair can be hampered by cost, complexity, and time associated with performing animal trials. A dynamically pressurized model was developed to control pressure and flowrate profiles in intact porcine hearts in order to quantify mitral regurgitation and evaluate the quality of mitral valve repair. Methods: A pulse duplication system was designed to replicate physiological conditions in explanted hearts. To test the capabilities of this system in measuring varying degrees of mitral regurgitation, the output of eight porcine hearts was measured for two different pressure waveforms before and after induced mitral valve failure. Four hearts were further repaired and tested. Measurements were compared with echocardiographic images. Results: For all trials, cardiac output decreased as left ventricular pressure was increased. After induction of mitral valve insufficiencies, cardiac output decreased, with a peak regurgitant fraction of 71.8%. Echocardiography clearly showed increases in regurgitant severity from post-valve failure and with increased pressure. Conclusions: The dynamic heart model consistently and reliably quantifies mitral regurgitation across a range of severities. Advantages include low experimental cost and time associated with each trial, while still allowing for surgical evaluations in an intact heart.

Persistent atrial fibrillation in a goat model of chronic left atrial overload

OBJECTIVES Atrial dilatation predisposes to atrial fibrillation. Although several animal models focus on the initiating mechanisms of atrial fibrillation in dilated atria, a model of left atrial overload resulting in persistent atrial fibrillation in nonanesthetized animals has not been presented thus far. METHODS In 24 goats a vascular shunt was implanted between the aorta and the left atrium through a left thoracotomy. In 6 animals the shunt was ligated immediately (control group). Ultrasonic crystals were implanted to monitor atrial dilatation. Bipolar electrodes were positioned epicardially on the left atrium for measurement of the atrial effective refractory period, conduction times, and atrial fibrillation duration. RESULTS Four weeks of overload resulted in an increase of left atrial pressure (23.1 +/- 6.8 mm Hg in the open-shunt group vs 7.0 +/- 1.9 mm Hg in the control group, P = .002) and a progressive dilatation of the left atrium (135% +/- 20% in the open-shunt group vs 98% +/- 8.0% in the control group, P = .002). Among the open-shunt groups long-term survivors (n = 12), 9 animals showed prolonged atrial fibrillation (>1 hour), and of these, 6 were in persistent atrial fibrillation (>1 week). The atrial effective refractory period increased during the first week and remained prolonged until death (182 +/- 11 ms in the open-shunt group vs 161 +/- 15 ms, P = .03). The conduction time did not change. An increase in collagen formation was noticed in both groups, without a significant difference between them. CONCLUSIONS A chronic aortic to left atrial shunt is a feasible model in the goat. It induces progressive left atrial dilatation with an increased atrial fibrillation duration up to hours in the majority of animals. Prolonged atrial fibrillation duration could not be explained by a shortening of atrial effective refractory period or increase in fibrosis.

Glutamine improves myocardial function following ischemia-reperfusion injury.

Myocardial ischemia-reperfusion injury is common during cardiac procedures. Glutamine may protect the myocardium by preserving metabolic substrates. Glutamine (0.52 g·kg−1) or Ringers lactate solution (control group) was administered intraperitoneally to 63 Sprague-Dawley rats at 4 or 18 hours prior to experimental ischemia and reperfusion. The hearts were excised and perfused on an isolated working heart model, exposed to global ischemia for 15 min and reperfusion for 1 hour. Left atrial pressure, mean aortic pressure, cardiac flow, coronary flow, and aortic output were measured 15 min before ischemia and every 15 min during reperfusion. There was significantly better cardiac output in the glutamine pretreated groups. Pretreatment at 4 hours before the experiment was superior to pretreatment at 18 hours, with better maintenance of cardiac output and coronary flow. The enhanced protective effect of pretreatment at 4 hours highlights the importance of timing, and suggests a potential clinical benefit.

Assessment of a continuous blood gas monitoring system in animals during circulatory stress

BackgroundThe study was aimed to determine the measurement accuracy of The CDI™ blood parameter monitoring system 500 (Terumo Cardiovascular Systems Corporation, Ann Arbor MI) in the real-time continuous measurement of arterial blood gases under different cardiocirculatory stress conditionsMethodsInotropic stimulation (Dobutamine 2.5 and 5 μg/kg/min), vasoconstriction (Arginine-vasopressin 4, 8 and 16 IU/h), hemorrhage (-10%, -20%, -35%, and -50% of the theoretical volemia), and volume resuscitation were induced in ten swine (57.4 ± 10.7 Kg).Intermittent blood gas assessments were carried out using a routine gas analyzer at any experimental phase and compared with values obtained at the same time settings during continuous monitoring with CDI™ 500 system. The Bland-Altman analysis was employed.ResultsBias and precision for pO2 were - 0.06 kPa and 0.22 kPa, respectively (r2 = 0.96); pCO2 - 0.02 kPa and 0.15 kPa, respectively; pH -0.001 and 0.01 units, respectively ( r2 = 0.96). The analysis showed very good agreement for SO2 (bias 0.04,precision 0.33, r2 = 0.95), Base excess (bias 0.04,precision 0.28, r2 = 0.98), HCO3 (bias 0.05,precision 0.62, r2 = 0.92),hemoglobin (bias 0.02,precision 0.23, r2 = 0.96) and K+ (bias 0.02, precision 0.27, r2 = 0.93). The sensor was reliable throughout the experiment during hemodynamic variations.ConclusionsContinuous blood gas analysis with the CDI™ 500 system was reliable and it might represent a new useful tool to accurately and timely monitor gas exchange in critically ill patients. Nonetheless, our findings need to be confirmed by larger studies to prove its reliability in the clinical setting.