Left ventricular venting during extracorporeal membrane oxygenation; the effects on cardiac performance in a porcine model of critical post-cardiotomy failure.

INTRODUCTION: Left ventricular distension is a major concern with postcardiotomy veno-arterial extracorporeal membrane oxygenation (VA-ECMO) supporting a critical heart failure after cardiac surgery. This porcine study evaluates the effects of left ventricular venting on cardiac function during ECMO-supported circulation and after weaning from ECMO. METHODS: Twenty anaesthetised open-chest pigs were put on cardiopulmonary bypass with aortic cross-clamping and suboptimal cardioplegic arrest for 40 min. After declamping and defibrillation, the animals were supported by VA-ECMO for 180 min either with or without additional left ventricular venting. Continuous haemodynamic evaluations were performed at baseline and at cardiac arrest, during VA-ECMO and for 120 min after weaning from circulatory support. Left ventricular perfusion and function were evaluated with microspheres, pressure-volume loops and epicardial echocardiography at baseline and after 1 and 2 h with unsupported circulation. RESULTS: In vented animals both mean aortic and left ventricular peak systolic pressure increased at the end of the ECMO-supported period compared to those not vented and remained increased also after weaning. Both at 60 min and 120 min after weaning from circulatory support, left ventricular stroke work and pressure-volume area were increased in vented compared to not vented animals. At 120 min left ventricular stroke volume was increased in vented compared to not vented animals, myocardial perfusion did not differ. The left ventricular mechanical efficiency, defined as the ratio between pressure volume area and myocardial perfusion, was increased (53.2 ± 5 vs 36.2 ± 2.1 J/mL/g, p = 0.011) in vented- compared to not vented hearts. CONCLUSION: This experimental study demonstrate that left ventricular venting during post-cardiotomy veno-arterial ECMO for 3 h attenuates deterioration of left ventricular function and haemodynamics early after weaning from circulatory support.

Vocal cord function during recurrent laryngeal nerve injury assessed by accelerometry and EMG.

OBJECTIVE: Gradual impairment of nerve conduction is expected to be tightly associated with simultaneous gradual loss of vocal cord contractility, related to the fact that injured axons are connected to a defined number of muscle cells. In clinical studies, there is a time gap between observed adverse electromyographic (EMG) changes and examination of vocal cord function. This study evaluates the impact of intraoperative EMG changes on synchronous vocal cord contractility by simultaneous use of continuous intraoperative neuromonitoring (C-IONM) and accelerometry for registration of actual vocal cord function at a given change of EMG amplitude. METHODS: EMG was obtained following vagus nerve stimulation by use of C-IONM. A vocal cord accelerometer probe that could be attached to the vocal cords was developed based on a LIS3DH ultra low-power high performance three axis linear accelerometer (STMicroelectronics, Geneva, Switzerland). Accelerometer data were registered continuously together with EMG data during traction injury of the recurrent laryngeal nerve (RLN) until an amplitude depression ≤100 µV. RESULTS: Six RLN from four immature domestic pigs were studied. Vocal cord contractility assessed by vocal cord accelerometry decreased in parallel with EMG amplitude, with significant correlations ranging from 0.707 to 0.968. CONCLUSION: Decrease of EMG amplitude during traction injury to the RLN injury is closely associated with a parallel drop in vocal cord contractility. LEVEL OF EVIDENCE: NA Laryngoscope, 130:1090-1096, 2020.

How do I get an emergency civilian walking blood bank running?

The shift toward using a transfusion strategy in a ratio to mimic whole blood (WB) functionality has revitalized WB as a viable option to replace severe blood loss in civilian health care. A military-civilian collaboration has contributed to the reintroduction of WB at Haukeland University Hospital in Bergen, Norway. WB has logistical and hemostatic advantages in both the pre- and in-hospital settings where the goal is a perfectly timed balanced transfusion strategy. In this paper, we describe an event leading to activation of our emergency WB collection strategy for the first time. We evaluate the feasibility of our civilian walking blood bank (WBB) to cover the need of a massive amount of blood in an emergency situation. The challenges are discussed in relation to the different stages of the event with the recommendations for improvement in practice. We conclude that the use of pre-screened donors as a WBB in a civilian setting is feasible. The WBB can provide platelet containing blood components for balanced blood resuscitation in a clinically relevant time frame.

Left ventricular dysfunction after two hours of polarizing or depolarizing cardioplegic arrest in a porcine model.

INTRODUCTION: This experimental study compares myocardial function after prolonged arrest by St. Thomas' Hospital polarizing cardioplegic solution (esmolol, adenosine, Mg2+) with depolarizing (hyperkalaemic) St. Thomas' Hospital No 2, both administered as cold oxygenated blood cardioplegia. METHODS: Twenty anaesthetized pigs on tepid (34°C) cardiopulmonary bypass (CPB) were randomised to cardioplegic arrest for 120 min with antegrade, repeated, cold, oxygenated, polarizing (STH-POL) or depolarizing (STH-2) blood cardioplegia every 20 min. Cardiac function was evaluated at Baseline and 60, 150 and 240 min after weaning from CPB, using a pressure-conductance catheter and epicardial echocardiography. Regional tissue blood flow, cleaved caspase-3 activity and levels of malondialdehyde were evaluated in myocardial tissue samples. RESULTS: Preload recruitable stroke work (PRSW) was increased after polarizing compared to depolarizing cardioplegia 150 min after declamping (73.0±3.2 vs. 64.3±2.4 mmHg, p=0.047). Myocardial tissue blood flow rate was high in both groups compared to the Baseline levels and decreased significantly in the STH-POL group only, from 60 min to 150 min after declamping (p<0.005). Blood flow was significantly reduced in the STH-POL compared to the STH-2 group 240 min after declamping (p<0.05). Left ventricular mechanical efficiency, the ratio between total pressure-volume area and blood flow rate, gradually decreased after STH-2 cardioplegia and was significantly reduced compared to STH-POL cardioplegia after 150 and 240 min (p<0.05 for both). CONCLUSION: Myocardial protection for two hours of polarizing cardioplegic arrest with STH-POL in oxygenated blood is non-inferior compared to STH-2 blood cardioplegia. STH-POL cardioplegia alleviates the mismatch between myocardial function and perfusion after weaning from CPB.

Carvedilol-Enriched Cold Oxygenated Blood Cardioplegia Improves Left Ventricular Diastolic Function After Weaning From Cardiopulmonary Bypass.

OBJECTIVES: To investigate whether adding carvedilol, a nonselective ß- and selective α1-receptor blocking agent with antioxidant properties, to oxygenated blood cardioplegia improves myocardial function after weaning from bypass. DESIGN: A randomized controlled study. SETTING: A university laboratory. PARTICIPANTS: Twenty anesthetized pigs, Norwegian Landrace. INTERVENTIONS: On cardiopulmonary bypass, cardiac arrest was induced with cold (12°C), oxygenated blood cardioplegia, enriched with carvedilol or vehicle, and repeated every 20 minutes. After 100 minutes, the heart was reperfused and weaned. MEASUREMENTS AND MAIN RESULTS: Left ventricular function was evaluated with pressure-volume loops, local myocardial systolic strain, and strain rate from Speckle tracking analysis and multilayer short-axis tissue Doppler Imaging. In the carvedilol group, the load-independent logarithmic end-diastolic pressure volume relationship, ß, decreased from 1 to 3 hours of reperfusion and was low, 0.028±0.004 v 0.042±0.007 (p<0.05) in controls at 3 hours, demonstrating improved left ventricular compliance. The diastolic relaxation constant τ was decreased, 28.9±0.6 ms v 34.6±1.3 ms (pg<0.035), and dP/dtmin was more negative,-1,462±145 mmHg/s v-1,105±105 mmHg/s (pg = 0.024), for carvedilol v control group. The systolic variables, preload recruitable stroke work and end-systolic pressure-volume relationship, did not differ between groups, neither did left ventricular systolic strain and strain rate. Myocardial oxidative stress, measured as tissue levels of malondialdehyde, was reduced by carvedilol, 0.19±0.01 compared to 0.24±0.01 nmol/mg (p = 0.004) in controls. CONCLUSIONS: Carvedilol added to blood cardioplegia improved diastolic cardiac function and reduced oxidative stress during the first 3 hours after reperfusion in a porcine model, with 100 minutes of cardioplegic arrest.

The influence of acute unloading on left ventricular strain and strain rate by speckle tracking echocardiography in a porcine model.

Noninvasive measurements of myocardial strain and strain rate by speckle tracking echocardiography correlate to cardiac contractile state but also to load, which may weaken their value as indices of inotropy. In a porcine model, we investigated the influence of acute dynamic preload reductions on left ventricular strain and strain rate and their relation to the pressure-conductance catheter-derived preload recruitable stroke work (PRSW) and peak positive first derivative of left ventricular pressure (LV-dP/dtmax). Speckle tracking strain and strain rate in the longitudinal, circumferential, and radial directions were measured during acute dynamic reductions of end-diastolic volume during three different myocardial inotropic states. Both strain and strain rate were sensitive to unloading of the left ventricle (P < 0.001), but the load dependency for strain rate was modest compared with strain. Changes in longitudinal and circumferential strain correlated more strongly to changes in end-diastolic volume (r = -0.86 and r = -0.72) than did radial strain (r = 0.35). Longitudinal, circumferential, and radial strain significantly correlated with LV-dP/dtmax (r = -0.53, r = -0.46, and r = 0.86), whereas only radial strain correlated with PRSW (r = 0.55). Strain rate in the longitudinal, circumferential and radial direction significantly correlated with both PRSW (r = -0.64, r = -0.58, and r = 0.74) and LV-dP/dtmax (r = -0.95, r = -0.70, and r = 0.85). In conclusion, the speckle tracking echocardiography-derived strain rate is more robust to dynamic ventricular unloading than strain. Longitudinal and circumferential strain could not predict load-independent contractility. Strain rates, and especially in the radial direction, are good predictors of preload-independent inotropic markers derived from conductance catheter.

Myocardial function after polarizing versus depolarizing cardiac arrest with blood cardioplegia in a porcine model of cardiopulmonary bypass.

OBJECTIVES: Potassium-based depolarizing St Thomas' Hospital cardioplegic solution No 2 administered as intermittent, oxygenated blood is considered as a gold standard for myocardial protection during cardiac surgery. However, the alternative concept of polarizing arrest may have beneficial protective effects. We hypothesize that polarized arrest with esmolol/adenosine/magnesium (St Thomas' Hospital Polarizing cardioplegic solution) in cold, intermittent oxygenated blood offers comparable myocardial protection in a clinically relevant animal model. METHODS: Twenty anaesthetized young pigs, 42 ± 2 (standard deviation) kg on standardized tepid cardiopulmonary bypass (CPB) were randomized (10 per group) to depolarizing or polarizing cardiac arrest for 60 min with cardioplegia administered in the aortic root every 20 min as freshly mixed cold, intermittent, oxygenated blood. Global and local baseline and postoperative cardiac function 60, 120 and 180 min after myocardial reperfusion was evaluated with pressure-conductance catheter and strain by Tissue Doppler Imaging. Regional tissue blood flow, cleaved caspase-3 activity, GRK2 phosphorylation and mitochondrial function and ultrastructure were evaluated in myocardial tissue samples. RESULTS: Left ventricular function and general haemodynamics did not differ between groups before CPB. Cardiac asystole was obtained and maintained during aortic cross-clamping. Compared with baseline, heart rate was increased and left ventricular end-systolic and end-diastolic pressures decreased in both groups after weaning. Cardiac index, systolic pressure and radial peak systolic strain did not differ between groups. Contractility, evaluated as dP/dtmax, gradually increased from 120 to 180 min after declamping in animals with polarizing cardioplegia and was significantly higher, 1871 ± 160 (standard error) mmHg/s, compared with standard potassium-based cardioplegic arrest, 1351 ± 70 mmHg/s, after 180 min of reperfusion (P = 0.008). Radial peak ejection strain rate increased and the load-independent variable preload recruitable stroke work was increased with polarizing cardioplegia after 180 min, 64 ± 3 vs 54 ± 2 mmHg (P = 0.018), indicating better preserved left ventricular contractility with polarizing cardioplegia. Phosphorylation of GRK2 in myocardial tissue did not differ between groups. Fractional cytoplasmic volume in myocytes was reduced in hearts arrested with polarizing cardioplegia, indicating reduction of cytoplasmic oedema. CONCLUSIONS: Polarizing oxygenated blood cardioplegia with esmolol/adenosine/magnesium offers comparable myocardial protection and improves contractility compared with the standard potassium-based depolarizing blood cardioplegia.

Intracoronary insulin administered at reperfusion in a porcine model of acute coronary syndrome.

BACKGROUND: Experimental studies have demonstrated that insulin elicits cardioprotection in coronary occlusion-reperfusion models. We studied the effects of intracoronary insulin on regional cardiac function in a porcine model with reperfusion after a critical coronary artery stenosis. METHODS: In 20 anaesthetized pigs with an extracorporeal shunt from the brachiocephalic to the left anterior descending coronary artery, a fixed stenosis was applied, obtaining 50% reduction of shunt flow for 60 min. Intracoronary insulin 1 1U [DOSAGE ERROR CORRECTED] or 0.9% saline was infused for 15 min, starting 5 min prior to initiation of 180 min of reperfusion. Microsphere injections confirmed ischaemia and reperfusion. Epicardial echocardiographic multilayer radial tissue Doppler strain and strain rate and one-layer speckle-tracking strain evaluated myocardial function. Apoptosis was evaluated by cleaved caspase-3 activity. Area at risk and infarct size were determined with Evans Blue and triphenyltetrazolium chloride staining. RESULTS: In both groups, the area at risk constituted approximately 26% of the left ventricular mass. Minor areas of infarction were predominantly seen subendocardially, where tissue blood flow rate was severely reduced during stenosis. After 180 min of reperfusion, recovery of speckle-tracking circumferential strain averaged 57.5 ± 11.4% of baseline values in insulin treated animals compared to 22.3 ± 8.7% in controls (p = 0.025). Multilayer radial strain and strain rate did not differ between groups. Cleaved caspase-3 activity was most prominent in the subepicardial layer in the saline-treated group. CONCLUSIONS: Intracoronary insulin at the onset of reperfusion alleviated regional myocardial dysfunction in acute ischaemia-reperfusion and was associated with a reduction of apoptosis.

Reperfusion therapy with low-dose insulin or insulin-like growth factor 2; myocardial function and infarct size in a porcine model of ischaemia and reperfusion.

In an open-chest porcine model, we examined whether myocardial pharmacological conditioning at the time of reperfusion with low-dose insulin or insulin-like growth factor 2 (IGF2), not affecting serum glucose levels, could reduce infarct size and improve functional recovery. Two groups of anaesthetized pigs with either 60 or 40 min. of left anterior descending artery occlusion (total n = 42) were randomized to receive either 0.9% saline, insulin or IGF2 infusion for 15 min., starting 5 min. before a 180-min. reperfusion period. Repeated fluorescent microsphere injections were used to confirm ischaemia and reperfusion. Area at risk and infarct size was determined with Evans blue and triphenyltetrazolium chloride staining. Local myocardial function was evaluated with multi-layer radial tissue Doppler strain and speckle-tracking strain from epicardial echocardiography. Western blotting and TUNEL staining were performed to explore apoptosis. Infarct size did not differ between treatment groups and was 56.7 ± 6.8%, 49.7 ± 9.6%, 56.2 ± 8.0% of area at risk for control, insulin and IGF2 group, respectively, in the 60-min. occlusion series. Corresponding values were 45.6 ± 6.0%, 48.4 ± 7.2% and 34.1 ± 5.8% after 40-min. occlusion. Global and local cardiac function did not differ between treatment groups. No differences related to treatment could be found in myocardial tissue cleaved caspase-3 content or the degree of TUNEL staining. Reperfusion therapy with low-dose insulin or with IGF2 neither reduced infarct size nor improved function in reperfused myocardium in this in vivo porcine model.

Is strain by Speckle Tracking Echocardiography dependent on user controlled spatial and temporal smoothing? An experimental porcine study.

BACKGROUND: Speckle Tracking Echocardiography (STE) strain analysis relies on both spatial and temporal smoothing. The user is often allowed to adjust these smoothing parameters during analysis. This experimental study investigates how different degrees of user controllable spatial and temporal smoothing affect global and regional STE strain values in recordings obtained from normal and ischemic myocardium. METHODS: In seven anesthetized pigs, left ventricular short- and long-axis B-mode cineloops were recorded before and after left anterior descending coronary artery occlusion. Peak- and postsystolic global STE strain in the radial, circumferential and longitudinal direction as well as corresponding regional strain in the anterior and posterior walls were measured. During post-processing, strain values were obtained with three different degrees of both spatial and temporal smoothing (minimum, factory default and maximum), resulting in nine different combinations. RESULTS: All parameters for global and regional longitudinal strain were unaffected by adjustments of spatial and temporal smoothing in both normal and ischemic myocardium. Radial and circumferential strain depended on smoothing to a variable extent, radial strain being most affected. However, in both directions the different combinations of smoothing did only result in relatively small changes in the strain values. Overall, the maximal strain difference was found in normal myocardium for peak systolic radial strain of the posterior wall where strain was 22.0 ± 2.2% with minimal spatial and maximal temporal smoothing and 30.9 ± 2.6% with maximal spatial and minimal temporal smoothing (P < 0.05). CONCLUSIONS: Longitudinal strain was unaffected by different degrees of user controlled smoothing. Radial and circumferential strain depended on the degree of smoothing. However, in most cases these changes were small and would not lead to altered conclusions in a clinical setting. Furthermore, smoothing did not affect strain variance. For all strain parameters, variance remained within the corresponding interobserver variance.

Multi-layer radial systolic strain vs. one-layer strain for confirming reperfusion from a significant non-occlusive coronary stenosis.

AIMS: The aim of this study was to investigate whether multi-layer radial strain and strain rate analysis is superior to one-layer strain analysis for confirming reperfusion following a non-occlusive coronary stenosis. METHODS AND RESULTS: In 10 anaesthetized pigs, an extracorporeal shunt was inserted from the brachiocephalic to the left anterior descending coronary artery. Microspheres were injected and left ventricular (LV) short- and long-axis echocardiographic views were recorded with the open shunt, during the 120 min of severe stenosis and 20 min (early) and 100 min (late) after reperfusion. The anterior wall was analysed for radial one-layer and three-layer tissue Doppler imaging (TDI) strain and strain rate, in addition to radial, circumferential, and longitudinal speckle-tracking echocardiography (STE) strain. During stenosis, perfusion was reduced in the two inner wall layers (P< 0.01). All peak systolic strain and strain rate parameters were reduced, whereas post-systolic longitudinal strain and post-systolic strain in the two inner layers increased (P< 0.001). At early reperfusion, hyperaemia was evident in all layers (P< 0.01). Peak systolic TDI strain and strain rate increased in the mid- and subendocardial layer, whereas post-systolic strain decreased (P< 0.05). Peak systolic STE strain increased in the circumferential and longitudinal direction, whereas post-systolic longitudinal strain decreased (P< 0.05). At late reperfusion, strain and strain rate were unchanged while perfusion returned to baseline values in the mid- and subendocardium. CONCLUSION: Both multi-layer radial TDI strain and strain rate and one-layer STE strain measurements in the circumferential and longitudinal direction can confirm reperfusion early after a non-occlusive coronary stenosis. An advantage of multi-layer analysis was not evident.

Multidose cold oxygenated blood is superior to a single dose of Bretschneider HTK-cardioplegia in the pig.

BACKGROUND: A single-dose strategy for cardioplegia is desired in minimal invasive approaches to valve surgery and aortic arch repairs. We hypothesized that a single infusion of Bretschneider HTK solution offers myocardial protection comparable to repeated cold oxygenated blood. METHODS: Sixteen pigs on bypass with 60 minutes of aortic cross-clamping were randomized to a single dose of Custodiol (HTK group) or repeated oxygenated blood cardioplegia (CBC group). Left ventricular function and perfusion were evaluated by conductance catheter, echocardiography, and microspheres. Myocardial injury was assessed with serum troponin-T. RESULTS: Baseline values showed no group differences. One hour after declamping cardiac index was reduced in the HTK group, 3.5 +/- 0.2 L x min(-1) x m(-2) (mean +/- standard error of the mean) compared with 4.7 +/- 0.4 L x min(-1) x m(-2) in the CBC group (p < 0.0005), decreasing to 4.0 +/- 0.2 and 3.9 +/- 0.2 L x min(-1) x m(-2) after 2 and 3 hours, respectively (p < 0.005 versus 1 hour). In the HTK group cardiac index remained low and unchanged. In the CBC group preload recruitable stroke work was 72.6 +/- 1.2 mm Hg 1 hour after declamping, decreasing to 65.2 +/- 2.5 and 60.3 +/- 3.9 mm Hg after 2 and 3 hours, respectively (p < 0.05 versus 1 hour). In the HTK group corresponding values after 1, 2, and 3 hours were low at 47.2 +/- 4.4, 48.4 +/- 4.2, and 50.7 +/- 4.3 mm Hg, respectively (p < 0.025 versus CBC for all). Subendocardial radial peak systolic strain averaged 80.5% +/- 4.8% after declamping in the CBC group versus 53.4% +/- 5.5% in the HTK group (p = 0.002). Serum troponin-T release was lower in the CBC group. CONCLUSIONS: Repeated oxygenated blood cardioplegia provides better myocardial protection and preservation of left ventricular function than a single dose of HTK during the early hours after declamping.

Esmolol before 80 min of cardiac arrest with oxygenated cold blood cardioplegia alleviates systolic dysfunction. An experimental study in pigs.

OBJECTIVE: Myocardial dysfunction after reperfusion can be a clinical problem in the early postoperative phase after on-pump cardiac surgery. The aim was, in an experimental setting, to investigate if administration of the beta-adrenergic receptor blocker esmolol prior to cross-clamping for 80 min with cold oxygenated blood cardioplegia would improve myocardial protection and early postoperative function. METHODS: Twenty-four anaesthetised pigs were randomly allocated into one of two equally sized groups and put on mild hypothermic cardiopulmonary bypass. Esmolol 1 mg kg(-1) or saline was administered into the arterial line 4 min prior to aortic cross-clamp. Cardiac arrest during 80 min of cross-clamp was obtained with repeated antegrade cold oxygenated blood cardioplegia; the pigs were weaned from bypass following a standardised protocol. Left ventricular global and regional myocardial function and tissue blood flow were evaluated with conductance catheter, echocardiography and coloured microspheres at baseline and at 1, 2 and 3 h after declamping. Four animals did not fulfil the protocol and were excluded. RESULTS: No significant differences between groups could be demonstrated for left ventricular global and local function and tissue blood flow at baseline. At 1h after declamping the slope of preload recruitable stroke work (PRSW(slope)) averaged 73.7+/-12.7 mm Hg (SD) in controls and 72.7+/-11.1 mm Hg in esmolol-treated animals. In controls PRSW(slope) decreased to 62.1+/-11.0 and 58.4+/-12.7 mm Hg after 2 and 3h, respectively (p<0.005 vs 1h for both). In the esmolol-treated animals PRSW(slope) remained unchanged at 72.0+/-11.4 and 73.7+/-12.9 mm Hg at 2 and 3 h after declamp and were significantly higher (p<0.025 and <0.001) than the corresponding values in the control group. The slope of the end systolic pressure volume relationship did not differ between groups at 1 and 2 h after declamp, but were 1.85+/-0.86 and 2.51+/-0.96 mm Hg ml(-1) in controls and in esmolol-treated animals, respectively, after 3h (p<0.025). CONCLUSIONS: Esmolol administered prior to cold oxygenated cardioplegic arrest alleviates left ventricular dysfunction in the early hours after cardiopulmonary bypass.

Multilayer radial systolic strain can identify subendocardial ischemia: an experimental tissue Doppler imaging study of the porcine left ventricular wall.

AIMS: This study investigates whether subendocardial ischemia can be detected by measuring multilayer radial systolic strain from epicardial tissue Doppler imaging. METHODS: In 10 anesthetized open-chest pigs an extracorporeal shunt from the proximal brachiocephalic to the left anterior descending coronary artery was constricted in steps. Color microsphere injections and short axis Tissue Velocity Imaging (TVI) recordings were performed with open shunt, with a non-significant stenosis, and with 2 steps of shunt flow reduction. RESULTS: With open shunt and no transmural flow gradient, there was a gradient of peak ejection strain with high values subendocardially for both 4 and 2 layer measurements. For 2 layer measurement strain was 56.0+/-10.5% subendocardially and 22.0+/-5.2% subepicardially. A non-significant stenosis, not altering transmural flow distribution, reduced strain to 40.3+/-5.4% in the endocardial half-layer. With reduced shunt flow resulting in subendocardial ischemia, peak ejection strain decreased further, primarily in inner wall layers, and postsystolic strain became evident. At severe stenosis (52.4+/-1.8% shunt flow reduction) strain was reduced to 3.8+/-3.6% in the subendocardium and 0.0+/-2.6% in the subepicardium. CONCLUSION: Evaluation of myocardial function with multilayer radial systolic strain has a potential for detecting subendocardial ischemia.

Radial strain gradient across the normal myocardial wall in open-chest pigs measured with doppler strain rate imaging.

BACKGROUND: One of the reasons for the large variation in radial strain measured with Doppler strain rate imaging in normal myocardium might be the different strain length (SL) used during analyses. The aim of this study was to evaluate the effect of different SL settings on strain recordings and the method's ability to detect transmural radial strain gradients. METHODS: In 8 anesthetized pigs (mean weight 54 kg) epicardial echocardiography was performed. Strain analysis was carried out by defining the wall as a 1-, 2-, 3-, and 4-layer structure with suitable regions of interest. Peak ejection strain was measured with SL settings of 2 to 14 mm. RESULTS: The systolic (ejection) strain showed large variation with SL. Sampling in one layer gave no significant reduction in strain for increasing SL. The strain in the subepicardial layer was low and decreased when the wall was divided into several layers (15.9 +/- 4.8% [2 layers]-2.1 +/- 2.4% [4 layers]; both measurements with SL = 4 mm). The method could separate 4 layers with SL of 4 mm or less, 3 layers with SL of 6 mm or less, and 2 layers with SL of 8 mm or less. CONCLUSION: When measuring radial strain in the myocardial wall the SL must be low to evaluate transmural strain gradients. With correct settings of SL and region of interest, strain in 4 layers can be distinguished. As a rule of thumb the SL should be set to approximately half the systolic thickness of the wall or half the wall layer.