Effect of Intraoperative Phenylephrine Infusion on Redistribution Hypothermia During Cesarean Delivery Under Spinal Anesthesia.

An observational clinical study to evaluate the effect of phenylephrine infusion on maternal temperatures during scheduled cesarean delivery under spinal anaesthesia was conducted in 40 ASA physical status II parturients. Following placement of spinal anesthesia, phenylephrine infusion was initiated at 40 µg/min and titrated to maintain mean arterial pressure within 20 percent of baseline. Maternal oral temperature, heart rate, and blood pressure were measured at baseline, spinal placement, every 10 minutes thereafter for 60 minutes. Phenylephrine dose received was documented every ten minutes. The range in maternal temperature change was 0.06-0.29°C. The lowest recorded temperature was 36.3°C. Decreased maternal temperature was associated with duration of anesthesia and cumulative phenylephrine dose in a univariate model (P<0.001 for all). The multivariable model showed an association between a greater decrease in maternal temperature with larger doses of phenylephrine being administered.

Amlodipine therapy in congestive heart failure: hemodynamic and neurohormonal effects at rest and after treadmill exercise.

This study examined the acute effects of amlodipine treatment on left ventricular pump function, systemic hemodynamics, neurohormonal status, and regional blood flow distribution in an animal model of congestive heart failure (CHF), both at rest and with treadmill exercise. A total of 14 pigs were studied under control conditions and after the development of pacing-induced CHF (240 beats per minute, 3 weeks, n = 7) or with CHF and acute amlodipine treatment for the last 3 days of pacing (1.5 mg/kg per day, n = 7). Under resting conditions, left ventricular stroke volume (mL) was reduced with CHF compared with the normal state (15+/-2 vs. 31+/-1, p<0.05) and increased with amlodipine treatment (23+/-4, p<0.05). At rest, systemic vascular resistance increased with CHF compared with the normal state (3,078+/-295 vs. 2,131+/-120 dyne x s cm(-5), p<0.05) and was reduced after amlodipine treatment (2,472+/-355 dyne x s cm(-5), p<0.05). With exercise, left ventricular stroke volume remained lower and systemic vascular resistance higher in the CHF group, but was normalized with amlodipine treatment. With exercise, left ventricular myocardial blood flow increased from resting values, but was reduced from the normal state with CHF (normal: 1.69+/-0.12 to 7.62+/-0.74 mL/min per gram vs. CHF: 1.26+/-0.12 to 4.77+/-0.45 mL/min per gram, both p<0.05) and was normalized with acute amlodipine treatment (1.99+/-0.35 to 6.29+/-1.23 mL/min per gram). Resting plasma norepinephrine was increased by >5-fold in the CHF group at rest and was not affected by amlodipine treatment. However, with exercise, amlodipine treatment blunted the increase in plasma norepinephrine by >50% when compared with untreated CHF values. Resting plasma endothelin levels increased with CHF compared with the normal state (10.9+/-0.9 vs. 2.8+/-0.4 fmol/mL, p<0.05) and was reduced with amlodipine treatment (7.5+/-1.5 fmol/mL, p<0.5). In other vascular beds, acute amlodipine treatment with CHF improved pulmonary and renal blood flow both at rest and with exercise; however, there were no effects observed on skeletal muscle blood flow. With the development of CHF, acute amlodipine treatment does not negatively influence left ventricular pump function, but rather may provide favorable hemodynamic and neurohormonal effects.

ATP-sensitive potassium channel activation before cardioplegia. Effects on ventricular and myocyte function.

BACKGROUND: Pretreatment with potassium channel openers (PCOs) has been shown to provide protective effects in the setting of myocardial ischemia. The goal of the present study was to examine whether PCO pretreatment would provide protective effects on left ventricular (LV) and myocyte function after cardioplegic arrest. METHODS AND RESULTS: The first study quantified the effects of PCO pretreatment on LV myocyte contractility after simulated cardioplegic arrest. LV porcine myocytes were randomly assigned to 3 groups: (1) normothermic control: 37 degrees C x 2 hours (n = 116); (2) cardioplegia: K+ 24 mEq/L, 4 degrees C x 2 hours followed by reperfusion and rewarming (n = 62); and (3) PCO/cardioplegia: 5 minutes of PCO treatment (50 mumol/L, SR47063, 37 degrees C; n = 94) followed by cardioplegic arrest and rewarming. Myocyte contractility was measured after rewarming by videomicroscopy. The second study determined whether the effects of PCO pretreatment could be translated to an in vivo model of cardioplegic arrest. Pigs (weight 30 to 35 kg) were assigned to the following: (1) cardioplegia: institution of cardiopulmonary bypass (CPB) and cardioplegic arrest (K+ 24 mEq/L, 4 degrees C x 2 hours) followed by reperfusion and rewarming (n = 8); and (2) PCO/cardioplegia: institution of CPB, antegrade myocardial PCO perfusion without recirculation (500 mL of 50 mumol/L, SR47063, 37 degrees C), followed by cardioplegic arrest (n = 6). LV function was examined at baseline (pre-CPB) and at 0 to 30 minutes after separation from CPB by use of the preload-recruitable stroke work relation (PRSWR; x 10(5) dyne.cm/mm Hg). LV myocyte velocity of shortening was reduced after cardioplegic arrest and rewarming compared with normothermic control (37 +/- 3 vs 69 +/- 3 microns/s, P < 0.05) and was improved with 5 minutes of PCO treatment (58 +/- 3 microns/s). In the intact experiments, the slope of the PRSWR was depressed in the cardioplegia group compared with baseline with separation from CPB (1.07 +/- 0.15 vs 2.57 +/- 0.11, P < 0.05) and remained reduced for up to 30 minutes after CPB. In the PCO-pretreated animals, the PRSWR was higher after cessation of CPB when compared with the untreated cardioplegia group (1.72 +/- 0.07, P < 0.05). However, in the PCO pretreatment group, 50% developed refractory ventricular fibrillation by 5 minutes after CPB, which prevented further study. CONCLUSIONS: PCO pretreatment improved LV myocyte contractile function in an in vitro system of cardioplegic arrest. The in vivo translation of this improvement in contractile performance with PCO pretreatment was confounded by refractory arrhythmogenesis. Thus the application of PCO pretreatment as a protective strategy in the setting of cardiac surgery may be problematic.

Chronic dual inhibition of angiotensin-converting enzyme and neutral endopeptidase during the development of left ventricular dysfunction in dogs.

Angiotensin-converting enzyme (ACE) inhibition as well as neutral endopeptidase (NEP) inhibition was demonstrated to influence hemodynamics in various cardiac disease states. However, specific effects of chronic combined ACE and NEP inhibition on left ventricular (LV) and myocyte geometry and function remain unclear. In this study, a dual-acting metalloprotease inhibitor (DMPI), which possesses both ACE and NEP inhibitory activity, was used in a rapid-pacing model of LV dysfunction. LV and myocyte geometry and function were examined in control dogs (n = 6), in dogs with pacing-induced LV dysfunction (216 +/- 2 beats/min, 28 days, n = 7), and in dogs with DMPI treatment during rapid pacing (10 mg/kg p.o., b.i.d., n = 6). With chronic rapid pacing, LV end-diastolic volume increased (84 +/- 4 vs. 49 +/- 3 ml), and LV ejection fraction decreased (38 +/- 3% vs. 68 +/- 3%) compared with control (p < 0.05). DMPI concomitantly administered during long-term rapid pacing did not change LV ejection fraction (35 +/- 3%), but LV end-diastolic volume was reduced (70 +/- 5 vs. 84 +/- 4 ml; p < 0.05) when compared with rapid pacing only. With long-term rapid pacing, myocyte cross-sectional area was decreased (278 +/- 5 vs. 325 +/- 5 microm2), and resting length increased (178 +/- 2 vs. 152 +/- 1 microm) when compared with control (p < 0.05). With DMPI concomitantly administered during rapid pacing, myocyte cross-sectional area (251 +/- 5 microm2) and resting length (159 +/- 4 microm) were reduced when compared with rapid pacing only (p < 0.05). Myocyte velocity of shortening decreased from control values with long-term rapid pacing (39.3 +/- 3.9 vs. 73.2 +/- 5.9 microm/s; p < 0.05) but improved with DMPI treatment during rapid pacing when compared with rapid pacing only (58.9 +/- 6.7 microm/s; p < 0.05). Myocyte velocity of shortening with beta-adrenergic-receptor stimulation (25 nM isoproterenol) was reduced from controls with rapid pacing (125 +/- 12 vs. 214 +/- 30 microm/s; p < 0.05) but was improved with DMPI treatment during rapid pacing when compared with rapid pacing only (178 +/- 12 microm/s; p < 0.05). In a model of rapid pacing-induced LV failure, concomitant DMPI treatment significantly reduced the degree of LV dilation with no apparent effect on LV pump function. At the level of the LV myocyte, long-term DMPI treatment with rapid pacing improved myocyte performance and beta-adrenergic response. Thus the improvement in isolated myocyte contractile function was not translated into improved global LV-pump performance. The mechanisms by which improved myocyte contractility was not translated into a beneficial effect on LV-pump function with DMPI treatment during rapid pacing remain speculative, but likely include significant changes in LV remodeling and loading conditions.

The effects of endothelin-A receptor blockade during the progression of pacing-induced congestive heart failure.

OBJECTIVES: We sought to identify the effects of endothelin (ET) subtype-A (ET(A))) receptor blockade during the development of congestive heart failure (CHF) on left ventricle (LV) function and contractility. BACKGROUND: Congested heart failure causes increased plasma levels of ET and ET(A) receptor activation. METHODS: Yorkshire pigs were assigned to four groups: 1) CHF: 240 beats/min for 3 weeks; n=7; 2) CHF/ET(A)-High Dose: paced for 2 weeks then ET(A) receptor blockade (BMS 193884, 50 mg/kg, b.i.d.) for the last week of pacing; n=6; 3) CHF/ET(A)-Low Dose: pacing for 2 weeks then ET(A) receptor blockade (BMS 193884, 12.5 mg/kg, b.i.d.) for the last week, n=6; and 4) CONTROL: n=8. RESULTS: Left ventricle fractional shortening decreased with CHF compared with control (12+/-1 vs. 39+/-1%, p < 0.05) and increased in the CHF/ET(A) High and Low Dose groups (23+/-3 and 25+/-1%, p < 0.05). The LV peak wall stress and wall force increased approximately twofold with CHF and remained increased with ET(A) receptor blockade. With CHF, systemic vascular resistance increased by 120%, was normalized in the CHF/ET(A) High Dose group, and fell by 43% from CHF values in the Low Dose group (p < 0.05). Plasma catecholamines increased fourfold in the CHF group and were reduced by 48% in both CHF/ET(A) blockade groups. The LV myocyte velocity of shortening was reduced with CHF (32+/-3 vs. 54+/-3 microm/s, p < 0.05), was higher in the CHF/ET(A) High Dose group (39+/-1 microm/s, p < 0.05), and was similar to CHF values in the Low Dose group. CONCLUSIONS: ET(A) receptor activation may contribute to the progression of LV dysfunction with CHF.

Chronic amlodipine treatment during the development of heart failure.

BACKGROUND: This study examined the effects of chronic amlodipine treatment on left ventricular (LV) pump function, systemic hemodynamics, neurohormonal status, and regional blood flow distribution in an animal model of congestive heart failure (CHF) both at rest and with treadmill exercise. In an additional series of in vitro studies, LV myocyte contractile function was examined. METHODS AND RESULTS: Sixteen pigs were studied under normal control conditions and after the development of chronic pacing-induced CHF (240 bpm, 3 weeks, n=8) or chronic pacing and amlodipine (1.5 mg . kg-1 . d-1, n=8). Under ambient resting conditions, LV stroke volume (mL) was reduced with CHF compared with the normal control state (16+/-2 versus 31+/-2, P<0.05) and increased with concomitant amlodipine treatment (29+/-2, P<0.05). At rest, systemic and pulmonary vascular resistance (dyne . s-1 . cm-5) increased with CHF compared with the normal control state (3102+/-251 versus 2156+/-66 and 1066+/-140 versus 253+/-24, respectively, both P<0.05) and were reduced with amlodipine treatment (2108+/-199 and 480+/-74, respectively, P<0.05). With CHF, LV stroke volume remained reduced and was associated with a 40% reduction in myocardial blood flow during treadmill exercise, whereas chronic amlodipine treatment normalized LV stroke volume and improved myocardial blood flow. Resting and exercise-induced plasma norepinephrine levels were increased by >5-fold in the CHF group and were reduced by 50% from CHF values with chronic amlodipine treatment. Resting plasma endothelin (fmol/mL) increased with CHF compared with the normal state (10.4+/-0.9 versus 3.1+/-0.3, P<0.05) and was reduced with amlodipine treatment (6.6+/-1.1, P<0.5). With CHF, LV myocyte velocity of shortening ( microm/s) was reduced compared with normal controls (39+/-1 versus 64+/-1, P<0.05) and was increased with chronic amlodipine treatment (52+/-1, P<0.05). CONCLUSIONS: Chronic amlodipine treatment in this model of developing CHF produced favorable hemodynamic, neurohormonal, and contractile effects in the setting of developing CHF.

Isolated left ventricular myocyte contractility in patients undergoing cardiac operations.

BACKGROUND: Because of methods required for obtaining isolated left ventricular myocytes, evaluation of the contractile function of isolated left ventricular myocytes in normal human patients has been limited. Accordingly, the goal of the present study was to develop a means to isolate human left ventricular myocytes from small myocardial biopsy specimens collected from patients undergoing elective coronary artery bypass operations and to characterize indices of myocyte contractile performance. METHODS: Myocardial biopsy specimens were obtained from the anterior left ventricular free wall of 22 patients undergoing coronary artery bypass operations. Myocytes were isolated from these myocardial samples by means of a stepwise enzymatic digestion method and micro-trituration techniques. Isolated left ventricular myocyte contractile function was assessed by computer-assisted high-speed videomicroscopy under basal conditions and in response to beta-adrenergic receptor stimulation with isoproterenol. RESULTS: A total of 804 viable left ventricular myocytes were successfully examined from all of the myocardial biopsy specimens with an average of 37+/-4 myocytes per patient. All myocytes contracted homogeneously at a field stimulation of 1 Hz with an average percent shortening of 3.7%+/-0.1% and shortening velocity of 51.3+/-1.3 microm/s. After beta-adrenergic receptor stimulation with isoproterenol, percent shortening and shortening velocity increased 149% and 118% above baseline, respectively (P < .05). CONCLUSION: The unique results of the present study demonstrated that a high yield of myocytes could be obtained from human left ventricular biopsy specimens taken during cardiac operations. These myocytes exhibited stable contractile performance and maintained the capacity to respond to an inotropic stimulus. The methods described herein provide a basis by which future studies could investigate intrinsic and extrinsic influences on left ventricular myocyte contractility in human beings.

Temporal relation of ATP-sensitive potassium-channel activation and contractility before cardioplegia.

BACKGROUND: Pharmacologic treatment using potassium-channel openers (PCOs) before cardioplegic arrest has been demonstrated to provide beneficial effects on left ventricular performance with subsequent reperfusion and rewarming. However, the PCO treatment interval necessary to provide protective effects during cardioplegic arrest remains to be defined. The present study was designed to determine the optimum period of PCO treatment that would impart beneficial effects on left ventricular myocyte contractility after simulated cardioplegic arrest. METHODS: Left ventricular porcine myocytes were assigned randomly to three groups: (1) normothermic control = 37 degrees C for 2 hours; (2) cardioplegia = K+ (24 mEq/L) at 4 degrees C for 2 hours followed by reperfusion and rewarming; and (3) PCO and cardioplegia = 1 to 15 minutes of treatment with the PCO aprikalim (100 micromol/L) at 37 degrees C followed by hypothermic (4 degrees C) cardioplegic arrest and subsequent rewarming. Myocyte contractility was measured after rewarming by videomicroscopy. A minimum of 50 myocytes were examined at each treatment and time point. RESULTS: Myocyte velocity of shortening was reduced after cardioplegic arrest and rewarming compared with normothermic controls (63+/-3 microm/s versus 32+/-2 microm/s, respectively; p < 0.05). With 3 minutes of PCO treatment, myocyte velocity of shortening was improved after cardioplegic arrest to values similar to those of normothermic controls (56+/-3 microm/s). Potassium channel opener treatment for less than 3 minutes did not impart a protective effect, and the protective effect was not improved further with more prolonged periods of PCO treatment. CONCLUSIONS: A brief interval of PCO treatment produced beneficial effects on left ventricular myocyte contractile function in a simulated model of cardioplegic arrest and rewarming. These results suggest that a brief period of PCO treatment may provide a strategy for myocardial protection during prolonged cardioplegic arrest in the setting of cardiac operation.

Time-dependent changes in matrix metalloproteinase activity and expression during the progression of congestive heart failure: relation to ventricular and myocyte function.

The development of congestive heart failure (CHF) is associated with left ventricular (LV) dilation and myocardial remodeling. However, fundamental mechanisms that contribute to this remodeling process with the progression of CHF remain unclear. The matrix metalloproteinases (MMPs) have been demonstrated to play a significant role in tissue remodeling in a number of pathological processes. The present project tested the hypothesis that the LV dilation and remodeling during the progression of CHF is associated with early changes in MMP expression and zymographic activity. LV and myocyte function, collagen content, and MMP expression and zymographic activity were serially measured during the progression of CHF caused by pacing-induced supraventricular tachycardia (SVT) in pigs. After 7 days of SVT, LV end-diastolic dimension and myocyte length both increased by 15% from control values, and LV fractional shortening fell by 20%. At the level of the myocyte, percent shortening fell by 16% after 7 days of SVT, with no change in the steady-state velocity of shortening. Longer durations of SVT caused progressive LV dilation, LV pump failure, and myocyte contractile dysfunction. Specifically, 21 days of SVT resulted in a >50% increase in LV dimension, a 56% fall in LV fractional shortening, and a 33% decline in myocyte velocity of shortening. The decline in LV and myocyte function with 21 days of SVT was accompanied by signs and symptoms of CHF. Thus, SVT causes time-dependent changes in LV geometry and function and the subsequent development of CHF. LV myocardial collagen content and confluence fell by >25% after 7 days of SVT and were accompanied by an 80% increase in LV myocardial MMP zymographic activity against the substrate gelatin. After 14 days of SVT, total LV myocardial collagen content was reduced by 24%, and LV myocardial MMP zymographic activity increased by >100% from control values. Interstitial collagenase (MMP-1), stromelysin (MMP-3), and 72-kD gelatinase (MMP-2) were increased by approximately 2-fold after 7 days of SVT. LV MMP zymographic activity and abundance remained elevated with longer durations of SVT. The results of the present study demonstrated that in this model of CHF, early changes in LV myocardial MMP zymographic activity and protein levels occurred with the initiation and progression of LV dilation and dysfunction. These findings suggest that an early contributory mechanism for the initiation of LV remodeling that occurred in this model of developing CHF is enhanced expression and potentially increased activity of LV myocardial MMPs.

Downstream defects in beta-adrenergic signaling and relation to myocyte contractility after cardioplegic arrest.

OBJECTIVE: Transient left ventricular dysfunction can occur after hypothermic, hyperkalemic cardioplegic arrest and is associated with decreased beta-adrenergic receptor responsiveness. Occupancy of the beta-adrenergic receptor activates adenylate cyclase, which phosphorylates the L-type Ca2+ channel-enhancing myocyte contractility. The goal of this study was to identify potential mechanisms that contribute to the defects in the beta-adrenergic receptor signaling cascade after cardioplegic arrest. METHODS: Isolated left ventricular porcine myocytes were assigned to one of two treatment groups: (1) cardioplegic arrest (24 mEq/L K+, 4 degrees C x 2 hours, then 5 minutes in 37 degrees C cell media; n = 130) or (2) normothermic control (cell media, 37 degrees C x 2 hours; n = 222). Myocyte contractility was assessed at baseline and after either beta-adrenergic receptor occupancy (25 nmol/L isoproterenol [INN: isoprenaline]), activation of adenylate cyclase (0.5 mumol forskolin), or direct activation of the L-type Ca(2+)-channel (10 nmol/L or 100 nmol/L (-)BayK 8644). RESULTS: Myocyte velocity of shortening (micron/sec) was increased with beta-adrenergic receptor occupancy or direct adenylate cyclase stimulation compared with baseline in the normothermic group (187.3 +/- 6.9, 181.7 +/- 10.2, and 73.9 +/- 2.9, respectively; p < 0.0001) and after cardioplegic arrest (128.6 +/- 8.9, 124.3 +/- 9.4, and 46.1 +/- 2.6, respectively; p < 0.0001). However, the response after cardioplegic arrest was significantly reduced compared with normothermic values under all conditions (p = 0.012). Direct activation of the L-type Ca(2+)-channel, which eliminates beta-adrenergic receptor-dependent events, increased myocyte contractility in the normothermic group (161.90 +/- 12.0, p < 0.0001) and after cardioplegic arrest (92.78 +/- 6.8, p < 0.0001), but the positive inotropic response appeared reduced compared with normothermic control values (p = 0.003). CONCLUSION: These findings suggest that contributory mechanisms for the reduced beta-adrenergic receptor-mediated response after hypothermic, hyperkalemic cardioplegic arrest lie downstream from these specific components of the transduction pathway and likely include defects in Ca2+ homeostasis, myofilament Ca2+ sensitivity, or both.

AT1 angiotensin II receptor inhibition in pacing-induced heart failure: effects on left ventricular performance and regional blood flow patterns.

BACKGROUND: AT1 angiotensin II (AT1 Ang II) receptor activation has been shown to cause increased vascular resistance in the systemic (SVR), pulmonary (PVR), and coronary vasculature which may be of particular importance in the setting of congestive heart failure (CHF). The overall goal of this study was to examine the effects of acute AT1 Ang II receptor inhibition on left ventricular (LV) pump function, systemic hemodynamics, and regional blood flow patterns in the normal state and with CHF, both at rest and with treadmill-induced exercise. METHODS AND RESULTS: Pigs (25 kg) were instrumented to measure cardiac output (CO), SVR, and PVR, and LV myocardial blood flow distribution in the conscious state and were assigned to one of two groups: (1) pacing-induced CHF (240 bpm for 3 weeks, n = 6) or (2) sham controls (n = 5). Measurements were obtained at rest and after treadmill exercise (15 degrees for 10 minutes). Studies were repeated 30 minutes after intravenous infusion of a low (1.1 mg/kg) or high (125 mg/kg) dose of the AT1 Ang II antagonist, valsartan. The low dose of valsartan reduced the Ang II pressor response by approximately 50% but had a minimal effect on arterial pressure, whereas the high dose eliminated the Ang II pressor response and reduced resting blood pressure by approximately 20%. With CHF, CO was reduced at rest (2.5+/-0.2 v 3.9+/-0.1 L/min) and with exercise (6.4+/-0.5 v 7.8+/-0.5 L/min) compared with controls (P < .05). Valsartan at the low and high dose increased resting CO by 28% in the control and CHF groups, but did not affect CO with exercise. Resting SVR in the CHF group was higher than controls (2,479+/-222 v 1,877+/-65 dyne x s x cm(-5), P < .05), but SVR fell to a similar degree with exercise (1,043+/-98 v 1,000+/-77 dyne x s x cm(-5)). The low and high dose of valsartan reduced resting SVR by more than 30% in both the control and CHF groups. PVR was increased by more than twofold in the CHF group at rest. The high dose of valsartan reduced resting PVR with CHF, but had no further effect with exercise. LV myocardial blood flow was reduced with pacing CHF, particularly with exercise. With exercise and CHF, a low or high dose of valsartan reduced coronary vascular resistance, but LV myocardial blood flow remained reduced from normal values. CONCLUSIONS: Heightened AT1 Ang II receptor activity occurred in this model of CHF, which contributed to alterations in systemic hemodynamics and vascular resistive properties. By using a low dose of a selective AT1 Ang II receptor antagonist reduced SVR, PVR, and coronary vascular resistive properties and therefore may provide beneficial effects in a setting of CHF.

Potassium channel opener-augmented cardioplegia: protection of myocyte contractility with chronic left ventricular dysfunction.

BACKGROUND: An increased number of patients with preexisting left ventricular (LV) dysfunction and congestive heart failure (CHF) are undergoing cardiac surgery with a higher risk for decreased LV contractility after hyperkalemic cardioplegic arrest. Activation of adenosine triphosphate-sensitive potassium channels by potassium channel openers (PCO) within the myocyte appears to confer a protective effect in the setting of ischemia. Accordingly, the present study was designed to determine whether PCO supplementation during hyperkalemic cardioplegic arrest would provide protective effects on myocyte contractile function, particularly in the setting of CHF. METHODS AND RESULTS: LV myocytes were isolated from control pigs (n=7) and pigs with CHF (rapid pacing, 240 beats per minute; n=7) and then assigned to the following treatment groups: normothermia (cell culture media, 2 hours, 37 degrees C); cardioplegia (24 mEq/L K+, 2 hours, 4 degrees C; then 10 minutes of reperfusion); or PCO/cardioplegia (cardioplegia supplemented with 100 micromol/L of the PCO aprikalim). Myocyte velocity of shortening was reduced in both control (66+/-2 versus 33+/-1 microm/s) and CHFmyocytes (32+/-1 versus 22+/-1 microm/s) after hyperkalemic cardioplegic arrest (P<.05). Contractility after PCO cardioplegia was similar to normothermic values in control (57+/-2 microm/s) and CHF (33+/-1 microm/s) myocytes (P<.05). Intracellular free Ca2+ increased from normothermia during hyperkalemic cardioplegia in control (81+/-4 to 145+/-7 nmol/L) and CHF (262+/-30 to 823+/-55 nmol/L) myocytes (P<.05). PCO cardioplegia attenuated the intracellular increase in free Ca2+ during the cardioplegic interval in control (110+/-6 nmol/L) and CHF (383+22 nmol/L) myocytes (P<.05). CONCLUSIONS: PCO-augmented cardioplegic arrest preserved myocyte contractility and reduced the intracellular free Ca2+ release, which therefore may be of particular benefit in the setting of preexisting LV dysfunction.

Preservation of myocyte contractile function after hyperthermic cardioplegic arrest by activation of ATP-sensitive potassium channels.

BACKGROUND: Left ventricular (LV) dysfunction can occur after hyperkalemic cardioplegic arrest and subsequent reperfusion and rewarming. Activation of adenosine triphosphate (ATP)-sensitive potassium (KATP) channels within the myocyte sarcolemma has been shown to be cardioprotective for myocardial reperfusion injury and ischemia and may play a contributory role in preconditioning for cardioplegic arrest. Accordingly, the present study tested the hypothesis that cardioplegic arrest and activation of KATP channels by a potassium channel opener (PCO) would attenuate alterations in ionic homeostasis and improve myocyte contractile function. METHODS AND RESULTS: Porcine LV myocytes were isolated and randomly assigned to the following treatment groups: normothermic control, incubation in cell culture media for 2 hours at 37 degrees C (n=60); hyperkalemic cardioplegia, incubation for 2 hours in hypothermic hyperkalemic cardioplegic solution (n=60); or PCO/cardioplegia, incubation in cardioplegic solution containing 100 micromol/L of the PCO aprikalim (n=60). Hyperkalemic cardioplegia and rewarming caused a significant reduction in myocyte velocity of shortening compared with normothermic control values (33+/-2 versus 66+/-2 microm/s, P<.05). Cardioplegic arrest with PCO supplementation significantly improved indices of myocyte contractile function when compared with hyperkalemic cardioplegia (58+/-4 microm/s, P<.05). Myocyte intracellular calcium increased during hyperkalemic cardioplegic arrest compared with baseline values (147+/-2 versus 85+/-2 nmol/L, P<.05). The increase in intracellular calcium was significantly reduced in myocytes exposed to the PCO-supplemented cardioplegic solution (109+/-4 nmol/L, P<.05). CONCLUSIONS: Cardioplegic arrest with simultaneous activation of KATP channels preserves myocyte contractile processes and attenuates the accumulation of intracellular calcium. These findings suggest that changes in intracellular calcium play a role in myocyte contractile dysfunction associated with cardioplegic arrest. Moreover, alternative strategies may exist for preservation of myocyte contractile function during cardioplegic arrest.

Modulation of the renin-angiotensin pathway through enzyme inhibition and specific receptor blockade in pacing-induced heart failure: I. Effects on left ventricular performance and neurohormonal systems.

BACKGROUND: The goal of this study was to determine the effects of ACE inhibition (ACEI) alone, AT1 angiotensin (Ang) II receptor blockade alone, and combined ACEI and AT1 Ang II receptor blockade on LV function, systemic hemodynamics, and neurohormonal system activity in a model of congestive heart failure (CHF). METHODS AND RESULTS: Pigs were randomly assigned to each of 5 groups: (1) rapid atrial pacing (240 bpm) for 3 weeks (n=9), (2) ACEI (benazeprilat, 0.187 mg x kg(-1) x d(-1)) and rapid pacing (n=9), (3) AT1 Ang II receptor blockade (valsartan, 3 mg x kg(-1) x d(-1)) and rapid pacing (n=9), (4) ACEI and AT1 Ang II receptor blockade (benazeprilat/valsartan, 0.05/3 mg x kg(-1) d(-1)) and rapid pacing (n=9), and (5) sham controls (n=10). In the pacing group, LV fractional shortening (LVFS) fell (13.4+/-1.4% versus 39.1+/-1.0%) and end-diastolic dimension (LVEDD) increased (5.61+/-0.11 versus 3.45+/-0.07 cm) compared with control (P<.05). With AT1 Ang II blockade and rapid pacing, LVEDD and LVFS were unchanged from pacing-only values. ACEI reduced LVEDD (4.95+/-0.11 cm) and increased LVFS (20.9+/-1.9%) from pacing-only values (P<.05). ACEI and AT1 Ang II blockade reduced LVEDD (4.68+/-0.07 cm) and increased LVFS (25.2+/-0.9%) from pacing only (P<.05). Plasma norepinephrine and endothelin increased by more than fivefold with chronic pacing and remained elevated with AT1 Ang II blockade. Plasma norepinephrine was reduced from pacing-only values by more than twofold in the ACEI group and the combination group. ACEI and AT1 Ang II receptor blockade reduced plasma endothelin levels by >50% from rapid-pacing values. CONCLUSIONS: These findings suggest that the effects of ACEI in the setting of CHF are not solely due to modulation of Ang II levels but rather to alternative enzymatic pathways and that combined ACEI and AT1 Ang II receptor blockade may provide unique benefits for LV pump function and neurohormonal systems in the setting of CHF.

Modulation of the renin-angiotensin pathway through enzyme inhibition and specific receptor blockade in pacing-induced heart failure: II. Effects on myocyte contractile processes.

BACKGROUND: The goal of this study was to determine the effects of ACE inhibition alone, AT1 angiotensin (Ang) II receptor blockade alone, and combined ACEI and AT1 Ang II receptor blockade in a model of congestive heart failure (CHF) on isolated LV myocyte function and fundamental components of the excitation-contraction coupling process. METHODS AND RESULTS: Pigs were randomly assigned to one of five groups: (1) rapid atrial pacing (240 bpm) for 3 weeks (n=9), (2) concomitant ACEI (benazeprilat, 0.187 mg x kg(-1) x d(-1)) and rapid pacing (n=9), (3) concomitant AT1 Ang II receptor blockade (valsartan, 3 mg/kg/d) and rapid pacing (n=9), (4) concomitant ACEI and AT1 Ang II receptor blockade (benazeprilat/valsartan, 0.05/3 mg x kg(-1) x d(-1)) and rapid pacing (n=9), and (5) sham controls (n=10). LV myocyte shortening velocity was reduced with chronic rapid pacing compared with control (27.2+/-0.6 versus 58.6+/-1.2 microm/s, P<.05) and remained reduced with AT1 Ang II receptor blockade and rapid pacing (28.0+/-0.5 microm/s, P<.05). Myocyte shortening velocity increased with ACEI or combination treatment compared with rapid pacing only (36.9+/-0.7 and 42.3+/-0.8 microm/s, respectively, P<.05). Myocyte beta-adrenergic response was reduced by >50% in both the rapid pacing group and the AT1 Ang II blockade group and improved by 25% with ACEI and increased by 54% with combined treatment. Both L-type Ca2+ channel density and the relative abundance of sarcoplasmic reticulum Ca2+ ATPase density were reduced with rapid pacing and returned to control levels in the combined ACEI and AT1 Ang II blockade group. CONCLUSIONS: The unique findings of this study were twofold. First, basic defects in specific components of the myocyte excitation-contraction coupling process that occur with CHF are reversible. Second, combined ACEI and AT1 Ang II blockade may provide unique benefits on myocyte contractile processes in the setting of CHF.

Left ventricular regional myocyte contractility in normal and heart failure states.

Fundamental determinants of left ventricular (LV) pump performance are preload, afterload and myocyte contractility. Regional variability in LV end systolic wall stress, an important index of LV afterload, has been well defined in both control and congestive heart failure (CHF) states. The goal of this study was to examine end systolic wall stress and myocyte contractile function in three circumferential regions of the LV in both control and CHF states. Accordingly, LV end systolic wall stress and myocyte velocity of shortening were measured from the basal, mid and apical regions in control pigs (n=5) and following the induction of pacing-induced CHF (3 weeks, 240 beats/min, n=5). LV mid wall, circumferential, end systolic wall stress decreased from base to apex in both control (35+/-7 v 16+/-4 g/cm2, P<0.05) and CHF (155+/-23 v 92+/-24 g/cm2, P<0.05) states. In the CHF group, LV end systolic wall stress was elevated by 300% compared to control values in all regions. LV myocyte velocity of shortening was equivalent in the basal and mid regions of control myocytes (52+/-2 v 57+/-2 m/s), and was higher in the apical region (63+/-3 microm/s, P<0.05). In the CHF group, LV myocyte velocity of shortening was reduced by 45% compared to controls with no regional variation. beta-adrenergic stimulation increased myocyte velocity in both the control and CHF groups, however, regional variation was observed only in the CHF group. These unique results demonstrated that minimal regional variations in myocyte contractile function exist in both control and congestive heart failure states, and does not necessarily parallel patterns of regional LV end systolic wall stress.

Relationship between external load and isolated myocyte contractile function with CHF in pigs.

Past studies have demonstrated that the negative relationship between afterload and contractile performance of papillary muscles is shifted downward and to the left with the development of hypertrophy. However, it remained unclear whether a similar load-contractility relationship could be constructed for isolated myocytes, particularly with the development of congestive heart failure (CHF). Accordingly, the effect of incrementally increased external loads on the contractile performance of left ventricular (LV) myocytes isolated from pigs in the normal state (n = 5) and after the development of chronic supraventricular tachycardia (SVT)-induced CHF (SVT-CHF; 240 beats/min, 3 wk; n = 5) was examined. This study used precalibrated microspheres to impose a quantifiable load on isolated myocytes, and myocyte contractility was assessed by videomicroscopy. Steady-state unloaded extent of shortening was 5.4 +/- 0.2 microns in control myocytes (n = 80) and was significantly reduced in the myocytes with the development of SVT-CHF (4.4 +/- 0.2 microns, n = 93; P < 0.05). Inverse relationships between relative resistive load and myocyte contractile function were observed at both normal and CHF states (r2 > 0.85). For myocyte velocity of shortening, the slope of this relationship was significantly reduced in the SVT-CHF state compared with controls (-46.3 x 10(-6) and -34.6 x 10(-6) microns3.microN-1.s-1, respectively; P < 0.05). At higher relative resistive loads (> 0.18 x 10(-6) microN/microns2), the reduction in myocyte shortening extent under an equivalent relative resistive load was significantly greater in the SVT-CHF myocytes compared with controls (62.8 +/- 3.9 vs. 45.6 +/- 4.7%, respectively, P < 0.05). The present study demonstrated for the first time that a load-dependent relationship can be derived for intact isolated LV myocytes in both normal and CHF states. The defect in the capacity of SVT-CHF myocytes to respond to an increased relative resistive load is a likely contributory mechanism for the LV pump dysfunction that occurs in this model of CHF.

Protective effects of adenosine on myocyte contractility during cardioplegic arrest.

BACKGROUND: Adenosine delivery to the left ventricular myocardium has been demonstrated to provide protective effects in the setting of ischemia and reperfusion. However, whether adenosine has direct protective effects on isolated myocytes in the setting of cardioplegic arrest was unclear. METHODS: Isolated porcine left ventricular myocytes were assigned to one of the following treatment groups: (1) cardioplegia: 24 mEq/L K+, 4 degrees C for 2 hours followed by rewarming (cell media, 37 degrees C; n = 29); (2) cardioplegia augmented with adenosine (1 to 200 micromol/L) followed by rewarming (n = 98); and (3) normothermic control (cell media, 37 degrees C, 2 hours; n = 175). Myocyte contractility was measured by computer-aided videomicroscopy. RESULTS: Cardioplegic arrest and rewarming reduced myocyte shortening velocity compared with normothermic control (25.3 +/- 2.5 microm/s versus 50.9 +/- 1.4 microm/s, p < 0.05). Adenosine-augmented cardioplegic arrest improved myocyte contractility with rewarming in a concentration-dependent fashion. For example, cardioplegia augmented with 10 micromol/L adenosine improved myocyte shortening velocity by 33% (33.6 +/- 3.0 microm/s versus 25.3 +/- 2.5 microm/s, p < 0.05), whereas 200 micromol/L adenosine improved shortening velocity by 97% (49.9 +/- 3.4 microm/s vs 25.3 +/- 2.5 microm/s, p < 0.05) compared with conventional cardioplegia. CONCLUSIONS: This study demonstrated concentration-dependent protective effects of adenosine-augmented cardioplegia on myocyte contractile function with subsequent reperfusion and rewarming. These results suggest that stimulation of putative myocyte adenosine receptors may provide enhanced protective effects on myocyte contractile processes during cardioplegic arrest.