Richard P. Wyeth

Demonstration of exercise-induced painless myocardial ischemia in survivors of out-of-hospital ventricular fibrillation

To ascertain if myocardial ischemia is the mechanism of out-of-hospital ventricular fibrillation (VF), left ventricular (LV) function was assessed at rest and during submaximal exercise in 15 patients who survived out-of-hospital VF. They were separated into asymptomatic (9 patients, group A) and symptomatic (6 patients, group S) groups for a history of angina or myocardial infarction. Both groups had significant (at least 70% diameter stenosis) coronary artery disease. At catheterization no patient had angina during exercise, but 12 of 15 had ST depression or increased ST depression (group A, 1.9 +/- 1.4 mm; group S, 1.1 +/- 1.2 mm) and 11 had abnormal wall motion. From rest to exercise, patients in group S had increased LV end-diastolic pressure (from 21 +/- 9 to 37 +/- 11 mm Hg, p = 0.009) and volume (from 100 +/- 25 to 107 +/- 26 ml/m2, p = 0.006), with no significant change in LV ejection fraction (from 40 +/- 13 to 42 +/- 12%). In group A LV end-diastolic pressure increased from 19 +/- 4 to 31 +/- 8 mm Hg (p = 0.001), but neither end-diastolic volume nor ejection fraction changed significantly (from 83 +/- 13 to 92 +/- 23 ml/m2 and from 55 +/- 13% to 46 +/- 13%, respectively). Thus, patients with coronary artery disease who survive out-of-hospital VF may have evidence of myocardial ischemia during exercise without pain. Painless ischemia may have a role in out-of-hospital VF.

Prohormone atrial natriuretic peptides 1–30, 31–67, and 99–126 increase in proportion to right ventricular pacing rate

To determine whether heart rate contributes to release of three new peptide hormones synthesized in the heart, right ventricular pacing at rates of 100, 125, 150, and 180 bpm was performed in six dogs with measurement of the plasma concentration of these peptides at each pacing rate while right atrial and systemic blood pressures were simultaneously monitored. These three peptides of the 126-amino-acid prohormone of atrial natriuretic factor (ANF), consisting of amino acids 1-30 (pro ANF 1-30), 31-67 (pro ANF 31-67), and 99-126 (ANF), increased incrementally at paced heart rates of 125, 150, and 180 bpm (r = 0.8, p less than 0.001). Right atrial pressure decreased with increasing heart rate but systemic blood pressure did not decrease until the heart rate was 180 bpm, at which time these peptides had obtained their maximal circulating concentrations. After pacing, mean right atrial pressure and levels of ANF returned to prepacing values within 30 minutes. Mean arterial blood pressure, on the other hand, increased throughout the 120-minute period after pacing. At 2 hours after pacing, levels of pro ANFs 1-30 and 31-67 were elevated compared with prepacing values. These data demonstrate that, at heart rates of 125 bpm and above, pro ANF 1-30, pro ANF 31-67, and ANF (99-126) are simultaneously and incrementally released in direct proportion to heart rate. The sustained elevation in pro ANFs 1-30 and 31-67 seen 2 hours after pacing suggests that they may contribute to the prolonged diuresis seen after cardiac pacing or tachycardia.

Intracoronary prostaglandin E1 plus streptokinase in acute myocardial infarction

Fourteen patients with acute myocardial infarction (duration of chest pain 5 +/- 2 hours) received intracoronary infusion of prostaglandin E1 (PGE1) and streptokinase. Intracoronary PGE1 was followed by intracoronary streptokinase in 10 patients (group A), with successful recanalization in all patients. Of 4 patients in whom recanalization failed with intracoronary streptokinase given first (group B), 2 had successful recanalization after addition of intracoronary PGE1. Immediately after successful recanalization, left ventricular ejection fraction increased from 50 +/- 9% to 62 +/- 10% (p less than 0.0008), left ventricular end-diastolic pressure decreased from 20 +/- 10 to 16 +/- 10 mm Hg (p less than 0.05) and stroke volume index increased from 34 +/- 10 to 44 +/- 12 ml/m2 (p less than 0.02). Infarct segment shortening improved from 9 +/- 5 to 18 +/- 4% (p less than 0.0002). Transient hypotension in 1 patient was the only complication. Follow-up catheterization in recanalized patients at 2 to 10 days showed maintained improvement in left ventricular global and infarct segment function. Reocclusion occurred in 1 patient. Thus, intracoronary infusion of PGE1 was effective in establishing reperfusion in all patients when followed by streptokinase and was associated with immediately improved left ventricular global and regional function. PGE1 deserves further evaluation in acute myocardial infarction.

Acute and sustained release of atrial natriuretic factor with acute myocardial infarction

The present investigation was designed to determine if acute ischemic cardiac injury causes the release of atrial natriuretic factor (ANF). Seventeen patients with acute myocardial infarction but without clinical evidence of congestive heart failure had their circulating concentration of ANF and creatine phosphokinase monitored daily for 14 days. All 17 patients had an elevated plasma ANF concentration at time of presentation. Maximal increase in ANF was on day 2 and 3 post-infarction. This maximal increase correlated with the size of infarction estimated by the maximal creatine phosphokinase concentration (r = 0.475; p less than 0.05), but did not correlate with the amount of left ventricular dysfunction. ANF began to decrease by day 4 post-infarction and was normal at 10 days post-infarction in 14 of the 17 (82%) patients. At 12 days post-infarction, all 17 patients had normal ANF levels. Another three patients with acute myocardial infarction were treated with tissue plasminogen activator (tPA). The measured ANF levels in these patients were within our normal range and were significantly lower (p less than 0.001) than those seen in patients with acute myocardial infarction not given thrombolytic therapy. Six patients with unstable angina likewise had normal circulating ANF concentrations during prolonged episodes of chest pain. These levels were also significantly lower (p less than 0.001) than the 17 patients with acute infarcts not given tPA. The distinct pattern of release of ANF may be useful as an adjunct to serum cardiac enzymes in determining if a myocardial infarction has occurred.

Pharmacokinetic Characterization of the Postdistribution Phase of Prohormone Atrial Natriuretic Peptides Amino Acids 1–98, 31–67, and Atrial Natriuretic Factor During and After Rapid Right Ventricular Pacing in Dogs

Release rate constants and disappearance rate constants were determined for three atrial natriuretic peptides consisting of amino acids 1–98 (i.e., proANF 1–98), the midportion of the ANF prohormone consisting of amino acids 31–67 (i.e., proANF 31–67) and amino acids 99–126 (i.e., ANF) after right ventricular pacing at 100, 125, 150, and 180 bpm in six male mongrel dogs. Right atrial and femoral vein blood was obtained at baseline, and at 5, 12, 19, 26, 56, 86, 116, 146, and 206 minutes after right ventricular pacing. Resulting plasma concentration‐time data derived parameters were compared. The disappearance rate constants for atrial and femoral venous proANF 1–98 were 0.0144 ± 0.0087 (X ± SD) and 0.0175 ± 0.0075 min−1, respectively (t = 0.6158) and release rate constants were 0.1569 ± 0.1504 and 0.0670 ± 0.0393 min−1, respectively (t = 1.8269; P > .05). The proANF 31–67 disappearance rate constants were 0.0139 ± 0.0082 and 0.0148 ± 0.0132 min−1, respectively (t = 0.1192) and release rate constants were 0.0957 ± 0.0414 and 0.1984 ± 0.1762 min−1, respectively (t = 1.4812). The ANF elimination phase disappearance rate constants were 0.0663 ± 0.0273 and 0.1116 ± 0.0539 min−1 (t = 2.0923, P > .05), respectively, and the release rate constants were 0.1335 ± 0.0532 and 0.1638 ± 0.0520 min−1 (t = 0.7878, P > .05), respectively. These data indicate that proANF 1–98 and proANF 31–67 circulating β post‐distribution half‐lives are approximately 45 minutes whereas β half‐life of ANF is 10 minutes. Persisting concentrations of proANF 1–98 and proANF 31–67 in plasma may better explain the proported sustained pharmacologic effects that have been attributed to ANF, which has a mean a distribution phase half‐life of 3.5 minutes and a β half‐life of 10 minutes.

Effects of gender on the sensitivity of rat cardiac muscle to extracellular Ca2

Experiments were designed to determine if the inotropic response to increasing buffer calcium concentration differs in male and female cardiac muscle. Left atrial and papillary muscles were isolated from hearts of 3-4-month old male and female rats, bathed in Krebs-Henseleit solution (30 degrees C), and stimulated at 1.5 Hz. Isometric developed tension was monitored continuously as extracellular Ca2+ was increased in a cumulative fashion. When compared to male atrial muscle, female atrial preparations were more sensitive to the resulting positive inotropic action; EC50 values were 2.89 +/- 0.22 and 1.86 +/- 0.21 mM in male and female atria, respectively. Two-way analysis of variance (ANOVA) also indicated that there was a significant gender-associated difference in the Ca2+ dose-response curves in atrial muscle. In contrast, papillary muscle did not show a significant gender-related difference in EC50 values (0.88 +/- 0.07 and 0.74 +/- 0.06 mM in males and females); however, the Ca2+ dose-response curves obtained from male and female preparations were found to be significantly different when compared by ANOVA.

Exercise increases the circulating concentration of the N-terminus of the atrial natriuretic factor prohormone in normal individuals☆

Recently two peptides consisting of amino acids (aa) 1 to 30 and 31 to 67 of the N-terminus of the 126 aa prohormone of atrial natriuretic factor (proANF), as well as atrial natriuretic factor (ANF, aa 99 to 126; C-terminus), were found to have vasodilatory and natriuretic properties. These peptides, as well as ANF, circulate in humans as part of the N-terminus of the prohormone. To determine the effect of graded exercise on the circulating concentrations of the N-terminus and C-terminus of the ANF prohormone in normal persons, 12 healthy individuals (mean age 45 +/- 2 years) were evaluated before, for 2 hours after, and during bicycle exercise at a work loads of 25, 50, 75, 100, 125, 150, and 175 W. Both the N- and C-terminus of the ANF prohormone were released simultaneously with graded exercise in direct proportion to the intensity of the work load, measured objectively via maximal oxygen consumption (VO2max), respiratory quotient, and heart rate. Both the N-terminus and C-terminus of the ANF prohormone had strong positive correlations (p less than 0.001) with blood pressure, heart rate, VO2max, and respiratory quotient. Following exercise, the C-terminus returned to preexercise levels within 30 minutes, while the N-terminus remained significantly elevated at 30 and 60 minutes postexercise, reflecting the longer half-life of the N-terminus in the circulation.

Left ventricular thrombi diagnosed by echocardiography in patients with acute myocardial infarction treated with intracoronary streptokinase followed by intravenous heparin

Thirty patients with acute myocardial infarction (AMI) treated with intracoronary streptokinase (7 X 10(5) +/- 3 X 10(5) IU) followed by 10 days of intravenous heparin (800 to 1,500 IU/hour) therapy were prospectively studied by serial 2-dimensional echocardiography for left ventricular (LV) thrombus. Within the first 24 hours, evidence of a thrombolytic state appeared as indicated by fibrin and fibrinogen degradation products (123 +/- 45 mg/dl at 24 hours). Throughout the course of this study partial thromboplastin times were maintained within therapeutic range (40 to 100 seconds). Apical LV thrombus developed in 8 of 30 patients (27%). Apical thrombus developed within 24 hours in 3 patients with anterior AMI and persisted through day 10. By day 10, apical thrombus developed in 3 additional patients with anterior AMI and 2 patients with inferior AMI. In these patients, anterior AMI and apical dysfunction were significant (p less than 0.01 for both) determinants of LV thrombus formation. Hence, the incidence of LV thrombus in patients treated with streptokinase/heparin is similar to that reported earlier in comparable patients not receiving thrombolytic therapy.

Negative inotropic actions of nitric oxide require high doses in rat cardiac muscle

Initial experiments were designed to determine if vasoactive concentrations of nitric oxide (NO) alter contractility in rat heart. Contractile function was monitored in left atrial and papillary muscles (30 °C; paced at 0.5 Hz) during cumulative addition of 3-morpholino-sydnonimine-HCl(SIN-l), an agent that releases NO. At concentrations between 10−7 and 10−4 M (NO concentrations of approximately 10−8-3 × 10−7 M), SIN-1 did not affect contractility in either tissue. Similarly, 10−4 M SIN-1 did not alter the positive inotropic responses to isoproterenol or increasing extracellular [Ca+2] ([Ca+2]o). To obtain higher concentrations of NO, additional studies were conducted using authentic NO. NO-saturated stock solutions and a corresponding control solvent were adjusted to pH 1.6 with HC1. Dose-dependent effects of NO were examined by adding aliquots of the stock solutions (or control solvent) to the bathing solution. At final concentrations of 1 × 10−5- 5 × 10−4 M, NO produced transient, concentration-dependent decreases in contractility that were paralleled by reductions in buffer pH. Control solvent elicited similar reductions in pH0 and transient decreases in contractility; however, the negative inotropic action elicited by the NO-containing solution was approximately 20% greater than that observed in control conditions. These data demonstrate that only high concentrations of NO depress contractility in isolated rat cardiac muscle, and suggest that this effect is mediated by both acidosis and a pHo-independent mechanism.

Acute and Sustained Release of the Atrial Natriuretic Factor Prohormone N-Terminus with Acute Myocardial Infarction

This investigation was designed to determine if acute ischemic cardiac injury causes the release of the 98 amino acid (aa) N-terminus of the 126 aa atrial natriuretic factor prohormone (pro ANF). Seventeen patients with acute myocardial infarction, but without clinical evidence of congestive heart failure, had their circulating concentrations of the whole N-terminus (ie, pro ANF 1-98), the midportion of the N-terminus of the ANF prohormone (consisting of aa 31-67; pro ANF 31-67) and creatine phosphokinase (CPK) monitored daily for 14 days. All seventeen patients had elevated plasma pro ANF 1-98 and pro ANF 31-67 concentrations at the time of presentation. Maximal increase on day three post-infarction correlated with the size of infarction estimated by the maximal CPK (r = 0.675; p less than 0.05) but did not correlate with the amount of left ventricular dysfunction. Another three patients with acute myocardial infarction were treated with tissue plasminogen activator (tPA). The measured pro ANF 1-98 and pro ANF 31-67 levels in these patients were within our normal range and significantly lower (p less than 0.001) than seen in patients with acute myocardial infarction not given thrombolytic therapy. Six patients with unstable angina, likewise, had normal circulating pro ANFs 1-98 and 31-67 concentrations during prolonged episodes of chest pain. These data suggest that myocardial necrosis but not ischemia triggers the release of the entire 126 aa prohormone.