Contractile reserve in patients with peripartum cardiomyopathy and recovered left ventricular function

OBJECTIVES

Peripartum cardiomyopathy is a rare complication of pregnancy. Thirty percent of patients with this disorder are reported to recover baseline ventricular function within 6 months of delivery, but the ability of these ventricles to respond to hemodynamic stress is unknown. The aim of this investigation was to quantitatively assess the contractile reserve of patients with a history of peripartum cardiomyopathy and recovered left ventricular function.

STUDY DESIGN

Baseline left ventricular contractility was assessed by use of the load and heart rate-independent relationship between end-systolic stress and rate-corrected velocity of fiber shortening. Data were acquired from "recovered" patients (10.5 +/- 11.6 months after delivery) and compared with data from matched nonpregnant controls with use of two-dimensionally targeted M-mode echocardiography and calibrated subclavian pulse tracings that were recorded over a wide range of afterloads (end-systolic stress) generated by methoxamine (1 mg/min) infusion. Contractile reserve was assessed by a dobutamine challenge (5 micrograms/kg/min) and quantified as the vertical deviation of the dobutamine end-systolic stress minus the corrected velocity of fiber shortening data point from the baseline contractility line.

RESULTS

Patients with peripartum cardiomyopathy and matched controls had normal baseline heart rates, blood pressures, ventricular dimensions, and left ventricular function. Contractile reserve, however, was reduced in patients with recovered peripartum cardiomyopathy (0.30 +/- 0.12 vs 0.17 +/- 0.04 circ/sec, p < 0.03).

CONCLUSIONS

Women with a history of peripartum cardiomyopathy who have regained normal resting left ventricular size and performance have decreased contractile reserve revealed by the use of a dobutamine challenge test. Ventricles of these women may respond suboptimally to hemodynamic stress in spite of evidence of recovery by routine echocardiographic evaluation.

Peripartum cardiomyopathy

Congestive heart failure is an uncommon complication of pregnancy with potentially life-threatening consequences. Peripartum cardiomyopathy is a disease of unknown cause in which severe left ventricular dysfunction occurs during late pregnancy or the early puerperium. In the past, the diagnosis of this entity was made on clinical grounds; however, modern echocardiographic techniques have allowed more accurate diagnoses by excluding cases of diseases that mimic the clinical symptoms and signs of heart failure. Risk factors for peripartum cardiomyopathy include advanced maternal age, multiparity, African descent, twinning, and long-term tocolysis. An extensive search for the causes of peripartum cardiomyopathy has been unrevealing. Treatment includes digitalis, diuretic agents, and vasodilators. Anticoagulation is strongly recommended, especially if ventricular function is persistent. The prognosis of peripartum cardiomyopathy is related to the recovery of ventricular function. Caution is advised in recommending subsequent pregnancy, especially if left ventricular dysfunction is persistent.

Peripartum heart failure associated with prolonged tocolytic therapy

beta-Adrenergic receptor agonist tocolysis has been reported to cause noncardiogenic pulmonary edema. We report an association between chronic terbutaline therapy and cardiomyopathy in peripartum women. Among 15 gravidas who had peripartum heart failure, 4 had received prolonged terbutaline tocolysis. Although those four patients had completely normalized ventricular function, only 7 of the 11 others recovered. We suggest that gravidas receiving long-term beta-sympathomimetic tocolysis undergo close evaluation of cardiac function.

Generation of nitrogen-chlorine oxidants by human phagocytes

Human phagocytes can be triggered to generate large quantities of long-lived nitrogen-chlorine derivatives. This class of oxidants can be detected as early as 5 min after the addition of phorbol myristate acetate or opsonized zymosan particles. Unlike all other oxygen metabolites known to be generated by phagocytes, the nitrogen-chlorine compounds can be readily detected in cell supernatants 90 min after stimulation. The generation of these oxidants is linear with neutrophil concentration, favored at alkaline pH, and inhibited by supraphysiologic concentrations of iodide or bromide. The oxidants are hydrophilic in nature and have a half-life ranging from 5 h at 37 degrees C to greater than 100 h at 4 degrees C. Gel filtration chromatography of the accumulated nitrogen-chlorine derivatives revealed that the oxidants generated by neutrophils or monocytes are a complex mixture of products whose Mr range from 150-5,000. One-half of the nitrogen chlorine derivatives migrate as a single peak with an Mr of approximately 150. Amino acid analysis of this fraction identified the beta-amino acid, taurine, as the single nitrogenous compound present. Neutrophils triggered in the presence of serum albumin accumulated increased amounts of the nitrogen-chlorine derivatives while continuing to generate their endogenous low Mr oxidants. Quantitative analysis of the 36Cl incorporation revealed that the albumin molecule was chlorinated with the formation of both nitrogen-chlorine and carbon-chlorine bonds. We conclude that human phagocytes can chlorinate both endogenous and exogenous nitrogenous compounds at inflammatory sites to generate a heterogeneous mixture of nitrogen-chlorine derivatives. The ability of phagocytes to generate this class of long-lived oxidants whose hydrophilic characteristics restrict their localization to the extracellular space suggests that these species play an important role in modulating the inflammatory response.

Long-lived oxidants generated by human neutrophils: characterization and bioactivity

Human neutrophils were found to generate an unusual class of oxidants with a half-life of approximately 18 hours and with characteristics similar to, if not identical with, those of N-chloroamines. These neutrophil-derived N-chloroamines have sufficient oxidizing potential to attack sulfhydryl- or thioether-containing compounds and can react with both a methionine-containing chemotactic peptide and a plasma protease inhibitor. As judged by their stability and selective reactivity, the N-chloroamines generated by stimulated neutrophils may play an important role in the local and systemic regulation of inflammatory events in vivo.

The chlorinating potential of the human monocyte

Human monocytes incubated with phorbol myristate acetate (PMA) or opsonized zymosan particles can chlorinate the beta-amino acid taurine to its monochloramine derivative. Taurine monochloramine can then be quantitated by its ability to oxidize 5-thio-2-nitrobenzoic acid to its disulfide or by its characteristic absorption peak at 252 nm. Stimulated, but not resting, monocytes chlorinated taurine by a process dependent on time, cell concentration, and pH. The formation of taurine chloramine by stimulated monocytes could be inhibited by catalase, azide, or cyanide, was unaffected by superoxide dismutase, and was stimulated by exogenous myeloperoxidase. Thus, taurine chloramine generation by human monocytes appeared dependent on both H2O2 and myeloperoxidase. Compared to human neutrophils, the monocyte could generate similar amounts of chloramine when stimulated with phorbol myristate acetate, but far less if opsonized zymosan particles were used as the trigger. Based on the known ability of the H2O2-myeloperoxidase-Cl- system to generate free HOCl, it would seem that this oxidant is the most likely species responsible for the monocyte-mediated chlorination reactions. Thus, we have used a simple quantitative assay to demonstrate the ability of the human monocyte to generate large quantities of a highly reactive and toxic oxygen metabolite.