Hemodynamic effects of inhaled nitric oxide in right ventricular myocardial infarction and cardiogenic shock

Pulmonary hypertension secondary to left ventricular systolic dysfunction: contemporary diagnosis and management

Pulmonary hypertension secondary to left ventricular systolic dysfunction is often a poor prognostic marker in chronic heart failure. In this article, we review evidence supporting modern strategies addressing pulmonary hypertension in patients with left ventricular systolic dysfunction, including right-sided heart catheterization with vasoreactivity testing and subsequent parenteral, oral, and inhaled therapy. We delineate a diagnostic approach to secondary pulmonary hypertension and outline evidence-based therapeutic strategies for management in acute and chronic heart failure.

Thrombospondin-1 and CD47 regulate blood pressure and cardiac responses to vasoactive stress

Nitric oxide (NO) locally regulates vascular resistance and blood pressure by modulating blood vessel tone. Thrombospondin-1 signaling via its receptor CD47 locally limits the ability of NO to relax vascular smooth muscle cells and increase regional blood flow in ischemic tissues. To determine whether thrombospondin-1 plays a broader role in central cardiovascular physiology, we examined vasoactive stress responses in mice lacking thrombospondin-1 or CD47. Mice lacking thrombospondin-1 exhibit activity-associated increases in heart rate, central diastolic and mean arterial blood pressure and a constant decrease in pulse pressure. CD47-deficient mice have normal central pulse pressure but elevated resting peripheral blood pressure. Both null mice show exaggerated decreases in peripheral blood pressure and increased cardiac output and ejection fraction in response to NO. Autonomic blockade also induces exaggerated hypotensive responses in awake thrombospondin-1 null and CD47 null mice. Both null mice exhibit a greater hypotensive response to isoflurane, and autonomic blockage under isoflurane anesthesia leads to premature death of thrombospondin-1 null mice. Conversely, the hypertensive response to epinephrine is attenuated in thrombospondin-1 null mice. Thus, the matricellular protein thrombospondin-1 and its receptor CD47 serve as acute physiological regulators of blood pressure and exert a vasopressor activity to maintain global hemodynamics under stress.

Nitric Oxide in the Pulmonary Vasculature

Homeostasis in the pulmonary vasculature is maintained by the actions of vasoactive compounds, including nitric oxide (NO). NO is critical for normal development of the pulmonary vasculature and continues to mediate normal vasoregulation in adulthood. Loss of NO bioavailability is one component of the endothelial dysfunction and vascular pathology found in pulmonary hypertension (PH). A broad research effort continues to expand our understanding of the control of NO production and NO signaling and has generated novel theories on the importance of pulmonary NO production in the control of the systemic vasculature. This understanding has led to exciting developments in our ability to treat PH, including inhaled NO and phosphodiesterase inhibitors, and to several promising directions for future therapies using nitric oxide-donor compounds, stimulators of soluble guanylate cyclase, progenitor cells expressing NO synthase (NOS), and NOS gene manipulation.

Inhaled NO as a therapeutic agent

In 1991, Frostell and colleagues reported that breathing low concentrations of nitric oxide (NO) decreased pulmonary artery pressure (PAP) in awake lambs with experimental pulmonary hypertension (PH) [Frostell C, Fratacci MD, Wain JC, Jones R, Zapol WM. Inhaled nitric oxide. A selective pulmonary vasodilator reversing hypoxic pulmonary vasoconstriction. Circulation 1991;83:2038-47]. Subsequently, efforts of multiple research groups studying animals and patients led to approval of inhaled NO by the US Food and Drug Administration in 1999 and the European Medicine Evaluation Agency and European Commission in 2001. Inhaled NO is currently indicated for the treatment of term and near-term neonates with hypoxemia and PH. Since regulatory approval, several studies have suggested that NO inhalation can prevent chronic lung disease in premature infants. In addition, unanticipated systemic effects of inhaled NO may lead to treatments for a variety of disorders including ischemia-reperfusion injury. This review summarizes the pharmacology and physiological effects of breathing NO. The application of inhaled NO to hypoxemic neonates with PH is discussed including recent studies exploring the use of inhaled NO to prevent bronchopulmonary dysplasia in premature infants. This review also highlights the application of inhaled NO to treat adults with cardiopulmonary disease, strategies to augment the efficacy of inhaled NO, and potential applications of the systemic effects of the gas.

Resuscitation and recovery from acute right ventricular failure using a percutaneous right ventricular assist device

A number of techniques have been proposed for circulatory support in patients with severe right heart failure. We report on a patient with right ventricular (RV) infarction complicated by cardiogenic shock, who was resuscitated by the novel use of a percutaneous right ventricular assist device. The moribund patient had striking hemodynamic and clinical improvement after placement of a right atrial to pulmonary artery assist circuit. RV decompression for 3 days was accompanied by recovery of contractile function, and the patient was successfully weaned from the device. Future trials are needed to assess the effectiveness of the percutaneous ventricular assist device in patients with RV failure.

Cardiomyocyte-Specific Overexpression of NO Synthase-3 Protects Against Myocardial Ischemia-Reperfusion Injury

OBJECTIVE

The protective effect of NO synthase-3 (eNOS)-derived NO in limiting myocardial ischemia-reperfusion (MI-R) injury is well established. We reported previously that systemic genetic overexpression of eNOS attenuates MI-R injury. The purpose of the current study was to investigate tissue-specific genetic overexpression of the human eNOS gene.

METHODS AND RESULTS

To accomplish this, we used 2 distinct murine models of transgenic overexpression, a cardiomyocyte-specific eNOS overexpresser (CS eNOS-Tg) under the control of the alpha-myosin heavy chain promoter, and a systemic eNOS transgenic mouse (SYS eNOS-Tg) under control of the native eNOS promoter with an upstream endothelial enhancer element. Mice were subjected to 30 or 45 minutes of left coronary artery ischemia and 24 or 72 hours of reperfusion. CS eNOS-Tg mice displayed significantly decreased infarct size beyond that of mice with systemic overexpression. Additionally, CS eNOS-Tg mice exhibited better preservation of cardiac function compared with SYS eNOS-Tg mice after myocardial infarction.

CONCLUSIONS

These results provide evidence that site-specific targeting of eNOS gene therapy may be more advantageous in limiting MI-R injury and subsequent cardiac dysfunction.

Monitoring of right-sided heart function

PURPOSE OF REVIEW

Because the right side of the heart supplies blood to the pulmonary circulation, its integrity is required for both adequate respiratory and circulatory function. By reducing pulmonary perfusion, right-sided heart failure may compromise arterial oxygenation and left ventricular filling, and monitoring of right-sided heart function at the bedside in critically ill patients is fundamental. Two recent clinical commentaries have focused on the invaluable help provided by echocardiography for this purpose.

RECENT FINDINGS

Bedside echocardiography has supplanted invasive procedures as the best tool to evaluate right-sided heart function. Although not recent, this technique, previously reserved for cardiologists, has recently gained a larger acceptance in respiratory intensive care units. Echocardiographic examination detects excessive right ventricular afterload, visualized by septal dyskinesia, and its usual consequence, right ventricular enlargement, which impairs left ventricular filling.

SUMMARY

Monitoring of right-sided heart function is essential in a clinical setting associated with hemodynamic instability, such as severe sepsis or acute coronary artery obstruction, and also in that it is associated with increased pulmonary vascular resistance, as in massive pulmonary embolism or acute respiratory failure. Moreover, use of mechanical ventilation requires regular evaluation of its effects on the right side of the heart.