Pediatric cardiogenic shock: What is the role of medical and mechanical circulatory support?

Cardiogenic shock, defined as cardiac pump impairment that results in insufficient delivery of blood flow to tissues to meet resting metabolic demands, is considered the most severe expression of left ventricular failure. This clinical syndrome of low cardiac output state with resultant end-organ dysfunction can mimic other forms of severe shock, thus making it challenging from both a diagnostic and management standpoint. Despite these challenges, the prompt evaluation and timely medical or mechanical management, or both, of cardiogenic shock is associated with improved outcomes and increasing survival in pediatric patients presenting with cardiogenic shock.

Cardiogenic shock is a relatively uncommon form of shock occurring in 5 to13 percent of pediatric emergencies, but in up to 20 percent of patients in shock admitted to the pediatric intensive care unit. It can represent a fulminant form of myocarditis preceded by a short prodrome of viral symptoms or, more commonly, an acute exacerbation of chronic heart failure as seen in various forms of cardiomyopathy.

Common causes of cardiogenic shock in this population include cardiomyopathy, myocarditis, congenital heart disease and arrhythmia. "Acute heart failure and cardiogenic shock is associated with need for prolonged hospitalization, with a typical hospitalization lasting two to three weeks," says Charlotte S. Van Dorn, M.D., a pediatric cardiologist and intensivist at Mayo Clinic's campus in Rochester, Minnesota. "Approximately a third of these children either die or undergo heart transplantation within one year of presentation."

The evaluation and subsequent diagnosis of cardiogenic shock can be challenging for the clinician first encountering a child in shock. Immediate attention must be given to the child presenting with acute-onset respiratory distress, poor perfusion and altered mental status not responsive to usual therapies of fever abatement, volume administration and oxygen supplementation.

Persistently altered vital signs, including tachycardia and hypotension, as well as specific physical examination findings such as hepatomegaly, jugular venous distension and gallop, may be indicative of impending cardiac failure in the previously well pediatric patient.

A targeted outpatient or emergency department evaluation, to include an electrocardiogram, chest X-ray, laboratory testing, focused critical care cardiac ultrasounds and formal echocardiogram, if available, may result in a timely diagnosis and expedite treatment measures.

Specific laboratory markers that may be helpful in differentiating cardiogenic shock from other forms of pediatric shock may include a relatively normal complete blood count and C-reactive protein, elevated renal and liver function tests, serum lactate, as well as high levels of brain natriuretic peptide, a peptide secreted by the ventricles in response to stretch. Subsequent electrocardiogram findings may demonstrate a primary arrhythmia, acute or chronic ischemia, or ventricular hypertrophy with strain pattern. A chest X-ray prior to and after volume administration may reveal cardiomegaly with and without associated pulmonary edema.

Finally, an echocardiogram may demonstrate previously undiagnosed congenital heart disease, cardiomyopathy with diminished function or pericardial effusion with tamponade physiology. While the echocardiogram may be helpful in diagnosing cardiogenic shock, further patient stabilization within the emergency department or intensive care unit should not be delayed to obtain this study.

Management options

Initial management of the pediatric patient presenting with suspected cardiogenic shock should first include the rapid identification of his or her pathophysiological state. A cold and dry state represents reduced myocardial contractility but normal ventricular end-diastolic pressures as seen in systolic dysfunction. In contrast, the warm and wet state describes the patient presenting with intact myocardial contractility but high left ventricular end-diastolic pressures indicative of diastolic dysfunction.

"The most ominous state is that of the cold and wet patient that has both reduced myocardial contractility and increased left ventricular end-diastolic pressures characteristic of simultaneous systolic and diastolic dysfunction," says Dr. Van Dorn. Once identified, targeted medical management can be pursued to alleviate symptoms, support end-organ perfusion and improve cardiac dysfunction.

Medical interventions

Primary goals for the medical management of cardiogenic shock must include optimization of preload and afterload while limiting myocardial demand and augmenting systolic function, diastolic function or both. For the pediatric patient presenting with any form of cardiogenic shock, immediate measures should be taken to reduce myocardial oxygen demand. These include oxygen supplementation, consideration of either noninvasive positive pressure ventilation or mechanical ventilation, administration of antipyretics if fever is present, and careful use of opiates or sedatives prior to painful procedures.

Specifically, in those patients demonstrating signs of cold and dry shock, judicious use of isotonic fluids in 5-10 cc/kg aliquots may be required to augment preload with diligent attention to signs of volume overload such as worsening tachypnea, bibasilar crackles and increasing hepatomegaly. This is necessary prior to the administration of any form of sedation as suboptimal preload may predispose this patient to cardiovascular collapse. However, the opposite holds true for the patient presenting in a wet state, as more volume administration may worsen respiratory symptoms leading to respiratory failure and need for mechanical ventilation.

In this pathophysiological state, patients benefit from the use of diuretic infusions or bolus dosing depending on their hemodynamic state. Abnormal systemic vascular resistance, or afterload, must also be addressed in the pediatric patient presenting with cardiogenic shock. In the cold, poorly perfused patient in shock, infusions of either epinephrine or dopamine may be needed to augment myocardial contractility to improve end-organ perfusion. Of note, vasoactive support should be initiated and escalated with caution as infusions of epinephrine or dopamine can predispose the patient to arrhythmia and frequently increase myocardial oxygen demand in the already poorly contractile heart.

If a child in cardiogenic shock has signs of high afterload, vasodilator therapy such as nitroprusside or nicardipine may be necessary to decrease the work performed by the failing left ventricle. In addition to vasodilators, inodilators, such as milrinone or dobutamine, are almost always used in systolic and diastolic failure due to their ability to provide inotropy and luscitropy as well as vasodilatation.

The use of beta blockers, while excellent for reducing afterload in chronic heart failure, should be avoided in acute decompensated heart failure and cardiogenic shock as this may potentiate myocardial dysfunction due to downregulation of beta receptors.

During the acute setting, intravenous medications such as inotropes, vasodilators and diuretics are the mainstay of therapy. However, depending on disease progression and response to therapy, certain patients may ultimately tolerate transition to an oral heart failure regimen including angiotensin-converting enzyme inhibitors and beta blockers, as well as oral diuretics.

Mechanical circulatory support

Unfortunately, for certain pediatric heart failure populations, medical management alone is not enough to support the failing myocardium. In those patients with ongoing hypotension, persistent acidosis, low urinary output or clinical evidence of poor perfusion despite escalation in inotropic therapy or both, the use of mechanical circulatory support may be needed. Fortunately, options for mechanical support in pediatric cardiogenic shock have grown exponentially in the last two decades.

At this time, two primary forms of mechanical circulatory support are available for medically refractory cardiac failure: extracorporeal membrane oxygenation (ECMO) and ventricular assist devices (VADs).

ECMO cannulation can be achieved from a neck, femoral or open sternotomy approach and is most often used for urgent and short-term mechanical circulatory support. "Despite its invasive nature, the timely initiation of ECMO has been associated with decreasing morbidity and improved survivability to decannulation, VAD support and subsequent heart transplantation," says Dr. Van Dorn.

If cardiac function does not immediately recover on ECMO, the decision may be made to transition to a longer term form of mechanical support, a VAD. Options currently available include the Berlin Heart EXCOR in very small children and the HeartWare HVAD or Thoratec HeartMate II in older children and young adults.

VAD use, as compared to ECMO support, is gaining favorability as more pediatric patients are able to tolerate extubation, ambulation, cardiac rehabilitation and, in some populations, hospital discharge. In addition to allowing for improved functional status, the transition to VAD support has also been associated with improved survival up to and following heart transplantation.

Outcomes

The prompt identification, evaluation and treatment of cardiogenic shock can improve outcomes and decrease mortality in critically ill pediatric patients with heart failure. However, despite improvements in both medical and mechanical management, morbidity and mortality remain high as compared to other forms of pediatric shock. The current estimated mortality rate is as high as 5 to 10 percent, but increases up to fivefold in the presence of comorbidities such as acute kidney or liver failure and sepsis. Early myocardial support, both with medical or mechanical support, can improve end-organ function and perfusion, and thus reduce morbidity and mortality in this patient population.

Conclusions

Pediatric cardiogenic shock, although not common, is a nonspecific and challenging clinical scenario of decompensated heart failure and impending cardiovascular collapse. The presence of persistent signs and symptoms of myocardial distress and end-organ hypoperfusion should prompt clinicians to broaden their evaluation and initiate timely interventions.

While medical management can improve preload, afterload and myocardial contractility, ultimately mechanical support may be required in medically refractory shock. While ECMO and VADs are both excellent options for mechanical support, VAD therapy has been associated with improved functional status and survival to heart transplantation. Outcomes in cardiogenic shock continue to improve; however, mortality remains high, especially in those patients with comorbidities.

For more information

Brissaud, et al. Experts' recommendations for the management of cardiogenic shock in children. Annals of Intensive Care. 2016;6:14.