Learn about single ventricle physiology and more with Dr. Mike Fahey, chief of pediatric cardiology at the University of Massachusetts and director of their pediatric residency program. We discuss how congestive heart failure presents in children, various forms of congenital heart disease, and how to approach these patients when they present to the hospital for non-cardiac complaints.
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Congestive Heart Failure is a constellation of physical findings, which include tachycardia, tachypnea, dyspnea, peripheral edema, poor perfusion, poor weight gain, fatigue, and hepatomegaly. Classically, it is thought of as pump failure, where the left ventricle has difficulty pumping blood forward due to ischemic injury, myocarditis, or another cardiomyopathy. But in congenital heart disease, we often see excess volume in the left side of the heart because of increased blood flow to the lungs, or pulmonary overcirculation.
The symptoms that follow are due to increased sympathetic tone. In pump failure, the body must increase sympathetic drive to increase cardiac output despite the low contractility. In pulmonary overcirculation and congenital heart disease, the body must increase its cardiac output to pump the extra volume returning to the left side of the heart. In both cases, the response is the same.
Increased sympathetic tone causes diaphoresis, tachycardia, and peri-oral cyanosis. In addition, it upregulates the Renin-Angiotensin-Aldosterone System, causing fluid retention. Since the most common cause of right-sided heart failure is left-sided heart failure, the blood continues to back-up into the venous system, leading to hepatomegaly, JVD, and peripheral edema.
Kashlak Pearl: Be mindful of throwing around the term “Congestive Heart Failure” with patients and their families. It is a scary term, and Dr. Fahey recommends explaining that the heart is not failing, rather there is a constellation of signs and symptoms that come about when the heart is challenged by a congenital heart problem.
Pulmonary diseases often mimic congestive heart failure, as pulmonary congestion can often sound like wheezing on lung auscultation.
According to Dr. Fahey, most young patients with congestive heart failure have crackles or wheezing on lung auscultation (or congestion on chest xray) and a palpable liver below the costal margin. Although many patients present to the emergency room with tachypnea or failure-to-thrive, the diagnosis is unlikely CHF without exam findings of congestion.
Today, congenital heart disease is often diagnosed in the fetal and newborn periods. The Critical Congenital Heart Disease Screen (CCHD) screens newborns for cyanotic heart disease with pulse oximetry. This test picks up right-to-left shunting lesions with either hypoxemia or differences between the right upper and lower extremities, identifying a ductal dependent lesion. Nevertheless, this test will miss acyanotic congenital heart disease, such atrial or ventricular septal defects, which are commonly left-to-right shunting lesions.
In addition, when the pulmonary vascular resistance (PVR) is still high, there might not be nearly as much shunting across a VSD. So the defect may go unnoticed for the first two-three weeks of life until the PVR completely drops. But when the PVR hits its nadir, the path of least resistance for a red blood cell will be to travel from the left side of the heart through the unrestricted VSD to the right side of the heart. As blood flows across the VSD, the murmur is heard and the symptoms develop from the pulmonary overcirculation and eventual left sided volume overload.
Kashlak Pearl: Be mindful of a new murmur at the 14 day well child check. If the baby is tachypneic or having difficulty with feeds, it may be new left-to-right shunting after a drop in pulmonary vascular resistance.
VSD is a very common lesion, with an incidence of roughly 1 in 240 live births (CDC). The size of the VSD often dictates how symptomatic it will be. Many muscular VSDs will close within the first 2-3 years of life. But if the hole is large enough, not closing sufficiently enough by age 1, or congestive heart failure symptoms are unable to be controlled with medication, then the child will likely need surgical repair.
Young patients who present with an ASD are not as symptomatic as those with VSDs. In ASDs, left atrial pressures do not get nearly as high because blood can be shunted across the ASD to the right atrium like a pop-off valve. This prevents significant backup of fluid into the lungs. Since these patients are often not congested, Dr. Fahey tends to wait for the ASD to close on its own. Generally, if ASDs will close on their own, it will be within the first 2-3 years of life (JACC 2011). If not, the patient can have a transcatheter device closure.
The reason to follow left-to-right shunting lesions closely (and to eventually surgically close those that do not close on their own) is to prevent Eisenmenger Syndrome. This syndrome results after years of increased pressure/flow to the pulmonary arteries, the smooth muscle in those arteries eventually hypertrophies (an irreversible process). This leads to increased PVR, pulmonary hypertension, and eventual change in shunting direction to a cyanotic right-to-left shunt.
Tetralogy of Fallot can be thought of as a very large VSD with some pulmonary stenosis. It is a spectrum of disease, where the severity of pulmonary stenosis can dictate which direction blood is shunted across the VSD.
The growth curve is a fifth vital sign for all patients with congenital heart disease. In congestive heart failure, the activation of the sympathetic nervous system, the increased cardiac output, and the extra effort put into breathing all consume extra calories.
In the adult literature, medications have been proven to improve mortality for classical pump failure. This has been unable to be proven in the pulmonary overcirculation phenotype that is often seen in congenital heart disease. Nevertheless, medication choices have been extrapolated from the adult data. The following medications are most commonly used:
Definition: Any congenital heart problem that leads to a left ventricular cavity that is not big enough to supply a cardiac output to the system. It is usually caused by significant mitral stenosis and aortic stenosis, which leads to little blood flow through the left ventricle during fetal life. Without flow, the left ventricle never really forms (“No Flow, No Grow” Theory). This means the right ventricle needs to do the work of two ventricles, which we call single ventricle physiology.
Currently, there is a sequence of surgical procedures designed to palliate the single ventricle physiology. It cannot be cured, as we cannot insert a new ventricle into the body. Nevertheless, the goal of this surgery is to align the single ventricle with the aorta to pump blood to the body, to volume unload that ventricle, to separate oxygenated and deoxygenated blood, and to circulate predominantly oxygenated blood to the body.
The sequence of procedures culminates in the Fontan Procedure, which connects the systemic venous return (blue blood) directly to the lungs without a pump. The superior vena cava and inferior vena cava connect directly to the pulmonary arteries and the lungs. Red blood then returns to the single ventricle, which pumps the blood out to the aorta and the rest of the body.
The downside to this system is the pressure in the fontan circulation must be close to 15 mmHg compared to regular venous pressures of 0-5 mmHg. This is because fontan circulation is hooked directly to the pulmonary circulation, which has a mean pulmonary artery pressure of approximately 15 mmHg, a byproduct of flow and pulmonary vascular resistance. Such a high central venous pressure is consistent with the physiology we see in right heart failure, such as JVD, hepatomegaly, and ascites.
In addition, when a single ventricle system tries to augment its cardiac output (such as in exercise or physiologic stress), it can’t bolus the left ventricle with increased preload from the right side. Instead, it takes a couple cardiac cycles to increase the systemic venous return, which acts as preload for the single ventricle.
The reason why kids with single ventricle palliation rarely have hepatosplenomegaly or ascites is the advent of the Fenestrated Fontan. At the end of the Fontan procedure, the surgeons create a connection between the Fontan circuit and the right atrium. This “pop-off” window acts like a low resistor in parallel, ultimately lowering the overall resistance of the system, and thus, lowering the central venous pressure. The downside is there is deoxygenated blue blood that travels directly to the system circulation instead of the lungs. Due to the mixing, a patient with a Fenestrated Fontan generally has an oxygen saturation of 90-92%.
The following are a list of medications for patients with single ventricle palliation:
One of the best success stories of pediatric medicine, single ventricle lesions used to be lethal conditions. Now, patients are living much longer. Many of the patients from the earliest surgeries are alive today in their 30 and beyond (Int Journal Cardiology 2016).
This is closely followed by pediatric cardiologists, as it is an incredibly important outcome in single ventricle palliation. In general, the risk of neurodevelopmental issues are lower in more simple congenital heart diseases, such as ASD, VSD, and PDA. But in single ventricle lesions, the incidence of significant neurodevelopmental delays is > 50% (Circulation 2012). The delays vary from mild speech delay to severe learning disabilities.
There is also a well documented difference in outcomes due to racial disparities. Social determinants of health play a large role in not only neurodevelopmental outcomes, but also mortality. (Circulation 2018, Pediatric Cardiology 2013)
These patients can get very sick very fast. If a patient with a single ventricle loses vascular tone (from sepsis or other causes of distributive shock), then there will be a large drop in his/her cardiac output. This is because systemic venous pressure completely controls the ventricular preload. Therefore, they must be treated with massive fluid resuscitation to keep the venous pressure high.
In addition, these patients are at high risk of bacteremia. Unless the patient presents with a very clear viral infection, Dr. Fahey recommends drawing blood cultures and starting these patients on broad spectrum antibiotics.
Any disease process that causes increased pulmonary pressures, such as a lobar pneumonia, will create increased central venous pressure. For those with a fenestrated Fontan, this will cause additional shunting through the fenestration, thereby increasing the mixing of oxygenated-red and deoxygenated-blue blood. So in this case, hypoxemia is caused by both cardiac AND pulmonary forms of shunt physiology. Therefore, it is very important to know the patient’s baseline oxygen saturation.
Per Dr. Fahey, it is very safe to give patients with mixing lesions supplemental oxygen, including single ventricle patients. Supplemental oxygen cannot change the mixing of blue deoxygenated and red oxygenated blood. The only common case where this is a problem is left-to-right shunting lesions, such as VSD. Oxygen can further decrease pulmonary vascular resistance and increase pulmonary overcirculation, worsening congestive heart failure symptoms.
Dr. Fahey does not recommend NSAID use for patients with hypoplastic left heart syndrome because they are already on aspirin. We should also be mindful of renally excreted medications as patients with single ventricle physiology may have complications such as chronic kidney disease.
Listeners will learn how congestive heart failure presents in children, various forms of congenital heart disease, and how to approach these patients when they present to the hospital for non-cardiac complaints.
After listening to this episode listeners will…
Dr. Fahey reports no relevant financial disclosures. The Cribsiders report no relevant financial disclosures.
Masur S, Fahey M, Chui C, Berk J. “CHF in CHD”. The Cribsiders Pediatric Podcast. https:/www.thecribsiders.com/ 4/28/21, 2020.
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