**2.3 Fontan physiology**

By creating a TCPC, a new portal system is made. A portal system occurs when one capillary bed pools blood into another capillary bed through veins without passing through the heart.

The Fontan morphophysiology has two essential components. First, the presence of a SV pumping oxygenated blood to the systemic circulation, this ventricle can be either, a morphologic right or left depending on the type of CHD. The second

### **Figure 3.**

*Fontan anatomy. Shows how systemic venous blood passively enters the pulmonary artery (PA) circulation through a total cavopulmonary anastomosis (TCPA). Blood prevents the right atrium through a baffle or conduit. Blood is oxygenated in the lungs and enters the pulmonary venous (PV) system reaching the left atrium. The right and left atrium now function as a common pulmonary venous atrium (CPVA). A single functional ventricle (SFV) actively drives blood flow through the systemic arteries and capillaries, with a systemic venous return that passively enters the pulmonary circulation. The final stage of Fontan results in the conversion of a parallel circulation to a pulmonary and systemic circulation that is in series.*

**109**

**Figure 4.**

*ventricle; CPVA, common pulmonary venous atrium).*

*Physiopathological Approach of the Fontan Patient for Noncardiac Surgery for the Anesthesiologist*

component is that the systemic venous return will reach the pulmonary arterial

The driving force that maintains adequate blood flow and therefore cardiac output (CO), is the pressure difference between the central venous pressure (CVP) and the common atrial pressure (CAP), that is also known as the transpulmonary gradient, for it to be adequate requires a well-functioning SV, decrease afterload and

The Fontan operation produces a state of chronic low CO [8] and relies on nonpulsatile, passive flow of caval blood to the PAs. Because there is not a subpulmonary ventricle, the circulation relies on low pulmonary pressures and low PVR. Forward flow through the pulmonary vasculature depends on a differential between the CVP and CAP [5]. Systemic venous hypertension is necessary to drive blood flow through the pulmonary vasculature with systemic venous pressure typically 5 mmHg higher than the pulmonary venous-atrial pressure [7].

An important feature of Fontan procedures, particularly lateral tunnel TCPC, is the fenestration or a surgically created small opening between the Fontan baffle pathway and the atrium. This 4-mm hole serves as a "pop-off" during times of high PVR and in essence maintains CO at the expense of a right-to-left shunt [5, 9]

There is evidence including a prospective randomized trial that fenestration decreases the incidence of prolonged post-operative effusions, reduce post-operative

*Fontan physiology. The right-to-left shunt through the fenestration allows the systemic venous blood to bypass the Fontan portal system, thereby increasing the single ventricle preload, increasing cardiac output, and decreasing systemic venous congestion at expense of cyanosis that results from a lower arterial oxygen saturation (SVC, superior vena cava; IVC, inferior vena cava; Ao, aorta; PA, pulmonary artery; SFV, single functional* 

lengths of hospital stay, and lessen the need for early reinterventions [4].

system without direct influence of a pumping chamber [2, 5].

*DOI: http://dx.doi.org/10.5772/intechopen.93388*

sufficient preload [5] (**Figure 4**).

**2.4 Fenestration**

(**Figure 4**).

*Physiopathological Approach of the Fontan Patient for Noncardiac Surgery for the Anesthesiologist DOI: http://dx.doi.org/10.5772/intechopen.93388*

component is that the systemic venous return will reach the pulmonary arterial system without direct influence of a pumping chamber [2, 5].

The driving force that maintains adequate blood flow and therefore cardiac output (CO), is the pressure difference between the central venous pressure (CVP) and the common atrial pressure (CAP), that is also known as the transpulmonary gradient, for it to be adequate requires a well-functioning SV, decrease afterload and sufficient preload [5] (**Figure 4**).

The Fontan operation produces a state of chronic low CO [8] and relies on nonpulsatile, passive flow of caval blood to the PAs. Because there is not a subpulmonary ventricle, the circulation relies on low pulmonary pressures and low PVR. Forward flow through the pulmonary vasculature depends on a differential between the CVP and CAP [5]. Systemic venous hypertension is necessary to drive blood flow through the pulmonary vasculature with systemic venous pressure typically 5 mmHg higher than the pulmonary venous-atrial pressure [7].

### **2.4 Fenestration**

*Advances in Complex Valvular Disease*

surgical centers.

**2.2 Fontan anatomy**

**2.3 Fontan physiology**

passing through the heart.

• The extracardiac cavopulmonary connection also consists of a direct anastomosis of the SVC to the PA. However, an extracardiac conduit is used to route IVC blood directly to the PA without traversing the right atrium [5, 7].

Initially, adult survivors were mainly APC Fontan patients, but increasing numbers of both forms of TCPC Fontan patients now survive to adult life [7]. The extracardiac cavopulmonary connection is the main method employed currently in

The systemic venous blood passively entering the pulmonary circulation through a total cavopulmonary anastomosis (TCPA). Blood bypasses the right atrium via a baffle or a conduit. Blood is oxygenated in the lungs and enters the pulmonary venous system reaching the left atrium. The right and left atrium now function as a common pulmonary venous atrium (CPVA). A single functional ventricle actively drives blood flow through the systemic arteries and capillaries, with systemic venous return passively entering the pulmonary circulation. The final Fontan stage results in the conversion of a parallel circulation to a pulmonary and

By creating a TCPC, a new portal system is made. A portal system occurs when one capillary bed pools blood into another capillary bed through veins without

The Fontan morphophysiology has two essential components. First, the presence of a SV pumping oxygenated blood to the systemic circulation, this ventricle can be either, a morphologic right or left depending on the type of CHD. The second

*Fontan anatomy. Shows how systemic venous blood passively enters the pulmonary artery (PA) circulation through a total cavopulmonary anastomosis (TCPA). Blood prevents the right atrium through a baffle or conduit. Blood is oxygenated in the lungs and enters the pulmonary venous (PV) system reaching the left atrium. The right and left atrium now function as a common pulmonary venous atrium (CPVA). A single functional ventricle (SFV) actively drives blood flow through the systemic arteries and capillaries, with a systemic venous return that passively enters the pulmonary circulation. The final stage of Fontan results in the* 

*conversion of a parallel circulation to a pulmonary and systemic circulation that is in series.*

systemic circulation that is in series [2, 5] (**Figure 3**).

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**Figure 3.**

An important feature of Fontan procedures, particularly lateral tunnel TCPC, is the fenestration or a surgically created small opening between the Fontan baffle pathway and the atrium. This 4-mm hole serves as a "pop-off" during times of high PVR and in essence maintains CO at the expense of a right-to-left shunt [5, 9] (**Figure 4**).

There is evidence including a prospective randomized trial that fenestration decreases the incidence of prolonged post-operative effusions, reduce post-operative lengths of hospital stay, and lessen the need for early reinterventions [4].

### **Figure 4.**

*Fontan physiology. The right-to-left shunt through the fenestration allows the systemic venous blood to bypass the Fontan portal system, thereby increasing the single ventricle preload, increasing cardiac output, and decreasing systemic venous congestion at expense of cyanosis that results from a lower arterial oxygen saturation (SVC, superior vena cava; IVC, inferior vena cava; Ao, aorta; PA, pulmonary artery; SFV, single functional ventricle; CPVA, common pulmonary venous atrium).*

The right-to-left shunt through the fenestration allows the systemic venous blood to bypass the Fontan portal system, thereby increasing the SV preload, increasing CO, and decreasing systemic venous congestion at expense of cyanosis that results from a lower arterial oxygen saturation [9, 10].

Theoretically, the fenestration poses a risk for systemic embolic events and persistent cyanosis; however, the improved CO may have beneficial effects on oxygen delivery and will also help to alleviate the congestion felt in upstream organs, particularly the liver [2, 5].

### **2.5 Fontan failure**

Though life-saving, the univentricular Fontan circulation does not reproduce biventricular physiology and although generally well tolerated in childhood, it seems to be less well tolerated over time, affecting organ systems outside the heart. Fontan physiology can best be thought of as a man-made form of chronic heart failure (CHF) [10] and there are a significant number of medical complications associated with the long-term. There is evidence that circulatory failure rather than ventricular failure is most important in the failing Fontan.

Griffiths et al. evaluated the outcomes of failing Fontan patients listed for transplant and observed decreased survival in patients with preserved ventricular function compared with those with impaired ventricular function [11]. The clinical deterioration can occur in the absence of ventricular dysfunction, suggesting that distinct mechanisms are contributive in comparison with heart failure patients from other etiologies.

Depiction of the hemodynamic profile of Fontan failure has been similar to traditional heart failure: elevated CVP, pulmonary capillary wedge pressure and systemic vascular resistance (SVR) with a low cardiac index (CI). Hebson et al. [12] evaluated the hemodynamic profile of a symptomatic adult Fontan (SAF) cohort with significant symptoms such as refractory edema, ascites, protein-losing enteropathy (PLE) or considerable exercise intolerance regardless of ventricular function. In the SAF patients, although CVP and pulmonary capillary wedge pressures were elevated, SVR index was low and CI was preserved even in the context of more severe symptoms. This suggests additional mechanisms influencing the hemodynamics and contributing to the symptoms of Fontan failure.

Fontan patients cannot proportionately augment their CO above a certain threshold, thus potentiating renal hypoperfusion and leading to refractory symptoms [12] and in cases where the systemic ventricle functions poorly, the heart can make an already compromised circulation worse.

In a biventricular system, systolic performance will only affect CO at rest when the ventricular function is severely depressed. In a normal subject, CO is not influenced by an increase of PVR up to 5 Woods Units. In Fontan patients, PVR is the primary modulator of CO. Failing Fontans typically have a high PVR. The loss of pulsatile flow after TCPC affects the usual vasoreactivity of the pulmonary bed. Ideally the lung vessels should be slightly oversized with low resistance. However, more frequently the abnormal development may result in relative hypoplasia of the large vessels coupled with endothelial dysfunction.

In all Fontan patients, an increase in PVR is invariably associated with a decrease in CO. If PVR is low, a reasonable output is achieved in patients with normal or moderately depressed ventricular function. However, severely depressed ventricular function results in low output [2] (**Figure 5**).

Late Fontan failure might present gradually and insidiously over years. The nature of Fontan failure is heterogenous, it is likely that not all patients "fail" in the same way, and each patient should be evaluated individually when looking for underlying causes [12].

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**Figure 6.**

*Physiopathological Approach of the Fontan Patient for Noncardiac Surgery for the Anesthesiologist*

The circulatory problem in Fontan is the limit in the preload created primarily by the damming effect of this neoportal system. The strategy is to maximize the efficiency of this system, which could have better outcomes than more traditional

*Modulation of CO by PVR in normal and Fontan patients. In Fontan patients, PVR is the primary modulator of CO. If PVR is low, a reasonable CO is achieved in patients with normal or moderately depressed ventricular function. However, severely depressed ventricular function results in low CO (CO, cardiac output; PVR,* 

The components that make up the Fontan system are critically important in the overall function of the Fontan circuit. These components include the venoarterial Fontan connection itself, PAs, pulmonary capillary network, pulmonary veins, and the venoatrial connection. Impairment at any level of this portal system will have profound consequences on the output of the Fontan circuit [2] (**Figure 6**). Impairments at any component level include, but are not limited to, stenosis, hypoplasia, distortion, vasoconstriction, pulmonary vascular disease, loss or exclusion

*The failing Fontan (PA, pulmonary artery; PV, pulmonary vein; AV, atrioventricular; SVR, systemic vascular* 

*resistance; SVC, superior vena cava; IVC, inferior vena cava; PLE, protein-losing enteropathy).*

*DOI: http://dx.doi.org/10.5772/intechopen.93388*

heart failure therapies [2].

*pulmonary vascular resistance; LV, left ventricle).*

**Figure 5.**

*Physiopathological Approach of the Fontan Patient for Noncardiac Surgery for the Anesthesiologist DOI: http://dx.doi.org/10.5772/intechopen.93388*

### **Figure 5.**

*Advances in Complex Valvular Disease*

particularly the liver [2, 5].

**2.5 Fontan failure**

The right-to-left shunt through the fenestration allows the systemic venous blood to bypass the Fontan portal system, thereby increasing the SV preload, increasing CO, and decreasing systemic venous congestion at expense of cyanosis

Theoretically, the fenestration poses a risk for systemic embolic events and persistent cyanosis; however, the improved CO may have beneficial effects on oxygen delivery and will also help to alleviate the congestion felt in upstream organs,

Though life-saving, the univentricular Fontan circulation does not reproduce biventricular physiology and although generally well tolerated in childhood, it seems to be less well tolerated over time, affecting organ systems outside the heart. Fontan physiology can best be thought of as a man-made form of chronic heart failure (CHF) [10] and there are a significant number of medical complications associated with the long-term. There is evidence that circulatory failure rather than

Griffiths et al. evaluated the outcomes of failing Fontan patients listed for transplant and observed decreased survival in patients with preserved ventricular function compared with those with impaired ventricular function [11]. The clinical deterioration can occur in the absence of ventricular dysfunction, suggesting that distinct mechanisms are contributive in comparison with heart failure patients from other etiologies. Depiction of the hemodynamic profile of Fontan failure has been similar to traditional heart failure: elevated CVP, pulmonary capillary wedge pressure and systemic vascular resistance (SVR) with a low cardiac index (CI). Hebson et al. [12] evaluated the hemodynamic profile of a symptomatic adult Fontan (SAF) cohort with significant symptoms such as refractory edema, ascites, protein-losing enteropathy (PLE) or considerable exercise intolerance regardless of ventricular function. In the SAF patients, although CVP and pulmonary capillary wedge pressures were elevated, SVR index was low and CI was preserved even in the context of more severe symptoms. This suggests additional mechanisms influencing the hemody-

that results from a lower arterial oxygen saturation [9, 10].

ventricular failure is most important in the failing Fontan.

namics and contributing to the symptoms of Fontan failure.

make an already compromised circulation worse.

large vessels coupled with endothelial dysfunction.

lar function results in low output [2] (**Figure 5**).

Fontan patients cannot proportionately augment their CO above a certain threshold, thus potentiating renal hypoperfusion and leading to refractory symptoms [12] and in cases where the systemic ventricle functions poorly, the heart can

the ventricular function is severely depressed. In a normal subject, CO is not influenced by an increase of PVR up to 5 Woods Units. In Fontan patients, PVR is the primary modulator of CO. Failing Fontans typically have a high PVR. The loss of pulsatile flow after TCPC affects the usual vasoreactivity of the pulmonary bed. Ideally the lung vessels should be slightly oversized with low resistance. However, more frequently the abnormal development may result in relative hypoplasia of the

In a biventricular system, systolic performance will only affect CO at rest when

In all Fontan patients, an increase in PVR is invariably associated with a decrease

in CO. If PVR is low, a reasonable output is achieved in patients with normal or moderately depressed ventricular function. However, severely depressed ventricu-

Late Fontan failure might present gradually and insidiously over years. The nature of Fontan failure is heterogenous, it is likely that not all patients "fail" in the same way, and each patient should be evaluated individually when looking for

**110**

underlying causes [12].

*Modulation of CO by PVR in normal and Fontan patients. In Fontan patients, PVR is the primary modulator of CO. If PVR is low, a reasonable CO is achieved in patients with normal or moderately depressed ventricular function. However, severely depressed ventricular function results in low CO (CO, cardiac output; PVR, pulmonary vascular resistance; LV, left ventricle).*

The circulatory problem in Fontan is the limit in the preload created primarily by the damming effect of this neoportal system. The strategy is to maximize the efficiency of this system, which could have better outcomes than more traditional heart failure therapies [2].

The components that make up the Fontan system are critically important in the overall function of the Fontan circuit. These components include the venoarterial Fontan connection itself, PAs, pulmonary capillary network, pulmonary veins, and the venoatrial connection. Impairment at any level of this portal system will have profound consequences on the output of the Fontan circuit [2] (**Figure 6**). Impairments at any component level include, but are not limited to, stenosis, hypoplasia, distortion, vasoconstriction, pulmonary vascular disease, loss or exclusion

### **Figure 6.**

*The failing Fontan (PA, pulmonary artery; PV, pulmonary vein; AV, atrioventricular; SVR, systemic vascular resistance; SVC, superior vena cava; IVC, inferior vena cava; PLE, protein-losing enteropathy).*

of large vessels or microvessels, turbulence and flow collision, flow mismatch and obstruction by external compression [2].

Bypassing the pulmonary vasculature can partially reverse the restrictions to CO imposed by the neoportal system. A Fontan fenestration allows flow to bypass the neoportal system, which results in venous decongestion and increase in CO.

However, while a fenestration can increase overall output, it does so at the expense of diminished arterial oxygen saturation. Nevertheless, in the setting of a fenestration, the increase in CO can result in an increase in peripheral oxygen delivery even if the saturation is diminished.

The strategy to manage a failing Fontan starts by determining modifiable conditions and intervene if it is deem necessary. The first step is imaging, using transthoracic echocardiography (TTE) and cardiac magnetic resonance (CMR) to obtain a full image of the Fontan anatomy. Assessment of atrioventricular valve regurgitation could be difficult therefore the use of transesophageal echocardiography (TEE) is needed sometimes. Catheter-based intervention is used if obstruction is identified. Surgical interventions are necessary in certain cases.

The goal of the management of the patient with Fontan physiology is to preserve symptom-free survival for as long as possible.
