When we describe the heart in this chapter, and in subsequent chapters, our account will be based on the organ as viewed in its anatomical position.1 Where appropriate, the heart will be illustrated as it would be viewed by the surgeon during an operative procedure, irrespective of whether the pictures are taken in the operating room, or are photographs of autopsied hearts. When we show an illustration in non-surgical orientation, this will be clearly stated.

In the normal individual, the heart lies in the mediastinum, with two-thirds of its bulk to the left of the midline (Figure 1.1). The surgeon can approach the heart, and the great vessels, either laterally through the thoracic cavity, or directly through the mediastinum anteriorly. To make such approaches safely, knowledge is required of the salient anatomical features of the chest wall, and of the vessels and the nerves that course through the mediastinum (Figure 1.2).

The aim of hemodynamic monitoring is to enable the optimization of cardiac output and therefore improve oxygen delivery to the tissues, avoiding the accumulation of oxygen debt, in the perioperative period. Instigating goal-directed therapy based on validated optimization algorithms has been shown to reduce mortality in high-risk patients and complications in moderate- to high-risk patients.

A number of devices are available to facilitate this goal. Devices that continuously analyze the arterial pressure waveform to calculate various flow parameters have been developed and validated. These devices have facilitated the introduction of hemodynamic monitoring to the wider surgical population, providing useful clinical information that enables the judicious use of fluid therapy whilst avoiding hypervolemia.

This chapter explores the role that hemodynamic optimization plays in perioperative care, describes some of the commonly used invasive hemodynamic monitors, and explains how to use the information produced effectively. Used correctly, any monitor can be useful to improve outcome if applied to the right population, at the right time, and with the right strategy.

Clinical decision support and closed-loop systems are ubiquitous to any modern lifestsyle. From maintaining ambient temperature to flying our airplanes, we have accepted and benefited from these tools. In this chapter, we discuss key concepts in design and clinical goals, as well as the challenges, of these systems in the context of perioperative medicine. We particularly focus on the past and present development of automated and decision support systems for hemodynamic optimization with fluids and vasopressors.

Regardless of the surgical approach, once having entered the mediastinum, the surgeon will be confronted by the heart enclosed in its pericardial sac. In the strict anatomical sense, this sac has two layers, one fibrous and the other serous. From a practical point of view, the pericardium is essentially the tough fibrous layer, since the serous component forms the lining of the fibrous sac, and is reflected back onto the surface of the heart as the epicardium. It is the fibrous sac, therefore, which encloses the mass of the heart. By virtue of its own attachments to the diaphragm, it helps support the heart within the mediastinum. Free-standing around the atrial chambers and the ventricles, the sac becomes adherent to the adventitial coverings of the great arteries and veins at their entrances to and exits from it, these attachments closing the pericardial cavity.1

The disposition of the conduction system in the normal heart has already been emphasized (see Chapter 2). In that earlier chapter, we pointed to the importance, during surgical procedures, of avoiding the cardiac nodes and ventricular bundle branches, and scrupulously protecting the vascular supply to these structures. In this chapter, we will consider the anatomy of these tissues relative to the treatment of intractable problems of cardiac rhythm, specifically the normal and abnormal atrioventricular conduction axis. The abnormal dispositions of the conduction tissues to be found in congenitally malformed hearts, features of obvious significance to the congenital cardiac surgeon, will be discussed in the sections devoted to those lesions in the chapters that follow. In this chapter, nonetheless, we will also discuss surgical procedures performed to treat arrhythmias that develop in the setting of the Fontan circulation.

The experimental microcirculatory analysis of treating anemia by blood transfusion shows that it minimally increases oxygen (O2) delivery by the capillary circulation, where O2 pressure (pO2), hematocrit (Hct) and capillary hydraulic pressure (pC) are normally 1/5 of systemic, and further depressed by anemia. The concomitant decrease of functional capillary density becomes lethal when falling below a specific threshold due to the decrease in pC, and requires re-pressurizing the microcirculation without increasing the heart’s work load. These effects are achieved by increasing plasma blood viscosity using a viscous plasma expander. This approach significantly elevates capillary blood viscosity and shear stress, increasing the production of the vasodilator NO, becoming significantbecause of the large capillary endothelial surface area, and because increased NO tends to lower O2 consumption. We show that using hyperviscous plasma expanders increases FCD, blood flow velocity and the rate of RBC delivery to the tissues. They could ultimately justify transfusing blood when DO2 falls to ¼ of normal, which is 4 times the normal organism metabolic requirement at rest.

Abnormal systemic venous connections are usually of little surgical significance, since their clinical consequences are limited, although in the severest form, totally anomalous connection, the changes can be profound. Fortunately, totally anomalous systemic venous connection is very rare. The less severe variants are more likely to be encountered as the surgeon pursues a more complex associated intracardiac anomaly, such as the sinus venosus interatrial communication. The anomalous connections in general are of most significance in the setting of isomeric atrial appendages, which we discuss in Chapter 11, emphasizing how so-called visceral heterotaxy is best considered in terms of right versus left isomerism. In this chapter, we consider the features of the anomalous systemic venous connections in their own right. They may be grouped into the categories of absence or abnormal drainage of the right caval veins, persistence or abnormal drainage of the left caval vein, abnormal hepatic venous connections, and totally anomalous systemic venous connections.

The body fluid spaces consist of the plasma, the interstitial fluid volume, and the intracellular fluid volume. The sizes of these spaces are tightly controlled by hormonal and neuronal mechanisms, but their size may be of interest to assess by scientific methods, as disturbances often occur in the wake of trauma and surgery.

A key approach is to use a tracer, by which the volume of distribution of an injected substance is measured after full distribution. Useful tracers must solely occupy a specific body fluid space. The volume effect of an infusion fluid can be calculated by applying a tracer method before and after the administration.

Guiding estimates of the sizes of the body volumes can be obtained by bioimpedance measurements and anthropometric equations.

The Hb concentration is a frequently used endogenous tracer of changes in blood volume. Hb is the inverse of the blood water concentration and Hb changes indicate the volume of distribution of an infused water volume. Volume kinetics is based on mathematical modeling of Hb changes over time, which, together with measurements of the urinary excretion, can be used to analyze and simulate the distribution and elimination of infusion fluids over time.

Photoplethysmography (PPG) has been extensively used for pulse oximetry monitoring in perioperative and intensive care. However, some components of PPG signal have been employed for other purposes, such as non-invasive hemodynamic monitoring. Perfusion index (PI) is derived from PPG signal and represents the ratio of pulsatile on non-pulsatile light absorbance or reflectance of the PPG signal. PI determinants are complex and closely interlinked, involving and reflecting the interaction between peripheral and central hemodynamic characteristics, such as vascular tone and stroke volume. Several studies have shed light on the interesting performances of this variable, especially for hemodynamic monitoring in perioperative and intensive care.

In the first section of this chapter the physiological and pathophysiological determinants of PI are exposed, along with relevant measuring techniques and potential limitations. Second, the existing data concerning the usefulness of PI in different clinical settings are presented and discussed. Lastly, we review known perspectives and identify new perceptions concerning the use of PI that should be explored regarding its utilization.

Cardiopulmonary exercise testing (CPET) is a dynamic and objective investigation that studies the responses of the cardiovascular, respiratory, and skeletal muscular systems to exercise stress in an integrated way.

This is achieved by the measuring gas exchange, respiratory rate and volume, heart rate and ECG parameters, BP, and oxygen saturation (Figure 1.1) whilst a patient undertakes exercise using an ergometer (a device that is used to quantify physical performance by providing a known workload).

Increasingly CPET is being used as part of the pre-operative work-up of patients for major surgery. Whilst CPET can not necessarily be used to define a specific risk for a specific patient, it can provide a broad risk stratification which can guide the need for optimisation, prehabilitation, or potential post-operative level of care. It is part of a global assessment of the patient and hard cut-off values should be avoided. A useful mental model is the ‘traffic light model’ (Figure 29.1).

VCO2 versus VO2 Plot