Accurate measurement of the blood pressure depends on selection of an appropriate cuff size of a sphygmomanometer. By convention, an appropriate cuff size is a cuff with an inflatable bladder width that is at least 40% of the arm circumference at a point midway between the olecranon and the acromion. For a cuff to be optimal for an arm, the cuff bladder length should cover 80% to 100% of the circumference of the arm. Such a requirement demands that the bladder widthtolength ratio be at least 1:2. If the cuff size is too small, the blood pressure will be overestimated, and if it is too large, the blood pressure will be underestimated.

Auscultation of the diastolic component of the blood pressure exhibits two end points, Korotkoff phases IV and V, respectively. In children, Korotkoff phase IV (i.e., the point of diminution or muffling of the Korotkoff sound) is generally considered a more accurate representation of the diastolic pressure. Korotkoff phase V (i.e., the disappearance of the Korotkoff sounds) should be considered the diastolic end point if it falls within 6 mm Hg of Korotkoff phase IV.

The hyperoxia test can be useful for differentiating cardiac and pulmonary causes of cyanosis, and it is one of the first evaluations performed when confronted with a cyanotic newborn. Cyanosis usually becomes apparent at a mean capillary concentration of at least 3.0 g/dL of deoxygenated hemoglobin, a concentration that corresponds to an oxygen saturation of 70% to 80% in the child with a normal hemoglobin level.

In infants with cyanotic congenital heart disease (CHD) (transposition of the great arteries [TGA] or a lesion with restrictive pulmonary blood flow [tricuspid
atresia with pulmonary stenosis or atresia, pulmonary atresia or critical pulmonary stenosis with intact ventricular septum, or tetralogy of Fallot]) and hypoxemia, the arterial oxygen tension (PaO₂) is generally <50 mm Hg on 100% oxygen. In an infant with cyanotic CHD and a complete mixing lesion without restrictive pulmonary blood flow (truncus arteriosus, total anomalous pulmonary venous return, TGA with ventricular septal defect, single ventricle, hypoplastic left heart syndrome, and tricuspid atresia without pulmonary stenosis or atresia), the PaO₂ is generally <150 mm Hg in response to the administration of 100% oxygen. In an infant with a pulmonary cause for the cyanosis, administration of 100% oxygen increases the PaO₂ to a level significantly >150 mm Hg. In patients with CHD, this phenomenon is attributable to right-to-left shunting (i.e., the mixing of deoxygenated blood and oxygenated blood within the circulatory system). Right-to-left shunting may be either intracardiac or extracardiac (intrapulmonary shunting from ventilation-perfusion mismatch) (see section on “Agitated Saline Contrast Echocardiography”).

Brain natriuretic peptide (BNP) and N-terminal pro-brain natriuretic peptide (NT-proBNP) assays are used in algorithms for the diagnosis and management of acute and chronic heart failure in adults. BNP is biologically active with a half-life of 20 minutes, yet NT-proBNP is inactive with a half-life of 60 to 120 minutes. These assays should always be interpreted with caution as the results are method-dependent and comparisons amongst different laboratories may not be possible. In the pediatric age group and in patients with varying forms of CHD, there are no absolute standards to date concerning levels of BNP or NT-proBNP. Heterogeneous etiologies for heart failure in children as compared to adults have lead to studies that attempt to define the clinical relevance of BNP and NT-proBNP levels. In pediatrics, cardiac disease enhances natriuretic peptide expression due to hemodynamic stress and neurohormonal activation. Reference ranges are difficult to establish and are based on age, gender, and underlying pathophysiology (especially those with univentricular physiology). In light of this background, studies have suggested that BNP and NT-proBNP may be increased in concert with clinical severity amongst the following conditions: (1) hemodynamic load on either the right or the left ventricle in those with dilated cardiomyopathy, (2) excessive shunt with a patent ductus arteriosus (PDA), (3) right ventricular volume overload (e.g., s/p tetralogy of Fallot repair with resultant pulmonary regurgitation), (4) right ventricular pressure overload, and (5) with cardiac involvement in Kawasaki disease. Some studies suggest an adjunct utility of these assays in those rejecting post heart transplant, although absolute values have not been established. Similar to adult uses, longitudinal assessment may be helpful in an individual patient to monitor disease process or response to heart failure treatment. Finally, elevation of these markers may be noted in those postchemotherapy which portends the likely development of cardiac dysfunction.

Troponin is a vital protein involved in the cascade leading to actin and myosin contraction. Cardiac contraction is regulated by calcium via a tropomyosin-like protein factor, which was discovered to be a complex of tropomyosin and troponin. Troponin is the calcium receptive protein and is integral in the contraction and relaxation of cardiac muscle. Troponin I and Troponin T are noted only in cardiac muscle. Troponin levels in pediatrics have been used to predict the degree of myocardial damage, either postoperatively or after use of cardiotoxic medications (including chemotherapy), and longitudinal evaluation has been helpful in predicting recovery or mortality. In neonates, troponin levels may be useful to assess the degree of cardiac damage associated with asphyxia. Troponin levels may be helpful in other disease states such as active myocarditis and determining cardiac damage to ischemia in those rare coronary anomalies noted in pediatrics.

The electrocardiogram provides data concerning the following: