There is no doubt that CMR is the gold standard technique for right as well as left ventricular volume assessment and no other technique has as excellent a reproducibility. This quality of CMR is the reason fewer patients are needed to power clinical trials [19]. However, there are important differences in approaches and measurements made by different operators across various institutions. Awareness of these is important to determine the applicability of published literature to the individual patient in an individual institution. Defining the valve planes may be ambiguous. The pulmonary valve may be absent or just a small remnant. The basal short-axis slice may include right atrial tissue even in systole when the RV is dilated. In the context of a heavily trabeculated ventricle, the volumes may be operator dependent. Whether the approach chosen is a transaxial ventricular volume stack or short axis and whether the trabeculations are excluded from the blood pool or ignored, each operator and centre requires a robust and reproducible protocol. A transaxial stack approach has been argued for because some operators have found it more reproducible and certainly it may be easier to determine the tricuspid valve plane. An argument in favour of a short-axis approach is that TOF is a biventricular disease. LV dysfunction is an important predictor of mortality, though it is likely to develop late and partly as a consequence of RV dysfunction. Given right as well as left ventricular volumes are valuable, having an approach that may be easier for the RV but requiring the LV to be measured at a different time with a different data set adds time and biological variability to the CMR study. In TOF, RV assessment is as pertinent as the left but poses challenges in accurately assessing the thin myocardium and coarse trabeculations, which increase towards the apex. These complex trabeculations increase in the presence of RV hypertrophy and can be difficult to visualise and outline individually. Ignoring RV trabeculations may be a more rapid and reproducible way [20] to approach ventricular volume assessment. However, not only may this be inaccurate for RV mass measurement but as others have also stated, this leads to incorrectly large volume estimates for the RV and prohibits the internal validation of stroke volumes through comparison with aortic and pulmonary flow volumes [21]. Our own practice is to exclude trabeculations from the blood pool (Fig. 9.8). Careful demarcation of the borders of the RV can give highly reproducible results even in the context of complex operated RVs in TOF. [22] Whilst reproducible with a single experienced operator, this method is labour intensive and requires at least 30 min per patient. However, for research, this degree of reproducibility enabled adequate powering of a randomised controlled trial in repaired TOF with chronic pulmonary regurgitation to assess the effects of ramipril (the APPROPRIATE study) [23].

Consistency between serial measurements should be optimised through standardisation of scanning approaches and protocols and regular quality assurance. Practically, because intraobserver variability is lower [22], it may be important for a single operator to remeasure a previous CMR scan at the time of a current report to be certain if there is true change in RV ventricular volumes. Awareness of technical issues regarding acquisition and analysis is important as RV volume measurements are pivotal to clinical decision-making regarding the indications for pulmonary valve implantation in asymptomatic patients and assessment of the haemodynamic benefits of surgery.

Numerous contributions have been made to the literature in the last 10 years describing the value of CMR RV volume assessment for determining indications for pulmonary valve replacement [24–32] though still more data are needed to determine optimal timing in asymptomatic TOF patients. Oosterhof et al. have implied surgical PVR should be carried out before RV end-diastolic volume exceeds 160 mL/m² or RV end-systolic volume >82 mL/m² as these thresholds predict return of RV volumes to normal size following PVR [30]. Another group found RV end-systolic volume <90 mL/m² to be a predictor of normal RV size and function postoperatively [33]. The implication is that beyond this degree of RV dilatation, there is limited reversibility of RV dilatation and dysfunction. Other authors suggest PVR might be indicated even earlier before RV end-diastolic volume exceeds 150 mL/m² [28, 31]. In a number of centres, an RV:LV diastolic volume ratio of ≥2:1 is also considered significant. Consensus has been established amongst ACHD clinicians that the previous clinical management of operating on repaired TOF patients later when symptoms are established is too late.

European Society of Cardiology (ESC) Guidelines for ACHD [34] advocate pulmonary valve replacement in symptomatic TOF patients with severe pulmonary regurgitation and/or stenosis with RV systolic pressure >60 mmHg/TR velocity >3.5 m/s with a Class 1 indication. In asymptomatic patients, Class IIa indications for pulmonary valve intervention in the presence of severe pulmonary regurgitation and/or stenosis are:

These guidelines are not prescriptive with regard to nonserial CMR measures. In our centre RV:LV ratio ≥2:1 with RVEDVi >150 mL/m² usually prompts multidisciplinary discussion of elective pulmonary valve implantation which is an individualised decision based also on non-CMR-based data such as objectively measured exercise capacity.

In older patients, reflecting the earlier era of TOF repair, akinetic and or aneurismal areas in the RVOT are common and present even in the absence of patch reconstruction of the RVOT [17] (Fig. 9.9). Given the limits of the RV are the tricuspid and pulmonary valves, any akinetic or aneurismal region in the RVOT is included in the ventricular volumes. Such akinetic and or aneurismal regions are adverse not only as they relate to RV systolic dysfunction [17] but also because they cause conduction delay within the RV contributing to prolonged QRS duration [35] and are associated with scar [36, 37]. These dilated or dyskinetic RVOT regions therefore lower the calculated ejection fraction as they are included in the ventricular volume. The disadvantage of including them is that small progressive reductions in function of the contractile RV beneath the akinetic area may be masked. A reproducible method to characterise the function of these regions separately is, however, not widely available. We report a simple linear measurement based on the sagittal RVOT view. We use this feasible measure to help describe the relative contribution of outflow tract pathology to impaired RV ejection fraction and to describe size. Recently a prospective follow-up study for clinical outcomes demonstrated that larger akinetic area length predicted sustained ventricular arrhythmia [38]. Routine views such as four-chamber cine may be misleadingly normal, whereas long-axis views (RV outflow tract, LV outflow tract, oblique RV views) are more likely to show wall thinning and regional motion abnormality because the primary pathology is of the RV infundibulum.

LV regional wall motion abnormality may be present in TOF. A small area (<1 cm) at the apex may be present and related to apical vent insertion at the time of surgery in order to deair the heart. However, more extensive abnormalities have been noted and associated with scarring either in small localised areas or in a larger anteroapical distribution [36

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