Response to Letter Regarding Article, “Cardiac Magnetic Resonance Imaging: A New Gold Standard for Ventricular Volume Quantification During High-Intensity Exercise”

Abstract

We thank Drs Yoneyama and Akashi for their important reference to the confounding influence of respiration on biventricular volume assessment by real-time cardiac magnetic resonance imaging. As we noted in the Discussion, changes in biventricular volumes "may be caused by physiological differences in preload attributable to the fall in intrathoracic pressures during inspiration and cardiac translation through the imaging plane."1 Real-time cardiac magnetic resonance imaging provides a novel means of expanding on the eloquent work of Natarajan et al 2 on assessing the influence of the respiratory pump on cardiac filling and function. This interaction between breathing and cardiac function has received limited attention, but now we have an excellent noninvasive tool for very accurately detailing changes in both right and left ventricular volumes with various respiratory maneuvers. We hope to provide novel data in the peer-reviewed literature soon that will detail the importance of this respiratory pump in enhancing cardiac filling. We slightly disagree with the assertion that breath-hold imaging should be considered a gold standard. Breath-holding is a nonphysiological surrogate that has previously been necessary to enable gating of cardiac magnetic resonance images. Real-time imaging enables the investigator to apply the accuracy of cardiac magnetic resonance to real physiological settings. We can neither ignore the fact that our patients breathe nor ignore the fact that most of our patients develop symptoms with exertion. This new methodology finally enables us to accurately measure cardiac function when it really matters. DisclosuresNone. References

The relationship between biventricular myocardial performance and metabolic parameters during incremental exercise and recovery in healthy adolescents

“…However, our group and others have shown significant stroke volume increase also during supine exercise by using cardiac magnetic resonance imaging (23,36), and a comparative study in children between upright and supine CPET has additionally found good correlation of parameters (29).…”

Sildenafil Improves Exercise Hemodynamics in Fontan Patients

“…11 Using this novel CMR methodology with simultaneous invasive vascular pressure recordings during exercise, we evaluated exercise hemodynamics and the effect of sildenafil on exercise hemodynamics in Fontan patients. We hypothesized that (1) the exercise capacity in patients with a Fontan circulation and seemingly normal anastomotic and ventricular function is limited attributable to an impaired augmentation in pulmonary vascular flow, and (2) sildenafil would improve pulmonary vascular flow and ventricular preload during exercise.…”

“…24 Although CI nearly doubled during exercise in this study, peak CI was still lower than would be expected in healthy young individuals. 11 First, as measures reflecting preload, changes in EDVi and TPRi were evaluated. In a normal circulation, preload is determined by upstream factors such as venous return as well as right ventricular, pulmonary vascular, and atrial function.…”

“…However, our CMR protocol corrects for respiratory phase translation so that all contours were delineated during the same phase of respiration, thus avoiding the potential for confounding and inaccuracy resulting from comparing cardiac volumes under different states of filling. 11 Third, pulmonary blood flow was not measured directly but estimated to be similar to systemic cardiac , (B) lactate, (C) mixed venous oxygen saturation, and (D) arteriovenous (AV) oxygen difference from rest to peak exercise before and after sildenafil. An asterisk indicates a significant change from the previous exercise intensity.…”

Right ventricular and pulmonary vascular reserve in asymptomatic BMPR2 mutation carriers

“…We developed a methodology which combines invasive PAP measures with gold-standard cardiac magnetic resonance (CMR) quantification of RV function and Q during exercise and have used this technique to identify sub-clinical pulmonary vascular dysfunction and RV dysfunction (9,10). Thus, this technique is ideally suited to assess our hypothesis that abnormal pulmonary vascular and RV function would be demonstrable during exercise in asymptomatic subjects with a known BMPR2 mutation.…”