Quantification of pulmonary/systemic shunt ratio by single-acquisition phase-contrast cardiovascular magnetic resonance.

PURPOSE: Phase-contrast cardiovascular magnetic resonance (PC-CMR) quantification of intracardiac shunt (measuring the pulmonary to systemic flow ratio, Qp/Qs) is typically determined by measuring flow through planes perpendicular the pulmonary trunk (PA) and ascending aorta (Ao). This method is subject to error from presence of background velocity offsets and requires two scan acquisitions. We evaluated an alternate PC-CMR technique for quantifying Qp/Qs using a single modified plane that encompasses both the PA and Ao. MATERIAL AND METHODS: In 53 patients evaluated for intracardiac shunting, PC-CMR measurement in the individual Ao and PA planes and also in a single-acquisition plane was obtained and Qp/Qs calculated by each method. Bland-Altman analysis was performed to evaluate the agreement between the two methods. RESULTS: The 95% confidence limits of agreement ranged from -0.52 to +0.34 indicating good agreement between the two methods. There was excellent agreement on the clinically relevant threshold value of Qp/Qs ratio of 1.5 (representing criteria for surgical correction of shunt). CONCLUSIONS: Qp/Qs determined from the single-acquisition approach agrees well with that of the individual PA and Ao method and offers potential improved accuracy (due to background velocity offset).

Effect of primary mitral regurgitation on left ventricular synchrony.

Mitral regurgitation (MR) promotes left ventricular (LV) dilatation and eccentric remodeling. In the presence of LV dyssynchrony and heart failure, cardiac resynchronization therapy decreases the severity of MR. Whether primary MR can cause LV dyssynchrony is unknown. We investigated whether moderate to severe primary MR causes LV dyssynchrony in the presence of LV dilation and an ejection fraction (EF) >55%. We studied 37 normal subjects and 22 patients with moderate to severe MR and no coronary artery disease. Electrocardiographically gated cine and tagged cardiac magnetic resonance imaging was performed. Two-dimensional, maximum-circumferential shortening strain and time-to-peak strain (TTPS) were computed using harmonic-phase analysis of tagged magnetic resonance imaging. LV dyssynchrony was assessed by comparing TTPS delay of various LV quadrants and TTPS dispersion among the contralateral quadrants in patients with MR and normal subjects. Statistical comparison was done using a generalized linear model for repeated measurements. LV end-diastolic and LV end-systolic volumes were significantly larger in patients with MR versus normal subjects (207 +/- 11 vs 130 +/- 4 and 73 +/- 5 vs 47 +/- 2 ml, p <0.001). LVEF did not differ in patients with MR and normal subjects. The difference in the TTPS among various quadrants and the dispersion among the contralateral quadrants of the LV myocardium was similar between patients with MR and normal subjects. In conclusion, moderate to severe MR does not cause LV dyssynchrony in patients with LV dilatation and normal LVEF. Thus, cardiac resynchronization therapy in the absence of LV dyssynchrony may not decrease the severity of MR.

Determining exercise-induced blood flow reserve in lower extremities using phase contrast MRI.

PURPOSE: To study the changes in limb blood flow during lower extremity exercise using phase contrast (PC) MRI in normal volunteers. MATERIALS AND METHODS: Healthy volunteers performed plantar flexion exercise (<1 W) for four minutes. Flow velocity was measured using cardiac-gated, cine PC-MRI sequences (fast gradient recalled echo [GRE]; multishot echo planar imaging [EPI]) on a 3T scanner at the level of the superficial femoral artery (SFA): 1) preexercise; 2) immediately postexercise; 3) during three minutes recovery; and 4) postrecovery. RESULTS: At rest there was a triphasic flow waveform in the SFA. During exercise it changed to a monophasic pattern with an increase in total flow; there were variable changes in vessel size and flow velocity. The waveform regained the triphasic pattern during recovery. The exercise-induced flow reserve (FR) was 167 +/- 90%. CONCLUSION: PC-MRI demonstrates that the resting triphasic flow waveform transforms into a monophasic pattern with submaximal exercise and returns to baseline with recovery. This increase in the regional blood flow allows for measurement of exercise-induced FR in the SFA.

Feasibility and potential clinical utility of goal-directed transthoracic echocardiography performed by noncardiologist intensivists using a small hand-carried device (SonoHeart) in critically ill patients.

OBJECTIVE: This study was designed to assess the clinical applicability of a small, handheld, portable transthoracic echocardiography device by noncardiologist intensivists. DESIGN: Prospective, observational study. After 10 one-hour tutorials, intensivists performed a limited transthoracic echocardiography (TTE) (2-4 views, without Doppler or M-mode) examination with the 5.6-lb SonoHeart Echo System (SonoSite, Bethell, WA) on critically ill patients admitted to the surgical intensive care unit. After initial cardiac clinical assessment in 90 patients, a limited TTE was performed by an intensivist to assess left ventricular (LV) function and LV volume status. Each study was immediately reviewed and repeated by an echocardiographer to determine the technical quality of the TTE and the accuracy of the intensivist's interpretation. Data were analyzed and presented in proportions using descriptive statistics. SETTING: Surgical intensive care unit of an academic medical center. PARTICIPANTS: Ninety critically ill adult patients. INTERVENTIONS: After initial cardiac clinical assessment, a limited TTE was performed by an intensivist to assess LV size and function, to rule out significant pericardial effusions, and to estimate circulatory volume. RESULTS: Intensivists successfully performed a diagnostic limited TTE in 94% of patients and interpreted their studies correctly in 84%. Limited TTE provided new cardiac information and changed management in 37% of patients. TTE added useful information in an additional 47% of patients but did not alter immediate management. The mean "goal-directed TTE" acquisition time was 10.5 +/- 4.2 minutes. CONCLUSION: After a brief formal training in using this handheld echocardiographic system in intensive care unit patients, surgical intensivists successfully performed and correctly interpreted a limited TTE in critically ill patients. Limited TTE provided new information and altered management in a significant number of patients. This study supports incorporating bedside goal-directed, limited TTE into intensivists' training programs.