BackgroundMeasurement of myocardial T2* is becoming widely used in the assessment of patients at risk for cardiac iron overload. The conventional breath-hold, ECG-triggered, segmented, multi-echo gradient echo (MGRE) sequence used for myocardial T2* quantification is very sensitive to respiratory motion and may not be feasible in patients who are unable to breath-hold. We propose a free-breathing myocardial T2* mapping approach that combines a single-shot gradient-echo echo-planar imaging (GRE-EPI) sequence for T2*-weighted image acquisition with automatic non-rigid motion correction (MOCO) of respiratory motion between single-shot images.MethodsECG-triggered T2*-weighted images at different echo times were acquired by a black-blood, single-shot GRE-EPI sequence during free-breathing. A single image at a single TE is acquired in each heartbeat. Automatic non-rigid MOCO was applied to correct for in-plane respiratory motion before pixel-wise T2* mapping. In a total of 117 patients referred for clinical cardiac magnetic resonance exams, the free-breathing MOCO GRE-EPI sequence was compared to the breath-hold segmented MGRE approach. Image quality was scored independently by 2 experienced observers blinded to the particular image acquisition strategy. T2* measurements in the interventricular septum and in the liver were compared for the two methods in all cases with adequate image quality.ResultsT2* maps were acquired in all 117 patients using the breath-hold MGRE and the free-breathing MOCO GRE-EPI approaches, including 8 patients with myocardial iron overload and 25 patients with hepatic iron overload. The mean image quality of the free-breathing MOCO GRE-EPI images was scored significantly higher than that of the breath-hold MGRE images by both reviewers. Out of the 117 studies, 21 breath-hold MGRE studies (17.9 % of all the patients) were scored to be less than adequate or very poor by both reviewers, while only 2 free-breathing MOCO GRE-EPI studies were scored to be less than adequate image quality. In a comparative evaluation of the images with at least adequate quality, the intra-class correlation coefficients for myocardial and liver T2* were 0.868 and 0.986 respectively (p < 0.001), indicating that the T2* measured by breath-hold MGRE and free-breathing MOCO GRE-EPI were in close agreement. The coefficient of variation between the breath-hold and free-breathing approaches for myocardial and liver T2* were 9.88 % and 9.38 % respectively. Bland-Altman plots demonstrated good absolute agreement of T2* in the interventricular septum and the liver from the free-breathing and breath-hold approaches (mean differences -0.03 and 0.16 ms, respectively).ConclusionThe free-breathing approach described for T2* mapping using MOCO GRE-EPI enables accurate myocardial and liver T2* measurements and is insensitive to respiratory motion.

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His bundle recordings obtained in a patient with progressive shortening of the PR interval observed during and after acute diaphragmatic myocardial infarction showed abbreviated AH and HV intervals. Though atrial pacing at rapid rates produced prolongation of the AH interval, this was not as great as is seen in normal subjects and the abbreviated HV interval remained unchanged. The results of His bundle electrograms during atrial pacing on another patient with an old inferior myocardial infarction and intermnittent Wolff-ParkinsonWhite syndrome were similar to the response of normal subjects, but the Wolff-Parkinson-White configuration was only seen with premature supraventricular beats.Possible mechanisms are discussed, and it is suggested that the most likely is infarction of the AV nodal tissue responsible for the normal nodal delay. Accelerated atrioventricular (AV) conduction associated with myocardial ischaemia is rare, though all grades of AV block are commonplace. Accelerated AV conduction manifesting as Wolff-ParkinsonWhite syndrome (anomalous AV excitation) has been reported to occur after acute carbon monoxide poisoning (Seling, i966), during acute articular rheumatism (Ougier, Page, and Marc, i964), in myocarditis, cardiomyopathy, and digitalis toxicity (Ohnell, I944; Vakil, I955; Mathur, Wahal and Seth, i969), and in some congenital heart diseases. There have been occasional reports of Wolff-Parkinson-White syndrome occurring with acute myocardial infarction (Apostolov, I964; Forin and Tammaro, I969; Angelino, Mina, and Gallo, I964).Two patients with accelerated AV conduction associated with acute ischaemic heart disease have recently been observed and studies performed to elucidate the mechanisms by which this may occur. MethodsBoth patients were studied in the postabsorptive state and were premedicated with I0 mg diazepam intramuscularly one hour before cardiac catheterization. The procedure was explained to the patients in detail and the necessary consent was obtained. Under i per cent xylocaine local anaesthesia, a bipolar (io mm) 6 Fr. electrode catheter Received I5 February I973. was introduced into the right or left femoral vein percutaneously. The catheter tip was positioned using fluoroscopic control across the tricuspid ring, as described by Scherlag et al. (I969) and Damato and Lau (1970).His bundle potentials were recorded over a frequency range of 40-500 Hz on a Cambridge six-channel photographic recorder at a paper speed of ioo mm/sec. A second 5 Fr. bipolar electrode catheter was passed percutaneously from the right subclavian vein and positioned at the site of the sinoatrial node, for pacing the right atrium from an external battery-powered pacemaker up to a rate of 170/min. Atrium to His bundle (AH) times were measured from the P wave of a simultaneous standard lead III, and His to ventricle (HV) times from the intracardiac recording.Case reports Case I A 59-year-old man with a two-year history of palpitation and a three-month history of dizzy attacks, was admitted to hospital in ...

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