Brady-tachycardia syndrome after radiotherapy for lung cancer. Assessment by computed tomography and carbon-11 methionine positron emission tomography.

A 74-year-old male who had received radiotherapy (total 54 Gy) for right lung cancer 7 months earlier developed a symptomatic brady-tachycardia syndrome requiring the implantation of a permanent pacemaker. Chest CT showed a pulmonary tumor of 2-cm diameter in the right lower lobe with direct extension into the surrounding tissue, suggesting the possibility of cardiac invasion. Carbon-11 methionine positron emission tomography (PET) indicated the absence of visible invasion of the heart with lung cancer. The bradytachycardia syndrome, therefore, was considered to be associated with sinus node injury due to radiation. Carbon-11 methionine PET metabolic imaging might play an important role in evaluating noninvasively the cause of the arrhythmia in this patient.

Evaluation of appropriate pacing with myocardial perfusion and cardiac function as a treatment of end-stage idiopathic dilated cardiomyopathy.

We sought to determine an appropriate pacing mode on the basis of myocardial perfusion and cardiac function as assessed by nitrogen-13 ammonia positron emission tomography in a patient with end-stage idiopathic dilated cardiomyopathy.

Possible mechanism of ECG features in patients with idiopathic ventricular fibrillation studied by heart model and computer simulation.

The possible contribution of localized conduction delay and abnormal action potentials to ventricular fibrillation (VF) was studied by applying an anisotropic cardiac computer model to clinical cases of the Brugada-type electrocardiogram (ECG), which shows right bundle branch block (RBBB), a normal QT interval, ST-segment elevation, and late r' in leads V1 and V2. The anisotropic heart model was composed of 50,000 discrete units with a spatial resolution of 1.5 mm and was mounted in a human torso model. The longitudinal/transverse conduction velocity ratio was 3:1. For the normal ECG, a conduction velocity of 0.75 m/s was required. In the abnormal area of the right anterior epicardial wall, the conduction velocity was set at 0.2 m/s, with decreasing action potential amplitude and 10% prolonged action potential duration. The ECG features of ST-segment elevation and Brugada-type right bundle branch block pattern were simulated. The action potential duration was able to change dynamically with coupling interval of stimulation, with a ratio of 9% for normal ventricular muscle and 50% for Purkinje fibers. Five successive stimuli were applied to the left lateral epicardium 300 ms after the first sinus excitation, and sustained VF was induced with the transmural conduction delay at the right anterior ventricle as a block increasing the vulnerability. At the initiation of VF, reentry circuits were shown around the border zone of the right epicardium and were very heterogeneous around the conduction delayed area and septal area. In an area with the characteristics of nontransmural conduction delay, sustained VF was prevented, and the pattern of transient right bundle branch block appeared on the simulated ECG and body surface potential maps. The late r' wave was calculated in the precordial leads and right anterior site on the body surface potential maps. These results suggest that increased multipolarity in the border zone between the Purkinje fibers and delayed conduction area in the right ventricle might play an important role as a functional block for the persistence of VF.

Microdosimetric considerations of effects of heavy ions on E. coli K-12 mutants.

The inactivation cross sections of E. coli K-12 recombination-deficient mutants, JC1553 (recA) and AB2470 (recB), for several MeV/u alpha-particles and N ions have been successfully analyzed by Katz's target theory in which radiosensitivity parameter E0 is assumed to be LET independent and equal to D37 for gamma-rays. For E. coli K-12 wild type, AB1157 (rec+, uvr+), however, it is impossible to interpret the inactivation cross section data by an LET-independent E0-value. In the latter case, as in the case of B. subtilis spore, it is necessary to assume that the radiosensitivity of the target for the core of a heavy ion is higher than that for delta-electrons. As well as Waligorski, Hamm and Katz's dose, the dose around the trajectory of an ion based on Tabata and Ito's energy deposition algorithm for electrons has been used in the course of analysis.

Post-pacing T loop abnormalities.

Vectorcardiograms of paced and unpaced beats were recorded from 18 patients with implanted pacemakers to investigate the characteristics of post-pacing T inversions. The intraventricular conduction during sinus rhythm of unpaced beats was normal in 13 of 18 patients and abnormal in the other 5 (RBBB in 3, LBBB in 2). The directions of the maximum QRS vector in paced beats (max QRSp.V) and maximum T vector in unpaced beats (max T unp.V) were studied. In 8 of 13 patients with normal intraventricular conduction (group A) and in 3 patients with right bundle branch block (RBBB), the differences between the directions of max QRSp.V and max T unp.V in both frontal and horizontal planes were less than 30 degrees, and in 5 of 13 patients with normal intraventricular conduction (group B) and 2 patients with left bundle branch block (LBBB), differences exceeded 30 degrees. The direction of max T unp.V tended to be superiorly, posteriorly and to the right regardless of max QRSp.V direction. The similarity in direction of max QRSp.V and max T unp.V supports the hypothesis by Rosenbaum et al that post-pacing T inversions may be, in part, explained on the basis of 'cardiac memory'. However the absence of correlation between the max QRSp.V and max T unp.V suggests that the post-pacing T inversions may be caused by other unknown mechanisms.