Tetsuro Toeda

Immediate effects of percutaneous transvenous mitral commissurotomy on pulmonary hemodynamics at rest and during exercise in mitral stenosis

Hemodynamics were evaluated during exercise in 33 patients with mitral stenosis who underwent percutaneous transvenous mitral commissurotomy (PTMC). PTMC was performed using an Inoue balloon. Each patient underwent a supine ergometer exercise test before and on the day after PTMC. Ergometer work load was started at 20 W and increased in increments of 20 W at 3-minute intervals until terminated by the patients fatigue or shortness of breath. Mitral valve area increased by 0.8 +/- 0.4 cm2 (1.1 +/- 0.3 to 1.9 +/- 0.4 cm2, p less than 0.001). Mean mitral pressure gradient decreased (12 +/- 5 to 6 +/- 2 mm Hg, p less than 0.001). Pulmonary arterial pressure significantly decreased and the cardiac index significantly increased both at rest and during exercise after PTMC. Before PTMC, the increases in pulmonary arterial pressure, total pulmonary resistance and pulmonary arteriolar resistance during exercise were greater in patients with a mitral valve area less than 1.0 cm2 than in patients with an area greater than or equal to 1.0 cm2. After PTMC, total pulmonary resistance still increased during exercise. However, pulmonary arteriolar resistance did not change during exercise in patients with a mitral valve area greater than or equal to 1.5 cm2, whereas it increased in patients with an area less than 1.5 cm2. An enlarged mitral valve area greater than or equal to 1.5 cm2, which may prevent pulmonary vasoconstriction and permits a greater increase in pulmonary blood flow during exercise, is considered a good result immediately after PTMC.

Optimal Pacemaker Sensing with Respect to Amplitude and Slew Rate of Intracardiac Electrograms: Theoretical Analysis by Computer Simulation

The optimal amplitude and slew rate of intracardiac electrograms for pacemaker sensing Here examined on a theoretical basis by computer simulation. The simulation was based on the concept that it is the voltage at the position of the pacing electrode in an electrical field of a moving electrical dipole. By changing the distance between the electrode and the myocardium and the moving velocity of the electrical dipole, simulated ECGs with arbitrary amplitudes and slew rates were generated by the computer and fed to a bandpass filter. This filter was equivalent to those assembled in some models of permanent pacemakers and had a center pass‐band frequency of 50 Hz and a Q of 1.0. The outputs of the filter were measured. The results showed that, for pacemaker sensing, simulated intracardiac electrograms with high amplitude should have high slew rates and those with low amplitudes should have low slew rates, although the absolute values depend on the characteristics of the bandpass filter and the sensing threshold of the pacemaker.

Exercise Induced Atrioventricular Block with Gap Phenomenon in Atrioventricular Conduction

A 54‐year‐old man with normal atrioventricuiar (AV) conduction at rest gave a 4‐year history of presyncope during exercise. Treadmill testing showed exercise induced AV block. Electrophysiological study demonstrated rate dependent infranodal AV block and abnormal refractory period of the His‐Purkinje system. The gap phenomenon in AV conduction occurred during the programmed stimulation. Supernormal conduction could be considered as the mechanism of the gap phenomenon in this patient.

ATRIAL CONTRIBUTION TO VENTRICULAR FILLING IN PATIENTS WITH CORONARY ARTERY DISEASE AS ASSESSED BY CARDIAC PACING

Analysis of beat to beat changes in left ventricular (LV) ejection time during cardiac pacing was utilized to assess the atrial contribution to ventricular filling in coronary artery disease. The recordings of aortic pressure were made during atrial and ventricular pacing at a rate of 5 to 10 beats/min above sinus rhythm. During ventricular pacing, LV ejection time became maximum when an atrial contraction preceded a ventricular contraction by a physiologic interval and was similar to that obtained during atrial pacing (max ET). When the atrial systole occurred with or followed the paced ventricular contraction, LV ejection time became minimum (min ET). The atrial contribution was calculated as (max ET--min ET)/max ET X 100(%). Patients with coronary artery disease had a significantly large atrial contribution. In patients without myocardial infarction, the atrial contribution was increased to compensate for impaired early diastolic filling. In patients with myocardial infarction, the atrial contribution was reduced when LV end-diastolic pressure was markedly high. The atrial contribution generally plays an important role in increasing stroke volume, but it had less effect despite the forceful atrial contraction as LV filling pressure became more elevated.