Safety threshold of R-wave amplitudes in patients with implantable cardioverter defibrillator.

OBJECTIVE: A safety threshold for baseline rhythm R-wave amplitudes during follow-up of implantable cardioverter defibrillators (ICD) has not been established. We aimed to analyse the amplitude distribution and undersensing rate during spontaneous episodes of ventricular fibrillation (VF), and define a safety amplitude threshold for baseline R-waves. METHODS: Data were obtained from an observational multicentre registry conducted at 48 centres in Spain. Baseline R-wave amplitudes and VF events were prospectively registered by remote monitoring. Signal processing algorithms were used to compare amplitudes of baseline R-waves with VF R-waves. All undersensed R-waves after the blanking period (120 ms) were manually marked. RESULTS: We studied 2507 patients from August 2011 to September 2014, which yielded 229 VF episodes (cycle length 189.6±29.1 ms) from 83 patients that were suitable for R-wave comparisons (follow-up 2.7±2.6 years). The majority (77.6%) of VF R-waves (n=13953) showed lower amplitudes than the reference baseline R-wave. The decrease in VF amplitude was progressively attenuated among subgroups of baseline R-wave amplitude (≥17; ≥12 to <17; ≥7 to <12; ≥2.2 to <7 mV) from the highest to the lowest: median deviations -51.2% to +22.4%, respectively (p=0.027). There were no significant differences in undersensing rates of VF R-waves among subgroups. Both the normalised histogram distribution and the undersensing risk function obtained from the ≥2.2 to <7 mV subgroup enabled the prediction that baseline R-wave amplitudes ≤2.5 mV (interquartile range: 2.3-2.8 mV) may lead to ≥25% of undersensed VF R-waves. CONCLUSIONS: Baseline R-wave amplitudes ≤2.5 mV during follow-up of patients with ICDs may lead to high risk of delayed detection of VF. TRIAL REGISTRATION NUMBER: NCT01561144; results.

[Usefulness of exercise Doppler in the diagnosis of severe mitral stenosis]. / Valor del Doppler de esfuerzo para el diagnóstico de la estenosis mitral severa.

BACKGROUND: Exercise in mitral stenosis produces an increase in cardiac output and heart rate which determines the increment in the transmitral gradient. However, it has not yet been established what level is reached by the gradients on exercise in severe mitral stenosis nor whether the rise in the gradient during such exercise is different to that occurring in non-severe stenosis. OBJECTIVE: To evaluate the effect of exercise in patients with severe mitral stenosis on the mitral valve gradients in absolute values and on the increment with respect to base values. METHODS: Forty-eight mitral stenosis patients (mean age: 48.8 +/- 11 years) underwent 50 exercise Doppler echocardiographic studies using supine bicycle ergometry in two stages with increases of 25 W every 3 minutes; from each of these we obtained the peak and mean mitral gradient using a non-imaging continuous-wave Doppler probe. We also conducted this procedure on 14 patients with a mean age of 50 +/- 6 who had Bjork mitral prostheses which were functioning normally. RESULTS: We defined a hemodynamic profile of severity based on the data from 18 patients whose basal mitral valve areas was < 1.2 cm2 (group I), and compared them with the data from the 32 studies of mitral stenosis patients with an area > 1.1 cm2 (group II) and with the patients with mitral prostheses (group III). The mean mitral gradient (mmHg) in group I was greater than in group II at rest (9.3 +/- 3.2 and 6.6 +/- 2.7; p < 0.001), at 25 W (20.6 +/- 4.8 and 14.1 +/- 5; p < 0.001) and at 50 W (25.9 +/- 5.4 and 17.3 +/- 5.8; p < 0.001). The increase in mean mitral gradient from the baseline to 50 watts was 16.7 +/- 4.5 mmHg in group I, which was greater than in group II and III (11.1 +/- 4.1 and 6.8 +/- 2.6 mmHg; p < 0.001). CONCLUSIONS: Exercise Doppler echocardiography enabled us to define a differential hemodynamic profile in patients with severe mitral stenosis which can be used in isolation as an indicator of severity in this condition.

[Calculation of the mitral valve area using Hatle's method. Effect of the preload change induced by nitrates]. / Cálculo del área valvular mitral por el método de Hatle. Efecto de la modificación en la precarga inducida por nitritos.

The aim of the present study was to assess the effect of changes in preload induced by nitrates on calculated mitral valve area by Doppler pressure half-time. Forty patients (mean age 51 +/- 10 years), 23 with mitral stenosis, ten with mechanical prosthesis and seven with bioprosthesis were studied by Doppler echocardiography. Twelve were in sinus rhythm and 28 had atrial fibrillation. Mitral valve area by Doppler pressure half-time, peak and mean mitral gradient and pulmonary artery systolic pressure were measured before and after isosorbide dinitrate (5 mg) or nitroglycerin (0.4 mg). The nitrates produced a significant reduction of pre-load in total group (p less than 0.001) but did not change the mitral valve area (1.9 +/- 0.8 to 1.9 +/- 0.8). The subsets of patients with size valvular area (greater than 2 cm2, less than 2 cm2, less than 1.5 cm2, mechanical prosthesis, bioprosthesis, sinus rhythm and atrial fibrillation) had an insignificant change in mitral valve area after administration of nitrates. We conclude that the mitral valve area by Doppler pressure half-time method do not modify in different conditions of preload. These findings remain in patients with prosthesis, different sizes of mitral valve area and atrial fibrillation.