Left ventricular or biventricular pacing improves cardiac function at diminished energy cost in patients with dilated cardiomyopathy and left bundle-branch block.

BACKGROUND: Left ventricular or biventricular pacing/stimulation can acutely improve systolic function in patients with dilated cardiomyopathy (DCM) and intraventricular conduction delay by resynchronizing contraction. Most heart failure therapies directly enhancing systolic function do so while concomitantly increasing myocardial oxygen consumption (MVO(2)). We hypothesized that pacing/stimulation, in contrast, incurs systolic benefits without raising energy demand. METHODS AND RESULTS: Ten DCM patients with left bundle-branch block (ejection fraction 20+/-3%, QRS duration 179+/-3 ms, mean+/-SEM) underwent cardiac catheterization to measure ventricular and aortic pressure, coronary blood flow, arterial-coronary sinus oxygen difference (DeltaAVO(2)), and MVO(2). Data were measured under sinus rhythm or with left ventricular or biventricular pacing/stimulation at the same heart rate. These results were then contrasted to intravenous dobutamine (n=7) titrated to match systolic changes during LV pacing. Systolic function rose quickly and substantially from LV pacing (18+/-4% rise in arterial pulse pressure, which correlates with cardiac output, and 43+/-6% increase in dP/dt(max); both P<0.01). However, DeltaAVO(2) and MVO(2) declined -4+/-2% and -8+/-6.5%, respectively (both P<0.05). Similar results were obtained with biventricular activation. In contrast, dobutamine raised dP/dt(max) 37+/-6%, accompanied by a 22+/-11% rise in per-beat MVO(2) (P<0.05 versus pacing). CONCLUSIONS: Ventricular resynchronization by left ventricular or biventricular pacing/stimulation in DCM patients with left bundle-branch block acutely enhances systolic function while modestly lowering energy cost. This should prove valuable for treating DCM patients with basal dyssynchrony.

Efficiency of the heart as estimated from uncalibrated diagrams of intraventricular pressure related to conductance.

Using a diagram representing the relationship of intraventricular pressure and conductance, we determined ventricular efficiency from the weighted relationship between the area encompassed by the loop (the stroke work) and the total area surrounded by the end-diastolic curve, the systolic segment of the diagram, and the end-systolic line. The basic concept underlying this calculation stems from the linear relationship between consumption of oxygen by the heart and the total area discussed above, a relationship already well established in the literature. In five animals investigated under control conditions, values ranged, as expected, from 17.5 to 30.6% (average 21.78%, SD 5.06). They showed a significant increase (P less than 0.05) after an inotropic maneuver (range 19.9-40.0%, average 31.17, SD 7.43). An attractive feature is that the diagrams need not be calibrated in absolute terms. The procedure can be easily applied during routine cardiac catheterization to obtain complementary information (ventricular efficiency) which is of value in the evaluation of cardiac performance.

Intracardiac measurements with the impedance technique.

The author describes how intracardiac volume can be assessed by means of the impedance presented to the passage of an electric current by the blood contained in that volume. It begins with an overview of impedance measurement, and then describes the measurement of cardiac impedance using transventricular electrodes. The calibration of intraventricular blood conductance in absolute volume terms, a major problem that is not as yet fully solved, is discussed. Three applications are examined: intraventricular pressure-volume diagrams: measurements of cardiac efficiency; and detection of regional myocardial ischemia.

Low-cost digital impedance meter for the detection of micro-organisms.

The digital impedance meter is a microprocessor-based instrument able to detect, quantify and identify micro-organisms. The equipment makes use of the bipolar technique of measuring the impedance modulus of six cells containing inoculated culture broth. It performs temperature compensation automatically. Growth curves are stored in memory as time course events and can be displayed on any suitable device.

Detection of left ventricular regional myocardial ischaemia in dogs by intraventricular conductance catheter.

Nine adult mongrel dogs were instrumented with ultrasonic microcrystals to measure left ventricular basal anteroposterior diameter and midwall myocardial segment length near the cardiac apex. Pneumatic cuff occluders were positioned around the left circumflex coronary artery near its origin and around the left anterior descending coronary artery two thirds of the way along its length. A pressure microtransducer was implanted into the left ventricle. Ten days after instrumentation the animals were anaesthetised with morphine chlorhydrate and pentobarbital sodium. An eight electrode catheter was advanced into the left ventricle to measure ventricular apical and basal regional and total electrical conductance. Minor ischaemia caused by occlusion of the left anterior descending artery was detected only by the electrode pair located near the apex, as decreased local ejection fraction. Major ischaemia caused by left circumflex artery occlusion was detected by both apical and basal electrode pairs and by total conductance, the three conductance signals indicating reduced ejection fractions compared with control values. The basal diameter signal indicated that basal regional motility changed only during major ischaemia, thus confirming the specificity of the changes in the basal conductance signals. The apical segment length signal confirmed the altered motility indicated by the apical conductance signal. These results suggest that regional wall motion abnormalities may be detected by the use of a multielectrode conductance catheter.

Impedancimetric bacterial detection: theoretical and experimental aspects.

By means of the bipolar impedance technique, we detected bacterial growth in an inoculated broth as its time course absolute impedance. From it, the impedance change relative to sterile medium was obtained, calculating also its time derivative. The repeatability of the derivative curves (they overlapped within a band better than 3.3%) permitted the identification of a double-hump pattern which, in principle, could be accepted as an indicator of the type of bacteria (Escherichia coli). After six experimental series, the growth curves appeared as sensitive to the initial concentration of bacteria and to the culture time preceding inoculation; they were also dependent on the temperature and on the average basal impedance. Temperature showed a greater effect (one order of magnitude) on the lag-phase of the growth curve than on the stationary-phase. This effect occurs because the impedance growth curves tend to get away from the reference offered by the sterile medium. The best working conditions were obtained for an average basal impedance of 510 ohms under well controlled temperature conditions (variations smaller than or equal to 0.20 degrees C) with wire stainless steel electrodes vertically immersed in the culture broth. This impedance technique appears as inexpensive and easy to automatizing for large number of samples.

Laplace's law of the heart and left ventricular wall thickness

A lei de Laplace aplicada ao coraçäo prevê uma parede mais espessa em direçäo à base do ventrículo esquerdo do que ao ápice. Inspeçäo visual de dissecaçöes anatonômicas näo demonstra esta diferença, principalmente por causa de irregularidades geométricas do endocárdio. O objetivo deste estudo foi de encontrar um padräo de distribuiçäo da espessura da parede ao longo do eixo base-ápice para demonstrar (ou rejeitar) a previsäo. Com mediçöes realizadas em coraçöes de oito pessoas normais os resultados foram ajustados por uma parábola do tipo hr = Bo + B1 1r + B2 1r onde os coeficientes B säo iguais, respectivamente, a 76.32, o.77 e 6.64x10, hr é espessura relativa e 1r é o comprimento relativo base-ápice. O máximo das médias de espessura foi localizado em 61% do comprimento do ventrículo (a partir do ápice) com uma regiäo de "parede mais espessa" que variou de 27.7% a 93.1% (aproximadamente 30% a 90%) daquele comprimento. Estes resultados, confirmam a previsäo da lei. Além disto, foi encontrado que isto é verdade somente, (1) para coraçöes em sístole, e (2) quando os músculos papilares fossem incluídos como parte da espessura da parede

Left intraventricular pressure-impedance diagrams (DPZ) to assess cardiac function. Part I: morphology and potential sources of artifacts.

Left ventricular function can be assessed with pressure-volume diagrams (DPV). Since there exists a relationship between ventricular volume changes and changes in intraventricular impedance (ZIV), we propose a diagram, DPZ, obtained from the intraventricular pressure (PIV) and the ZIV signals. This method was tested in 10 anesthetized mongrel dogs (morphine, sc, 30 mg/kg, and pentobarbital, sc, 5-7 mg/kg). PIV was measured with a Millar microtip catheter advanced under fluoroscopy via the femoral artery. ZIV was measured with a laboratory impedance meter (100 microA rms constant current, 12 kHz) in a tetrapolar configuration using another intraventricular catheter. ECG, aortic pressure and basal ZIV were also recorded to help identification of the different cardiac cycle phases on the diagram. Single-beat and multiple-beat loops were obtained in bradycardia and tachycardia to test for repeatability. These loops were always of a quadrangular-like shape with clockwise rotation. No attempt was made to calibrate the impedance axis in terms of volume. Apparent small volume changes in the isovolumic phases were probably due to ZIV catheter bending and/or movement. It is suggested that DPZ can serve in itself as a complementary evaluation tool of ventricular function by application of different maneuvers (physical, physiological of pharmacological).

Left intraventricular pressure-impedance diagrams (DPZ) to assess cardiac function. Part II: determination of end-systolic loci.

UNLABELLED: By means of tetrapolar intraventricular impedancimetric measurements and by modifying the aortic impedance with a brief volume unit step afterload increase, with a balloon catheter, we obtained the geometric locus of the end-systolic pressure-admittance points (PES-YES) from the beat to beat pressure-impedance diagram (DPZ), usually three or four beats after inflation. Six experiments in five anesthetized mongrel dogs (average weight 21.6 kg, SD 2.5) were carried out under control conditions and after a slow infusion (4 micrograms/kg/min) of epinephrine to change the myocardial inotropic state. In control, the PES-YES points fell in all cases on a straight line (average correlation 0.968, SD 0.033). After epinephrine, linearity was still good in four experiments (average correlation 0.938, SD 0.059). All animals showed displacements of the regression lines after epinephrine with respect to control. However, the direction of the shifts was not always consistent: three dogs yielded an upward-leftward shift; one showed a crossing point between the two regression lines with an increase in slope after epinephrine; in the remaining two experiments (same dog in different days), the post-epinephrine regression lines of the pressure-admittance end-systolic points were displaced downwards and rightwards. Five out of the six experiments increased the slopes of the lines after infusion of epinephrine. IN CONCLUSION: the method supplied the end-systolic point locus obtained from simple cardiac catheterization and this locus was altered by inotropic intervention.

Multichannel tetrapolar admittance meter (MY) for intracardiac volume measurements in animals.

With an 8-electrode catheter, this instrument measures simultaneously five intraventricular sections of admittance and, also, total admittance, the latter obtained as the sum of five component sections. It injects through the two outermost electrodes of the catheter a constant current (828 microA rms) of high frequency (14 kHz). Actually, the instrument measures the mathematical inverse of the resistive component (conductance) of the impedance seen by the voltage sensing electrodes. The sensitivity per channel was adjusted to 25 V/mho, resulting in an overall sensitivity of 5.28 V/mho for the total intraventricular admittance. Nonlinearity in any single channel was less than or equal to 3.4% while, for the total admittance, it was less than or equal to 1.5%. The difference between any two individual channels when the same calibration resistor was connected, relative to the expected value, was less than or equal to 4.8%. The equipment demonstrated good performance in animal experiments and showed the possibility of detecting localized dysfunctions. Human applications still remain to be done.

High-sensitivity, high-linearity, low-leak, self-balanced impedance cardiograph.

An impedance cardiograph (so-called cardioimpedance meter) with the following characteristics is described: preadjustable current generator range of 0-4 mA rms at 100 kHz, crystal-controlled; sensitivity up to 50 V/omega with a resolution of 2 m omega; maximum nonlinearity of 2%; 0.7 microA arms of maximum leak current at 50 Hz; flat frequency response between 0 and 19 Hz. The instrument is self-balanced, using Arenson's bridge [1] with minor modifications, and is also able to operate as a plethysmograph, respirograph, and as an intracardiac Z-meter. Preliminary test as an impedance cardiograph yielded a correlation coefficient better than 0.8 when the stroke volume was evaluated by Kubicek's method and compared with values obtained using thermodilution.

Stroke volume in the dog: measurements by the impedance technique and thermodilution.

The main objective of this paper was to assess the efficacy of a laboratory prototype cardio impedance meter, to determine stroke volume in experimental dogs, using Kubicek's classic model. A second objective, complementary to the first, was to evaluate the method itself, under the carefully controlled condition in which cardiac frequency was increased from the initial to the final value. Measurements were performed on ten mongrel dogs (average body weight = 15.2 kg, SD = 4.7), employing the standard thermodilution procedure as reference. Based on a total of 179 determinations (about 18 per animal), the following regression equation was obtained: SVd = (0.36 SVz + 3.94) ml where SVd = stroke volume by thermodilution, SVz = stroke volume by impedance, with a standard error of the estimate SEE = 4.26 ml, a coefficient of variation CV = 32.8%, and 0.84 as correlation r. Thus, the impedance technique overestimated consistently by an average factor in the order of 2. These conclusions were made: In the experimental dog, the impedancimetric method can measure non-invasively directional and relative changes in stroke volume; this permits the effect of several types of maneuvres to be followed on a beat-to-beat basis. The lack of accuracy would require the development of a more sophisticated mathematical model; however, a practical statistical expression for laboratory use is easily derivable, making the determination as if the measurement had been made with the thermodilution procedure.(ABSTRACT TRUNCATED AT 250 WORDS)