Narrow complex (supraventricular) tachycardias.

Patients experiencing a narrow complex tachycardia are usually at a lower risk than those in whom a broad complex tachycardia occurs. Therefore, in the UK cardiologists are frequently involved in broad complex dysrhythmias at an early stage, while general physicians and general practitioners will often have greater involvement in the management of patients with narrow complex arrhythmias. We describe the management of narrow complex arrhythmias likely to be encountered, including the ubiquitous atrial fibrillation.

Haemodynamic response to a small intravenous bolus injection of epinephrine in cardiac surgical patients.

BACKGROUND AND OBJECTIVE: The aim was to study the rapid changes in cardiac output and systemic vascular resistance produced by intravenous epinephrine (5 microg) on a beat-by-beat basis. METHODS: Ten patients were studied during cardiac surgery. Radial or brachial arterial pressure was recorded continuously during intravenous administration of epinephrine (5 microg). Cardiac output and systemic vascular resistance were derived for each beat using arterial pulse contour analysis calibrated by lithium indicator dilution. In each patient a further dose of epinephrine (5 microg) was administered during cardiopulmonary bypass with the blood flow kept constant so that changes in arterial pressure corresponded to changes in systemic vascular resistance. RESULTS: When the patients were not on cardiopulmonary bypass, the epinephrine produced an initial increase in systemic vascular resistance to 129 +/- 15% (mean +/- SD) of control, followed by a more prolonged reduction to 57 +/- 13% of control. Cardiac output showed a small initial reduction coincident with the increase in systemic vascular resistance, followed by an increase to 152 +/- 24% of control. During cardiopulmonary bypass, the changes produced by epinephrine on systemic vascular resistance were qualitatively similar but smaller in amplitude, probably because of a greater volume of dilution in the bypass circuit. CONCLUSIONS: Small bolus doses of epinephrine produce an initial increase in systemic vascular resistance followed by a much greater reduction that may cause hypotension.

Estimation of changes in cardiac output from the arterial blood pressure waveform in the upper limb.

We have developed a new pulse contour cardiac output (PulseCO) algorithm based on frequency analysis studies of the arterial system. PulseCO was compared with thermodilution cardiac output (TDCO) in 10 patients undergoing cardiac surgery. Results from one patient were unsuitable for analysis. In the remaining nine patients, 142 TDCO determinations were compared with PulseCO after logarithmic transformation and after being normalized by the initial cardiac output in each patient. Each determination was usually the average of three measurements. Least squares regression gave y = 0.77 x (r2 = 0.81) and the limits of agreement were from -26% to +21%. The accuracy of PulseCO in determining short-term changes in cardiac output was assessed by comparing the ratios of consecutive PulseCO determinations with the ratios of the corresponding, consecutive TDCO determinations. Least squares regression gave y = 0.71 x (r2 = 0.70) and the limits of agreement were from -21% to +25%. After phenylephrine had been given to five patients, PulseCO showed an increase in systemic vascular resistance consistent with the known pharmacological actions of the drug. The PulseCO algorithm was incorporated into a computer program that acquires arterial pressure data from an analogue-to-digital converter and displays beat-to-beat trend values.

Cardiac output measured by lithium dilution and transpulmonary thermodilution in patients in a paediatric intensive care unit.

OBJECTIVE: To compare the results of cardiac output measurements obtained by lithium dilution and transpulmonary thermodilution in paediatric patients. DESIGN: A prospective study. SETTING: Paediatric intensive care unit in a university teaching hospital. PATIENTS: Twenty patients (age 5 days-9 years; weight 2.6-28.2 kg) were studied. INTERVENTIONS: Between two and four comparisons of lithium dilution cardiac output (LiDCO) and transpulmonary thermodilution (TPCO) were made in each patient. MEASUREMENTS AND RESULTS: Results from three patients were excluded: in one patient there was an unsuspected right-to-left shunt, in two patients there was a problem with blood sampling through the lithium sensor. There were 48 comparisons of LiDCO and TPCO in the remaining 17 patients over a range of 0.4-6 l/min. The mean of the differences (LiDCO-TPCO) was -0.1 +/- 0.3 (SD) l/min. Linear regression analysis gave LiDCO = 0.11 + 0.90 x TPCO l/min (r2 = 0.96). There were no adverse effects in any patient. CONCLUSIONS: These results suggest that the LiDCO method can be used to provide safe and accurate measurement of cardiac output in paediatric patients. The method is simple and quick to perform, requiring only arterial and venous catheters, which will already have been inserted for other reasons in these patients.

Cardiac output measured by lithium dilution, thermodilution, and transesophageal Doppler echocardiography in anesthetized horses.

OBJECTIVE: To assess the suitability of lithium dilution as a method for measuring cardiac output in anesthetized horses, compared with thermodilution and transesophageal Doppler echocardiography. ANIMALS: 6 horses (3 Thoroughbreds, 3 crossbreeds). PROCEDURE: Cardiac output was measured in 6 anesthetized horses as lithium dilution cardiac output (LiDCO), thermodilution cardiac output (TDCO), and transesophageal Doppler echocardiographic cardiac output (DopplerCO). For the LiDCO measurements, lithium chloride was administered i.v., and cardiac output was derived from the arterial lithium dilution curve. Sodium nitroprusside, phenylephrine hydrochloride, and dobutamine hydrochloride were used to alter cardiac output. Experiments were divided into 4 periods. During each period, 3 LiDCO measurements, 3 DopplerCO measurements, and 3 sets of 3 TDCO measurements were obtained. RESULTS: 70 comparisons were made between LiDCO, DopplerCO, and triplicate TDCO measurements over a range of 10 to 43 L/min. The mean (+/- SD) of the differences of LiDCO - TDCO was -0.86 +/- 2.80 L/min; LiDCO = -1.90 + 1.05 TDCO (r = 0.94). The mean of the differences of DopplerCO - TDCO was 1.82 +/- 2.67 L/min; DopplerCO = 2.36 + 0.98 TDCO (r = 0.94). The mean of the differences of LiDCO - DopplerCO was -2.68 +/- 3.01 L/min; LiDCO = -2.53 + 0.99 DopplerCO (r = 0.93). CONCLUSIONS AND CLINICAL RELEVANCE: These results indicate that lithium dilution is a suitable method for measuring cardiac output in horses. As well as being accurate, it avoids the need for pulmonary artery catheterization and is quick and safe to use. Monitoring cardiac output during anesthesia in horses may help reduce the high anesthetic mortality in this species.

A new technique for measuring cardiac output and shunt fraction during venovenous extracorporeal membrane oxygenation.

A new indicator dilution technique is described for measuring cardiac output and shunt fraction in patients undergoing venovenous extracorporeal membrane oxygenation (ECMO). Shunt fraction is the proportion of the ECMO pump flow which recirculates through the ECMO circuit (passing directly from the inflow cannula to the outflow cannula) instead of flowing through the pulmonary and systemic circulations. The indicator is an isotonic (150 mmol/l) solution of lithium chloride which is injected into the ECMO flow returning to the patient. Two lithium sensors are used simultaneously to record the resulting lithium dilution curves in arterial blood and in the blood in the ECMO circuit. Cardiac output and shunt fraction are derived from these curves. The techniques, which is simple and safe, provides measurements that allow optimal adjustment of ECMO flow and cardiovascular support.

A comparison of lithium dilution cardiac output measurements made using central and antecubital venous injection of lithium chloride.

OBJECTIVE: We have previously described an indicator dilution technique of measuring cardiac output in which lithium chloride is injected as a bolus via a central venous catheter and cardiac output derived from the arterial lithium dilution curve recorded from a lithium-selective electrode, which we have developed for this purpose. It would be an advantage if the lithium could be injected via the basilic vein (in the antecubital fossa) in those patients who do not need central venous catheterisation for other reasons. We have therefore compared cardiac output measurements made using these two routes of lithium chloride administration. METHODS: Lithium dilution cardiac output was measured 10 times in each of 10 patients, injecting the lithium chloride alternately via the basilic or central venous catheter. RESULTS: The mean difference was 0.8 +/- 5.2% (SD) (range -8.5 to +7.0%) over a range of cardiac output of 4.5-13 l/min. CONCLUSIONS: Injection of lithium chloride via the basilic vein in the antecubital fossa allows accurate lithium dilution cardiac output measurements to be made in patients who do not have central venous catheters in place.

The shape of indicator dilution curves used for cardiac output measurement in man.

1. In six patients arterial plasma lithium concentration-time curves were recorded following injection of lithium chloride into the right or left atrium. 2. Lognormal curve fitting was used to derive the areas under the first pass dilution curves. 3. Subjecting the curves produced by left atrial injection to a delay and sequential filtering produced curves that closely approximated those produced by right atrial injection. 4. We conclude that the transfer function of the right heart and lungs is equivalent to a delay and sequential filtering, that the primary indicator dilution curve is closely approximated by a lognormal curve and that loss of lithium in the lungs following right atrial injection is clinically insignificant.

A new method of analysing indicator dilution curves.

OBJECTIVE: We are currently developing a new indicator dilution method of measuring cardiac output using lithium chloride as the indicator. The aim of the present study was to develop a simple and accurate method of deriving the area under the primary indicator dilution curve: that is, the area which would have been inscribed had there been no recirculation of the indicator. METHOD: A model based upon the representation of the mixing in the circulation as similar to that of the passage of an impulse through a series of filter elements was studied. This was represented physically by a model which consisted of a series of mixing chambers. The model was analysed theoretically using Laplace transforms and was used to test the new method of deriving the area of primary indicator dilution curves. RESULTS: Theoretical analysis showed that such a filter model produces curves which closely approximate the shape of a lognormal distribution over a range of skewness greater than that of human indicator dilution curves. The single pass curves from the physical model were shown to be similar in shape to lognormal distributions, as were the curves obtained from patients to the point when recirculation occurred. A method of estimating the area under the primary curve based upon the lognormal distribution was developed and equations derived. The use of these equations to calculate flows from lithium dilution curves in the mixing chamber model was validated by comparing the results with simultaneous timed collection. CONCLUSIONS: Theoretical justification for treating primary indicator dilution curves as lognormal is presented. A simple method of deriving the integral of the primary indicator dilution curve is described. It uses the whole of the curve up to a point short of recirculation, avoiding the problem which can occur with the classical Hamilton extrapolation method when the cardiac output is low and recirculation distorts the primary curve in the early part of the washout.