Correct positioning of a central venous catheter (CVC) is essential to avoid serious complications such as perforation, thrombosis or dysrhythmias caused by interactions with the vessel wall or the endocardium . The correct position of the tip of the CVC for therapy and measurement of the central venous pressure is considered to be in the superior vena cava close to its entrance to the right atrium . Blood flow conditions are then optimal to keep the catheter away from the intima and to dilute infused drugs immediately. Owing to the risk of malpositioning, the most common way to control the catheter position is still by radiography or fluoroscopy during or after placement, which is occasionally enhanced by injection of contrast medium . The reliability of this method is limited and additional costs and radiation exposure are involved. Moreover, repeated catheterization and chest radiographical films are required if the CVC is located incorrectly. An alternative method for correct placement of the CVC is to record an intravascular electrocardiogram (ECG), which was first described by Hellerstein and colleagues in 1949 . Using this technique, an increased P-wave can be detected only if the catheter tip is intravascular and has passed through the entrance to the right atrium. Further advancement of the catheter tip turns the P-wave biphasically after passing the sinoatrial node and changes its deflection as the tip reaches the right ventricle, when a broadened R-peak appears. Originally, the method was used for positioning pacer probes and for intracardial diagnosis of complex cardiac dysrhythmias , and later for accurate positioning of ventriculoatrial shunts . With increasing use of CVC, the method was also adopted as an accurate means of confirming the correct CVC position [7-10]. The technique was further simplified and made commercially available with the Arrow-Johans® electrographical adapter (ARROW, Erding, Germany) .
Recently, a modification of this technique has been described using the Seldinger guidewire as a unipolar lead of intravascular ECG [12,13]. The CVC set includes a connecting cable with an alligator clip to connect the guidewire, which is marked to indicate when the tips of the wire and the catheter are co-located. It also includes a universal adapter, which allows connection to the usual ECG lead systems. Several lumen CVC sets are available and in clinical use (Certofix® Mono, Duo, Trio, Trio HF, Quinto, and Cavafix® Certodyn®; all catheters by: B. Braun, Melsungen, Germany).
The hypothesis of the present authors was that the intravascular ECG obtained by guidewire would show better quality in terms of an enhanced P-wave than a system based on a fluid column. Furthermore, it was desirable to discover whether advancing the guidewire under immediate ECG monitoring after introduction could prevent any cardiac dysrhythmias from occurring.
The authors' institutional review board approved the protocol, and informed consent was obtained from 80 patients, who were enrolled into two studies. Patients were excluded if less that 18 yr of age, if they were carrying a pacemaker or if they had manifest cardiac dysrhythmia. A triple-lumen CVC (Certofix® Trio, B. Braun, Melsungen, Germany) - indicated for clinical reasons - was placed using intravascular ECG monitoring via a guidewire. A modified bipolar lead II configuration was recorded. ECG placement was standardized in all patients by connecting the reference red electrode to a universal adapter equipped with a switching function (Certodyn® - Universal adapter, B. Braun, Melsungen, Germany) on the right thoracal side (mid-clavicular, second intercostal space). The yellow electrode was placed on the left thoracic side (mid-clavicular, second intercostal space) and the neutral green electrode on the lower left chest (midaxillary, eighth intercostal space) (Fig. 1).
In the first study on 40 patients undergoing cardiac surgery (n = 20) or requiring intensive care therapy (n = 20), the correct position of the CVC introduced via the subclavian (n = 20) or internal jugular vein (n = 20) was confirmed by chest radiography. After venepuncture, the guidewire was introduced and advanced without strict regulation in the study. Adjusting the black marking on the guidewire to the end of the CVC connector matched the tips of the catheter and the wire. To test the influence of the exact position of the guidewire relative to the tip of the catheter, ECG readings were recorded at different positions, namely with the wire 1 cm inside or outside the catheter. After the CVC had reached an intra-atrial position as seen from an enhanced P-wave, the guidewire was changed to the fluid column method (i.e. the lumen flushed with physiological saline solution 0.9%) to compare the ECG signal quality. Therefore, at this position of the CVC, the guidewire was withdrawn and the electrolyte-filled system (Alphacard®, B. Braun, Melsungen, Germany) connected to record again the intra-atrial ECG. Subsequently, the guidewire was reinserted and the catheter and wire retracted until there was a decrease of the P-wave, with an additional 2 cm. ECG readings were again recorded at various wire positions. After taking a chest radiograph in the supine position, the distance of the catheter tip to the entrance of the atrium was measured and documented.
In a second part of the study on another 40 patients, the authors tried to avoid guidewire-induced dysrhythmias by continuous intravascular ECG reading during CVC advancement. After venepuncture, the Seldinger guidewire was introduced through the intravenous needle not more than 10 cm for a position just safely within the vessel. The needle was withdrawn, the catheter inserted and the tips matched by adjusting the connector and mark on the wire. The catheter and wire were then slowly advanced under continuous ECG monitoring. After recording of an increased P-wave, they were drawn back immediately until P-wave amplitude returned to normal, and an additional 2 cm.
Data and statistical analysis
P-wave increases were quantified as the peak height (mV) of the printed ECG signal. All patient data from trials of cannulation were averaged. Data (mean ± standard deviation, SD) were analysed for statistical significance of differences between the groups using the U-test with P < 0.05 being taken as the level of significance.
All 80 catheters were placed in the correct position without any complications. Regardless of the venous access sites, up to three trials of punctures were necessary. In all cases, the catheter was placed in the superior vena cava. During the first study, brief dysrhythmias without clinical impact were observed in 16 of 40 patients (40%). By contrast, no case of dysrhythmia occurred in the 40 patients during the second study where unmonitored advancement of the guidewire was avoided.
In all 80 patients, a variable but distinct increase of the P-wave was seen (Fig. 2; 2a), allowing a correct position to be reached. After withdrawal until complete restoration of the original P-wave configuration (Fig. 2; 4a) and an additional 2 cm, the radiologically controlled tip of the catheter showed a position 2.3 ± 0.5 cm above the entrance level to the right atrium in the 40 patients. The correct position was evaluated by a radiologist.
The positioning of the guidewire tip 1 cm inside or outside of the catheter did not change the configuration of the P-wave, except for some noise, when fluid conductivity was added by drawing back the wire into the catheter (Fig. 2; 2b, c). The change-over to a pure lead via the fluid column was always accompanied by a disturbance of the electric signal, sometimes accompanied by a decrease in P-wave amplitude, sometimes by a drifting baseline from the monitor (3 in Fig. 2). In 19 of 40 (47.5%) of patients, the P-wave increase was more pronounced when the intra-atrial ECG was measured via guidewire instead of the fluid-filled catheter. The Pmax/Pmin ratio was significantly increased when the intra-atrial ECG was measured via the guidewire instead of the fluid-filled catheter (6.5 ± 1.8 versus 4.8 ± 1.1; P < 0.05 (Fig. 3a). Similarly, no significant change was seen with different positions of the guidewire in the catheter after the CVC was withdrawn to the original P-wave amplitude (Fig. 2; 4b, c). The Pmax/R ratio was significantly increased using the ECG wire lead compared with the fluid lead (0.60 ± 0.11 versus 0.44 ± 0.15; P < 0.05) (Fig. 3b).
The present study showed that monitoring of intravascular ECG tracing via the guidewire is a reliable method for the control of correct placement of a CVC and it offers a number of advantages (Table 1). A brief increase of the P-wave proves an intra-atrial position of the catheter tip; the subsequent normalization after withdrawal indicates the correct position. A chest radiograph is then only required to control for complications.
Guidelines for CVC placement recommend that catheter tips never enter the atrium, and previous studies have shown that the tips of catheters can migrate 1-3 cm caudally with movement of the patient's arms. A further 1-3 cm withdrawal is therefore essential, since otherwise an intra-atrial position or an impingement angle between catheter and vessel wall >40° with an increased risk of vena cava traumatization may occur . The intravascular lead has also been successfully used for position control in the sitting position in specific neurosurgical procedures, where a CVC is used for diagnosis and therapy of intraoperative air embolism and the correct position of the catheter tip is intra-atrial [15,16]. After the insertion of CVCs, chest radiographs are usually obtained to ensure correct positioning of the catheter tip in the superior vena cava and to exclude mechanical complications such as pneumothorax. Thus, using the intravascular lead is accompanied by a significant saving of time, labour and costs, with a reduction in risks associated with exposure to radiation and contrast medium. In a recent analysis of the time and cost expenditure, 13-fold higher costs were calculated for the radiographic control compared with the ECG control [12,17]. The efficacy rate with regard to the correct position of the method is 92% [10,17], but correction of a malposition can be achieved in the remaining 8% without delay and in most cases without a new puncture.
After blind placement of a CVC, an intracardial position is found in up to 50% of cases , but with the risk of endocardial injury that can cause cardiac tamponade, a rare but serious complication with a mortality rate between 65 and 78% [18,19]. Intraoperative dysrhythmias are further complications of an intra-atrial CVC position . Brief dysrhythmias induced during insertion of a catheter or a guidewire usually lack a clinical impact in otherwise healthy cardiac patients, but they still must be regarded as indicators of endocardial irritation. In patients with impaired cardiac output or aortic valvular stenosis, iatrogenic dysrhythmias can be deleterious if the introduced guidewire induces atrial flutter. As demonstrated in the present paper, such dysrhythmias can be easily avoided by using intravascular ECG monitoring soon after introduction during catheter advancement.
The use of the guidewire as a lead provides several advantages compared with the fluid column. With fluid-filled catheters, the ECG tracing can be impaired by air bubbles, even when solutions of high ionic strength are used. However, the metal of the wire provides constant excellent conductivity and a clear-cut recording of an increase in the P-wave. The universal adapter permits switching of ECG monitoring from the patient to the catheter and back while maintaining sterility, thus avoiding the need for technical assistance.
The exact position of the wire tip related to the catheter tip turned out not to be crucial. Therefore, intra-atrial ECG can be used for position control even with catheters that are too short to reach the atrium, e.g. cannulas for dialysis (Table 2). Failure of ECG-guided CVC positioning has been reported for cases where sodium chloride solution-filled short catheters were used . Instead, when the ECG has shown the intra-atrial position of the guidewire, a correct position of the catheter advanced over the wire can be assumed. Pre-existing atrial fibrillation has been considered a limitation, but in a prospective study on 40 patients, sinus rhythm was no absolute prerequisite for registration of increased P-waves and its use for position control . Neither atrial fibrillation, nor atrial flutter nor paroxysmal atrial tachycardia with block interfere with ECG tracing for CVC placement. Cardiac pacemakers pose a problem if no P-wave is available. Knot formation cannot be detected, but it can be excluded with some certainty if the distance from the tip to the skin does not exceed 20 cm and a P-wave increase was previously seen in the ECG. While the guidewire is in place, defibrillation, cardioversion or electrocauterization is allowed after disconnection of the lead.
The authors are unaware of any previous study that prospectively and directly compared signal qualities of intravascular ECG in the same patient using different lead systems. It is concluded that placement of CVCs using the guidewire assists placement of the CVC in the correct position because ECG quality is improved. Furthermore, iatrogenic dysrhythmias can be avoided by CVC placement in the described manner.
The authors thank David Tracey, PhD, Department of Anatomy, University of New South Wales, Sydney, Australia, for helpful comments on the manuscript. There was no financial support or author involvement with organizations with financial interest in the subject-matter.
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