temporary transvenous pacemaker placement: what criteria constitute an adequate pacing site?

EDITORIALS

Temporary transvenous pacemaker placement: What criteria constitute an adequate pacing site?

Jeffrey Goldberger, MD, Jane Kruse, RN, Frederick A. Ehlert, MD, and

Alan Kadish, MD Chicago, Ill.

Temporary transvenous pacemaker insertion has be- come a common procedure in coronary care units in selected patients with acute myocardial infarctions and those with symptomatic bradyarrhythmias. 1, 2 Various complications are attributable to temporary transvenous pacemaker placement. Specifically, perforation of £he thin-walled right ventricular apex is a well-recognized complication, with an incidence as low as 1% to 2% 3.5 or as high as 30%, 3, 6 depending on the method used to diagnose its presence.

Successful capture of the atria or ventricles re- quires the pacing catheter to be in contact with the atrial or ventricular endocardium. Currently, temporary transvenous pacing catheters are inserted el- ther by fluoroscopic or electrocardiographic guidance. The degree of contact or pressure the catheter needs to exert against the ventricular wall to ensure capture has never been evaluated with either technique. It seems likely that the greater the pressure that is applied by the catheter on the ventricular wall, the likelier the incidence of cardiac perforation. Fur- thermore, it has been suggested that ST elevation is expected during positioning of these catheters 7, s and that marked ST elevation is characteristic of myocardial perforation. 9,10 We therefore evaluated the amount of PR or ST elevation associated with the positioning of transvenous pacing catheters in the right atrium and ventricle, respectively. We hypoth- esized that the amount of PR or ST elevation indi- cares the degree of contact made by the catheter with the atrial or ventricular wall and can be used to guide

From the Division of Cardiology, Department of Internal Medicine, North- western University Medical School.

Received for publication November 27, 1992; accepted January 8, 1993.

Reprint requests: Jeffery Goldberger, MD, 250 E. Superior St., Suite 524, Chicago, IL 60611.

AM HEART J 1993;126:488-493.

Copyright ® 1993 by Mosb~Year Book, Inc. 0002-8703/93/$1.00 + .10 4/1/47090

the placement of the catheter. Finally, we evaluated whether electrogram amplitude may also be used as a measure of the degree of contact made by the catheter with the atrial or ventricular wall and whether the pacing threshhold may be correlated with electrogram characteristics.

Methods. Eleven consecutive patients undergoing electrophysiologic studies at Northwestern Memo- rial Hospital in July 1991 were enrolled in the study. Six patients were women and five were men. Their mean age was 50 + 15 years old (range 27 to 86 years old). Patients were undergoing electrophysiologic studies for evaluation of ventricular arrhythmias (n = 6), supraventricular tachycardia (n = 4), or heart block (n = 1). All patients provided written in~ formed consent before the procedure. All patients had normal electrolytes at the time of electrophysiologic studies.

All patients underwent standard electrophysiologic studies in the nonsedated, fasting state after antiarrhythmic medications had been discontinued for at least five half lives. Two or more quadripolar catheters (6F USCI, Bard Inc., Billerica, Mass.) with 5 mm interelectrode spacing were positioned in the heart through sheaths placed in the femoral vein. One catheter was positioned in the right atrial appendage and another was positioned in the right ventricular apex. Initially the catheters were positioned under fluoroscopic guidance so that they lightly abutted the atrial wall and ventricular wall, respectively (position 1). The ability to pace (bipolar) the appropriate chamber at an output of <2 mA was confirmed. Af- ter the appropriate electrogram recordings and threshold measurements were performed, the catheters were advanced approximately 2 to 3 cm until a secondary bend was noted in the catheter on fluoros- copy (position 2). Electrogram recordings and threshold measurements were repeated at this position. Intracardiac electrograms were recorded with a

488

Volume 126, Number 2 '~ ~=~' , ~ o l " ~ ' e ~ " e r et al. 489 American Heart Journal

POSITION 1 POSITION 2

II

Bipolar RA

Unipolar RA~

/

Fig. 1. Electrocardiographic lead II and intracardiac unipolar and bipolar atrial electrograms recorded when pacing catheter lightly abuts right atrial appendage (POSITION 1) and when it is advanced further (POSITION 2). Arrows indicate PR elevation. PR elevation is greater at position 2 than at position 1.

bandpass filter of 0.05 to 100 Hz (same bandpass filter as an electrocardiogram machine). Electrocardio- graphic leads I, II, III, V~, and V6 and the intracardiac electrograms were displayed on an oscilloscope and recorded at a paper speed of 100 mm/sec (As- tromed MT-96000, West Warwick, R.I.). The following electrograms were recorded at each position: (1) bipolar atrial electrogram from the distal two electrodes of the right atrial appendage catheter; (2) unipolar atrial electrogram from the distal tip of the right atrial catheter, with a skin electrode placed on the left thigh as the indifferent electrode; (3) bipolar ventricular electrogram from the distal two electrodes of the right ventricular catheter; and (4) unipolar ventricular electrogram from the distal tip of the right ventricular catheter, with a skin electrode placed on the left thigh as the indifferent electrode. Pacing thresholds were determined during bipolar pacing from the distal two electrodes of each catheter and also during unipolar pacing by using the distal electrode of each catheter and an indifferent electrode placed on the left thigh. Pacing thresholds were determined by using a programmable stimulator (Bloom Associates, Reading, Pa.) that delivers rect- angular stimuli 2 msec in duration. The pacing threshold was determined by applying 15 stimuli at a rate of 100 beats/min starting at an output of 0.2 mA and increasing by 0.1 mA increments for each subsequent 15-beat trial. The pacing threshold was defined as the minimal output (in milliamps) that resulted in capture of all 15 pacing pulses.

Data analysis. The following parameters were recorded from each of the electrograms: (1) amplitude calculated as the mean amplitude of 10 consecutive beats; (2) PR (atrial) or ST (ventricular) elevation, which represents the mean elevation of 10 consecutive beats: the PR elevation was measured from the baseline to the peak of the PR segment (Fig. 1), and the ST elevation was measured from the baseline to the J-point (Fig. 2); (3) the ratio of the PR or ST elevation to the electrogram amplitude: the differences in these parameters and the pacing threshholds with the two catheter positions (for the atrium and ventricle) were compared by using a paired t test. Indi- vidual p values are reported. However, because six comparisons were performed in the atrium and ventricle (unipolar and bipolar threshhold, amplitudes, and PR or ST elevation at each position), after application of the Bonferroni correction only p _< 0.008 was considered to be statistically significant. We also evaluated whether the pacing threshhold correlated with the electrogram amplitude, PR or ST elevation, or the ratio of PR or ST elevation to electrogram amplitude by calculation of correlation coefficients.

OBSERVATIONS Right atrial appendage. Pacing threshholds and

electrogram characteristics are shown in Table I. The mean unipolar electrogram amplitude for the initial placement of the catheter (position 1) was 2.5 + 1.3 mV and when the catheter was advanced (position 2)

August 1993 490 Goldberger et al. American Heart Journal

II

Bipolar RV

Unipolar RV ~-~

POSITION 1

__Y

POSITION 2

J

Fig. 2. Electrocardiographic lead II and intracardiac unipolar and bipolar ventricular electrograms recorded when pacing catheter lightly abuts right ventricular apex (POSITION 1) and when it is advanced further (POSITION 2). Arrows indicate ST elevation. ST elevation is greater at position 2 than at position 1.

it was 1.8 _+ 0.9 mV (p = NS). The mean bipolar electrogram ampl i tude for the initial p lacement of the ca the ter was 3.2 _+ 1.5 mV, and when the catheter was advanced it was 2.9 _+ 1.6 mV (p = NS). The PR elevations at these two positions were 0.5 __ 0.4 mV and 1.2 _+ 0.6 mV (p = 0.009), respectively, for the unipolar recording and 0.6 _+ 0.4 mV and 1.3 _+ 0.6 mV (p = 0.004), respectively, for the bipolar recording. Unipolar and bipolar PR elevation _<0.5 mV was noted in 7 of 11 pat ients when the ca theter was in position 1 and in only 1 of 11 pat ients when the ca theter was in position 2. Unipolar atrial pacing threshholds were >10 mA in four patients. In these pat ients a value of 10 mA was used as the pacing threshhold for calculation purposes. Unipolar pacing threshholds were 4.6 -- 4.3 mA for initial ca theter p lacement and 3.4 _+ 4.2 mA when the catheter was advanced (p = NS). Bipolar pacing threshholds were 1.1 _+ 0.5 mA for initial ca theter p lacement and 1.0 + 0.5 mA when the catheter was advanced (p = NS). There was no correlat ion between the atrial threshhold for ei ther unipolar or bipolar pacing and the electrogram characterist ics (Table II).

Right ventricular apex. Pacing threshholds and elec- t rogram characterist ics are shown in Table III. Th e mean unipolar electrogram ampl i tude for the initial p lacement of the ca the ter (position 1) was 8.9 _+ 4.5

mV, and when the catheter was advanced (position 2) it was 8.7 + 5.5 mV (p = NS). The mean bipolar electrogram ampli tude for the initial p lacement of the ca theter was 6.3 _+ 2.9 mV, and when the catheter was advanced it was 9.1 _+ 3.2 mV (p = 0.04). The unipolar ST elevations at these two positions were 2.4 + 2.1 mV and 4.6 + 1.9 mV, respectively (p = 0.004). The bipolar ST elevations at these two positions were 1.4 + 1.5 mV and 3.9 + 1.8 mV, respectively (p = 0.0004). Unipolar ST elevation --<2 mV was noted in 6 of 11 pat ients when the ca theter was in position I and in no pat ients when the catheter was in position 2. Bipolar ST elevation <2 mV was noted in 9 of 11 pat ients when the catheter was in position 1 and in only 1 of 11 pat ients when the ca theter was in position 2. Unipolar pacing threshholds were 0.57 _+ 0.29 mA for the initial ca theter position and 0.71 _+ 0.80 mA when the ca theter was advanced (p = NS). Bipolar pacing threshholds were 0.50 _+ 0.20 mA for the initial ca theter position and 0.50 _+ 0.34 mA when the catheter was advanced (p = NS). An adequate pacing threshhold was ob- ta ined in only one pat ient with no unipolar or bipolar ST elevation. The electrogram characterist ic with the highest correlat ion coefficient for both unipolar and bipolar pacing threshhold was the unipolar elec- t rogram ampli tude (Table IV), with an R 2 of 0.19 for

Volume 126, Number 2 American Heart Journal Goldberger et al. 491

Table I. Unipolar and bipolar atrial pacing thresholds, electrogram amplitude, PR elevation, and ratio of PR elevation to amplitude when pacing catheter lightly abutted right atrial wall (position 1)and when catheter was advanced further (position 2)

Threshold (mA) Amplitude (mV) PR elevation (m V) PR elevation/amplitude

Unipolar Bipolar Unipolar Bipolar Unipolar Bipolar Unipolar Bipolar

Position 1 4.6 _+ 4.3 1.1 _+ 0.5 2.5 _+ 1.3 3.2 _+ 1.5 0.5 +_ 0.4 0.6 _+ 0.4 0.4 _+ 0.5 0.2 + 0.3 Position 2 3.4 + 4.2 1.0 _+ 0.5 1.8 +_ 0.9 2.9 _+ 1.6 1.2 _+ 0.6* 1.3 + 0.6** 0.8 _+ 0.5 0.6 _+ 0.3

Values are mean +_ SD. *p = 0.009 compared with position 1. **p = 0.004 compared with position 1.

the unipolar threshhold and 0.25 for the bipolar threshhold.

Comments. This study demonstrates that once a pacing catheter is in contact with the atrial or ventricular walls, further advancement leads to more marked PR or ST elevation recorded in the intracardiac electrograms from the pacing catheter. However, there is no improvement in the pacing threshholds when the catheter is advanced. There is also no significant change in electrogram amplitude. Finally, some degree of PR or ST elevation was noted in all but one successful pacing sites in either the atrium or ventricle, respectively. Thus although some current of injury appears to be needed to achieve adequate pacing, there appears to be no advantage (and potential harm) in advancing a pacing catheter once it is in contact with the endocardial surface of the atrium or ventricle.

The optimal catheter position for temporary pacing has low pacing threshholds and high intracardiac electrogram amplitues. In the present study the fluoroscopic appearance of a temporary transvenous pacing catheter was used to evaluate the electrogram characteristics and pacing threshholds when a pacing catheter lightly abutted the atrial or ventricular myocardium and when it was advanced an additional 2 to 3 cm. Although it seems plausible that pacing threshholds should improve when the catheter is advanced (with the tip at the same site), this concept is not supported by our findings. Although there was a trend for bipolar electrogram amplitude to be higher during recordings from the right ventricle in position 2 than in position 1, overall, as expected, there was no significant difference in electrogram amplitude in position 2 versus position 1. Although catheter contact with the myocardium is required to record an adequate electrogram, once adequate contact is achieved (as in positions 1 and 2) it is likely that other factors more strongly influence the electrogram amplitude. However, PR and ST elevations were signif- icantly higher in position 2 than in position 1. The

Table II. Correlation coefficients and R 2 values between atrial pacing thresholds and electrogram characteristics

Unipolar threshold Bipolar threshold

Correlation Correlation coefficient R 2 coefficient R 2

Unipolar amplitude -0.24 0.06 0.07 0.005 Bipolar amplitude -0.39 0.15 -0.10 0.01 Unipolar PR elevation -0.22 0.05 -0.21 0.04 Bipolar PR elevation -0.11 0.01 -0.03 0.001 Unipolar PR elevation/ 0.26 0.07 0.15 0.02

amplitude Bipolar PR elevation/ 0.36 0.13 -0 .6 0.003

amplitude

increase in PR and ST elevation may reflect an increase in the "current of injury" induced by the increase in pressure exerted by the catheter against the atrial or ventricular walls, respectively, when it is advanced 2 to 3 cm. When electrocardiographic monitoring is used to advance temporary pacing wires, a cutoff of 0.5 mV of PR segment elevation in the atrium and 2 mV of ST segment elevation in the ventricle appears to provide the best separation between position 1 and position 2, that is, sites at which adequate pacing and sensing thresholds are obtained with the pacing catheter lightly abutting the atrial or ventricular myocardium and sites where the catheter has been advanced and has produced only additional PR or ST segment elevation without improving either pacing or sensing characteristics.

Because temporary transvenous pacing has be- come such a widespread modality it is important to have parameters to guide the insertion of temporary transvenous pacing catheters. These catheters may be inserted under fluoroscopic guidance or by using electrocardiographic monitoring of the intracardiac electrograms recorded by the tip electrode of the catheter as it passes through the heart on its course to the atrial or ventricular wall. Frequently, only

August 1993 492 Goldberger et al. American Heart Journal

Table III. Unipolar and bipolar ventricular pacing thresholds, electrogram amplitude, ST elevation, and ratio of ST elevation to amplitude when pacing catheter lightly abutted right ventricular wall (position 1) and when catheter was advanced further (position 2)

Threshold (mA) Amplitude (m V) ST elevation (m V) PR elevation/amplitude

Unipolar Bipolar Unipolar Bipolar Unipolar Bipolar Unipolar Bipolar

Position 1 0.57 + 0.29 0.50 + 0.20 8.9 ± 4.5 6.3 + 2.9 2.4 + 2.1 1.4 __ 1.5 0.46 + 0.55 0.31 ± 0.44 Posit ion 2 0.71 _+ 0.80 0.50 ± 0.34 8.7 _+ 5.5 9.1 __ 3.2 4.6 + 1.9" 3.9 + 1.8"* 0.96 _+ 0.91 0.57 + 0.66

Values are mean _+ SD. *p = 0.004 compared with Position 1. **p = 0.0004 compared with Position 2.

Table IV. Correlation coefficients and R 2 values between ventricular pacing thresholds and electrogram characteristics

Unipolar threshold Bipolar threshold

Correlation Correlation coefficient R 2 coefficient R 2

Unipolar ampli tude 0.44 0.19 0.50 0.25 Bipolar ampli tude -0.05 0.003 -0 .06 0.003 Unipolar ST elevation 0.05 0.002 -0.06 0.004 Bipolar ST elevation -0.12 0.01 -0.16 0.03 Unipolar ST elevation/ -0.25 0.06 -0.33 0.11

ampli tude Bipolar ST elevation/ -0.12 0.02 -0.17 0.03

ampli tude

electrocardiographic monitoring is used during insertion of these catheters. In 19727 a single-page report showed electrograms recorded in each chamber while a pacing catheter was advanced under fluoroscopic guidance in a single patient from the superior vena cava to the right atrium and then to the right ventricle. It is interesting to note that the electrograms recorded when the catheter was against the right ventricular wall demonstrate "marked" ST elevation, but a measure of the degree of elevation cannot be obtained because the maximal ST elevation was beyond the range of the recording and no calibration marks are provided. It has been recom- mended that intracardiac recordings be used during pacemaker positioning, s The desired position in the right ventricle should demonstrate ST elevation, which represents the "current of injury.'7, s Despite the fact that a "current of injury" has been suggested as necessary during positioning of temporary pacing catheters, no investigation has been done to quanti- tate the degree of ST elevation that is required to achieve adequate pacing. Furthermore, marked ST elevation has been suggested as a characteristic sign of myocardial perforation. 9,10 Therefore while some degree of ST elevation appears to be required to

achieve successful pacing, too much ST elevation may indicate a greater risk of perforation. This concept is supported by a report on early malfunction of permanent pacemaker electrodes, ~ in which a greater degree of ST elevation was noted in patients with perforation than those with malposition and disloca- tion. The goal of temporary transvenous pacing is to achieve reliable pacing at a reasonable threshhold and to limit the potential for serious complications. Because one of the potentially serious complications is perforation of the pacing catheter through either a thin-walled right atrium or right ventricle, an estab- lished protocol should be followed to minimize this risk.

It is difficult to quantify the risk of perforation of a pacing catheter through the right atrium or right ventricle. However, depending on the technique used to make this diagnosis its incidence may be as high as 3(l%6~and as low as 1% to 2%. 3-5 Perforations may occur with both stiff pacing catheters and the newer more flexible catheters. 12 Generally perforations are asymptomatic13,14 and are often noted during surgery or on autopsy when they were not diagnosed an- temortem. They may be associated with pericardial effusions and, on occasion, with pericardial tamponade, which may lead to death. 15, 26 Perforations usu- ally seal on their own without causing any significant morbidity. However, in this era of thrombolysis and continued anticoagulation in patients with acute myocardial infarction, the potential risks related to cardiac perforation will increase. We recently cared for a patient with a previously asymptomatic catheter perforation who had cardiac tamponade after anticoagulation for pulmonary embolism. Despite the lack of quantifiable risk factors for pacing catheter perforation, it seems likely that the risk of perforation increases when the pacing catheter is advanced unnecessarily, thereby exerting a higher pressure on the atrial or ventricular wall and producing more marked PR or ST segment elevation.

Limitations. The major limitation of this study is

Volume 126, Number 2 American Heart Journal Goldberger et al. 493

that the amount of pressure exerted by the pacing catheters on the atrial or ventricular walls could not be quantified. It seems likely that the pressure exerted by the pacing catheter in position 2 is greater than the pressure exerted by the catheter in position 1, which is consistent with the finding of a larger "current of injury." We have also presumed that when the pacing catheter is advanced the risk of perforation is increased. Although this seems to be a logical assumption it is possible that there is no significant change in the risk of perforation between the two positions. It also is possible that the stability of the pacing catheter for long-term pacing differs between position 1 and position 2. Although there are no data to support this, it may be that for long-term pacing in the coronary care unit the incremental risk of cardiac perforation with the application of increased pressure by the pacing catheter against the atrial or ventricular wall is counterbalanced by a lower risk of catheter dislodgement. Finally, this study addressed only the acute findings during temporary transvenous pacemaker insertion. Because there are likely time-dependent changes in the "current of injury," our results can only be applied in the setting of initial catheter placement.

Clinical implications. On the basis of the findings of this study, we recommend that intracardiac electrograms be obtained during atrial and ventricular temporary transvenous pacemaker insertions. There does not appear to be a difference as to whether unipolar or bipolar electrograms are recorded. For conve- nience and ease of hook-up, unipolar electrograms can be easily obtained by attaching the distal electrode of the pacing catheter to the V lead of an electrocardiography machine with the limb leads at- tached in a standard fashion. The pacing catheter should be positioned to obtain the minimum possible PR or ST elevation associated with an acceptable pacing threshhold. An at tempt should be made to position the pacing catheter against the atrial wall to achieve <0.5 mV of PR elevation and against the ventricular wall to achieve <2 mV of ST elevation. Once PR or ST elevation of this magnitude has been noted and the pacing threshhold is inadequate, repositioning the catheter to another site should be considered rather than advancing it further. With these steps the incidence of pacing catheter perforation can hopefully be decreased.

Conclusions. Temporary transvenous pacing catheters are frequently positioned by using electrocardiographic monitoring. Although it has been suggested that ST elevation should be used to demonstrate contact with the myocardium, the most

desirable degree of ST elevation indicating adequate contact has not been evaluated. This study evaluated atrial and ventricular electrogram characteristics and pacing threshholds in 11 patients undergoing electrophysiologic studies by using two different catheter configurations for each site and for each patient. Our findings demonstrate that when a pacing catheter is advanced at a particular site on the atrial or ventricular walls, more marked PR or ST elevation is noted on the intracardiac electrograms, with no improvement in the pacing threshholds. On the basis of these findings we suggest transvenous pacing catheters be positioned against the atrial wall to achieve <0.5 mV of PR elevation and against the ventricular wall to achieve <2 mV of ST elevation.

We thank Nora Goldschlager, MD, for reviewing the manuscript and for her helpful suggestions.

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temporary transvenous pacemaker placement: what criteria constitute an adequate pacing site?

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