Transcoronary Pacing: Are The Modern Wires Effective?
Neeraj Parakh, Sanjeev Asotra, Sandeep Singh, S. Ramakrishnan, Ganeshan Karthikeyan,
Sandeep Seth, Balram Bhargava
Department of Cardiology, All India Institute of Medical Sciences, New Delhi, India
Department of Cardiology, Indira Gandhi Medical College, Shimla, India

effectiveness of currently available commonly used coronary guide wires for pacing, thereby precluding the need for insertion
of temporary pacing catheter.
MATERIAL AND METHODS
25 patients who were scheduled to undergo elective coronary angioplasty were taken up for the study. Patient with acute myocardial infarction, acute coronary syndrome and severe left ventricular dysfunction were excluded. Patients underwent coronary angioplasty either through femoral approach or radial approach. After the cannulation of coronary artery ostium with a guiding catheter, a 0.014" coronary guide wire was advanced distally across the lesion into the coronary artery. Proximal end of the guide wire was connected to an external pulse generator (5348, Medtronic Inc, Minneapolis, MN, USA), using an adaptive alligator clip. The pulse generator provided a variable output current while maintaining a fixed pulse width of 40 miliseconds. The negative pole (cathode) was attached to the end of angioplasty wire and the positive role (anode) to the patient in the groin near
the puncture site making the angioplasty wire function as a unipolar lead. Pacing was started at a rate of 100 pulses per

Correspondence: Dr Balram Bhargava, Suite No-20, 7th Floor, Cardiothoracic sciences center, A.I.I.M.S, Ansari Nagar, New Delhi, India-110029
E-mail:balrambhargava@yahoo.com

minute or higher than the intrinsic heart rate, at the maximum output of pulse generator (20 mA). The output was then decreased to determine the threshold current and pacing was continued for about 30 seconds. If the coronary pacing was not possible at maximum output of pulse generator, the guide wire was advanced more deeply or introduced into a different intramyocardial branch. After threshold testing, the output current was set two to three times above the capture threshold output to provide the safety margin. All patients received intravenous heparin at the beginning of intervention. Non-ionic contrast was used in all cases. Glycoprotein (Gp)IIb/IIIa inhibitor was used during or after the intervention, if indicated. The site of pacing was recorded according to the location of target lesion. After the procedure, we measured the resistance of coronary guide wire ex vivo. Resistance was measured using a commercial grade Ohmmeter with a constant 2.6 volt charge across the wire. Each wire was placed in a straight line on a nonconductive surface. One Ohmmeter electrode was securely attached within 2 cm of the wire tip and the other placed at 150 cm from the tip. Additional measurements of resistance were made with one electrode at 175 cm and 190 cm (if available), keeping the position of electrode at the tip unchanged. The circuit of voltmeter along with the alligator clips had an intrinsic resistance of 0.17 ohms. At the each electrode location, three measured resistances were recorded after the stable readings had been obtained. At the 150 cm from tip, the alligator clip was roughly at the point, where the wire would exit the distal end of an over the wire balloon.
RESULTS
Coronary guide wire pacing was done in 25 patients who underwent coronary angioplasty. Out of which 21 (84%) were males and 4 (16%) were females. Mean age was 53.7 + 8.97 years. 21 patients underwent coronary angioplasty through right femoral artery approach and 4 patients through left radial approach. In three patients pacing was done in more than one cardiac territory. In eleven patients, Galeo wire (Biotronik, Berlin, Germany) was used. BMW wire (Guidant Corp., St. Paul, MN, USA) was used in twelve
patients. Magic wire (Meditech/Boston Scientific, Natick, Massachusetts, USA) and Couger wire (Medtronic, Santa Rosa, CA, USA) was used in one patient each. Pacing thresholds of the various guide wires are described in table-1. In fifteen patients wire was placed in the terminal branch of left anterior descending artery (LAD) and in three patients wire was placed in the terminal obtuse marginal branch (OMB). In the RCA territory, wire was kept in terminal posterior descending artery (PDA) branch in three patients

and terminal posterolateral ventricular (PLV) branch in six patients. No patient required repositioning of wire. There were no coronary guide wire related complications. Most patients had infrequent unifocal ventricular ectopics. In all patients intravenous heparin was given to maintain activated
clotting time (aCT) level above 300 seconds. No patient had any pericardial collection during or after the procedure. Bench top testing of resistance, at l50 cms, l75cms and l90 cms from the tip of guide wire was done ex vivo and results are described in table-2.

Table-1 Pacing thresholds with various coronary guide wires

Table-2. Ex vivo mean resistance (In ohms) at various distances from the tip of coronary guide wire

* Galeo wire has a usable length of 175 cm only with 3 cm of radio-opaque tip.

DISCUSSION
Complications associated with transvenous pacing catheter has prompted the society of cardiac angiography and intervention to advice against routine pacemakers during coronary angioplasty4. A normal ECG or absence of ongoing myocardial ischemia is no guarantee against severe bradycardia during coronary angioplasty and even diagnostic invasive procedure5, 6. Temporary pacing is routinely recommended during complex PTCA and during rheolytic thrombectomy. In the earlier reports of rheolytic thrombectomy, temporary pacing was required in approximately 35% of interventions in RCA and 16% of interventions in LAD artery7. In Vegas II trial using rheolytic thrombectomy, significant bradycardia occurred in 24% of patients8. Severe bradyarrthymia requires prompt pacing and the introduction of venous catheter at that moment. It may necessitate cardiac massage until pacing is available. External pacing systems require additional material and are uncomfortable for the patient9. An ideal pacing system for standby during invasive cardiology should be expeditious and efficient when required. It should necessitate little additional time and material, and be free of serious side effects. Coronary guide wire pacing meets the above said criteria.

Transcoronary cardiac pacing during myocardial ischemia using coronary guide wire have been well established in animal studies and may serve as a reliable back up system during interventional procedures complicated by bradyarrhythmias10. Meier et al had previously demonstrated feasibility and safety of temporary pacing using coronary guide wire as a unipolar pacemaker lead. They established ventricular pacing in 25 coronary arteries at acceptable pacing thresholds and without any apparent adverse events8. Although first reported in 1985, this technique is not yet widely used as the need of pacing is infrequent during PCI. de la Serna et al have supported the safety and efficacy of this technique in a large series of 300 patients11. They reported a failure rate of 3% which was due to pacing attempts in the infracted areas where thresholds were likely to be high. Another reason cited by them was insufficient contact of the pacing wire with the myocardium. In our study, coronary pacing proved reliable and there was no failure to capture in all the 25 patients. Coronary mapping of pacing thresholds in animals showed that the lowest thresholds are found when guide wires are placed distally in small intra myocardial arteries. If it is not possible to advance the wire into an intramyocardial branch, pacing may fail even at maximum output levels of conventional pulse generators. In our study we kept the pacing wire at the predetermined sites and there was no difficulty in placing of coronary angioplasty wire at different vascular sites. de la Sarna et al had a success rate of 99%, 99% and 93% in the LAD, left circumflex ( LCX) and RCA territories respectively. The observed difference in the success rates between various vessels is difficulty in reaching intramyocardial branches with guide wire in RCA11. In our study no patient had pacing wire related complication. de La serna et al observed a 2% incidence of coronary artery spasm which is not different from the prevalence of coronary artery spasm in the routine coronary angioplasty11. Prolonged coronary pacing at high output is likely to produce spasm and thrombosis. Should prolonged pacing be necessary, a right ventricular pacing catheter can be introduced under the protection of coronary to left ventricular pacing. Recently Heinroth et al12 have demonstrated the safety and feasibility of transcoronary pacing in 70 patients undergoing PTCA. They demonstrated a pacing efficacy of 85.7%. 3 (4.3%) patients developed coronary spasm that reversed with intracoronary nitroglycerine. In their study they used only guide wires from Guidant (Guidant Corp, St. Paul; USA).