Effects of coronary bypass surgery on the electrical activity of revascularized myocardium Immediate and early postoperative observations

Four-chamber pacing in patients with poor ejection fraction but normal QRS durations undergoing open heart surgery

BACKGROUND

Poor ejection fraction (EF) comprises a critical risk factor in cardiac bypass surgery (CABG). It has been unclear, whether biventricular or four-chamber pacing confers benefit upon patients with intact atrioventricular and interventricular conduction especially following surgery.

METHODS

Twenty-one consecutive patients with an EF <or= 35% underwent hemodynamic evaluation (continuous pressures and thermodilution) 3, 6, and 18 hours post-CABG and biatrial (AA), biatrial-right ventricular (AAV), and biatrial-biventricular (AAVV) pacing were compared.

RESULTS

Patients (65 +/- 9 years) presented with an average EF of 29.5% (15-35%). 514 measurements of cardiac index (CI) were taken. Nineteen patients (91%) showed highly significant increases in CI with AAVV as compared to AA pacing (P < 0,001) at all times post surgery. The increase in CI with pacing mode varied from 6% to 25% and decreased with time following surgery. No consistent difference in CI was seen between four-chamber (AAVV) and biventricular pacing (AVV). The QRS-widths prior to surgery never exceeded 120 ms; postoperatively QRS-complexes widened in all patients on average by 15.9 ms +/-6 and returned to starting values by 48 hours.

CONCLUSIONS

Biventricular pacing improves CI in patients with poor EF following cardiac surgery in the absence of preoperative atrioventricular- or interventricular conduction block. This benefit decreases with time after surgery as the QRS width returns to preoperative values. Four-chamber pacing did not confer additional benefit as compared to biventricular pacing in this series. Biventricular pacing should be considered as an adjunct in patients with critically low EF undergoing cardiac surgery.

Influence of valve prosthesis type on the recovery of ventricular dysfunction and subendocardial ischaemia following valve replacement for aortic stenosis

BACKGROUND

Long-standing aortic stenosis (AS) causes significant progressive left ventricular (LV) dysfunction and may result in subendocardial ischaemia. Following aortic valve surgery, LV function may improve and this may be accompanied by reversal of ischaemia. There is debate about the differential effects of valve substitutes.

METHODS

We studied 33 patients with significant AS and impaired LV systolic function. Patients underwent trans-thoracic Doppler echocardiography and 12-lead electrocardiography pre-operatively, prior to discharge from hospital and at 2.5 (range 1.5-3) years follow-up.

RESULTS

Twenty patients received a stentless valve and 13 a stented valve. No patient had significant aortic regurgitation, other valvular disease or coronary artery disease. LV fractional shortening (FS) increased from 19+/-6% to 26+/-7% post-operatively and to 33+/-12% at follow-up in the stentless group (p<0.001). In the stented group, no significant change was seen in the post-operative FS, although it improved at follow-up and at this point did not differ from the stentless group. LV mass fell from 338+/-72 to 265+/-64 g post-operatively and to 170+/-77 g at follow-up (p<0.001) in the stentless group, whereas in the stented group a significant fall was seen only at follow-up (329+/-51 g pre-operatively, 304+/-68 g post-operatively, 166+/-28 g at follow-up, p=0.01). LV free wall excursion increased from 0.8+/-0.3 to 1.1+/-0.4 cm (p=0.05) and to 1.4+/-0.3 cm (p=0.02 compared with pre-operative values) in the stentless group. In the stented group, values were 1.0+/-0.4, 1.0+/-0.3 and 1.3+/-0.2 cm (p=0.05 compared with pre-operative) at the three time points, respectively. QRS duration fell from 113+/-36 ms pre-operatively to 99+/-12 ms at follow-up in the stentless group and from 117+/-28 to 99+/-19 ms in the stented group, p=0.01 for both comparisons. QT interval fell from 385+/-54 ms pre-operatively to 366+/-39 ms at follow-up (p=0.04) in the stentless group with no significant change in the stented group (387+/-52 and 375+/-33 ms, p=0.24). There was reversal of LV strain pattern in 11 (55%) of the stentless group and 6 (46%) of the stented group and normalisation of the inverted U wave in two thirds of patients.

CONCLUSION

In patients with AS and severe LV dysfunction, there is a more rapid improvement in LV function following aortic valve replacement with a stentless prosthesis. Improvements in those receiving stented valves appear delayed, although there were no differences between the groups in LV function or mass at follow-up. Normalisation of LV free wall systolic behaviour, narrowing of the QRS complex and a reduction in the QT interval suggest that AS is associated with subendocardial ischaemia that reverses following valve replacement.

Effects of lidocaine on regional intraventricular conduction in patients with coronary artery disease

Studies of isolated heart muscle and canine models of myocardial ischemia have demonstrated that lidocaine slows conduction in abnormal but not in normal tissues. To determine lidocaine's effects on intraventricular conduction (IVENT) in patients with coronary artery disease (CAD), we studied this agent in seven patients following left anterior descending coronary artery (LAD) bypass surgery. Epicardial electrodes were placed on the right atrium, left ventricle (LV) in the distribution of the LAD, and on the right ventricle (RV). On postoperative day 7, lidocaine was administered as 100 mg bolus followed by 4 mg/minute infusion for 2 hours. At constant atrially paced rate, bipolar electrograms were recorded from the LV and RV for the 2 hours of infusion and for 2 hours after discontinuation of infusion. Conduction intervals were measured from the earliest onset of QRS in three simultaneously recorded surface ECG leads to the major deflection of the electrogram from each ventricle. At peak effect, with mean lidocaine level of 2.7 +/- 0.5 mg/ml, lidocaine slowed LV conduction by a mean of 6 +/- 1 msec (14 +/- 2%) (p less than 0.001) and in the RV by 1 +/- 0.3 msec (4 +/- 1%) (p less than 0.01), QRS duration changed 1 +/- 1 msec) 1 +/- 1%) (NS). The values returned to baseline within 2 hours after discontinuation of lidocaine infusion. The difference in lidocaine's effect between the diseased LV and the normal RV was significant (p less than 0.001).

Electrophysiologic effects of acute myocardial infarction in man

Six patients undergoing surgery for ischemic heart disease were studied by means of epicardial electrodes affixed to the left ventricle. One patient who underwent triple coronary arterial bypass and plication of a left ventricular aneurysm had evidence of an acute myocardial infarction 1 day after operation. A surface electrocardiogram and a bipolar electrogram from the left ventricle were recorded before and after development of the infarction. The bipolar electrogram showed a marked loss of voltage and delay of conduction that were not present in the patients who underwent surgery but did not sustain an acute myocardial infarction. Thus, any acute myocardial infarction in conscious persons appears to be associated with areas of delayed epicardial action and diminution of local voltage. This observation suggests that the electrophysiologic mechanisms of infarction in man are similar to those of infarction in the dog.