Mickleborough Ll

Endocardial mapping of ventricular tachycardia in the intact human ventricle. III. Evidence of multiuse reentry with spontaneous and induced block in portions of reentrant path complex

OBJECTIVES This study was conducted to characterize the functional nature of the reentrant tract responsible for ventricular tachycardia due to ischemic heart disease. BACKGROUND A zone of slow conduction forming the return path is though to form a critical component of the reentrant mechanism in ventricular tachycardia. Despite its importance, detailed knowledge of the return path is rare in clinical studies. METHODS Multielectrode arrays were used intraoperatively to obtain unipolar and high gain bipolar recordings of left ventricular endocardium in patients undergoing map-directed surgical ablation of ventricular tachycardia. A total of 224 local electrograms were analyzed for each tachycardia. RESULTS Of 10 consecutive patients undergoing intraoperative cardiac mapping, detailed recording of the return tracts of eight ventricular tachycardias were obtained in three patients. The recordings demonstrated that return tracts can be complex and extensive, with multiple paths of entry and exit. Potential and actual alternate paths were observed. Spontaneous and induced block occurred within portions of the complex. Intermittent block in one of two paths of entry resulted in intermittent cycle length changes of the tachycardia without a change in configuration. Block in one exit path resulted in a shift to alternative exit paths, with dramatic changes in ventricular activation and tachycardia configuration. Termination of the tachycardia could result from block close to the entrant or exit portion of the return tract. Different tachycardias were seen to share common portions of a return tract. CONCLUSIONS These observations enlarge and extend our knowledge of the functional repertoire of complex reentrant tracts that occur in infarct-related ventricular tachycardia. The use of common portions of a reentrant tract by several tachycardias is confirmed. Utilization of alternate pathways can account for changes in configuration and cycle length. Spontaneous and induced block can occur at points of entry and exit in a reentrant tract and may identify optimal targets for ablation attempts. Further advances will require greater emphasis on diastolic activation mapping.

Mechanisms of spontaneous shift of surface electrocardiographic configuration during ventricular tachycardia.

OBJECTIVES The aim of this study was to examine, with multichannel direct cardiac mapping techniques, the mechanisms of spontaneous shift of the QRS configuration in the surface electrocardiogram during episodes of ventricular tachycardia. BACKGROUND Ventricular tachycardias demonstrating a spontaneous shift in their surface electrocardiographic (ECG) features are occasionally encountered. It is not known whether such changes in configuration are primarily due to a significant change in the tachycardia site of origin or represent alterations in patterns of endocardial and epicardial activation. Knowledge of these features would be helpful, particularly when ablative therapy is considered for the arrhythmias. METHODS During map-directed cardiac surgery, episodes of ventricular tachycardia were mapped from 224 epicardial and endocardial sites. Episodes of pleomorphic tachycardia were identified and isochronal maps of endocardial and epicardial activation were constructed from representative beats before and after the change in configuration. RESULTS From 52 consecutive patients who underwent detailed intraoperative mapping, 9 patients with pleomorphic ventricular tachycardia were identified in whom 14 episodes of spontaneous shift occurred. An analysis of the epicardial activation patterns revealed that the sites of earliest epicardial breakthrough showed significant alteration at the time of QRS shift in all occurrences. In 10 of these shift episodes, however, the sites of tachycardia origin, located on the endocardial surface, remained closely adjacent (< 2 cm apart). Although these sites of origin remained relatively constant, significant alterations in the patterns of endocardial activation were seen in most episodes. These included changes in the direction of propagation of the wave front of activation and shifts between monoregional and figure eight patterns of activation. CONCLUSIONS In most episodes of pleomorphic ventricular tachycardia, the arrhythmia site of origin remains relatively constant. However, patterns of epicardial activation do undergo significant change and appear to be the major determinant of the QRS configuration on the surface ECG.

Ventricular reconstruction for ischemic cardiomyopathy.

Left ventricular surgical reconstruction has been advocated for patients with coronary artery disease, prior myocardial infarction, and poor left ventricular function. The objective of the approach is to resect or exclude all akinetic or dyskinetic nonfunctioning portions of the ventricular cavity and to restore the left ventricle size and shape toward normal as much as possible. We review the pathophysiology of ischemic cardiomyopathy and suggest guidelines for preoperative assessment and patient selection for ventricular reconstruction. Because of the prevalence and prognostic significance of ventricular arrhythmias in this patient population we include in our operative approach a visually directed ablation procedure in those with significant septal scarring. We describe our operative technique and review results achieved with this approach. The procedure results in a significant decrease in ventricular volume, increase in ejection fraction and improvement in apical geometry. We conclude that in selected patients with ischemic cardiomyopathy, left ventricular reconstruction can be accomplished with low operative mortality and results in significant improvement in left ventricular function. During follow up symptom class is decreased in most patients and overall survival at 5 years is 84% and freedom from sudden death is 96%. Ventricular reconstruction should be considered in all patients with coronary artery disease and akinetic or dyskinetic scar.

Rewarming hypovolemia after aortocoronary bypass surgery

Coronary bypass performed with moderate systemic hypothermia (25°C) and cold-potassium cardioplegia was associated with a fall and subsequent rise in core (pulmonary arterial) temperature. Serial hemodynamic measurements during rewarming and recovery revealed a decrease in cardiac index (CI) without a decrease in the left atrial pressure (LAP) of 17 patients recovering from uneventful coronary bypass surgery. Nuclear ventriculograms performed during rewarming demonstrated a decrease in left ventricular end-diastolic volume index (EDVI, calculated from the thermodilution stroke index divided by the nuclear ejection fraction) without a change in LAP. Volume loading during both mild hypothermia (35 ± 5[SD]°C) and normothermia revealed that myocardial performance (the relation between CI and EDVI) was unchanged, but diastolic compliance (the relation between LAP and EDVI) decreased with rewarming. LAP was a poor indicator of left ventricular preload (EDVI) during rewarming, and volume loading was required to maintain preload and prevent hypoperfusion.

Complement consumption during cardiopulmonary bypass: bubble versus membrane oxygenators

The purpose of this study was to compare levels of C3 and C4 during cardiopulmonary bypass, using bubble and membrane oxygenators. In vitro studies were performed using human blood in a simple circuit involving an oxygenator, roller pump and connector tubing. In vivo studies were carried out in two separate institutions using a variety of bubble and membrane oxygenators. Samples were taken throughout the pump run (30-1 20 minutes). Complement levels were corrected for haemodilution. All oxygenators tested caused a rapid decrease in C3 and C4 complement levels on institution of bypass. The magnitude and timing of these decreases were similar in the membrane and bubble groups. Thereafter, complement levels were stable throughout the pump run. These data do not suggest that there is any difference in complement activation during relatively short pump runs using bubble and membrane oxygenators.