Continuous right ventricular volume assessment by catheter measurement of impedance for antitachycardia system control

Current implantable defibrillators are unable to differentiate between hemodynamically stable and unstable arrhythmias. This may result in unnecessary high energy shocks during arrhythmias that are better managed with other interventions. This study assessed the efficacy of the impedance catheter in sensing relative volumetric changes in the right ventricle as a measure of the hemodynamic status during an arrhythmia. During electrophysiological testing, 37 arrhythmias were induced in 12 patients aged 28-74 years. Rhythms recorded were: (A) hemodynamically stable tachyarrhythmias (supraventricular tachycardia and sustained monomorphic ventricular tachycardia)--21 episodes; and (B) hemodynamically unstable ventricular arrhythmias causing syncope (hypotensive ventricular tachycardia and ventricular fibrillation)--16 episodes. During unstable arrhythmias, stroke impedance (32 +/- 17%), arterial systolic pressure (40 +/- 11%), and right ventricular pulse pressure (15 +/- 20%), expressed as percentages of corresponding sinus rhythm values, were significantly lower than in stable arrhythmias (84 +/- 26%, 72 +/- 8%, and 111 +/- 37%, respectively); P less than 0.001. There was a good correlation between stroke impedance and mean arterial pressure during arrhythmia (r = 0.84). Impedance sensing is a practical method for distinguishing between hemodynamically stable and unstable arrhythmias. Implementation of hemodynamic sensing into the algorithm of future antitachycardia systems may improve the management of arrhythmias by adding options for selective pace termination or cardioversion.

Preexcitation syndromes: surgical ablation therapy. The Cleveland Clinic experience

Thirty-four patients with preexcitation syndrome had surgical ablation of the accessory atrioventricular connection. All presented with sustained symptomatic arrhythmias, which had resulted in syncope in seven patients and aborted sudden cardiac death in four. Arrhythmias induced at electrophysiologic evaluation included orthodromic reciprocating tachycardia in 32 patients, antidromic reciprocating tachycardia in five patients, and atrial fibrillation in 29 patients. A single accessory atrioventricular connection was located in 32 patients and two patients had multiple accessory connections. The accessory connection was located with intraoperative mapping in all patients and the pathway was successfully ablated in 32. Eleven patients underwent a transmural approach and 23 patients underwent an epicardial dissection. Cryotherapy was used in 22 patients. After a mean follow-up of 32 months, 28 patients were free from all arrhythmias without drug therapy. Six patients continued to have symptomatic arrhythmias but only one case was suspected to be secondary to unsuccessful ablation of the accessory connection. One patient with heart block induced at the surgical procedure is dependent upon a pacemaker.

Analysis of amikacin-resistant Pseudomonas aeruginosa developing in patients receiving amikacin

During a 36-month period, 28 patients treated for infections due to amikacin-susceptible Pseudomonas aeruginosa subsequently developed infections or colonization with amikacin-resistant P aeruginosa at the same site. Eleven amikacin-susceptible/-resistant pairs of isolates were analyzed for aminoglycoside-inactivating enzymes, plasmid profiles, cellular proteins, outer membrane proteins (OMPs), lipopolysaccharide (LPS) profiles, and amikacin uptake. While clearly distinct from isolates of other patients, sensitive and resistant isolates from the same patients were indistinguishable in plasmid profile, LPS profiles, and OMPs. These results suggest that the resistant P aeruginosa isolates were derived from the sensitive isolates. None of the resistant isolates produced enzymes known to inactivate amikacin. In nine of 11 resistant isolates tested, transport of amikacin into P aeruginosa was reduced. A major mechanism of in vivo development of amikacin resistance in P aeruginosa is alteration in permeability to amikacin, but the aquisition of plasmids or changes in OMPs or LPS profile may not account for this phenomenon.

Effects of extracorporeal shock wave lithotripsy on cardiac pacemakers and its safety in patients with implanted cardiac pacemakers

Effects of extracorporeal shock wave lithotripsy (ESWL) were studied on 15 pacemakers (standard single chamber n = 5, dual chamber n = 6, rate responsive single chamber [Activitrax] n = 4). In-vitro testing involved suspending the pacemakers in a bath of degassified, deionized water firmly taped to a platform at the point of maximal pressure, i.e., second focal point (F2), where they received pressure shocks (means = 1300) from the HM3 Dornier lithotriptor. The pacemakers, programmed to their most sensitive setting, were continuously pacing at nominal outputs (atrial and ventricular pacing in the DDD mode). All units were assessed by a pacing system analyzer before and after the study, then underwent destructive analysis. During standard single chamber pacing (VVI) the pacing stimulus triggered ESWL. For dual chamber devices, ESWL was triggered by the atrial paced event which induced inhibition of the ventricular output in two pacemaker. This was eliminated by reprogramming to a less sensitive setting. The pacemaker can, hermetic seal and internal circuitry were undamaged in all units. Two rate responsive single chamber pacemakers had their activity sensing piezoelectric elements shattered when placed at F2. Two other units placed 5 cm from F2 were stimulated to their maximum upper programmed pacing rate with ESWL therapy, but were otherwise unaffected. Subsequent to this study, six patients with pacemakers programmed to the VVI (five), DDD (one) modes implanted in the thorax underwent successful ESWL without pacemaker or arrhythmic event.

CONCLUSIONS

(A) It is generally safe for patients implanted with standard single chamber devices in a ventricular application to undergo ESWL without modifying the pacing/sensing parameters. (B) Patients implanted with dual chamber devices who pace in the atrium should be reprogrammed to the VVI mode during ESWL. (C) Patients with piezoelectric activity sensing rate responsive single chamber pacemakers should have this feature programmed off during ESWL and, if implanted in the abdomen, probably should not undergo ESWL.

Atrial natriuretic peptide production in association with nonimmune fetal hydrops

The presence and elevation of atrial natriuretic peptide in fetuses has not previously been demonstrated. This study of right atrial pacing in fetal lambs demonstrated a threefold to fourfold increase in atrial natriuretic peptide during the production of fetal hydrops. Its rate of return to a normal level paralleled the clearance of fetal hydrops. Its possible role in fetal cardiovascular hemodynamics is discussed.

Ultrasound evaluation of tachycardia-induced hydrops in the fetal lamb

Nonimmune hydrops was induced in six fetal lambs at 120 days' gestation by right atrial pacing at 300 beats/min. Biochemical, hemodynamic, and Doppler parameters were observed and monitored by real-time ultrasound during the creation (18 to 42 hours) and resolution of hydrops. The significant changes seen were hypoproteinemia (34.3 to 29.0 mg/100 ml), venous hypertension (24.6 to 31.3 mm Hg), decreases in thoracic aorta flow, and decreases in systolic/diastolic ratios in the aorta and umbilical artery. These changes were reversed with the discontinuation of pacing and the resolution of fetal hydrops.

Electrode configurations for a respiratory impedance measurement suitable for rate responsive pacing

A rate responsive cardiac pacemaker will benefit the patient only if the input parameter is a reliable indicator of exercise. Part of the reliability is dependent upon selection of the best physiological parameter and part is dependent upon the measurement technique. Twenty-six patients have been studied in order to ascertain the best measurement configuration for an intravascular impedance respiratory monitor. Four electrode configurations have been examined at rest and during exercise. The results have been compared using measures of sensitivity and specificity. The ideal configuration requires that a current field be established between the right ventricular blood and the pacemaker case. And, that voltage sensing be done between an electrode in the SVC and the pacemaker case.

Fetal oxygen consumption, umbilical circulation and electrocortical activity transitions in fetal lambs

Chronically instrumented fetal lambs were employed to test the hypothesis that the high voltage electrocortical activity phase is a state of low fetal oxygen consumption compared with the low voltage electrocortical activity phase. Measurements of umbilical flow (electromagnetic flowmeter) together with oxygen saturations and haemoglobin concentration of umbilical venous and arterial blood were used to calculate oxygen consumption. Significant depression of umbilical flow occurred at the transition from low voltage electrocortical activity to high voltage electrocortical activity; the maximum change averaged 14% 2 min after the onset of the high voltage phase. Significant depressions of oxygen saturation in umbilical venous and arterial blood were found within 5 min of the onset of high voltage electrocortical activity, averaging 2.2% and 5.2% respectively. No depression of oxygen consumption was found during these transient changes in early high voltage electrocortical activity, as the venous-arterial oxygen content difference widened significantly as a consequence of a greater fall in umbilical arterial oxygen content (0.7 ml/dl) than in umbilical venous oxygen content (0.3 ml/dl). Overall, we detected no significant depression of oxygen consumption in high voltage electrocortical activity. However a small but significant depression of oxygen consumption (6%) was found late in the high voltage electrocortical activity phase when the level of oxygen consumption in low voltage electrocortical activity was greater than 7 ml/min per kg. We conclude that the high voltage electrocortical activity in fetal lambs is not associated with a marked depression of oxygen consumption, despite significant transient depressions of umbilical flow and oxygen levels in umbilical venous and arterial blood.(ABSTRACT TRUNCATED AT 250 WORDS)

Death anxiety in the outpatient leukemic child

Awareness of the seriousness of their illness seems to persist with fatally ill children, even when they are not in the hospital. As did the fatally ill hospitalized children in previous studies so, too, the fatally ill outpatient children in the present study related significantly more stories that contained elements of preoccupation with threat to their body integrity and functioning than did the control group of children with non-fatal chronic illnesses. Not only did they express a greater general anxiety and greater anxiety in relating the stories, but, in contrast to their chronically ill counterparts, the leukemic children exhibited a lack of adaptability to the necessity of clinic visits, becoming increasingly more anxious about the clinic both as visits became more frequent and as their illness became of longer duration. The children continue to dwell on their illness, even when treated as outpatients.