Farouk A. Pirzada

Experimental myocardial infarction. XIII. Sequential changes in left ventricular pressure-length relationships in the acute phase.

Diastolic pressure-length relationships of an ischemic region of the canine left ventricle were measured over a six-hour period following left anterior descending coronary artery ligation, and their evolution was compared with the extent of systolic aneurysmal bulging. Normalized ischemic segment length excursion, which after coronary artery ligation may be taken as a measure of systolic aneurysmal bulging, increased during the first hour after ligation but thereafter declined toward control values. Concurrently, reciprocal changes were demonstrated in the slope of the end-diastolic pressure-length curves obtained during transient pressure loading of the left ventricle. These data show that the magnitude of acute systolic aneurysmal bulging followed experimental coronary artery ligation is determined not only by loss of contractile function, but also by changes in passive pressure-length relationships of the myocardium. Moreover, the results indicate that development of akinesis in experimental ischemia, heretofore demonstrated only in the chronic phase of infarction, may begin within hours of the onset of myocardial ischemia.

Front-line management of pulmonary tuberculosis: An analysis of tuberculosis and treatment practices in urban Sindh, Pakistan

SETTING Karachi and Hyderabad, Pakistan. OBJECTIVE To describe the level and quality of tuberculosis (TB) case management by non-TB control program (TCP) physicians in urban Sindh, Pakistan. DESIGN We interviewed 152 adults with pulmonary TB confirmed by Karachis TB control program regarding the initial management of their TB symptoms before entering the TCP. We also surveyed 65 general practitioners (GPs) attending continuing education seminars with a multiple choice test to assess their management of suspected pulmonary TB. We compared both results to guidelines from the World Health Organization (WHO) and the International Union Against Tuberculosis and Lung Disease (IUATLD). RESULTS Eighty percent (122/152) of patients first sought GPs. Only 14% of GPs performed any sputum test. At most, 17 (40%) of the 42 patients recalling their GPs treatment, received the recommended 4-drug regimen. However, 68% (45/65) of surveyed GPs chose correct treatment from a multiple choice format. But their initial laboratory investigations, follow-up, and treatment cessation criteria (9%, 9-31%, and 11% correct, respectively) demonstrated under-utilization of sputum tests and over-reliance on unhelpful tests. CONCLUSIONS GPs first saw most of these TCP patients, but their weak management likely hinders TB control. A partnership between TB control programs and GPs could improve case management and hasten TB control.

Traumatic ventricular septal defect. Sequential hemodynamic observations.

THE treatment of traumatic ventricular septal defects produced by penetrating injuries of the heart is a subject of controversy. Some advocate surgical closure of all such defects whereas others su...

Initial Experience with 1.5-mm2 High Impedance, Steroid-luting Pacing Electrodes

In this human study, 21 atrial and 62 ventricular 1.5‐mm2 unipolar steroid‐eluting pacing electrodes were implanted in 64 patients. Pacing thresholds, lead impedance, and sensing measurements were measured via pacemaker telemetry within 24 hours postimplont, and at 1, 2, 3, 4, 6, 12. 24. and 52 weeks. Acute pacing impedances measured via a pacing systems analyzer were 1,039 ± 292 (atrial) and 1,268 ± 313 ohms (ventricular). A10%‐15% decline in the mean telemetered atrial and ventricular pacing impedances was observed at 1 week, but thereafter remained stable. Acute pacing thresholds at 0.5 ms were 0.5 ± 0.3 V (atrial) and 0.4 ± 0.1 V (ventricular). Filtered P and B wave amplitudes were 3.7 ± 2.3 mV and 14.9 ± 5.9 mV, respectively. In 21 patients, no complications related to the atrial electrode were observed. Of 62 patients with ventricular electrodes, 4 patients (6%) experienced complications and required surgical intervention. On these, causative factors included micro‐dislodgment (l patient), and perforation (l patient). Sudden unexplained exit block occurred late (> 6 weeks) in two patients. In the remainder of patients, pacing thresholds and sensed electrogram amplitudes remained stable throughout the 52‐week follow‐up period. Conclusions: The‐ present study validates that smaller surface (i.e., 1.5 mm2) steroid‐ eluting electrode designs offer excellent pacing and sensing performance with significantly higher pacing impedances. Although questions remain as to the cause of late exit block in two patients in this series, this relatively small surface electrode design offers promise toward achieving greater pacing efficiency and a theoretical 13%‐16% (minimum) enhancement in permanent pacemaker longevity.

Clinical Experience with Steroid‐Eluting Unipolar Electrodes

In continuing search of low chronic threshold leads, a new concept of electrode design which is capable of delivering corticosteroids at the myocardial tissue interface has been made available by Medtronic. Twenty‐three patients, 17 females and 6 males, were either implanted with 4003 (n = 21) or 5023 (n ‐ 2) steroid‐eluting electrodes in the ventricular chamber. Pacing modes utilized were WIM (n = 13) or DDD (n = 10). Pulse generators used were Medtronic (7005. 8317, 8329) Pacesetter (285) and Intermedics (283). Thresholds at the time of implantation at 0.50 msec pulse width were 0.40 ± 0.02 volts at 0.66 ± 0.05 milliamps. Resistance and R wave measured were 565.43 ± 22.07 ohms and 9.24 ± 1.06 mv, respectively. Chronic thresholds were checked on routine follow‐up visits by either decreasing pulse width and for pulse amplitude. Data is being reported between 1 and 88 (23.22 ± 4.35) weeks. Pulse width threshold at 2.5 volts were 0.10 msec (n = n) and 0.05 msec or lower (n = 12). At 5.0 volts no loss of capture was seen at 0.05 msec (n = 22) except in one patient at 0.10 msec. Pulse width thresholds in the first 24 weeks were lower than 0.20 msec at 2.5 volts (n = 15) and less than 0.70 msec, at 0.8 volts (n = 6). No loss of sensing was seen by electrocardiographic analysis at the time of threshold checks with the pulse generator at standard setting of the R wave. Thus, in this initial report, the steroid‐eluting electrodes have demonstrated very low thresholds both in the early and chronic follow‐up phase. Demonstration of consistently low thresholds, avoiding initial peaking, will permit routine low output setting without compromising safety and thus prolong the life of the pulse generators.

The “Pacemaker Syndrome” in a Properly Functioning Physiologic Pacing System

Manufacturers are introducing a multiplicity of dual-chamber pacing systems wbich, while markedly improving the patients quality of life, have not yet eliminated all problems associated with cardiac pacing. The complexity and limitations of these systems combined with the lack of familiarity of many physicians with them raises additional concerns as to pacing system malfunction. Such a case was recently encountered. AP, a 29-year-old gentleman, was seen in consultation for nocturnal episodes of dizziness and pre-syncope. His cardiac history dated back three years when he developed persistent complete heart block of unknown etiology and presented with fatigue, effort intolerance and presyncope. A permanent ventricular demand (V-VI, 0) pacemaker was inserted after which his effort intolerance, although improved, continued to be a prominent factor while his weakness and dizzy spells persisted. Approximately one year prior to his present evaluation, he was referred to another center and the pacing system was changed. He was then able to participate in all activities without experiencing any limitations; at night, however, he often awoke from sleep experiencing brief episodes of pre-syncope and dizziness similar to those during the complete heart block and his first pacing system. These episodes were often accompanied by an overwhelming sense of doom leading to his seeking care at our Emergency Room. His cardiac examination was normal; the pulse generator was located in the left pectoral fossa. The rhythm strips obtained at the time of his presentation are shown in Figure 1.

Pacemaker Oversensing: A Possible Example of Concealed Ventricular Extrasystoles

Figure 1 depicts two rhythm strips obtained shortly after implantation of a Biotronikf active fixation electrode {IVE-185) in an 83-year-old man in whom the establishment of effective stable pacing had proven to be a major clinical challenge. He had presented with recurrent syncopal spells secondary to intermittent high grade atrioventricular block manifested by a slow ventricular response to chronic atrial fibrillation. His underlying heart disease was a cardiomyopathy with massive ventricular dilitation and biventricular failure. It was assumed he had markedly flattened trabeculae in the dilated right ventricle due to the inability to successfully place the standard passive fixation electrode on three prior attempts. He was deemed too ill to tolerate even a limited thoracotomy for placement of epicardial electrodes and a fourth procedure was undertaken using the Irnich electrode. The biotronik bayonet connector was subsequently cut off and a standard terminal pin spliced on to fit the patients pulse generator which was a nonprogrammable model set at a pacing interval of 840 ms. Shortly thereafter the

Five‐Year Performance of the Medtronic 6971 Polyurethane Endocardial Electrode

There is a considerable debate over the long‐term performance of polyurethane electrodes. Observation to date has demonstrated surface cracking and some clinical failures in patients. Since 3978 we have implanted about 82 6971 Unipolar Medtronic electrodes in the ventricle. In 33 patients, lead integrity was assessed by chronic thresholds determined by decreasing pulse width and pulse amplitude. Sensing functions were assessed by electrocardiographic rhythm analysis. At a follow‐up between 7 and 67 months, chronic thresholds at 2.50 volts were 0.08 ± 0.04 milliseconds in 26 patients with Medtronic Pulse generators (Models 8423. 5985, and 7000). In two patients with similar units, no loss of capture was seen even at 0.05 milliseconds. Three patients, one with Cordis Unit (233F) showed loss of capture at 0.20 milliseconds at 2.00 MA, the other with a Pacesetter unit (255–6) showed loss of capture at 0.20 milliseconds, at 2.50 volts. One patient with Intermedies unit (283) lost capture at 0.07 milliseconds at 2.70 volts. Insulation breaks seen in two patients were demonstrated by pectoral stimulation and pacemaker oversensing. In addition, 24‐hour long‐term electrocardiographic monitoring was performed in 22 patients between 23 to 70 months. Appropriate pacemaker function was seen except in one patient who demonstrated oversensing. Interruption in insulation was demonstrated at the ligature site at exploration. Thus, in this series of patients who were paced in the ventricle by the 6971 Medtronic electrode, only two patients have demonstrated insulation failure. The incidence of insulation break in this polyurethane unipolar electrode is uncommon and occurs at further stress points.