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Biomedical subjects

M M Mower

Publications and source records attributed to M M Mower.

13 recordsLinked to original sources
PubMed1992

The automatic implantable cardioverter-defibrillator. Long-term clinical experience and outcome at a hospital without an open-heart surgery program.

From November 1982 through April 1989, 111 patients with refractory sustained ventricular tachycardia/fibrillation had the automatic cardioverter-defibrillator implanted at our institution, the first community hospital involved in implantation of such a device. We have reviewed our long-term clinical experience to assess the feasibility, learning curve, and efficacy of device implantation in a facility with cardiac electrophysiology expertise but without open-heart surgery facilities. All patients were considered inoperable or at high risk for other concomitant surgery. Eighty-six patients (77%) underwent uneventful implantation. Nine patients (8%) died prior to hospital discharge. Operative mortality declined from 10.9% to 5.4% during the first half (55 patients; November 1982 through September 1986) and second half (56 patients; October 1986 through April 1989) of the experience. Other postoperative complications occurred in 16 patients (14%), 12 of whom experienced complications during the first half of the experience. At 22 +/- 20 (mean +/- SD) months' follow-up, 78 (76%) of 102 patients discharged were alive, and 24 patients (24%) had died. Fifty patients (49%) had experienced at least one automatic cardioverter-defibrillator discharge associated with hypotensive symptoms. The actuarial incidence of sudden death at 1, 2, and 3 years was 1.2%, 5.5%, and 6.2%, respectively. We concluded that the automatic implantable cardioverter-defibrillator is an effective therapy for refractory ventricular tachycardia/fibrillation and that device implantation at community hospitals with an experienced cardiac electrophysiology team is both feasible and practical.

Adult↗
PubMed1992

Case report: myocardial ischemia: an overlooked substrate in syncope of aortic stenosis.

The cause of the syncope in aortic stenosis has been the subject of controversy partly because only a few patients have been monitored during their syncopal episodes. Among the mechanisms proposed are hypersensitive carotid sinus, complete A-V block, ventricular arrhythmias, and ischemic myocardial depression. It is now accepted that the syncope is caused by a vasodepressor response from stimulation of left ventricular baroceptors, resulting in reflex hypotension and bradycardia. This case report describes a patient who developed a syncopal episode during stress testing. Although the mechanism for the syncope is consistent with the vasodepressor response, ischemic changes were observed in the electrocardiogram before the development of syncope. Review of literature shows that, although different mechanisms for syncope have been described, all reported patients manifested myocardial ischemia before the development of their syncopal episodes even when the syncope was nonexertional and clearly caused by a vasodepressor response. The authors conclude that, independent of the mechanism proposed, myocardial ischemia is overlooked as an important substrate in which the syncopes are precipitated in aortic stenosis.

Aged↗
PubMed1992

Automatic implantable cardioverter defibrillator: surgical approaches for implantation.

Surgical approaches for implantation of the automatic cardioverter defibrillator are sternotomy, left thoracotomy, subxiphoid, and subcostal. Although any one of these may be combined with insertion of one or more of the electrodes transvenously, surgical entry into the chest is required for every noninvestigational defibrillator implantation operation. The approaches differ in exposure provided for selecting electrode sites and for handling untoward events, in amount and location of tissue that must be divided or dissected, and in average time required. The operation is an electrical one. Its purpose is to obtain reliable rhythm sensing so that defibrillation or cardioversion shocks will occur only when necessary, and to obtain low enough defibrillation thresholds for shocks of 30 joules or less to have a 10-joule defibrillation safety margin. Many of the patients have had previous cardiac operations. They usually have low or very low ejection fractions. Intraoperative electrophysiological testing with often multiple defibrillation episodes is required. The choice of approach varies with the state of the patient, the institutional experience, and the surgeon. This article describes technique, and the advantages and disadvantages of the four approaches as used by four surgeons in four different institutions.

Defibrillators, Implantable↗
PubMed1991

Effects of pacing rate and timing of defibrillation shock on the relation between the defibrillation threshold and the upper limit of vulnerability in open chest dogs.

To test the relation between the defibrillation threshold and the upper limit of vulnerability, the shock strength associated with 50% probability of successful defibrillation (DFT50) and that associated with 50% probability of reaching the upper limit of vulnerability (ULV50) were determined in 20 open chest dogs with use of the delayed up-down method, with pacing drive cycle lengths of 150 to 500 ms and either single 6-ms shocks (10 dogs) or 12-ms biphasic shocks (10 dogs) given at the mid-upslope, peak and mid-downslope of the T wave of electrocardiographic lead II. The shocks were given by means of a patch-patch configuration on the anterior and posterior surfaces of the heart, which was paced from a stimulating electrode attached to the left ventricular apex. Analysis of variance showed no statistically significant differences in ULV50 as determined with different pacing cycle lengths. For monophasic shocks, DFT50 (331 +/- 66 V or 5.8 +/- 2.7 J) was not significantly different from ULV50 determined at the mid-upslope of the T wave (318 +/- 64 V or 5 +/- 2 J). The correlation coefficients between the two values were 0.74 (p = 0.014) for voltage and 0.67 (p = 0.034) for energy. In contrast, DFT50 was significantly higher than ULV50 as determined at the peak of the T wave (219 +/- 43 V or 2.3 +/- 1 J) and mid-downslope of the T wave (200 +/- 38 V or 1.9 +/- 0.9 J). In three dogs, ventricular fibrillation could not be induced at the mid-downslope of the T wave with any baseline pacing (Si) cycle length.(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of Variance↗
PubMed1991

Clinical efficacy of low energy cardioversion in automatic implantable cardioverter defibrillator patients.

The inclusion of low energy cardioversion capability into modern implantable antiarrhythmic devices, although an appealing idea, is nevertheless unproven with regard to its potential benefits. Moreover, since occasional reports have surfaced suggesting that ineffective application of low energy shocks may prejudice subsequent arrhythmia reversion, we examined the effectiveness and risks of this feature in a large series of patients performed as part of a US Food and Drug Administration clinical trial performed under an investigational device exemption. A total of 813 induced monomorphic ventricular tachycardias were studied in 244 patients. We found that many of the arrhythmias could be reverted to sinus rhythm with small amounts of energy. Cardioversion energy was less than or equal to 6 joules (J) for 84 (53.2%) and less than or equal to 14 joules in 105 (66.4%) of the 158 patients tested at implant and subsequently remained unchanged through greater than 4 months follow up. The incidence of noncardioversion, acceleration or both occurred in 12.7%, 5.7%, and 13.1%, respectively on a per patient basis. On a per episode basis, nonconversion occurred in 51 (6.3%) and acceleration in 61 (7.5%) of the 813 inductions. There was no correlation between the occurrence of nonconversions and accelerations. The devices were allowed to recycle in the event the arrhythmia was not reverted. The subsequent shock was almost always effective, and in any event, no patient failed to be reverted by the second 30-J rescue shock. Over the entire follow-up period as long as 17 months, there were 17 deaths. Neither the incidence nor the mode of death was correlated with nonconversion or acceleration.(ABSTRACT TRUNCATED AT 250 WORDS)

Electric Countershock↗
PubMed1978

A chronically implanted system for automatic defibrillation in active conscious dogs. Experimental model for treatment of sudden death from ventricular fibrillation.

Ventricular defibrillation was acheived in active conscious dogs with a chronically implanted automatic system composed of a defibrillator and an alternating current fibrillator. The hermetically sealed defibrillator is encased in titanium, weighs 250 g and has a volume of 145 ml. The sensor continuously monitors ventricular electircal activity and recognizes fibrillation by the absence of isoelectric potential segments. Fibrillation is induced by placing a magnet over the implanted fibrillator. The resulting syncope closely resembles the clinical entity of sudden death, while the defibrillator automatically restores normal rhythm with a truncated exponential pulse of 30 J, 15 seconds after the onset of the arrhythmia. The operational status of the defibrillator can be tested in vitro and noninvasively in vivo with an external analyzer. This experimental model allows for the first time a long-term study of the automatic implantable defibrillator approach to prevent sudden death from ventricular fibrillation under a variety of physiopathologic conditions.

Animals↗
PubMed1978

Treatment of myocardial infarction in a community hospital coronary care unit. Experience with 1,246 patients.

The hospital mortality in 1,246 consecutive acute myocardial infarction patients treated in a large community hospital coronary care unit was 14.4%. Of the total, 52.3% showed no evidence of heart failure, 25.8% had mild to moderate failure, 9.9% had pulmonary edema, and 12% developed cardiogenic shock; the mortality in these groups was 2.2%, 7.4%, 8.9%, and 87.2%, respectively. The mortalitiy in the 1,097 patints who did not have cardiogenic shock was 4.5%. Only one patient died as a result of primary ventricular fibrillation (0.08%). The mortality of complete heart block in the absence of cardiogenic shock (8.3%) was not significantly different from that of comparable patients who did not have complete heart block (4.3%). These results are lower than those generally reported.

Acute Disease↗
PubMed1977

Terminal ECGs.

Explore the source record for details and available documents.

Arrhythmias, Cardiac↗
PubMedDate not supplied

Considerations in the development of the automatic implantable defibrillator.

A highly reliable ventricular fibrillation detector and a satisfactory electrode system for delivering defibrillating pulses to the heart play a central role in the development of an automatic implantable defibrillator suitable for clinical use. Among the four implanted electrode designs tested, the combination of an electrode placed in the superior vena cava with a conformal electrode on the apex of the heart provided satisfactory defibrillation thresholds with ease of implantation. A new sensing method is also described for which an electrogram derived from the defibrillating electrodes is used as input. A form of a density function is developed for a filtered version of the input, ventricular fibrillation being characterized by a density curve lacking a large peak occurring at a level corresponding to the baseline of the filtered signal. These ideas are being incorporated into the design of a prototype implantable defibrillator delivering pulses of 24 joules.

Animals↗