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J J Allan

Publications and source records attributed to J J Allan.

10 recordsLinked to original sources
PubMed2000

Interactions between CPR and defibrillation waveforms: effect on resumption of a perfusing rhythm after defibrillation.

BACKGROUND: Cardiopulmonary resuscitation (CPR) improves survival from cardiac arrest. The interactions between CPR and the new biphasic (BiP) defibrillation waveforms have not been defined. Our purpose was to compare the effect of CPR versus no CPR during BiP and damped sinusoidal (DS) shocks on the termination of ventricular fibrillation (VF) and the resumption of a perfusing rhythm. METHODS: We studied 20 pigs; VF was induced electrically and allowed to persist for 6 min. During VF episodes each pig received (in random order): (a) 6 min of full CPR (continuous ventilation and closed chest mechanical compression (Thumper, Michigan Instruments)) followed by DS defibrillation at 100 J; (b) no CPR, DS defibrillation; (c) 6 min of full CPR and BiP defibrillation at 100 J; and (d) no CPR, BiP defibrillation. RESULTS: BiP shocks with CPR terminated VF in 83% of attempts versus 45% without CPR (15/18 and 5/11 respectively, P<0.05). DS shocks with CPR were successful in terminating VF in 53% of attempts; DS shocks without CPR were successful in 44% (8/15 and 7/16, respectively, P=NS). No animal achieved a perfusing rhythm after shocks of either waveform if CPR did not precede the shocks during the 6-min VF period, whereas if CPR was administered during VF 46% (11/24) of the combined BiP/DS shocks restored a perfusing rhythm (P<0.01). CONCLUSION: In this experimental long duration VF model, CPR was essential for a perfusing rhythm after termination of VF by shocks with either waveform. CPR facilitated the termination of VF and resumption of a perfusing rhythm after biphasic waveform defibrillation but not after damped sinusoidal waveform defibrillation.

Animals↗
PubMed1998

Encircling overlapping multipulse shock waveforms for transthoracic defibrillation.

OBJECTIVES: This study was performed to determine the efficacy of new encircling overlapping multipulse, multipathway waveforms for transthoracic defibrillation. BACKGROUND: Alternative waveforms for transthoracic defibrillation may improve shock success. METHODS: First, we determined the shock success achieved by three different waveforms at varying energies (18-150 J) in 21 mongrel dogs after short-duration ventricular fibrillation. The waveforms tested included the traditional damped sinusoidal waveform, a single pathway biphasic waveform, and a new encircling overlapping multipulse waveform delivered from six electrode pads oriented circumferentially. Second, in 11 swine we compared the efficacy of encircling overlapping multipulse shocks given from six electrode pads and three capacitors versus encircling overlapping shocks given from a device utilizing three electrodes and one capacitor. RESULTS: In the first experiment, the encircling overlapping waveform performed significantly better than biphasic and damped sinusoidal waveforms at lower energies. The shock success rate of the overlapping waveform (six pads) ranged from 67+/-4% (at 18-49 J energy) to 99+/-3% at > or = 150 J; at comparable energies biphasic waveform shock success ranged from 26+/-5% (p < 0.01 vs. encircling overlapping waveforms) to 99+/-5% (p = NS). Damped sinusoidal waveform shock success ranged from 4+/-1% (p < 0.01 vs. encircling overlapping waveform) to 73+/-9% (p = NS). In the second experiment the three electrode pads, one capacitor encircling waveform achieved shock success rates comparable with the six-pad, three-capacitor waveform; at 18-49 J, success rates were 45+/-15% versus 57+/-12%, respectively (p = NS). At 100 J, success rates for both were 100%. CONCLUSIONS: We conclude that encircling overlapping multipulse multipathway waveforms facilitate transthoracic defibrillation at low energies. These waveforms can be generated from a device that requires only three electrodes and one capacitor.

Animals↗
PubMed1998

Echocardiographic quantitation of mitral regurgitation: a new Doppler technique.

Our objective is to develop a new transthoracic Doppler echocardiographic technique to determine mitral regurgitant fraction. The standard color Doppler method for assessment of mitral regurgitation is semiquantitative and dependent on instrument gain. By using the mitral and aortic valve continuous wave Doppler velocities, one can determine regurgitant fraction. This technique takes into account the flow dependence of the mitral valve area. Two constants, A and B, which represent the flow dependence of the mitral valve area and the ratio of the mitral valve area to aortic valve area at zero flow, respectively, were determined by regression in 36 patients without valvular disease (r = .89). Thirty patients with isolated mitral regurgitation were then studied. The mitral regurgitant fraction was calculated from the following: Regurgitant fraction = 1 - TVIav/Bf[Vmv/(1 - AVmv)]dt, where TVIav is the time velocity integral across the aortic valve, Vmv is the continuous wave velocity across the mitral valve, and A and B are constants. The regurgitant fraction was then compared with color Doppler assessment of mitral regurgitation assessed by independent observers. In patients with mitral regurgitation, there was a strong correlation between standard visual assessment and our new Doppler method (Kendall's tau b rank correlation = 0.65; p < .001). The new Doppler method was able to correctly categorize 90% of patients with mild mitral regurgitation and 88% of patients with severe mitral regurgitation; however, there was poorer agreement with the color Doppler assessment of moderate mitral regurgitation. Mitral regurgitant fraction can be calculated with our new Doppler method. This method is quantitative, objective, nongain dependent, and separates mild from severe mitral regurgitation well.

Aortic Valve↗
PubMed1998

Intracardiac echocardiographic imaging of the left ventricle from the right ventricle: quantitative experimental evaluation.

PURPOSE: Our purpose was to demonstrate that intracardiac ultrasound imaging from a transducer placed in the right ventricle can be used to quantitatively image the left ventricle in a swine model. BACKGROUND: The left ventricles and right ventricles of dogs and human beings have been studied with intracardiac echocardiography. Usually intracardiac echocardiography has been performed with the ultrasound catheter in the chamber being studied because of limited depth of field. Thus left ventricular imaging required that the ultrasound catheter be placed intra-arterially and manipulated into the left ventricle. The availability of lower frequency ultrasound catheters may allow left ventricular imaging from the right ventricle--a more clinically attractive approach. METHODS: In 10 closed chest swine, a 10F, 10-MHz ultrasound catheter was placed into the right ventricle through an introducer sheath placed in the right internal jugular vein. Two-dimensional transthoracic echo images were obtained for comparison. Two protocols were used to image global left ventricular function and regional wall motion during pharmacologic challenge. In protocol 1 (n = 4) we evaluated global left ventricular performance in response to interventions: dobutamine, halothane (a myocardial depressant), nitroprusside, and volume loading. In protocol 2 (n = 6) we evaluated regional contraction abnormalities induced by coronary arterial balloon inflation and deflation (reperfusion) and dobutamine. At baseline and after each intervention, global function of the right ventricle and left ventricle was measured as cross-sectional end-diastolic area and end-systolic area, and regional contraction was evaluated as the percentage of left ventricular circumference with a wall motion abnormality. Intracardiac pressures and cardiac output were also measured for comparison. Left ventricular cross-sectional area ejection fractions (area EF) were calculated for both intracardiac and transthoracic echo images as (end-diastolic cross-sectional area - end-systolic cross-sectional area)/end-diastolic cross-sectional area. RESULTS: The 10F, 10-MHz intracardiac ultrasound catheter successfully imaged the left ventricle from the right ventricle in all 10 swine. In protocol 1, dobutamine increased area EF from a baseline of 0.60 +/- 0.03 to 0.87 +/- 0.04 (P < .05). When dobutamine was added to the myocardial depressant halothane, left ventricular area EF increased from a baseline of 0.55 +/- 0.03 to 0.68 +/- 0.04. In protocol 2, coronary occlusion resulted in a detectable regional wall motion abnormality (circumferential percentage) of 23% +/- 3%. After reperfusion and during dobutamine stimulation, the wall abnormality decreased to 12% +/- 4%. Transthoracic echocardiography correlated well with these intracardiac findings. CONCLUSIONS: The left ventricle can be quantitatively imaged from the right ventricle with the use of a 10F, 10-MHz intracardiac catheter in swine. This system can detect changes in global and regional left ventricular systolic function. This technique warrants evaluation in clinical applications.

Animals↗
PubMed1997

Percutaneous balloon catheter closure of a patent foramen ovale in a patient with pulmonary disease, profound hypoxemia, and normal right heart pressures.

Right-to-left intracardiac shunting across a patent foramen ovale (PFO) has been reported in patients with pulmonary embolism, right ventricular (RV) infarction, positive pressure ventilation with positive end-expiratory pressure, heart failure with left ventricular assist devices, cardiac tamponade, and unilateral diaphragmatic paralysis. The primary driving force for these shunts is a reduction in the compliance of the pulmonary bed or right ventricle; right atrial pressure is usually elevated and pulmonary hypertension is frequently present. Significant shunting and hypoxemia are unusual in the absence of these diseases. We encountered a patient with normal pulmonary pressures, severe hypoxemia, pulmonary disease, and intracardiac shunting across a PFO in whom it was difficult to determine how great a role intracardiac shunting was playing in his hypoxemia. To assess this, we performed percutaneous balloon catheter occlusion of the PFO, using transthoracic echocardiography with contrast to confirm closure of the PFO. Therapeutic balloon occlusion has been reported in severe hypoxemia due to shunting across a PFO in a patient with RV infarction. Our case is unique, however, in two respects. First, this patient had normal right-sided cardiac pressures and normal RV function and, thus, no obvious driving force for a significant right-to-left shunt. Second, transthoracic echocardiography with contrast was used before and after balloon inflation to confirm closure of the PFO. This technique helped to answer the important clinical question of whether surgical closure of the PFO in this patient with both lung disease and intracardiac shunting would significantly improve his oxygenation.

Adult↗
PubMed1997

Cardiac troponin I levels are normal or minimally elevated after transthoracic cardioversion.

OBJECTIVES: The present study was designed to assess the impact of direct current shocks on cardiac troponin I (cTnI), which has greater sensitivity and specificity than creatine kinase (CK) for the diagnosis of myocardial injury. BACKGROUND: Transthoracic direct current shocks can cause myocardial injury. They also cause elevations of total CK and CK-MB fraction (CK-MB). METHODS: We obtained measurements of cTnI total CK and CK-MB before and after elective cardioversions in 38 patients. Blood samples were drawn before and 8, 16, 24 and 48 h after cardioversion. Shock energy, current, impedance and number of shocks delivered were tabulated. RESULTS: Patients received a mean (+/-SD) of 2.1 +/- 1.2 shocks with a median cumulative energy of 300 J (range 50 to 1,580). Three patients had minimal elevations (1.5, 1.2 and 0.8 ng/ml, normal < or = 0.6 ng/ml) of cTnI. Two of these patients had impaired left ventricular contractility by echocardiography. Thirty-five of the 38 patients had no elevations of cTnI. Sixty-two percent of patients had an increase in CK after cardioversion, but CK-MB was elevated to an abnormal level of 12.7 ng/ml (normal < 6.7) in only one patient after cardioversion. CONCLUSIONS: Cardiac troponin I levels are either normal or minimally elevated after elective direct current cardioversion, suggesting that subtle myocardial injury can be caused by direct current transthoracic shocks. However, substantial elevations of cTnI after cardioversion suggest the presence of myocardial injury from causes unrelated to the direct current shocks administered for cardioversion.

Aged↗
PubMed1993

Angioplasty versus bypass surgery for multivessel coronary artery disease with left ventricular ejection fraction < or = 40%.

Patients with multivessel coronary artery disease and left ventricular dysfunction represent a high-risk subgroup in whom coronary artery bypass grafting has been shown to improve survival compared with that of medically treated patients. The comparative benefits and risks of coronary angioplasty and bypass surgery in this subgroup of patients are unclear. This study retrospectively analyzes 100 consecutive patients treated with bypass surgery compared with a matched, concurrent cohort of 100 treated with multivessel angioplasty. Early results favored angioplasty; a hospital stay of 12.8 days was noted in the bypass group compared with 4.3 days in the angioplasty group (p < 0.001). In-hospital mortality rates were similar in the bypass (5%) and angioplasty (3%) groups (p = NS). Stroke was observed significantly more often in the bypass group (7 vs 0%). However, late follow-up favored bypass patients; repeat revascularization procedures and late myocardial infarction occurred more frequently during follow-up in the angioplasty group. During 5-year follow-up, superior relief from disabling angina (99 vs 89%; p = 0.01) and a trend toward improved survival (76 vs 67%; p = 0.09) were observed in the bypass group as compared with the angioplasty group. Multivariate correlates of late mortality included age and incomplete revascularization, but not mode of revascularization. Thus, in patients with multivessel coronary artery disease and left ventricular dysfunction, early results favor angioplasty, whereas late follow-up favors bypass surgery. However, late survival was similar in both groups of patients who were completely revascularized.

Actuarial Analysis↗